CN108702103B - Power conversion device - Google Patents

Abstract

The AC power control unit is provided with a power conversion unit for converting DC power inputted from a DC power supply into AC power and outputting the AC power to an AC power line, an AC power control unit for controlling the output frequency and output voltage of the AC power outputted from the power conversion unit, a voltage detection unit for detecting the output voltage of the AC power, and a current detection unit for detecting the output current of the AC power, wherein after the AC power control unit is put into a load on the AC power line and outputs the AC power to the load at a rated frequency and a rated voltage, after droop control is performed to reduce the output frequency and the output voltage of the alternating-current power from the rated frequency and the rated voltage, respectively, based on the output voltage detected by the voltage detection unit and the output current detected by the current detection unit, correction control is performed to gradually correct the output frequency and the output voltage to the rated frequency and the rated voltage.

Description

Power conversion device

Technical Field

The present invention relates to a power conversion device.

Background

With recent increase in interest in renewable energy and introduction of an electric power purchasing system by governments, solar power generation systems using solar cells (PV) are rapidly spreading, for example. This system can easily obtain electric power as long as solar radiation is present, but is susceptible to electric power fluctuation depending on solar radiation conditions, and cannot generate electric power at night. Therefore, a solar cell-battery cooperation system has been proposed in which a battery capable of storing electric power is connected to a solar cell, and the fluctuation amount of electric power generated by the solar cell is processed by charging and discharging the battery.

Important in the configuration of the solar cell-battery cooperative System is a Power Conditioning System (hereinafter sometimes referred to as PCS) device as a kind of Power conversion device. The PCS is provided between a dc power supply such as a solar cell or a battery and an ac power line, converts dc power supplied from the dc power supply into ac power, and supplies the ac power to an important load connected to the ac power line.

In a power converter, when a plurality of power conversion devices (PCS, etc.) are operated in parallel, it is assumed that each power conversion device shares the contributing power fairly, and control called droop control is performed in which the frequency and voltage of ac power supplied to a load are intentionally reduced (drooped) from the rated value.

Patent document 1 discloses a control method for effectively utilizing electric power of a dc power supply (generator) by changing droop characteristics that define a droop amount of a frequency and a droop amount of a voltage.

Prior art documents

Patent document

Patent document 1: international publication No. 2014/098104

Disclosure of Invention

Problems to be solved by the invention

When the droop control is performed, the frequency and voltage of the ac power supplied to the load are lower than the rated values. Therefore, the droop characteristics are set to fall within the allowable range of the load. However, even if the droop characteristic is within the allowable range of the load, the droop characteristic may be affected by the frequency and voltage of the frequency and voltage depending on the load to be connected. For example, when a load is clocked by a synchronous motor, a frequency reduced by droop control is accumulated as a timing error.

In addition, if the droop characteristics are set so as to reduce the amount of droop in order to suppress the influence of the droop control, the frequency and voltage deviations from the rated values due to the droop control are suppressed. However, when parallel operation with other power conversion devices is performed, control accuracy in which each power conversion device performs fair sharing is degraded.

Therefore, an object of the present invention is to provide a power conversion device capable of reducing the influence of droop control.

Means for solving the problems

To solve the above problem, the present invention includes: a power conversion unit that converts dc power input from a dc power supply into ac power and outputs the ac power to an ac power line; an alternating current power control unit that controls an output frequency and an output voltage of the alternating current power output from the power conversion unit; a voltage detection unit that detects an output voltage of the ac power; and a current detection unit that detects an output current of the ac power, wherein the ac power control unit performs droop control for reducing the output frequency and the output voltage of the ac power from the rated frequency and the rated voltage, respectively, based on the output voltage detected by the voltage detection unit and the output current detected by the current detection unit, after the ac power is input to the ac power line and the ac power is output to the load at the rated frequency and the rated voltage, and then performs correction control for gradually correcting the output frequency and the output voltage to the rated frequency and the rated voltage.

Effects of the invention

The effects obtained by representative inventions among the inventions disclosed in the present application will be briefly described below.

That is, according to the exemplary embodiment of the present invention, it is possible to provide a power conversion device in which the influence of droop control is reduced.

Drawings

Fig. 1 is a diagram showing an example of a system using a power conversion device according to embodiment 1 of the present invention.

Fig. 2 is a diagram showing an example of the configuration of a power conversion device in embodiment 1 of the present invention.

Fig. 3 is a diagram illustrating the drooping characteristic.

Fig. 4 is a diagram showing an example of the configuration of the command value correction unit in the correction control unit.

Fig. 5 is a diagram showing a flowchart relating to frequency control and voltage control in embodiment 1 of the present invention.

Fig. 6 is a diagram showing droop characteristics related to frequency control in embodiment 1 of the present invention.

Fig. 7 is a diagram showing droop characteristics relating to voltage control in embodiment 1 of the present invention.

Fig. 8 is a diagram showing a timing chart according to frequency control in embodiment 1 of the present invention.

Fig. 9 is a diagram showing a timing chart according to voltage control in embodiment 1 of the present invention.

Fig. 10 is a diagram showing an example of a system according to embodiment 2 of the present invention.

Fig. 11 is a diagram showing a flowchart relating to frequency control and voltage control in embodiment 2 of the present invention.

Fig. 12 is a diagram showing droop characteristics related to frequency control in embodiment 2 of the present invention.

Fig. 13 is a diagram showing droop characteristics relating to voltage control in embodiment 2 of the present invention.

Fig. 14 is a diagram showing a timing chart according to frequency control in embodiment 2 of the present invention.

Fig. 15 is a diagram showing a timing chart according to voltage control in embodiment 2 of the present invention.

Fig. 16 is a diagram showing an example of the configuration of a power conversion device according to embodiment 3 of the present invention.

Fig. 17 is a diagram showing an example of the configuration of the command value correction unit in embodiment 3 of the present invention.

Fig. 18 is a diagram showing an example of the configuration of the cooperation control unit in embodiment 3 of the present invention.

Fig. 19 is a diagram showing a flowchart relating to frequency control and voltage control in embodiment 3 of the present invention.

Fig. 20 is a diagram showing droop characteristics relating to frequency control in the case where the time constant is large.

Fig. 21 is a diagram showing droop characteristics relating to voltage control in the case where the time constant is large.

Fig. 22 is a diagram showing a timing chart relating to frequency control in the case where the time constant is large.

Fig. 23 is a diagram showing a timing chart relating to voltage control in the case where the time constant is large.

Fig. 24 is a diagram showing droop characteristics relating to frequency control in the case where the time constant is small.

Fig. 25 is a diagram showing droop characteristics relating to voltage control in the case where the time constant is small.

Fig. 26 is a diagram showing a timing chart relating to frequency control in the case where the time constant is small.

Fig. 27 is a diagram showing a timing chart relating to voltage control in the case where the time constant is small.

Fig. 28 is a diagram showing an example of the configuration of a power conversion device according to embodiment 4 of the present invention.

Fig. 29 is a diagram showing an example of the configuration of the command value correction unit in the correction control unit.

Fig. 30 is a flowchart showing the frequency control and the voltage control in the parallel operation in embodiment 4 of the present invention.

Fig. 31 is a diagram showing droop characteristics related to frequency control in the parallel operation in embodiment 4 of the present invention.

Fig. 32 is a diagram showing droop characteristics relating to voltage control in the parallel operation in embodiment 4 of the present invention.

Fig. 33 is a diagram showing a timing chart relating to frequency control during parallel operation in embodiment 4 of the present invention.

Fig. 34 is a diagram showing a timing chart relating to voltage control during parallel operation in embodiment 4 of the present invention.

Fig. 35 is a diagram showing an example of a system according to embodiment 5 of the present invention.

Fig. 36 is a diagram showing an example of a system according to embodiment 6 of the present invention.

Fig. 37 is a diagram showing an example of a system according to embodiment 7 of the present invention.

Fig. 38 is a diagram showing a timing chart for controlling the frequency and the voltage in the power converter studied by the present inventors.

Fig. 39 is a diagram showing characteristics of an output frequency and an output voltage in the power converter studied by the present inventors.

Fig. 40 is a graph showing droop characteristics of the output frequency and the output voltage in the power converter studied by the present inventors.

Fig. 41 is a diagram showing a timing chart relating to control of frequency and voltage in the power converter studied by the present inventors.

Fig. 42 is a graph showing droop characteristics of the output frequency in the power converter studied by the present inventors.

Fig. 43 is a graph showing the droop characteristics of the output voltage in the power converter studied by the present inventors.

Fig. 44 is a diagram showing a timing chart relating to frequency control in the power converter studied by the present inventors.

Fig. 45 is a diagram showing a timing chart relating to voltage control in the power converter studied by the present inventors.

Detailed Description

Hereinafter, embodiments will be described with reference to the drawings. In all the drawings for describing the embodiments, the same components are denoted by the same reference numerals as a principle, and redundant description thereof is omitted.

(embodiment mode 1)

In the present embodiment, a case where the power conversion device is used alone will be described.

[ constitution of the device ]

Fig. 1 is a diagram showing an example of a system using the power conversion device according to the present embodiment. The power conversion device 200 is connected to a dc power supply 111 on the dc side and to an ac power line 120 on the ac side. The power conversion device 200 converts dc power input from the dc power supply 111 into ac power and outputs the ac power to the ac power line 120. As the power conversion device 200, for example, a Power Conditioning System (PCS) which is a kind of power conversion device, or various devices having a function of converting dc power into ac power are used. The load 130 is driven by the supply of the ac power converted by the power converter 200.

The power conversion device 200 includes a power conversion unit 210, a frequency-voltage control unit 220, a droop control unit 230, and a correction control unit 240.

Fig. 2 is a diagram showing an example of the configuration of a power converter 200 according to the present embodiment. The power conversion device 200 includes a power conversion unit 210, a voltage detection unit 214, a current detection unit 215, and an alternating current power control unit 250.

The power conversion unit 210 converts dc power input from the dc power supply 111 into ac power and outputs the ac power to the ac power line 120. Ac power control unit 250 controls the output frequency and output voltage of the ac power output from power conversion unit 210. The power conversion unit 210 includes a semiconductor element 211, a reactor 212, and a transformer 213, and constitutes an inverter that converts dc power into ac power. The semiconductor element 211 pulse-width modulates the input dc power by a switching operation based on control of a frequency-voltage control unit 220 described later. The reactor 212 removes harmonics from the power pulse-width-modulated by the semiconductor element 211. Through these steps, the dc power is converted into 3-phase ac power. The transformer 213 transforms the pulse-width modulated ac voltage to a predetermined output voltage. The ac power subjected to the power conversion is output to the ac power line 120. The output frequency of the output ac power is, for example, 50Hz, 60Hz, or the like. The output voltage of the output ac power is, for example, 100V or 200V.

The voltage detection unit 214 detects an output voltage of the ac power. Specifically, the voltage detection unit 214 detects an output voltage of the ac power output to the ac power line 120.

The current detection unit 215 detects an output current of the ac power. Specifically, the current detection unit 215 detects an output current of the ac power output to the ac power line 120.

After the ac power control unit 250 outputs the ac power at the rated frequency and the rated voltage, droop control is performed to lower the output frequency and the output voltage of the ac power from the rated frequency and the rated voltage, respectively, based on the output voltage detected by the voltage detection unit 214 and the output current detected by the current detection unit 215, and then correction control is performed to gradually correct the output frequency and the output voltage to the rated frequency and the rated voltage.

The ac power control unit 250 includes a droop control unit 230, a correction control unit 240, and a frequency-voltage control unit 220.

The droop control unit 230 derives a contribution active power and a contribution reactive power of the ac power based on the output voltage and the output current, derives a frequency droop amount that lowers the output frequency from the rated frequency based on a frequency droop rate and the contribution active power specified by a frequency reduction amount per unit active power, and derives a voltage droop amount that lowers the output voltage from the rated voltage based on a voltage droop rate and the contribution reactive power specified by a voltage reduction amount per unit reactive power.

Specifically, the droop control unit 230 includes a power calculation unit 231 that derives a contribution active power and a contribution reactive power of the ac power based on the output voltage and the output current, and multiplies the contribution active power and the frequency droop rate derived by the power calculation unit 231 to derive a frequency droop amount, and multiplies the contribution reactive power and the voltage droop rate derived by the power calculation unit 231 to derive a voltage droop amount.

The electric power calculation unit 231 calculates the magnitude of the inner product of the output voltage detected by the voltage detection unit 214 and the output current detected by the current detection unit 215, for example, to derive the contributing active power. The electric power calculation unit 231 calculates the magnitude of the outer product of the output voltage detected by the voltage detection unit 214 and the output current detected by the current detection unit 215, for example, to derive the contributing reactive power.

Fig. 3 is a diagram illustrating the drooping characteristic. The droop control is control performed to share each power conversion device 200 fairly, assuming that, for example, a plurality of power conversion devices 200 are connected to the ac power line 120 and parallel operation is performed in which ac power is output from the plurality of power conversion devices 200.

Fig. 3 (a) is a graph showing a change in frequency with respect to active power. The frequency droop rate is the amount of decrease in frequency per unit active power, and is defined by the slope of the straight line shown in fig. 3 (a). The frequency droop rate is set, for example, such that the amount of decrease in frequency (frequency droop rate) falls within a range that is allowed for the maximum active power of the power conversion device 200.

Fig. 3 (b) is a graph showing a change in voltage with respect to reactive power. The voltage sag rate is the amount of voltage drop per unit reactive power, and is defined by the slope of the straight line shown in fig. 3 (b). The voltage droop rate is set, for example, such that the amount of voltage drop (voltage droop rate) falls within a range that is allowed for the maximum reactive power of the power conversion device 200.

Each part and each function constituting the droop control unit 230 may be configured by hardware or software. When each unit and each function constituting the droop control unit 230 are realized by software, the droop control unit 230 includes, for example, a CPU (or a dedicated processor) not shown, and the CPU executes a program stored in a memory or the like not shown to realize each unit and each function.

The correction control unit 240 sets a frequency target value for defining the output frequency in the process of gradually correcting the output frequency decreased by the droop control to the rated frequency based on the frequency correction value, and sets a voltage target value for defining the output voltage in the process of gradually correcting the output voltage decreased by the droop control to the rated voltage based on the voltage correction value.

The correction control unit 240 will be described in detail.

The correction control unit 240 includes: an output status monitoring unit 241 for monitoring the contributed real power and the contributed reactive power derived by the power calculation unit 231; a data storage unit 242 for storing a predetermined rated frequency, rated voltage, frequency droop rate, and voltage droop rate; and a command value correcting unit 243.

Various data such as the rated frequency, the rated voltage, the frequency droop rate, and the voltage droop rate stored in the data storage unit 242 are input through the operation panel 290, for example.

The operation panel 290 receives input of various data such as a rated frequency, a rated voltage, a frequency droop rate, and a voltage droop rate, and outputs the input various data to the data storage unit 242. The data storage section 242 stores various data outputted from the operation panel.

The operation panel 290 includes a display unit, not shown, and is configured to be capable of displaying various data such as the contributing active power and the contributing reactive power monitored by the output condition monitoring unit 241 on the display unit.

Fig. 4 is a diagram showing an example of the configuration of the command value correction unit in the correction control unit. The command value correcting unit 243 includes a first-order frequency hysteresis element (frequency hysteresis element) 244 ω and a first-order voltage hysteresis element (voltage hysteresis element) 244 v. The command value correcting unit 243 multiplies (original: load) the contribution active power monitored by the output condition monitoring unit 241 by the frequency droop rate stored in the data storage unit 242 to derive a frequency correction value, inputs the frequency correction value to the frequency first-order lag element 244 ω, and sets a value obtained by adding the frequency gradual correction value output from the frequency first-order lag element 244 ω to the rated frequency as a frequency target value for defining the output frequency in the process of gradually correcting the output frequency to the rated frequency. Here, the first-order lag element is used as a method of gradually changing the correction value, but a second-order lag element or a higher-order lag element may be used for the same purpose.

The command value correcting unit 243 multiplies the contributing reactive power monitored by the output condition monitoring unit 241 by the voltage droop rate stored in the data storage unit 242 to derive a voltage correction value, inputs the voltage correction value to the first-order voltage hysteresis element 244v, and sets a value obtained by adding the rated voltage to the voltage gradual correction value output from the first-order voltage hysteresis element 244v as a voltage target value for defining the output voltage in the process of gradually correcting the output voltage to the rated voltage.

The frequency first order lag element 244 ω and the voltage first order lag element 244v are used to gradually perform the correction control by the correction control unit 240, that is, to gradually and slowly perform the correction control. The frequency first order lag element 244 ω and the voltage first order lag element 244v are configured by, for example, a low-pass filter or a digital filter having a function equivalent thereto, and the low-pass filter is configured by a resistor, a capacitor, and the like. If the correction control is not performed by the frequency first order lag element 244 ω and the voltage first order lag element 244v, the correction control is performed for a time period of, for example, 10us to 100 us. On the other hand, when the correction control is performed by the frequency first order lag element 244 ω and the voltage first order lag element 244v, the correction control is performed for a time of, for example, several ms to 100 ms. Therefore, it takes a considerably longer time to perform the correction control than the case where the frequency first order lag element 244 ω and the voltage first order lag element 244v are not passed. Accordingly, the correction control can be performed while suppressing the variation of the contributing active power and the contributing reactive power before and after the correction control.

Each part and each function constituting the correction control unit 240 may be configured by hardware or software. When each unit and each function constituting the correction control unit 240 are realized by software, the correction control unit 240 includes, for example, a CPU (or a dedicated processor) not shown, and the CPU executes a program stored in a memory or the like not shown to realize each unit and each function.

The correction control unit 240 may be implemented by, for example, a programmable Logic Controller (hereinafter, referred to as PLC) mounted in the power conversion device 200.

The frequency-voltage control unit 220 performs droop control based on the lower frequency bias amount and the voltage droop amount calculated by the lower bias control unit 230, and after the droop control, performs correction control for gradually correcting the output frequency and the output voltage to the rated frequency and the rated voltage based on the target frequency value and the target voltage value set by the correction control unit 240.

The frequency-voltage control unit 220 includes a feedback control unit 221. The frequency-voltage control unit 220 inputs the rated frequency and the rated voltage stored in the data storage unit 242 to the feedback control unit 221 as a frequency command value and a voltage command value, and the feedback control unit 221 outputs ac power at the rated frequency and the rated voltage based on the input frequency command value and the input voltage command value.

Then, the frequency-voltage control unit 220 inputs a value obtained by adding the frequency droop amount derived by the droop control unit 230 to the rated frequency stored in the data storage unit 242 to the feedback control unit 221 as a frequency command value, and inputs a value obtained by adding the voltage droop amount derived by the droop control unit 230 to the rated voltage stored in the data storage unit 242 to the feedback control unit 221 as a voltage command value, and the feedback control unit 221 performs droop control based on the input frequency command value and voltage command value.

The frequency-voltage control unit 220 inputs the frequency target value and the voltage target value set by the command value correcting unit 243 of the correction control unit 240 to the feedback control unit 221 as a frequency command value and a voltage command value, and the feedback control unit 221 performs correction control for gradually correcting the output frequency and the output voltage to the rated frequency and the rated voltage based on the frequency command value and the voltage command value that are input.

The feedback control unit 221 is connected to the voltage detection unit 214, and monitors the output voltage detected by the voltage detection unit 214. The feedback control unit 221 controls the pulse modulation signal based on the monitored output voltage so that the output voltage becomes a predetermined voltage. The feedback control unit 221 is connected to the current detection unit 215, and monitors the output voltage detected by the current detection unit 215. The feedback control unit 221 controls the pulse modulation signal based on the monitored output current so that the output voltage becomes a predetermined voltage. Since the output voltage decreases due to the current flowing through the reactor 212, the feedback control unit 221 compensates the decreased voltage according to the information from the current detection unit 215. Therefore, the feedback control unit 221 performs feedback control of the output voltage and the output current. Accordingly, the contributing active power and the contributing reactive power of the ac power are stably output.

Each part and each function constituting the frequency-voltage control unit 220 may be constituted by hardware or software. When each unit and each function constituting the frequency-voltage control unit 220 are realized by software, the frequency-voltage control unit 220 includes, for example, a CPU (or a dedicated processor) not shown, and the CPU executes a program stored in a memory or the like not shown to realize each unit and each function.

[ method for controlling frequency and voltage ]

Here, a method of controlling the frequency and the voltage when the power conversion device 200 is used alone will be described.

Fig. 5 is a diagram showing a flowchart relating to frequency control and voltage control in the present embodiment. Fig. 6 is a diagram showing droop characteristics related to frequency control in the present embodiment. Fig. 7 is a diagram showing droop characteristics related to voltage control in the present embodiment. Fig. 8 is a diagram showing a timing chart according to frequency control in the present embodiment. Fig. 9 is a diagram showing a timing chart according to voltage control in the present embodiment.

For convenience of explanation, the control cycle of the power conversion unit (inverter) 210 is denoted by Δ T, and the control cycle Δ T of the correction control unit (PLC) is denoted by 4 Δ T. The time constants of the frequency first order lag element 244 ω and the voltage first order lag element 244v are set to 4 Δ T.

As shown in fig. 5, the power converter 200 controls the output frequency and the output voltage of the ac power by performing the respective steps of the rated output step S10, the frequency droop control step S20, the frequency correction control step S25, the voltage droop control step S30, and the voltage correction control step S35. Here, an example in which all the processes are included in a series of sequences from "start" to "end" is shown. Every time the sequence is started, the rated output process S10 is executed each time, and the drooping processes S20, S30 are executed in a certain proportion thinned out. That is, in the case of thinning out by N, nothing is done in the call of N-1 times, and the process contents are started only in the Nth time. Further, the correction steps S25 and S35 are also performed at a predetermined ratio. Further, these steps do not have to be a series of sequences, and may be called individually from a management sequence of a multitask OS or the like. In this case, it is also important that the frequency of calling each process is different for each process. In the description of the present example, it is assumed that the rated output process S10 and the drooping processes S20 and S30 are included in a series of sequences, and the process contents are executed at the same timing (timing), and the correction processes S25 and S35 are executed to be thinned out to some extent.

[ rated output Process S10]

First, the rated output process S10 is explained. Before the load 130 is loaded, the power conversion device 200 is autonomously operated. In this case, both the contributing active power and the contributing reactive power of the power conversion device 200 are "0". At this time, as shown in fig. 6 (a) and 7 (a), the output frequency and the output voltage are rated.

Specifically, the command value correcting unit 243 reads the rated frequency and the rated voltage stored in the data storage unit 242. At this time, since the correction control is performed before, the correction values of the frequency and the voltage are both "0". Therefore, the command value correcting unit 243 sets the frequency target value and the voltage target value as the rated frequency and the rated voltage. The correction control unit 240 outputs the rated frequency and the rated voltage as the frequency target value and the voltage target value to the frequency-voltage control unit 220.

In this case, since the droop control is performed before, the droop amount of the frequency and the droop amount of the voltage are both "0". Therefore, the frequency-voltage control unit 220 sets the frequency command value and the voltage command value to the rated frequency and the rated voltage. The frequency-voltage control unit 220 inputs the rated frequency and the rated voltage set as the frequency command value and the voltage command value to the feedback control unit 221. The feedback control unit 221 outputs ac power at a rated frequency and a rated voltage based on the input frequency command value and voltage command value.

When load 130 is input at time T1, power conversion unit (inverter) 210 causes current to flow to the load and maintains the ac voltage during control period Δ T. Then, as shown in fig. 8, the power conversion device 200 outputs P ω as contributing active power. Further, as shown in fig. 9, the power conversion device 200 outputs Qv as contributing reactive power.

[ frequency droop control Process S20]

When the ac power is output, the droop control unit 230 performs droop control on the frequency and the voltage. After the droop control is performed, correction control is performed on the frequency and the voltage. For convenience of explanation, the droop control and the correction control of the frequency are explained, and then the droop control and the correction control of the voltage are explained.

Here, the frequency droop control step S20 will be described. When the load 130 is input and the ac power is output, the power converter 200 performs droop control to lower the output frequency from the rated frequency, as shown in fig. 6 (b) and 8.

Specifically, the droop control unit 230 derives the contribution real power (P ω) of the ac power based on the output voltage and the output current, and derives the frequency droop (- ω) for reducing the output frequency from the rated frequency based on the frequency droop rate and the contribution real power (P ω) defined by the frequency reduction per unit real power.

For example, the electric power calculation unit 231 derives the contribution active power (P ω) of the ac power based on the output voltage detected by the voltage detection unit 214 and the output current detected by the current detection unit 215. The droop control unit 230 reads the frequency droop rate stored in the data storage unit 242, and multiplies the contribution active power (P ω) derived by the power calculation unit 231 by the frequency droop rate read from the data storage unit 242 to derive the frequency droop amount (- ω). The droop control section 230 outputs the thus derived frequency droop (- ω) to the frequency-voltage control section 220.

The correction control unit 240 outputs a rated frequency as a frequency target value to the frequency voltage control unit 220.

The frequency-voltage control unit 220 inputs a value obtained by adding the frequency droop (- ω) input from the droop control unit 230 to the rated frequency input from the correction control unit 240 to the feedback control unit 221 as a frequency command value. The feedback control unit 221 performs droop control for reducing the frequency by the droop amount (- ω) from the rated frequency based on the input frequency command value. As shown in fig. 8, the frequency-voltage control unit 220 performs droop control during the control period Δ t of the inverter.

[ frequency correction control step S25]

Next, the frequency correction control step S25 will be described. After the droop control is performed, the power conversion device 200 performs correction control for gradually correcting the frequency to the rated frequency from time T2 in fig. 8. Specifically, the correction control unit 240 sets the frequency target value based on a gradual correction value (+ Δ ω) for defining the output frequency in the process of gradually correcting the output frequency to the rated frequency based on the frequency correction value (+ ω), with the frequency droop (- ω) as a frequency correction value (+ ω) for correcting the output frequency to the rated frequency.

For example, the command value correction unit 243 multiplies the contributing active power monitored by the output condition monitoring unit 241 by the frequency droop rate read out from the data storage unit 242 to derive a frequency correction value (+ ω), and inputs the frequency correction value (+ ω) to the frequency first order lag element 244 ω. The frequency first-order lag element 244 ω outputs a frequency gradual correction value (+ Δ ω) based on the input frequency correction value. The command value correcting unit 243 sets a value obtained by adding the frequency gradual correction value (+ Δ ω) output from the frequency first-order lag element 244 ω to the rated frequency read from the data storage unit 242 as a frequency target value that defines the output frequency in the process of gradually correcting the output frequency to the rated frequency. The command value correcting unit 243 outputs the frequency target value set here to the frequency-voltage control unit 220.

The frequency-voltage control unit 220 performs correction control of the output frequency using the target frequency value input from the command value correction unit 243 as a frequency command value. At this time, as shown in fig. 6 (c) and 8, the output frequency increases by Δ ω in the first inverter control period Δ t from the start of the correction control.

In the next control period Δ T of the PLC, the frequency first-order lag element 244 ω outputs (+2 Δ ω) as a gradual correction value. The frequency-voltage control unit 220 further performs correction control of the frequency of the Δ ω component based on the gradual correction value. By repeating such correction control, the feedback control unit 221 performs correction control of the amount + ω on the output frequency as shown in fig. 6 (d) and 8. When the PLC control cycle Δ T in the last correction control has elapsed (T3), the frequency-voltage control unit 220 ends the correction control. Accordingly, the frequency-voltage control unit 220 gradually corrects the output frequency to the rated frequency. That is, the feedback control unit 221 gradually and gradually controls the output frequency to be corrected to the rated frequency by passing through the frequency first-order lag element 244 ω.

In fig. 8, the case where correction is performed in 4 stages has been described as an example of correction control, but the present invention is not limited to this case, and correction control may be performed in more stages, for example.

[ Voltage sag control Process S30]

Next, the voltage droop control process S30 will be described. As described above, the voltage droop control step S30 is performed in parallel with the frequency droop control step S20. When the load 130 is input and the ac power is output, the power conversion device 200 performs droop control for reducing the output voltage from the rated voltage, as shown in fig. 7 (b) and 9.

Specifically, the droop control unit 230 derives a contribution reactive power (Qv) of the ac power based on the output voltage and the output current, and derives a voltage droop (-v) by which the output voltage is reduced from the rated voltage based on a voltage droop rate defined by a voltage reduction per unit reactive power and the contribution reactive power (Qv).

For example, the power calculation unit 231 derives the contribution reactive power (Qv) of the ac power based on the output voltage detected by the voltage detection unit 214 and the output current detected by the current detection unit 215. The droop control unit 230 reads the voltage droop rate stored in the data storage unit 242, and multiplies the contributing reactive power (Qv) derived by the power calculation unit 231 by the voltage droop rate read from the data storage unit 242 to derive a voltage droop amount (-v). The droop control section 230 outputs the voltage droop (-v) thus derived to the frequency-voltage control section 220.

The correction control unit 240 outputs a rated voltage as a voltage target value to the frequency-voltage control unit 220.

The frequency-voltage control unit 220 inputs a value obtained by adding the voltage droop (-v) input from the droop control unit 230 to the rated voltage input from the correction control unit 240 to the feedback control unit 221 as a voltage command value. The feedback control unit 221 performs droop control for reducing the voltage by a droop amount (-v) from the rated voltage based on the input voltage command value.

As shown in fig. 9, the frequency-voltage control unit 220 reduces the output voltage by the voltage droop (-v) during the control period Δ t of the inverter.

[ Voltage correction control step S35]

Next, the voltage correction control step S35 will be described. As described above, the voltage correction control step S35 is performed in parallel with the frequency droop control step S30. After the droop control is performed, the power converter 200 performs correction control for gradually correcting the voltage to the rated voltage from time T2 in fig. 9. Specifically, the correction control unit 240 sets the voltage target value based on a gradual correction value (+ Δ v) for defining the output voltage in the process of gradually correcting the output voltage to the rated voltage based on the voltage correction value (+ v) by using the voltage sag (-v) as a voltage correction value (+ v) for correcting the output voltage to the rated voltage.

For example, the command value correcting unit 243 multiplies the contributing reactive power monitored by the output condition monitoring unit 241 by the voltage droop rate read from the data storage unit 242 to derive a voltage correction value (+ v), and inputs the voltage correction value (+ v) to the voltage first-order lag element 244 ω. The voltage first-order lag element 244v outputs a voltage gradual correction value (+ Δ v) based on the input voltage correction value. The command value correcting unit 243 sets a value obtained by adding the voltage gradual correction value (+ Δ v) output from the voltage first-order lag element 244v to the rated voltage read from the data storage unit 242 as a voltage target value that defines the output voltage in the process of gradually correcting the output voltage to the rated voltage. The command value correcting unit 243 outputs the voltage target value set here to the frequency-voltage control unit 220.

The frequency-voltage control unit 220 performs correction control of the output voltage using the voltage target value input from the command value correction unit 243 as a voltage command value. At this time, as shown in fig. 7 (c) and 9, the output voltage increases by Δ ω in the first control cycle Δ t of the inverter from the start of the correction control.

In the next control period Δ T of the PLC, the voltage first-order lag element 244v outputs (+2 Δ v) as a gradual correction value. Based on this, the frequency-voltage control unit 220 further performs correction control of the voltage of the Δ v portion. By repeating such correction control, the feedback control unit 221 performs correction control of the + ω amount on the output voltage as shown in fig. 7 (d) and 9. When the PLC control cycle Δ T in the last correction control has elapsed (T3), the frequency-voltage control unit 220 ends the correction control. Accordingly, the frequency-voltage control unit 220 gradually corrects the output voltage to the rated voltage. That is, the feedback control unit 221 gradually and gradually corrects and controls the output voltage to the rated voltage by passing through the voltage first-order lag element 244 v.

In fig. 9, the case where correction is performed in 4 stages has been described as an example of correction control, but the present invention is not limited to this case, and correction control may be performed in more stages, for example.

Through these steps S10 to S35, the power converter 200 controls the output frequency and the output voltage of the ac power to be output.

In the present embodiment, as described above, the droop control and the correction control are performed by different mechanisms (the droop control unit 230 and the correction control unit 240).

The control period Δ T of the inverter is often sufficiently shorter than the control period Δ T of the PLC, but these periods may be substantially equal, for example.

According to the present embodiment, after the frequency-voltage control unit 220 outputs ac power at the rated frequency and the rated voltage, a value obtained by adding the frequency droop amount derived by the droop control unit 230 to the rated frequency stored in the data storage unit 242 is input to the feedback control unit 221 as a frequency command value. The frequency-voltage control unit 220 inputs a value obtained by adding the voltage droop amount derived by the droop control unit 230 to the rated voltage stored in the data storage unit 242 to the feedback control unit 221 as a voltage command value. The feedback control unit 221 performs droop control based on the input frequency command value and voltage command value. The frequency-voltage control unit 220 inputs the frequency target value and the voltage target value set by the command value correcting unit 243 of the correction control unit 240 to the feedback control unit 221 as a frequency command value and a voltage command value, and the feedback control unit 221 performs correction control for gradually correcting the output frequency and the output voltage to the rated frequency and the rated voltage based on the frequency command value and the voltage command value that are input.

Accordingly, the output frequency and the output voltage reduced by the droop control can be corrected to the rated values, and therefore, the influence of the droop control can be reduced.

Further, according to the present embodiment, when the frequency correction control is performed, the frequency gradual correction value is sequentially increased by + Δ ω for each control cycle Δ T of the PLC after the frequency first-order lag element 244 ω starts the correction control (T2). Accordingly, since the command value correcting unit 243 is set to gradually increase the frequency target value, the feedback control unit 221 can gradually correct the output frequency to the rated frequency using the frequency target value as the frequency command value. In addition, according to this, the contribution active power can be maintained almost equal before and after the correction control.

In addition, according to the present embodiment, when the voltage correction control is performed, the voltage first-order lag element 244v increases the voltage gradual correction value by + Δ v in sequence for each control cycle Δ T of the PLC after the correction control is started (T2). Accordingly, since the command value correcting unit 243 is set to gradually increase the voltage target value, the feedback control unit 221 can gradually correct the output frequency to the rated frequency using the voltage target value as the voltage command value. In addition, according to this, the contributing reactive power can be maintained almost equal before and after the correction control.

Further, according to the present embodiment, the feedback control unit 221 is capable of monitoring the output voltage detected by the voltage detection unit 214 and the output current detected by the current detection unit 215. Accordingly, the feedback control unit 221 can perform feedback control of the output voltage and the output current. In addition, the contributing active power and the contributing reactive power of the ac power can be stably output. In addition, this enables stable supply of ac power to the load 130.

Here, differences between the power conversion device studied by the present inventors and the power conversion device 200 according to the present embodiment are studied. Fig. 38 is a diagram showing a timing chart for controlling the frequency and the voltage in the power converter studied by the present inventors. Fig. 39 is a diagram showing characteristics of an output frequency and an output voltage in the power converter studied by the present inventors. Fig. 38 shows a case where the correction control is not performed after the droop control is performed. Since the correction control is not performed, as shown in fig. 38, the ac power is supplied while the output frequency is reduced by the frequency droop (- ω 1) from the rated frequency. Further, the AC power is supplied while maintaining the output voltage lowered by the voltage sag (-v1) from the rated voltage.

Therefore, for example, in the case where the ac power line is connected to the system, the output frequency and the output power vary around the rated value as shown in fig. 39 (a), but in the case where the system is not connected, the output frequency and the output voltage continue to be lowered from the rated value by the frequency droop amount (for example, - ω 1) and the voltage droop amount (for example, -v1) as shown in fig. 39 (b).

(embodiment mode 2)

Next, embodiment 2 will be explained. In embodiment 2, a case where ac power is output to load 130 by a plurality of power conversion devices 200(PCS1, PCS2) will be described.

Fig. 10 is a diagram showing an example of a system according to the present embodiment. Power conversion device 200(PCS1) has dc power supply 121 connected to the dc side and ac power line 120 connected to the ac side. The power conversion device 200(PCS1) converts dc power input from the dc power supply 121 into ac power and outputs the ac power to the ac power line 120. The power conversion device 200(PCS2) has a dc power supply 122 connected to the dc side and an ac power line 120 connected to the ac side. The power conversion device 200(PCS2) converts dc power input from the dc power supply 122 into ac power and outputs the ac power to the ac power line 120.

[ method for controlling frequency and voltage ]

Here, a method of controlling the frequency and the voltage in the present embodiment will be described. Fig. 11 is a diagram showing a flowchart relating to frequency control and voltage control in the present embodiment. Fig. 12 is a diagram showing droop characteristics related to frequency control in the present embodiment. Fig. 13 is a diagram showing droop characteristics related to voltage control in the present embodiment. Fig. 14 is a diagram showing a timing chart according to frequency control in the present embodiment. Fig. 15 is a diagram showing a timing chart according to voltage control in the present embodiment.

As shown in fig. 11, each power conversion device 200(PCS1, PCS2) controls the output frequency and output voltage of ac power by performing the rated output step S110, frequency droop control step S120, frequency correction control step S125, voltage droop control step S130, and voltage correction control step S135. The steps S110 to S135 are performed in parallel in the power conversion devices 200. Therefore, in the description of each step, the operation of each power conversion device 200(PCS1, PCS2) will be collectively described.

For convenience of explanation, the control cycle of the power conversion unit (inverter) 210 is denoted by Δ T, and the control cycle Δ T of the correction control unit (PLC) is denoted by 4 Δ T. The time constants of the frequency first order lag element 244 ω and the voltage first order lag element 244v are set to 4 Δ T. Note that the following description will be made assuming that the control timing of the inverter and the control timing of the PLC are different between the power conversion devices 200(PCS1, PCS 2).

[ rated output Process S110]

First, the rated output process S110 is explained. Before the load 130 is input, the contribution active power and the contribution reactive power of the power conversion device 200(PCS1, PCS2) are both "0". At this time, the output frequency and the output voltage are in a nominally balanced state.

When load 130 is input at time T1, each power conversion device 200(PCS1 and PCS2) outputs ac power supplied to load 130 at substantially the same time. The ac power output from each power conversion device 200(PCS1, PCS2) is distributed according to its output impedance.

The power conversion unit (inverter) 210 of each power conversion device 200(PCS1, PCS2) causes current to flow to the load and maintains the ac voltage during the control period Δ t. Then, as shown in fig. 14, the power conversion device 200(PCS1) outputs P ω 1 as contributing active power. As shown in fig. 15, the power conversion device 200(PCS1) outputs Qv1 as contributing reactive power.

As shown in fig. 14, the power conversion device 200(PCS2) outputs P ω 2 as contributing active power. As shown in fig. 15, the power conversion device 200(PCS2) outputs Qv2 as contributing reactive power.

Therefore, the active power supplied to the load 130 becomes P ω 1+ P ω 2, and the reactive power supplied to the load 130 becomes Qv1+ Qv 2.

[ frequency droop control step S120]

When the ac power is output, the droop control unit 230 of each power conversion device 200(PCS1, PCS2) performs droop control on the frequency and the voltage. After the droop control is performed, correction control is performed on the frequency and the voltage. For convenience of explanation, the droop control and the correction control of the frequency are explained, and then the droop control and the correction control of the voltage are explained.

Here, the frequency droop control step S120 is explained. When load 130 is input and ac power is output, power conversion device 200(PCS1, PCS2) performs droop control to lower the output frequency from the rated frequency, as shown in fig. 12 a and 14. As shown in fig. 14, since the power conversion device 200(PCS1) has an earlier inverter control timing than the power conversion device 200(PCS2), the power conversion device 200(PCS1) starts droop control first.

Specifically, the droop control unit 230 of the power conversion device 200(PCS1) derives the frequency droop (- ω 1) based on the contributing active power (P ω 1). The feedback control unit 221 of the frequency-voltage control unit 220 performs droop control for reducing the output frequency by the droop amount (- ω 1) from the rated reduction frequency, using a value obtained by adding the droop amount (- ω 1) to the rated frequency as a frequency command value. Accordingly, as shown in fig. 14, the frequency-voltage control unit 220 reduces the output frequency by the frequency droop (- ω 1) during the control period Δ t of the inverter. As shown in fig. 14, the feedback control unit 221 performs droop control during the control period Δ t of the inverter.

As shown in fig. 14, the power conversion device 200(PCS2) starts the droop control after the droop control of the power conversion device 200(PCS1) is started and before the end of the droop control.

Specifically, the droop control unit 230 of the power conversion device 200(PCS2) derives the frequency droop (- ω 2) based on the contributing active power (P ω 2). The feedback control unit 221 of the frequency-voltage control unit 220 performs droop control for reducing the output frequency by the droop amount (- ω 2) from the rated reduction frequency, using a value obtained by adding the droop amount (- ω 2) to the rated frequency as a frequency command value. Accordingly, the frequency-voltage control unit 220 reduces the output frequency by the frequency droop amount (- ω 2) during the control period Δ t of the inverter.

The frequency droop amounts in the power conversion devices 200(PCS1, PCS2) are almost equal in the respective power conversion devices 200(PCS1, PCS 2). However, as described above, since the timing for performing the droop control differs between the power conversion devices 200(PCS1 and PCS2), a deviation occurs in the reflection of the amount of frequency droop in accordance with the contribution of active power. Due to this deviation, the current flows between the power conversion devices 200(PCS1, PCS2) as a cross current. However, during the control period Δ t of the next inverter, such a deviation converges, and as shown in fig. 12 (a) and 14, the power conversion devices 200(PCS1 and PCS2) are balanced by the same frequency droop (- ω 1- ω 2) corresponding to the respective contributing active powers.

[ frequency correction control step S125]

Next, the frequency correction control step S125 will be described. After the droop control is performed, the power conversion device 200(PCS1) performs correction control for gradually correcting the frequency to the rated frequency from time T2 in fig. 14. As shown in fig. 14, since the power conversion device 200(PCS1) has an earlier inverter control timing than the power conversion device 200(PCS2), the power conversion device 200(PCS1) first starts the correction control of the output frequency.

For example, the command value correction unit 243 of the power conversion device 200(PCS1) multiplies the contributing active power monitored by the output condition monitoring unit 241 and the frequency droop rate read out from the data storage unit 242 to derive a frequency correction value (+ ω 1), and inputs the frequency correction value (+ ω 1) to the frequency first order lag element 244 ω. The frequency first-order lag element 244 ω outputs a frequency gradual correction value (+ Δ ω 1) based on the input frequency correction value. The command value correcting unit 243 sets a value obtained by adding the frequency gradual correction value (+ Δ ω 1) output from the frequency first-order lag element 244 ω to the rated frequency read from the data storage unit 242 as a frequency target value that defines the output frequency in the process of gradually correcting the output frequency to the rated frequency. The command value correcting unit 243 outputs the frequency target value set here to the frequency-voltage control unit 220. The frequency-voltage control unit 220 performs correction control of the output frequency using the target frequency value input from the command value correction unit 243 as a frequency command value.

At this time, the output frequency of the power conversion device 200(PCS1) is increased by the correction control. Therefore, as shown in fig. 12 (b), the active power contributed by the power converter 200(PCS2) decreases, and the active power contributed by the power converter 200(PCS1) increases.

Then, when the time T3 comes after the correction control in the power converter 200(PCS1) is started, the power converter 200(PCS2) also starts the correction control of the output frequency.

For example, the command value correction unit 243 of the power conversion device 200(PCS2) multiplies the contributing active power monitored by the output condition monitoring unit 241 and the frequency droop rate read out from the data storage unit 242 to derive a frequency correction value (+ ω 2), and inputs the frequency correction value (+ ω 2) to the frequency first order lag element 244 ω. The frequency first-order lag element 244 ω outputs a frequency gradual correction value (+ Δ ω 2) based on the input frequency correction value. The command value correcting unit 243 sets a value obtained by adding the frequency gradual correction value (+ Δ ω 2) output from the frequency first-order lag element 244 ω to the rated frequency read from the data storage unit 242 as a frequency target value that defines the output frequency in the process of gradually correcting the output frequency to the rated frequency. The command value correcting unit 243 outputs the frequency target value set here to the frequency-voltage control unit 220. As shown in fig. 12 (c), the frequency-voltage control unit 220 performs correction control of the output frequency using the frequency target value input from the command value correction unit 243 as a frequency command value.

At this time, the output frequency of the power conversion device 200(PCS2) is increased by the correction control. Therefore, as shown in fig. 12 (c), the active power contributed by the power converter 200(PCS1) decreases, and the active power contributed by the power converter 200(PCS2) increases.

While the power conversion device 200(PCS2) is performing the correction control, the power conversion device 200(PCS1) starts the next correction control by the gradual correction value (+2 Δ ω 1) as shown in fig. 14. While the power conversion device 200(PCS2) performs the correction control for the gradual correction value (+2 Δ ω 1) portion, the power conversion device 200(PCS2) starts the correction control for the gradual correction value (+2 Δ ω 21). By repeating such operations, each power conversion device 200(PCS1, PCS2) corrects the output frequency to the rated frequency as shown in fig. 12 (d) and 14.

[ Voltage sag control step S130]

Next, the voltage droop control step S130 will be described. When load 130 is input and ac power is output, power conversion device 200(PCS1, PCS2) performs droop control for reducing the output voltage from the rated voltage, as shown in fig. 13 a and 15. As shown in fig. 15, since the power conversion device 200(PCS1) has an earlier inverter control timing than the power conversion device 200(PCS2), the power conversion device 200(PCS1) starts droop control first.

Specifically, the droop control unit 230 of the power conversion device 200(PCS1) derives the voltage droop (-v1) based on the contributing reactive power (Qv 1). The feedback control unit 221 of the frequency-voltage control unit 220 performs droop control for reducing the output voltage by the rated voltage droop (-v1) by using a value obtained by adding the voltage droop (-v1) to the rated voltage as a voltage command value. Accordingly, as shown in fig. 15, the frequency-voltage control unit 220 reduces the output voltage by the voltage droop (-v1) during the control period Δ t of the inverter. As shown in fig. 15, the feedback control unit 221 performs droop control during the control period Δ t of the inverter.

As shown in fig. 15, the power conversion device 200(PCS2) starts droop control after droop control of the power conversion device 200(PCS1) is started and before the droop control is ended.

Specifically, the droop control unit 230 of the power conversion device 200(PCS2) derives the voltage droop (-v2) based on the contributing reactive power (Qv 2). The feedback control unit 221 of the frequency-voltage control unit 220 performs droop control for reducing the output voltage by the rated voltage droop (-v2) by using a value obtained by adding the voltage droop (-v2) to the rated voltage as a voltage command value. Accordingly, the frequency-voltage control unit 220 reduces the output voltage by the voltage droop (-v2) during the control period Δ t of the inverter.

The voltage sag amounts in the power conversion devices 200(PCS1, PCS2) are almost equal in the power conversion devices 200(PCS1, PCS 2). However, as described above, the timing for performing the droop control differs between the power conversion devices 200(PCS1 and PCS2), and therefore, a variation occurs in the response of the voltage droop amount corresponding to the contribution of the reactive power. Due to this deviation, the current flows between the power conversion devices 200(PCS1, PCS2) as a cross current. However, during the control period Δ t of the next inverter, such a deviation converges, and as shown in fig. 13 (a) and fig. 15, the power conversion devices 200(PCS1 and PCS2) are balanced by the same voltage sag (-v1 to v2) corresponding to the respective contributing reactive powers.

[ Voltage correction control step S135]

Next, the voltage correction control step S135 will be described. After the droop control is performed, the power conversion device 200(PCS1) performs correction control for gradually correcting the voltage to the rated voltage from time T2 in fig. 15. As shown in fig. 15, since the power conversion device 200(PCS1) has an earlier inverter control timing than the power conversion device 200(PCS2), the power conversion device 200(PCS1) first starts the correction control of the output voltage.

For example, the command value correction unit 243 of the power conversion device 200(PCS1) multiplies the contribution active power monitored by the output condition monitoring unit 241 and the voltage droop rate read out from the data storage unit 242 to derive a voltage correction value (+ v1), and inputs the voltage correction value (+ v1) to the voltage first-order lag element 244 v. The voltage first-order lag element 244v outputs a voltage gradual correction value (+ Δ v1) based on the input voltage correction value. The command value correcting unit 243 sets a value obtained by adding the voltage gradual correction value (+ Δ v1) output from the voltage first-order lag element 244v to the rated voltage read from the data storage unit 242 as a voltage target value that defines the output voltage in the process of gradually correcting the output voltage to the rated voltage. The command value correcting unit 243 outputs the voltage target value set here to the frequency-voltage control unit 220. The frequency-voltage control unit 220 performs correction control of the output voltage using the voltage target value input from the command value correction unit 243 as a voltage command value.

At this time, the output voltage of the power conversion device 200(PCS1) is increased by the correction control. Therefore, as shown in fig. 13 (b), the reactive power contributed by the power conversion device 200(PCS2) decreases, and the reactive power contributed by the power conversion device 200(PCS1) increases.

When the time T3 is reached after the correction control in the power conversion device 200(PCS1) is started, the power conversion device 200(PCS2) also starts the correction control of the output voltage.

For example, the command value correction unit 243 of the power conversion device 200(PCS2) multiplies the contribution active power monitored by the output condition monitoring unit 241 and the voltage droop rate read out from the data storage unit 242 to derive a voltage correction value (+ v2), and inputs the voltage correction value (+ v2) to the voltage first-order lag element 244 v. The voltage first-order lag element 244v outputs a voltage gradual correction value (+ Δ v2) based on the input voltage correction value. The command value correcting unit 243 sets a value obtained by adding the voltage gradual correction value (+ Δ v2) output from the voltage first-order lag element 244v to the rated voltage read from the data storage unit 242 as a voltage target value that defines the output voltage in the process of gradually correcting the output voltage to the rated voltage. The command value correcting unit 243 outputs the voltage target value set here to the frequency-voltage control unit 220. As shown in fig. 13 (c), the frequency-voltage control unit 220 performs correction control of the output voltage using the voltage target value input from the command value correction unit 243 as a voltage command value.

At this time, the output voltage of the power conversion device 200(PCS2) is increased by the correction control. Therefore, as shown in fig. 13 (c), the reactive power contributed by the power conversion device 200(PCS1) decreases, and the reactive power contributed by the power conversion device 200(PCS2) increases.

While the power conversion device 200(PCS2) is performing the correction control, the power conversion device 200(PCS1) starts the next correction control by the gradual correction value (+2 Δ v1) as shown in fig. 15. While the power conversion device 200(PCS2) performs correction control for the gradual correction value (+2 Δ v1) portion, the power conversion device 200(PCS2) starts correction control for the gradual correction value (+2 Δ v21) portion. By repeating such operations, the output voltage of each power conversion device 200(PCS1, PCS2) is modified to the rated voltage as shown in fig. 13 (d) and fig. 15.

Through these steps S110 to S135, the power conversion device 200(PCS1, PCS2) controls the output frequency and output voltage of the ac power to be output. Here, the case where two power conversion devices 200(PCS1, PCS2) are operated in parallel has been described, but the present invention is not limited to this, and for example, three or more power conversion devices 200 may be connected in parallel.

According to the present embodiment, correction control is gradually performed in each of the plurality of power conversion devices 200(PCS1, PCS 2). Accordingly, even if the output frequency and the output voltage are corrected to the rated values by the correction control, the real power and the reactive power contributed by each of the power conversion devices 200(PCS1 and PCS2) can be maintained substantially equal before and after the correction.

Further, according to the present embodiment, after the droop control is performed, the correction control is performed. Accordingly, when the plurality of power conversion devices 200 are operated in parallel, the contribution of active power and the contribution of reactive power can be shared fairly among the power conversion devices 200. Therefore, the frequency and voltage can be maintained at the rated values while the controllability of sharing the load fairly is effectively utilized.

Further, since the correction control is performed after the droop control is performed, it is not necessary to reduce the droop amount in order to suppress the deviation from the rated value. This makes it possible to share information of the contributing power with the other power conversion devices 200(PCS1, PCS2) without degrading the control accuracy required for load sharing.

Here, differences between the power conversion device studied by the present inventors and the power conversion device 200 according to the present embodiment will be studied. Fig. 40 is a graph showing droop characteristics of the output frequency and the output voltage in the power converter studied by the present inventors. Fig. 41 is a diagram showing a timing chart relating to control of frequency and voltage in the power converter studied by the present inventors. Here, a case is shown in which the correction control is not performed after the droop control is performed.

When the droop control is performed, as shown in fig. 40 (a), the power conversion devices (PCS1 and PCS2) are balanced in a state where the output frequency is drooped from the rated frequency by the frequency droop amount (- ω 1). As shown in fig. 40 (b), the power conversion devices (PCS1 and PCS2) are balanced in a state where the output voltage is lowered by the voltage sag (-v1) from the rated voltage.

As shown in fig. 41, both power conversion devices (PCS1 and PCS2) supply ac power with the output frequency dropped by a frequency drop (- ω 1) from the rated frequency. As shown in fig. 41, both power conversion devices (PCS1 and PCS2) output ac power with the output voltage lowered by the voltage sag (-v1) from the rated voltage.

In this way, in the power converter studied by the present inventors, the output frequency and the output voltage cannot be corrected to the rated values in the state where the droop control is performed. Therefore, if the droop control is performed while suppressing the amount of droop, the control accuracy required for load sharing is lowered. Further, information that it is difficult to share the contributing power with other power conversion devices 200(PCS1, PCS2) may also occur.

(embodiment mode 3)

In the present embodiment, the following will be explained: when a plurality of power conversion devices are operated in parallel, the frequency correction values and the voltage correction values of all the power conversion devices in parallel operation are shared among the power conversion devices, and correction control is performed in cooperation with each other.

Fig. 16 is a diagram illustrating an example of the configuration of the power conversion device according to the present embodiment.

Fig. 17 is a diagram showing an example of the configuration of the command value correction unit in the correction control unit. Fig. 18 is a diagram showing an example of the configuration of the cooperation control unit in the correction control unit.

The power conversion device 300 includes a power conversion unit 210, a voltage detection unit 214, a current detection unit 215, and an alternating current power control unit 350.

The ac power control unit 350 includes a droop control unit 230, a correction control unit 340, and a frequency-voltage control unit 220.

As shown in fig. 16, the correction control unit 340 includes an output status monitoring unit 241, a data storage unit 242, a command value correction unit 343, a cooperation control unit 345, and a network interface unit 346.

The network interface unit 346 performs data transmission and reception with the other power conversion device 300 related to the parallel operation. Specifically, the network interface unit 346 realizes elements required for general network communication, such as elements satisfying a network protocol used for communication with the plurality of power conversion devices 300 and communication arbitration for each purpose.

The network interface unit 346 receives an external frequency correction value and an external voltage correction value, which will be described later, of another power conversion device 300 participating in the parallel operation. Specifically, the correction value entry control unit 361 described later refers to all other power conversion devices 300 participating in the parallel operation via the network interface unit 346. All the other power conversion devices 300 transmit the internal frequency correction value and the internal voltage correction value held by each power conversion device 300 as the external frequency correction value and the external voltage correction value. The network interface unit 346 receives the transmitted external frequency correction value and external voltage correction value of all other power conversion devices 300. The network interface unit 346 transmits the received external frequency correction value and external voltage correction value of the other power conversion device 300 to the cooperation control unit 345. The network interface unit 346 transmits its own internal frequency correction value and internal voltage correction value to the other power conversion device 300 as an external frequency correction value and an external voltage correction value.

The cooperative control unit 345 performs correction control in cooperation with the other power conversion devices 300 involved in the parallel operation. As shown in fig. 18, the cooperative control unit 345 includes a correction value entry control unit 361, an external frequency correction value storage unit 362 ω, an external frequency correction value comparison unit 363 ω, an external voltage correction value storage unit 362v, and an external voltage correction value comparison unit 363 v.

The correction value entry control unit 361 receives the input of the external frequency correction value and the external voltage correction value of another power conversion device 300 transmitted from the network interface unit 346. The correction value entry control unit 361 outputs the external frequency correction value of the input external frequency correction value and external voltage correction value to the external frequency correction value storage unit 362 ω and outputs the external voltage correction value to the external voltage correction value storage unit 362 v. The external frequency correction value storage section 362 ω stores the input external frequency correction value. The external voltage correction value storage unit 362v stores the input external voltage correction value.

The correction value entry control unit 361, the external frequency correction value storage unit 362 ω, and the external voltage correction value storage unit 362v perform these operations for all other power conversion devices 300 participating in the parallel operation.

The external frequency correction value comparing unit 363 ω compares all the external frequency correction values stored in the external frequency correction value storage unit 362 ω and outputs the maximum external frequency correction value to the command value correcting unit 343 as the maximum external frequency correction value. Specifically, the external frequency correction value comparison unit 363 ω reads all the external frequency correction values stored in the external frequency correction value storage unit 362 ω, compares the respective external frequency correction values, and outputs the maximum external frequency correction value to the command value correction unit 343 as the maximum external frequency correction value.

The external voltage correction value comparing unit 363v compares all the external voltage correction values stored in the external voltage correction value storage unit 362v, and outputs the maximum external voltage correction value to the command value correcting unit 343 as the maximum external voltage correction value. Specifically, the external voltage correction value comparison unit 363v reads all the external voltage correction values stored in the external voltage correction value storage unit 362v, compares the respective external voltage correction values, and outputs the maximum external voltage correction value to the command value correction unit 343 as the maximum external voltage correction value.

The command value correcting unit 343 specifies the output frequency and the output voltage in the correction control. As shown in fig. 17, the command value correcting unit 343 includes a frequency correction value comparing unit 347 ω, a voltage correction value comparing unit 347v, a first-order frequency lag element 244 ω, and a first-order voltage lag element 244 v.

The command value correction unit 343 multiplies the contributing active power monitored by the output condition monitoring unit 241 by the frequency droop rate stored in the data storage unit 242 to derive an internal frequency correction value. The derived internal frequency correction value is input to the frequency correction value comparison section 347 ω.

The frequency correction value comparison unit 347 ω receives an input of the maximum external frequency correction value output from the external frequency correction value comparison unit 363 ω. The frequency correction value comparison unit 347 ω compares the internal frequency correction value and the maximum external frequency correction value, and derives a larger value of either the internal frequency correction value or the maximum external frequency correction value as the frequency correction value. The frequency correction value inputs the frequency correction value to the frequency first order lag element 244 ω. The command value correction unit 343 sets a value obtained by adding the frequency gradual correction value output from the frequency first-order lag element 244 ω to the rated frequency as a frequency target value that defines the output frequency in the process of gradually correcting the output frequency to the rated frequency.

As described above, in the present embodiment, the frequency correction value is used as the maximum frequency correction value among the frequency correction values of all the power conversion devices 300 participating in the parallel operation. That is, in all the power conversion devices 300, the same frequency correction value is used for correction control, and therefore correction control is performed in cooperation with each other.

The command value correction unit 343 multiplies the contributing reactive power monitored by the output condition monitoring unit 241 by the voltage droop rate stored in the data storage unit 242 to derive an internal voltage correction value. The derived internal voltage correction value is input to the voltage correction value comparison section 347 v.

The voltage correction value comparison unit 347v receives an input of the maximum external voltage correction value output from the external voltage correction value comparison unit 363 v. The voltage correction value comparison unit 347v compares the internal voltage correction value and the maximum external voltage correction value, and derives a larger value of the internal voltage correction value and the maximum external voltage correction value as the voltage correction value. Voltage correction value the voltage correction value is input to the voltage first order lag element 244 v. The command value correcting unit 343 sets a value obtained by adding the rated voltage to the voltage gradual correction value output from the voltage first-order lag element 244v as a voltage target value that defines the output voltage in the process of gradually correcting the output voltage to the rated voltage.

In this way, in the present embodiment, the maximum voltage correction value among the voltage correction values of all the power conversion devices 300 participating in the parallel operation is used as the voltage correction value. That is, in all the power conversion devices 300, the same voltage correction value is used for correction control, and therefore correction control is performed in cooperation with this.

Each part and each function constituting the correction control unit 340 may be configured by hardware or software. When each unit and each function constituting the correction control unit 340 are realized by software, the correction control unit 340 includes, for example, a CPU (or a dedicated processor) not shown, and the CPU executes a program stored in a memory or the like not shown to realize each unit and each function.

The correction control unit 340 can be realized by using, for example, a Programmable Logic Controller (PLC) mounted on the power conversion device 300.

[ method for controlling frequency and voltage when time constant is large ]

Here, a method of controlling a frequency and a voltage using the power conversion device 300 according to the present embodiment will be described. Here, a case where two power conversion devices 300(PCS1, PCS2) participate in the parallel operation will be described.

For convenience of explanation, the control cycle of the power conversion unit (inverter) 210 is denoted by Δ T, and the control cycle Δ T of the correction control unit (PLC) is denoted by 4 Δ T. The time constants of the frequency first order lag element 244 ω and the voltage first order lag element 244v are set to 4 Δ T. In the two power conversion devices 300(PCS1 and PCS2), the control cycle Δ t of the inverter is the same, and the control timing of the inverter and the control timing of the PLC are different.

First, a case where the time constants of the frequency first order lag element 244 ω and the voltage first order lag element 244v are large will be described. Fig. 19 is a diagram showing a flowchart relating to frequency control and voltage control in the present embodiment. Fig. 20 is a diagram showing droop characteristics relating to frequency control in the case where the time constant is large. Fig. 21 is a diagram showing droop characteristics relating to voltage control in the case where the time constant is large. Fig. 22 is a diagram showing a timing chart relating to frequency control in the case where the time constant is large. Fig. 23 is a diagram showing a timing chart relating to voltage control in the case where the time constant is large.

As shown in fig. 19, the power conversion device 300 controls the output frequency and the output voltage of the ac power by performing each of the rated output step S210, the frequency droop control step S220, the frequency correction control step S225, the voltage droop control step S230, and the voltage correction control step S235. The rated output step S210, the frequency droop control step S220, and the voltage droop control step S230 are respectively controlled in the same manner as the rated output step S110, the frequency droop control step S120, and the voltage droop control step S130 in embodiment 2, and therefore, the description thereof is omitted here.

[ frequency correction control step S225]

The frequency correction control step S225 will be described. The frequency correction value comparison unit 347 ω of the power conversion device 300(PCS1) compares the external frequency correction value output from the external frequency correction value comparison unit 363 ω of the cooperative control unit 345 with the internal frequency correction value derived by the command value correction unit 343, and derives either one of the larger values as the frequency correction value. The frequency correction value comparison unit 347 ω inputs the derived frequency correction value to the frequency first order lag element 244 ω. The frequency first-order lag element 244 ω outputs a frequency gradual correction value based on the input frequency correction value. The feedback control unit 221 performs frequency correction control based on the frequency gradual correction value. In this way, correction control is performed with the largest value among the internal frequency correction values of all the power conversion devices 300(PCS1, PCS2) participating in parallel operation as a frequency correction value.

The power conversion device 300(PCS2) also derives the same frequency correction value as the power conversion device 300(PCS1), and performs frequency correction control based on the frequency correction value in cooperation therewith.

Here, when the time constant is large, the frequency gradual correction value output by the frequency first order lag element 244 ω does not immediately reflect the frequency target value (frequency command value). Therefore, a large imbalance in the contribution active power between the power conversion device 300(PCS1) and the power conversion device 300(PCS2) due to the correction value does not occur. As shown in fig. 12, 14, 20, and 22, the frequency correction control in this case is almost the same as the frequency correction control in the frequency correction control step S125 in embodiment 2.

[ Voltage correction control step S235]

The voltage correction control step S235 will be described. The voltage correction value comparison unit 347v of the power conversion device 300(PCS1) compares the external voltage correction value output from the external voltage correction value comparison unit 363v of the cooperative control unit 345 with the internal voltage correction value derived by the command value correction unit 343, and derives any one of the larger values as the voltage correction value. The voltage correction value comparison unit 347v inputs the derived voltage correction value to the voltage first-order lag element 244 v. The voltage first-order lag element 244v outputs a voltage gradual correction value based on the input voltage correction value. The feedback control unit 221 performs voltage correction control based on the voltage gradual correction value. In this way, correction control is performed with the largest value among the internal voltage correction values of all the power conversion devices 300(PCS1, PCS2) participating in parallel operation as the voltage correction value.

The power conversion device 300(PCS2) also derives the same voltage correction value as the power conversion device 300(PCS1), and performs voltage correction control based on the voltage correction value in cooperation therewith.

Here, when the time constant is large, the voltage gradual correction value output by the voltage first-order lag element 244v does not immediately reflect the voltage target value (voltage command value). Therefore, a large imbalance in the contribution reactive power between the power conversion device 300(PCS1) and the power conversion device 300(PCS2) due to the correction value does not occur. As shown in fig. 13, 15, 21, and 23, the voltage correction control in this case is almost the same as the voltage correction control in the voltage correction control step S135 in embodiment 2.

[ method for controlling frequency and voltage when time constant is small ]

Next, a case where the time constants of the frequency first order lag element 244 ω and the voltage first order lag element 244v are small will be described. Fig. 24 is a diagram showing droop characteristics relating to frequency control in the case where the time constant is small. Fig. 25 is a diagram showing droop characteristics relating to voltage control in the case where the time constant is small. Fig. 26 is a diagram showing a timing chart relating to frequency control in the case where the time constant is small. Fig. 27 is a diagram showing a timing chart relating to voltage control in the case where the time constant is small.

In the following, as an example of a case where the time constant is small, the time constant of the frequency first order lag element 244 ω and the voltage first order lag element 244v is set to 2 Δ T.

[ frequency correction control step S225]

Before the frequency correction control is performed, as shown in fig. 24 (a), the frequency droop amount (the contribution active power) is in a state of being balanced between the power conversion devices 300(PCS1, PCS 2).

When the time constant is small, the frequency gradual correction value output by the frequency first order lag element 244 ω immediately reflects the frequency target value (frequency command value). Therefore, when the power converter 300(PCS1) performs the frequency correction control at time T2, the contribution active power of the power converter 300(PCS1) temporarily and rapidly increases, the contribution active power of the power converter 300(PCS2) temporarily and rapidly decreases, and an unbalanced state of the contribution active power occurs, as shown in fig. 24 (b) and fig. 26.

The power conversion device 300(PCS2) performs frequency correction control at time T3. The power conversion device 300(PCS2) uses the frequency correction value of the power conversion device 300(PCS1) as a result of comparing the magnitude of the frequency correction value of the power conversion device 300(PCS1) with the magnitude of the frequency correction value of the power conversion device 300(PCS1) itself, without using the frequency correction value calculated from the contribution active power that is rapidly reduced by itself. Then, as shown in fig. 24 (c) and fig. 26, the imbalance of the contributing active power is eliminated. By repeating these frequency correction controls, as shown in fig. 24 d and 26, power conversion device 300(PCS1 and PCS2) corrects the output frequency to the rated value. At this time, in power conversion device 300(PCS1, PCS2), the contributing active power before and after the frequency correction control is maintained almost equal.

[ Voltage correction control step S235]

Before the voltage correction control is performed, as shown in fig. 25 (a), the voltage sag (contributing reactive power) is balanced between the power conversion devices 300(PCS1 and PCS 2).

When the time constant is small, the voltage gradual correction value output from the voltage first-order lag element 244v immediately reflects the voltage target value (voltage command value). Therefore, when the power conversion device 300(PCS1) performs the voltage correction control at the time T2, as shown in fig. 25 (b) and 27, the contribution reactive power of the power conversion device 300(PCS1) temporarily and rapidly increases, the contribution reactive power of the power conversion device 300(PCS2) temporarily and rapidly decreases, and an unbalanced state of the contribution reactive power occurs.

The power conversion device 300(PCS2) performs voltage correction control at time T3. The power conversion device 300(PCS2) uses the voltage correction value of the power conversion device 300(PCS1) as a result of comparing the voltage correction value of the power conversion device 300(PCS1) with the voltage correction value of the power conversion device 300(PCS1) itself, without using the voltage correction value calculated from the rapidly decreasing contribution reactive power itself. Then, as shown in fig. 25 (c) and 27, the imbalance of the contributing reactive power is eliminated. By repeating these voltage correction controls, as shown in fig. 25 d and 27, power conversion device 300(PCS1 and PCS2) corrects the output voltage to the rated value. At this time, in the power conversion device 300(PCS1, PCS2), the contributing reactive power before and after the frequency correction control is maintained almost equal.

According to the present embodiment, the maximum value among the internal frequency correction values of all the power conversion devices 300(PCS1, PCS2) participating in the parallel operation is derived as the frequency correction value. Accordingly, all the power conversion devices 300(PCS1, PCS2) can derive the maximum value as a common frequency correction value, and perform frequency correction control in cooperation with each other.

Although the time constant of the first-order frequency lag element 244 ω is small and the gradual frequency correction value output by the first-order frequency lag element 244 ω immediately reflects the frequency target value (frequency command value), the imbalance in the contribution active power due to the frequency correction control of the power converter 300(PCS1) is eliminated by the frequency correction control of the power converter 300(PCS2) according to the present embodiment. Accordingly, in the power conversion device 300(PCS1, PCS2), the contributing active power before and after the frequency correction control is maintained almost equal.

In addition, according to the present embodiment, the maximum value among the internal voltage correction values of all the power conversion devices 300(PCS1, PCS2) participating in the parallel operation is derived as the voltage correction value. Accordingly, all the power conversion devices 300(PCS1, PCS2) can derive the maximum value as a common voltage correction value, and perform voltage correction control in cooperation with each other.

Although the time constant of the voltage first-order lag element 244v is small and the voltage gradual correction value output by the voltage first-order lag element 244v immediately reflects the voltage target value (voltage command value), the voltage correction control of the power converter 300(PCS1) eliminates imbalance in the contribution reactive power according to the present embodiment, which occurs due to the voltage correction control of the power converter 300(PCS 2). Accordingly, in the power conversion device 300(PCS1, PCS2), the contributing reactive power before and after the voltage correction control is maintained almost equal.

Here, differences between the power conversion device studied by the present inventors and the power conversion device 300 according to the present embodiment are studied. Fig. 42 is a graph showing droop characteristics of the output frequency in the power converter studied by the present inventors. Fig. 43 is a graph showing the droop characteristics of the output voltage in the power converter studied by the present inventors. Fig. 44 is a diagram showing a timing chart relating to frequency control in the power converter studied by the present inventors. Fig. 45 is a diagram showing a timing chart relating to voltage control in the power converter studied by the present inventors.

In the power conversion device (for example, the power conversion device 200 according to embodiment 2) studied by the present inventors, for example, the power conversion devices participating in the parallel operation perform the frequency correction control not based on the common frequency correction value but using the individual frequency correction values derived in the respective power conversion devices.

Therefore, when the time constant of the first-order frequency lag element is small, for example, when the contribution active power becomes unbalanced by the frequency correction control of the power conversion device (PCS1) as shown in fig. 42 (b) and fig. 44, the imbalance of the contribution active power cannot be eliminated even by the frequency correction control of the subsequent power conversion device (PCS2) as shown in fig. 42 (c) and fig. 44. Then, as shown in fig. 42 (d) and 44, even if the frequency correction control is completed, the contribution active power becomes unbalanced.

Similarly, the power conversion devices participating in the parallel operation do not perform the voltage correction control based on the common voltage correction value, but perform the voltage correction control using the individual voltage correction values derived in the respective power conversion devices.

Therefore, when the time constant of the voltage first-order lag element is small, for example, when the contribution reactive power becomes unbalanced by the voltage correction control of the power conversion device (PCS1) as shown in fig. 43 (b) and 45, the imbalance of the contribution reactive power cannot be eliminated even by the voltage correction control of the power conversion device (PCS2) after the voltage correction control as shown in fig. 43 (c) and 45. Then, as shown in fig. 43 (d) and 45, even when the voltage correction control is completed, the reactive power contribution becomes unbalanced.

(embodiment mode 4)

In the present embodiment, a case will be described in which a new power conversion device is caused to participate in parallel operation with respect to an already operating power conversion device by applying an operation in which the power conversion devices participating in parallel operation share a frequency correction value and a voltage correction value and perform correction control in cooperation with each other.

Fig. 28 is a diagram showing an example of the configuration of the power conversion device according to the present embodiment.

Fig. 29 is a diagram showing an example of the configuration of the command value correction unit in the correction control unit.

As shown in fig. 28, the power conversion device 400 includes a power conversion unit 210, a voltage detection unit 214, a current detection unit 215, and an alternating current power control unit 450.

The ac power control unit 450 includes a droop control unit 230, a correction control unit 440, and a frequency-voltage control unit 220.

As shown in fig. 28, the correction control unit 440 includes an output status monitoring unit 241, a data storage unit 242, a command value correction unit 443, a cooperation control unit 345, and a network interface unit 346.

As shown in fig. 28 and 29, the command value correction unit 443 includes a frequency correction value comparison unit 347 ω, a voltage correction value comparison unit 347v, a frequency correction switch unit 444 ω, a voltage correction switch unit 444v, a frequency first-order lag element 244 ω, and a voltage first-order lag element 244 v.

The frequency correction switching unit 444 ω selects whether or not the frequency correction value output from the frequency correction value comparing unit 347 ω is input to the first-order lag element 244 ω. When the frequency correction switch 444 ω is activated (Active), the frequency correction value is input to the frequency first-order lag element 244 ω, and frequency correction control is performed. When the frequency correction switch 444 ω is deactivated, the frequency correction value is not input to the frequency first-order lag element 244 ω, and the frequency correction control is not performed. That is, switching frequency correction switch 444 ω to the active state is a parallel command instructing power converter 300 to perform parallel operation.

The voltage correction switch 444v selects whether or not the voltage correction value output from the voltage correction value comparison portion 347v is input to the voltage first-order lag element 244 v. When the voltage correction switch 444v is activated, the voltage correction value is input to the voltage first-order lag element 244v, and voltage correction control is performed. When the voltage correction switch 444v is deactivated, the voltage correction value is not input to the voltage first-order lag element 244v, and the voltage correction control is not performed. That is, switching of the voltage correction switch 444v to the active state is a parallel command instructing the power conversion device 300 to perform parallel operation.

Each part and each function constituting the correction control unit 440 may be configured by hardware or software. When each unit and each function constituting the correction control unit 440 are realized by software, the correction control unit 440 includes, for example, a CPU (or a dedicated processor) not shown, and the CPU executes a program stored in a memory or the like not shown to realize each unit and each function.

The correction control unit 440 can be realized by using, for example, a Programmable Logic Controller (PLC) mounted on the power conversion device 300.

[ method for controlling frequency and voltage during parallel operation ]

Next, a method of causing the power conversion device 400 according to the present embodiment to participate in the parallel operation will be described.

Here, a case where another power conversion device 300(PCS2) is operated in parallel with the power conversion device 400(PCS1) that supplies ac power to the load 130 will be described. In the two power conversion devices 300(PCS1 and PCS2), the control cycle Δ t of the inverter is the same, and the control timing of the inverter and the control timing of the PLC are different.

Fig. 30 is a diagram showing a flowchart relating to frequency control and voltage control during parallel operation. Fig. 31 is a diagram illustrating droop characteristics related to frequency control during parallel operation. Fig. 32 is a diagram illustrating droop characteristics related to voltage control during parallel operation. Fig. 33 is a diagram showing a timing chart relating to frequency control in the parallel operation. Fig. 34 is a diagram showing a timing chart relating to voltage control in the parallel operation.

As shown in fig. 30, in order to participate in the parallel operation, the output frequency and the output voltage of the ac power are controlled by performing the respective steps of the rated output step S310, the frequency droop control step S320, the frequency correction control step S325, the voltage droop control step S330, and the voltage correction control step S335.

[ rated output step S310, frequency droop control step S320]

In the initial state, power conversion device 300(PCS1) outputs ac power at a rated frequency and a rated voltage and supplies the ac power to load 130. Then, at time T1, the power conversion device 300(PCS2) is connected to the ac power line 120. At this time, as shown in fig. 31 (a), 32 (a), 33, and 34, both the contributing active power and the contributing reactive power from the power conversion device 300(PCS2) are "0". At this time, the frequency correction switch 444 ω and the voltage correction switch 444v of the power conversion device 300(PCS2) are inactive.

Next, at time T2, frequency correction switch 444 ω is switched to the active state by the parallel command. As shown in fig. 31 (b) and 33, the power conversion device 300(PCS2) increases the output frequency and the contributing active power based on the frequency correction value of the power conversion device 300(PCS 1).

In this way, when another power conversion device 300(PCS2) is operated in parallel with respect to the power conversion device 300(PCS1) that supplies ac power to the load 130, the other power conversion device 300(PCS2) starts parallel operation with the frequency correction switch 444 ω and the voltage correction switch 444v inactive, and after the parallel operation is started, the frequency correction switch 444 ω and the voltage correction switch 444v are activated.

At the inverter control timing T3 of the power conversion device 300(PCS1), the active power contributed by the power conversion device 300(PCS1) is reduced as shown in fig. 31 (c) and 33. Along with this, the output frequency of the power conversion device 300(PCS1) temporarily increases.

As shown in fig. 33, since there is a deviation between the power conversion device 300(PCS1) and the power conversion device 300(PCS2) in the inverter control period, a deviation occurs in the frequency droop amount according to the contribution active power. In this case, the current flows between the power conversion device 300(PCS1) and the power conversion device 300(PCS2) as a cross current. Such currents converge during the inverter control period Δ t, and are balanced when the output frequencies of the power conversion devices 300(PCS1 and PCS2) are the same.

[ frequency correction control step S325 and Voltage droop control step S330]

Next, at the inverter control timing (T2+ Δ T) of the next power conversion device 300(PCS2), the power conversion device 300(PCS2) sets the maximum value of the internal frequency correction values of all the power conversion devices 300(PCS1, PCS2) participating in the parallel operation as the frequency correction value. The power conversion device 300(PCS2) performs frequency correction control based on the frequency correction value. At this time, as shown in fig. 31 (b) and 33, since the contribution active power of the power conversion device 300(PCS1) is larger than that of the power conversion device 300(PCS2), the internal frequency correction value of the power conversion device 300(PCS1) is larger if the frequency droop rates are almost equal. In this case, the power converter 300(PCS2) performs frequency correction control using the internal frequency correction value of the power converter 300(PCS1) as the frequency correction value.

In contrast, the output frequency of the power conversion device 300(PCS1) is corrected in accordance with the reduced contributing active power, and the output frequency is temporarily reduced as shown in fig. 31 (c) and 33. However, since the contribution active power from power conversion device 300(PCS2) increases, the contribution active power of power conversion device 300(PCS1) further decreases, and the output frequency increases accordingly.

When these operations are repeated, the frequency correction values of the power conversion device 300(PCS1) and the power conversion device 300(PCS2) are balanced. Then, the frequency correction values of power conversion device 300(PCS1) and power conversion device 300(PCS2) do not change, and ac power is supplied to load 130 while sharing the load fairly at the rated frequency, as shown in fig. 31 (d) and 33.

Next, voltage control is explained. At time T2, voltage correction switch 444v is switched to the active state by the parallel command. As shown in fig. 32 (b) and 34, the power conversion device 300(PCS2) increases the output voltage and the contributing reactive power based on the voltage correction value of the power conversion device 300(PCS 1).

In this way, when another power conversion device 300(PCS2) is operated in parallel with respect to the power conversion device 300(PCS1) that supplies ac power to the load 130, the other power conversion device 300(PCS2) starts parallel operation with the frequency correction switch 444 ω and the voltage correction switch 444v inactive, and after the parallel operation is started, the frequency correction switch 444 ω and the voltage correction switch 444v are activated.

At the inverter control timing T3 of the power conversion device 300(PCS1), the reactive power contributed by the power conversion device 300(PCS1) decreases as shown in fig. 32 (c) and 34. Along with this, the output voltage of the power conversion device 300(PCS1) temporarily increases.

As shown in fig. 34, since there is a deviation between the power conversion device 300(PCS1) and the power conversion device 300(PCS2) in the inverter control period, a deviation occurs in the voltage droop amount according to the contribution reactive power. In this case, the current flows between the power conversion device 300(PCS1) and the power conversion device 300(PCS2) as a cross current. Such currents converge during the inverter control period Δ t, and the output voltages of the power conversion devices 300(PCS1 and PCS2) are balanced when the same phase is established.

[ Voltage correction control step S335]

Next, at the inverter control timing (T2+ Δ T) of the next power conversion device 300(PCS2), the power conversion device 300(PCS2) sets the maximum value of the internal voltage correction values of all the power conversion devices 300(PCS1, PCS2) participating in the parallel operation as the voltage correction value. The power conversion device 300(PCS2) performs voltage correction control based on the voltage correction value. At this time, as shown in fig. 32 (b) and fig. 34, since the reactive power contribution of the power conversion device 300(PCS1) is larger than that of the power conversion device 300(PCS2), the internal voltage correction value of the power conversion device 300(PCS1) is large if the voltage droop rates are almost equal. In this case, the power converter 300(PCS2) performs voltage correction control using the internal voltage correction value of the power converter 300(PCS1) as the voltage correction value.

In contrast, in the power conversion device 300(PCS1), the output voltage is corrected in accordance with the reduced contributing reactive power, and the output voltage is temporarily reduced as shown in fig. 32 (c) and fig. 34. However, since the contribution reactive power from the power conversion device 300(PCS2) increases, the contribution reactive power of the power conversion device 300(PCS1) further decreases, and the output voltage increases accordingly.

When these operations are repeated, the voltage correction values of the power conversion device 300(PCS1) and the power conversion device 300(PCS2) are balanced. Then, the voltage correction values of power conversion device 300(PCS1) and power conversion device 300(PCS2) do not change any more, and ac power is supplied to load 130 while sharing the load on the level at the rated voltage as shown in fig. 32 (d) and fig. 34.

According to the present embodiment, in the power conversion device 300(PCS2), the parallel operation of the frequency correction switch unit 444 ω and the voltage correction switch unit 444v is started in an inactive state, and after the parallel operation is started, the frequency correction switch unit 444 ω and the voltage correction switch unit 444v are set to an active state. Accordingly, droop control and correction control can be performed on the power conversion device 300(PCS1) and the power conversion device 300(PCS2), and load can be shared fairly. In this way, the power conversion device 300(PCS2) can be operated in parallel.

Here, an example in which one power conversion device 300(PCS1) is caused to participate in the parallel operation in a state in which one power conversion device 300(PCS1) is caused to operate is described, but the present invention is not limited to this case. For example, one or more power conversion devices 300 may be put into parallel operation while a plurality of power conversion devices 300 are operated.

[ departure from parallel operation ]

By applying the control method according to the present embodiment, when parallel operation is performed by a plurality of power conversion devices 300, any one of the power conversion devices 300 can be disengaged from the parallel operation. Specifically, by invalidating the parallel command for the power conversion device 300 to be disengaged so as not to perform the correction control in the power conversion device 300 to be disengaged, the contributing active power and the contributing reactive power are gradually reduced to "0".

By combining such operations, it is possible to easily perform flexible system change in consideration of the amount of power generation or the amount of charge of the dc power supply.

(embodiment 5)

In this embodiment, a case where a solar cell panel (QV panel) is used as a dc power supply will be described. Fig. 35 is a diagram showing an example of a system according to the present embodiment. In the present embodiment, the power conversion devices 200 and 300 according to embodiments 1 to 3 described above are used to perform frequency and voltage droop control and correction control.

The power conversion devices 200 and 300(PCS1) have a solar panel 131 connected to the dc side and an ac power line 120 connected to the ac side. The power conversion devices 200 and 300(PCS2) have the solar panel 132 connected to the dc side and the ac power line 120 connected to the ac side.

Conventionally, when a solar panel is connected to a power conversion device that operates in parallel without a system, the active power and the reactive power that are contributed from the power conversion device vary according to the intensity of solar radiation that is applied to the solar panel. Since in most cases maximum power point control is implemented. Therefore, the amount of frequency and voltage droop caused by droop control also varies similarly to solar radiation.

However, by performing correction control of the frequency and voltage drooped by the droop control using the power conversion devices 200 and 300, it is possible to suppress the frequency fluctuation caused by the fluctuation of solar radiation.

(embodiment mode 6)

In this embodiment, a case where a battery is used as a dc power supply will be described. Fig. 36 is a diagram showing an example of a system according to the present embodiment. As shown in fig. 36, in the present embodiment, the frequency and voltage droop control and the correction control are performed by using the power conversion device 400 according to embodiment 4.

Power conversion device 400(PCS3) has battery 141 connected to the dc side and ac power line 120 connected to the ac side. The power conversion device 400(PCS4) has the battery 142 connected to the dc side and the ac power line 120 connected to the ac side.

In the past, when the parallel operation is performed in a state where no system exists, it was difficult to cause other power conversion devices to participate (put into) the parallel operation at any time or to leave in the middle. However, by combining the power conversion device 400 and the storage batteries 141 and 142, the power conversion device 400(PCS3, PCS4) can be put in and taken out at any time depending on the state of charge of the storage batteries 141 and 142. Thus, the optimum operation according to the state of charge of the battery can be performed.

(embodiment 7)

In this embodiment, a case where a solar panel and a battery are used in combination as a dc power supply will be described. Fig. 37 is a diagram showing an example of a system according to the present embodiment.

The power conversion devices 200 and 300(PCS1) have a solar panel 131 connected to the dc side and an ac power line 120 connected to the ac side. The power conversion devices 200 and 300(PCS2) have the solar panel 132 connected to the dc side and the ac power line 120 connected to the ac side. Power conversion device 400(PCS3) has battery 141 connected to the dc side and ac power line 120 connected to the ac side. The power conversion device 400(PCS4) has the battery 142 connected to the dc side and the ac power line 120 connected to the ac side.

According to this configuration, when the solar cell panel is subjected to the droop control and the correction control, the frequency fluctuation due to the fluctuation of the solar radiation can be suppressed. Further, by performing the droop control and the correction control on the battery, the power converter can be put into the battery at any time or can be disconnected from the battery depending on the state of charge of the battery. Thus, the battery can be optimally used.

Further, the power generated by the solar cell panel can be charged into the storage battery, and stable power supply to the load can be ensured in a system-vulnerable area such as an inland area distant from an island or a power plant on the coast. Further, in the case where the system is lost due to an accident, disaster, or the like, stable power supply to the load can be ensured.

The invention developed by the present inventors has been specifically described above based on the embodiments, but it is needless to say that the invention is not limited to the embodiments and various modifications can be made without departing from the scope of the invention.

The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail to explain the present invention in an easily understandable manner, and are not limited to having all the configurations described.

In addition, a part of the structure of one embodiment may be replaced with the structure of another embodiment, and the structure of another embodiment may be added to the structure of one embodiment. Further, a part of the configuration of each embodiment can be added, deleted, or replaced with another configuration.

The above-described structures, functions, processing units, and the like may be partially or entirely implemented in hardware by designing them with integrated circuits, for example. The above-described structures, functions, and the like can be realized by software by interpreting and executing a program for realizing each function by a processor. Information such as programs, tables, and files for realizing the respective functions can be stored in a memory, a storage device such as a hard disk or an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

Note that the control lines and information lines are illustrated as parts which are considered necessary for the description, and not necessarily all the control lines and information lines on the product. In practice, it can be said that almost all structures are connected to each other.

Description of the symbols

110 … DC power; 120 … ac power line; 200 … power conversion device; 210 … power conversion unit; 220 … frequency voltage control part; 230 … droop control; 240 … correction control unit; 243 … instruction value correcting part; 300 … power conversion device; 340 … a correction control unit; 343 … an instruction value correction unit; 400 … power conversion device; 440 … correction control unit; 443 … instruction value correcting unit.

Claims (12)

1. A power conversion device is provided with:

a power conversion unit that converts dc power input from a dc power supply into ac power and outputs the ac power to an ac power line;

an ac power control unit that controls an output frequency and an output voltage of the ac power output from the power conversion unit;

a voltage detection unit that detects the output voltage of the ac power; and

a current detection unit that detects an output current of the AC power,

the ac power control unit, after a load is input to the ac power line and the ac power is output to the load at a rated frequency and a rated voltage, performs droop control for reducing the output frequency and the output voltage of the ac power from the rated frequency and the rated voltage, respectively, based on the output voltage detected by the voltage detection unit and the output current detected by the current detection unit, and performs correction control for gradually correcting the output frequency and the output voltage to the rated frequency and the rated voltage,

the alternating current power control unit includes:

a droop control unit that, after a load is input to the ac power line and the ac power is output to the load at the rated frequency and the rated voltage, derives a contribution active power and a contribution reactive power of the ac power based on the output voltage and the output current, derives a frequency droop that lowers the output frequency from the rated frequency based on a frequency droop that is defined by a frequency reduction per unit active power and the contribution active power, and derives a voltage droop that lowers the output voltage from the rated voltage based on a voltage droop that is defined by a voltage reduction per unit reactive power and the contribution reactive power;

a correction control unit that derives a frequency correction value for correcting the output frequency to the rated frequency, sets a frequency target value for defining the output frequency in a process of gradually correcting the output frequency to the rated frequency based on the frequency correction value, derives a voltage correction value for correcting the output voltage to the rated voltage, and sets a voltage target value for defining the output voltage in a process of gradually correcting the output voltage to the rated voltage based on the voltage correction value; and

a frequency-voltage control unit that performs the droop control based on the frequency droop amount and the voltage droop amount calculated by the droop control unit, and performs the correction control for gradually correcting the output frequency and the output voltage to the rated frequency and the rated voltage based on the frequency target value and the voltage target value set by the correction control unit after the droop control,

the droop control unit includes a power calculation unit that derives the contribution active power and the contribution reactive power of the ac power based on the output voltage and the output current, and is configured to derive the frequency droop by multiplying the contribution active power derived by the power calculation unit by the frequency droop, and to derive the voltage droop by multiplying the contribution reactive power derived by the power calculation unit by the voltage droop,

the correction control unit includes:

an output state monitoring unit that monitors the contribution active power and the contribution reactive power derived by the electric power calculation unit;

a data storage unit that stores the rated frequency, the rated voltage, the frequency droop rate, and the voltage droop rate, which are set in advance; and

a command value correcting unit that multiplies the contribution active power monitored by the output condition monitoring unit and the frequency droop stored in the data storage unit to derive the frequency correction value, inputs the frequency correction value to a frequency hysteresis element, sets a value obtained by adding the rated frequency to a frequency gradual correction value output from the frequency hysteresis element as the frequency target value for defining the output frequency in a process of gradually correcting the output frequency to the rated frequency, multiplies the contribution reactive power monitored by the output condition monitoring unit and the voltage droop stored in the data storage unit to derive the voltage correction value, inputs the voltage correction value to a voltage hysteresis element, and sets a value obtained by adding the rated voltage to a voltage gradual correction value output from the voltage hysteresis element to a value for gradually correcting the output voltage to the rated voltage The output voltage in the course of the rated voltage is subjected to the prescribed voltage target value,

the frequency-voltage control unit inputs the rated frequency and the rated voltage stored in the data storage unit to a feedback control unit as a frequency command value and a voltage command value when a load is input to the ac power line, and the feedback control unit outputs the ac power at the rated frequency and the rated voltage based on the frequency command value and the voltage command value that are input, and then inputs a value obtained by adding the frequency droop amount derived in the droop control unit to the rated frequency stored in the data storage unit to the feedback control unit as the frequency command value, and inputs a value obtained by adding the voltage droop amount derived in the droop control unit to the rated voltage stored in the data storage unit to the feedback control unit as the voltage command value, the feedback control unit performs the droop control based on the input frequency command value and the input voltage command value, and inputs the frequency target value and the voltage target value set by the command value correction unit of the correction control unit to the feedback control unit as the frequency command value and the voltage command value, and the feedback control unit performs the correction control of gradually correcting the output frequency and the output voltage to the rated frequency and the rated voltage based on the input frequency command value and the input voltage command value.

2. The power conversion device according to claim 1,

when a plurality of the power conversion devices are operated in parallel, the droop control and the correction control are performed in each of the power conversion devices.

3. The power conversion device according to claim 1,

when a plurality of the power conversion devices are operated in parallel, the droop control and the correction control are performed in each of the power conversion devices.

4. The power conversion device according to claim 1,

when a plurality of the power conversion devices are operated in parallel, the droop control and the correction control are performed in each of the power conversion devices.

5. The power conversion device according to any one of claims 1 to 4,

the direct current power supply is a solar panel.

6. The power conversion device according to claim 1,

the correction control unit further includes:

a network interface unit that performs data transmission and reception with the other power conversion devices involved in the parallel operation; and

a cooperative control unit that performs the correction control in cooperation with the other power conversion devices involved in the parallel operation,

the command value correction unit multiplies the contribution active power monitored by the output condition monitoring unit and the frequency droop rate stored in the data storage unit to derive an internal frequency correction value, the network interface unit receives the internal frequency correction value of another power conversion device output by another power conversion device, the cooperation control unit stores the internal frequency correction value of another power conversion device received by the network interface unit as an external frequency correction value in an external frequency correction value storage unit, compares all the external frequency correction values stored in the external frequency correction value storage unit, and outputs the maximum external frequency correction value to the command value correction unit as a maximum external frequency correction value, and the command value correction unit derives a larger value of any one of the internal frequency correction value and the maximum external frequency correction value as the frequency correction value A frequency correction value input unit that inputs the frequency correction value to a frequency hysteresis element, and sets a value obtained by adding the rated frequency to a frequency gradual correction value output from the frequency hysteresis element as the frequency target value that defines the output frequency in a process of gradually correcting the output frequency to the rated frequency, the command value correction unit multiplies the contributed reactive power monitored by the output condition monitoring unit by the voltage droop rate stored in the data storage unit to derive an internal voltage correction value, the network interface unit receives the internal voltage correction value of another power conversion device output by another power conversion device, and the cooperation control unit stores the internal voltage correction value of another power conversion device received by the network interface unit as an external voltage correction value in an external voltage correction value storage unit, and a command value correcting unit that compares all the external voltage correction values stored in the external voltage correction value storage unit and outputs the largest external voltage correction value to the command value correcting unit as a largest external voltage correction value, wherein the command value correcting unit derives a larger value of either the internal voltage correction value or the largest external voltage correction value as the voltage correction value, inputs the voltage correction value to a voltage hysteresis element, and sets a value obtained by adding the rated voltage to a voltage gradual correction value output from the voltage hysteresis element as the voltage target value that defines the output voltage in a process of gradually correcting the output voltage to the rated voltage.

7. The power conversion device according to claim 6,

the command value correction unit includes:

a frequency correction switch unit that selects whether or not to input the frequency correction value to the frequency hysteresis element; and

and a voltage correction switch unit that selects whether or not to input the voltage correction value to the voltage hysteresis element.

8. The power conversion device according to claim 7,

when another power conversion device is operated in parallel with the power conversion device that supplies ac power to the load,

the other power conversion device starts parallel operation in a state where the frequency correction switching section and the voltage correction switching section are inactive,

after the parallel operation is started, the frequency correction switch unit and the voltage correction switch unit are activated.

9. The power conversion device according to claim 6,

when a plurality of the power conversion devices are operated in parallel, the droop control and the correction control are performed in each of the power conversion devices.

10. The power conversion device according to claim 7,

when a plurality of the power conversion devices are operated in parallel, the droop control and the correction control are performed in each of the power conversion devices.

11. The power conversion device according to claim 8,

when a plurality of the power conversion devices are operated in parallel, the droop control and the correction control are performed in each of the power conversion devices.

12. The power conversion device according to any one of claims 6 to 11,

the direct current power supply is a storage battery.

Images