JP2017118782A - Electric power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power conversion device which enables the materialization of a highly reliable circuit design while holding down the cost.SOLUTION: An inverter 22 converts a DC power output by a DC power source 1 into an AC power, and supplies the AC power to a system 3. An inverter drive control unit 24 controls an active power output by the inverter and a reactive power output by the inverter. The inverter drive control unit controls output powers of the inverter so as to reduce them to a predetermined active power limit and a predetermined apparent power limit or less when at least one of the following conditions are satisfied: the active power exceeds the active power limit; and the apparent power exceeds the apparent power limit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conversion device that performs power factor control.

  Power factor control includes a method in which the amount of current phase shift is adjusted, and a method in which the amount of reactive power superimposed on active power is adjusted. The latter reactive power superposition type power factor control has a simple configuration and is widely used in power conditioners of solar cells (see, for example, Patent Document 1). Generally, the maximum rated output of the power conditioner is defined by the rated active power, and the power conditioner outputs power within the range of the rated active power.

  In general reactive power superposition type power factor control, a power factor is controlled by adjusting a reactive current command value superimposed on an active current command value in a control circuit that drives and controls an inverter in a power conditioner. In addition, in order to keep the power output from the inverter below the rated active power, when the output power of the inverter exceeds the rated active power, the DC-DC converter provided in the previous stage of the inverter is controlled and the power input to the inverter Limit.

JP 2013-93982 A

  In the above configuration, when the power factor is less than 1, the output apparent power increases as compared with the case where the power factor is 1. As the apparent power increases, the current flowing through the inverter also increases, increasing the stress on the components of the inverter. Considering the life of components and device reliability, ideally, a current resistance design that can withstand the maximum current at the lowest power factor should be made. However, if the resistance design is adopted, the cost increases.

  This invention is made | formed in view of such a condition, The objective is to provide the power converter device which can implement | achieve highly reliable circuit design, suppressing cost.

  In order to solve the above problems, a power conversion device according to an aspect of the present invention includes an inverter that converts DC power output from a DC power source into AC power and supplies the AC power to a system, and is output from the inverter. And a control circuit that controls the reactive power output from the inverter, wherein the control circuit is configured such that the active power exceeds a predetermined active power limit value, and When the apparent power exceeds a predetermined apparent power limit value, the output power of the inverter is controlled to be less than or equal to the active power limit value and the apparent power limit value when at least one of them is satisfied.

  It should be noted that any combination of the above-described constituent elements and a representation of the present invention converted between a method, an apparatus, a system, and the like are also effective as an aspect of the present invention.

  According to the present invention, it is possible to realize a highly reliable circuit design while suppressing cost.

It is a figure for demonstrating the structure of the power converter device which concerns on embodiment of this invention. It is a figure which shows the relationship between the output electric power value of a power converter device, and an active power limiting value. It is a figure which shows the structural example of the output measurement part and output restriction | limiting part which concern on Embodiment 1 of this invention. It is a figure which shows the table which put together the content of the excess determination process in the output control part which concerns on Embodiment 1. FIG. It is a figure for demonstrating the relationship between the output electric power value of the power converter device, active power limiting value, and apparent power limiting value based on Embodiment 1. FIG. It is a figure which shows the structural example of the output measurement part and output restriction | limiting part which concern on Embodiment 2 of this invention. It is a figure for demonstrating the relationship between the output electric power value of the power converter device which concerns on Embodiment 2, an active power limiting value, and an apparent power limiting value. It is a figure for demonstrating the restriction | limiting process of output electric power in case the response of current control by a converter drive control part is slower than the current control by an inverter drive control part. It is a figure for demonstrating the structure of the power converter device which concerns on Example 1. FIG. FIGS. 10A to 10B are diagrams illustrating an example of the power factor change before the sudden change restriction and the power factor change after the sudden change restriction. 3 is a flowchart illustrating a flow of power factor change processing according to the first embodiment. It is a figure for demonstrating the structure of the power converter device which concerns on Example 2. FIG. FIGS. 13A to 13C are diagrams illustrating an example of a change in the reactive current command value before the sudden change restriction and a change in the reactive current command value after the sudden change restriction. It is a figure for demonstrating the structure of the reactive current instruction | command part of the power converter device which concerns on Example 3. FIG. FIGS. 15A and 15B are diagrams illustrating an example of the reactive current ratio change before the sudden change restriction and the reactive current ratio change after the sudden change restriction. 12 is a flowchart illustrating a flow of power factor change processing according to the third embodiment. It is a figure which shows the table which put together the individual effect of Example 1-3. It is a figure for demonstrating the linearity of the power factor at the time of the power factor change in Example 1-3.

  FIG. 1 is a diagram for explaining a configuration of a power conversion device 2 according to an embodiment of the present invention. The power converter 2 converts the DC power supplied from the DC power source 1 into AC power and supplies the AC power to the commercial power system 3 (hereinafter simply referred to as the system 3). The DC power source 1 is, for example, a solar cell or a fuel cell. In this case, the power conversion device 2 functions as a power conditioner that converts DC power generated by the solar cell or fuel cell into AC power. Further, the DC power source 1 may be a storage battery. In that case, the power converter device 2 functions as a bidirectional power conditioner.

  The DC-DC converter 21 performs DC-DC conversion on the DC power supplied from the DC power supply 1. When the DC power supply 1 is a solar cell, the DC-DC converter 21 can be configured by a boost chopper equipped with MPPT (Maximum Power Point Tracking) control. The boost chopper controls the solar cell to generate power at the maximum power point (optimum operating point). Specifically, the maximum power point is searched by changing the voltage with a predetermined step width according to the hill-climbing method, and control is performed so that the output power of the solar cell maintains the maximum power point.

  The inverter 22 converts the DC power input from the DC-DC converter 21 into AC power and outputs the AC power. The inverter 22 includes, for example, a bridge circuit in which four switching elements (for example, IGBT (Insulated Gate Bipolar Transistor), MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor)) are bridge-connected. The output of the inverter 22 can be adjusted by controlling the duty ratio of the switching element. A filter circuit (not shown) is provided at the subsequent stage of the inverter 22, and the filter circuit attenuates the high-frequency component of the AC power output from the inverter 22 to bring the output voltage and output current of the inverter 22 closer to a sine wave. .

  The power conversion device 2 controls the drive of the DC-DC converter 21 and the inverter 22, and therefore the converter drive control unit 23, the inverter drive control unit 24, the output power factor setting unit 25, the output current detection unit 26, and the system voltage detection unit 27. The output measuring unit 28 and the output limiting unit 29 are included. The inverter drive control unit 24 includes a power balance control unit 241, an effective instantaneous current command unit 242, a reactive current command unit 243, a reactive instantaneous current command unit 244, an addition unit 245, a subtraction unit 246, and a drive unit 247. These configurations can be realized by cooperation of hardware resources and software resources, or only by hardware resources. As hardware resources, analog elements, microcomputers, DSPs, ROMs, RAMs, FPGAs, and other LSIs can be used. Firmware and other programs can be used as software resources.

  The power balance control unit 241 generates an effective current command value Ip that defines the effective current to be output from the inverter 22 so as to maintain the power balance between the output power of the DC-DC converter 21 and the input power of the inverter 22. By this control, the balance between the energy input from the DC-DC converter 21 to the inverter 22 and the energy output from the inverter 22 can be maintained. In particular, when the DC power source 1 whose power generation amount varies depending on the natural environment such as a solar cell is used, the output power of the DC-DC converter 21 varies, so the input power of the inverter 22 follows the variation of the output power. It is necessary to let

  The effective instantaneous current command unit 242 calculates the instantaneous value Ip · sinωt of the effective current command value based on the peak value Ip of the effective current command value input from the power balance control unit 241. The effective instantaneous current command unit 242 outputs the calculated instantaneous value Ip · sinωt of the effective current command value to the adding unit 245.

  The output power factor setting unit 25 sets the power factor cosφ in the reactive current command unit 243. As the power factor cosφ, a fixed value set by the designer at the time of installation of the power conversion device 2 may be continuously used, or from an operation unit (not shown) according to an instruction from a power supplier such as a power company. An arbitrary value may be set. Moreover, when the power converter device 2 has an output suppression function, when the output power supplied from the power converter device 2 to the system 3 exceeds the set value, the phase advance control with the power factor cosφ lowered is activated.

  Further, when an output suppression command is received from an external management system via a network, the power factor cosφ may be reduced. An electric power supplier such as an electric power company needs to stably supply electric power, and it is necessary to keep the frequency and voltage of the entire electric power system including the reverse power flow within a certain range. When many renewable energy power generation facilities are connected to the grid 3, the amount of power generation varies greatly depending on weather conditions. If the amount of power supplied to the grid 3 from the renewable energy power generation facility becomes too large and the frequency or grid voltage of the grid 3 is predicted to exceed or exceed the upper limit of the reference range, the grid management system will An output suppression command is transmitted to the power generation facility. The power conversion device 2 that has received the output suppression command directly controls the current command value to suppress the output power and contribute to the reduction of the system frequency, and advance the phase control of the power factor cosφ to contribute to the reduction of the system voltage. . Similarly, when the voltage of the grid 3 is predicted to fall below or below the lower limit, the power factor cosφ may be controlled in a slow phase based on the command to contribute to the rise of the grid voltage.

  The reactive current command unit 243 generates a reactive current ratio tanφ that is a ratio of the reactive current to the effective current based on the power factor cosφ set by the output power factor setting unit 25. The reactive current command unit 243 generates a peak value Iq of the reactive current command value based on the generated reactive current ratio tanφ and the peak value Ip of the active current command value input from the power balance control unit 241. The reactive instantaneous current command unit 244 calculates the instantaneous value Iq · cos ωt of the reactive current command value based on the peak value Iq of the reactive current command value input from the reactive current command unit 243. The reactive instantaneous current command unit 244 outputs the calculated instantaneous value Iq · cosωt of the reactive current command value to the adding unit 245.

  The adding unit 245 adds the instantaneous value Ip · sin ωt of the active current command value and the instantaneous value Iq · cos ωt of the reactive current command value, generates a final current command value, and outputs it to the subtracting unit 246. The subtractor 246 subtracts the output current value detected by the output current detector 26 from the current command value to generate a current deviation. A command value based on the current deviation is output to the drive unit 247. The drive unit 247 drives the inverter 22 based on the command value.

  The converter drive control unit 23 controls the drive of the DC-DC converter 21. Specifically, a PWM signal is generated based on the command value and supplied to the control terminal of the switching element included in the DC-DC converter 21. For example, when the MPPT control function is installed, a voltage command value is determined by MPPT control, and a PWM signal based on the voltage command value is generated.

  The output measurement unit 28 measures the output of the power conversion device 2 based on the output current detected by the output current detection unit 26 and the system voltage detected by the system voltage detection unit 27. Hereinafter, general processing will be described before describing processing of the present embodiment.

  The output measuring unit 28 calculates the instantaneous active power value by multiplying the instantaneous value of the output current detected by the output current detecting unit 26 and the instantaneous value of the system voltage detected by the system voltage detecting unit 27. The output measuring unit 28 calculates the average value per unit cycle of the instantaneous active power value. This average value is the output active power value P = 1 / T∫IVdt of the power converter 2. The output measuring unit 28 outputs the calculated output active power value P to the output limiting unit 29.

  The output limiting unit 29 determines whether or not the output active power value P exceeds the active power limit value Plim. The rated output power value of the power converter 2 is set as the active power limit value Plim. In addition, a power threshold value at which output suppression is activated may be set. The output limiting unit 29 outputs a suppression signal to the converter drive control unit 23 when the output active power value P exceeds the active power limit value Plim. When receiving the suppression signal, the converter drive control unit 23 reduces the duty ratio of the PWM signal and reduces the power output from the DC-DC converter 21.

  FIG. 2 is a diagram illustrating a relationship between the output power value of the power conversion device 2 and the active power limit value. The magnitude of the output power value (output apparent power value) to which the active power limit value Plim is limited when the power factor cos φ is other than 1.0 is as follows. It becomes larger than the magnitude of the output power value (output apparent power value) that is subject to the restriction on the apparent power value). Therefore, when the tolerance of the circuit element in the inverter 22 is designed based on the active power limit value, if the power factor cosφ is set to a value other than 1.0, a great stress is applied to the circuit element.

  FIG. 3 is a diagram illustrating a configuration example of the output measuring unit 28 and the output limiting unit 29 according to Embodiment 1 of the present invention. The output measurement unit 28 includes an output active power calculation unit 281 and an output apparent power calculation unit 282. The output limiting unit 29 includes an active power excess determination unit 291, an apparent power excess determination unit 292, and an OR circuit 293.

  The output active power calculation unit 281 corresponds to the processing content of the general output measurement unit 28 described above. That is, based on the instantaneous value of the output current detected by the output current detection unit 26 and the instantaneous value of the system voltage detected by the system voltage detection unit 27, the output active power value P = 1 / T of the power conversion device 2 Calculate IVdt. The output active power calculation unit 281 outputs the calculated output active power value P to the active power excess determination unit 291.

The output apparent power calculation unit 282 squares the instantaneous value of the output current detected by the output current detection unit 26, calculates an average value per unit cycle of the squared value, and calculates the square root of the average value. The output apparent power calculation unit 282 squares the instantaneous value of the system voltage detected by the system voltage detection unit 27, calculates the average value per unit cycle of the squared value, and calculates the square root of the average value. Then, the output apparent power value S = √1 / T∫V ² dt · √1 / T∫I ² dt of the power converter ² is calculated by multiplying both values. The output apparent power calculation unit 282 outputs the calculated output apparent power value S to the apparent power excess determination unit 292.

  The active power excess determining unit 291 determines whether or not the output active power value P input from the output active power calculating unit 281 exceeds the active power limit value Plim. When it exceeds, a high level signal is output to the OR circuit 293, and when it does not exceed, a low level signal is output to the OR circuit 293. The apparent power excess determination unit 292 determines whether or not the output apparent power value S input from the output apparent power calculation unit 282 exceeds the apparent power limit value Slim. When it exceeds, a high level signal is output to the OR circuit 293, and when it does not exceed, a low level signal is output to the OR circuit 293.

  The OR circuit 293 calculates the logical sum of the signal input from the active power excess determination unit 291 and the signal input from the apparent power excess determination unit 292, and suppresses the converter drive control unit 23 when the calculation result is high level. Issue a signal. When the calculation result is at a low level, no suppression signal is issued.

  FIG. 4 is a diagram showing a table summarizing the contents of the excess determination process in the output restriction unit 29 according to the first embodiment. As shown in FIG. 4, when at least one of the output active power value P and the output apparent power value S of the power converter 2 exceeds the limit value, a suppression signal is issued.

  FIG. 5 is a diagram for explaining the relationship between the output power value of the power conversion device 2, the active power limit value, and the apparent power limit value according to the first embodiment. As shown in FIG. 5, the apparent power limit value is set concentrically. When the output power value of the power conversion device 2 reaches the apparent power limit value, the output active power value is reduced as compared with the case of operating at the maximum output power value of power factor = 1. However, the operation within the current tolerance of the circuit element can be compensated.

  When the output power value of the power converter 2 does not reach the apparent power limit value, the reactive power is superimposed on the desired output active power, so that the active power can be output as it is without waste. Therefore, even when the power factor is set low, the power factor can be used for power sale or home consumption without reducing the effective power. On the other hand, in the phase control system, the desired output active power at power factor = 1 is rotated while maintaining the magnitude of the apparent power other than power factor = 1 by phase control. The effective power will be reduced. In this case, there is a case where the amount of power sold is reduced or the power supply to home consumption is reduced to purchase power.

  As described above, in the first embodiment, not only the effective power limit value but also the apparent power limit value is used to determine whether the output power limit is exceeded, and the smaller value of both is used as the power limit value in each output power value. To do. As a result, the power factor control of the reactive power superimposing method can be realized without applying excessive current stress in the power converter 2 having a current tolerance design compliant with the active power limit value. Since the current resistance design conforms to the effective power limit value, an increase in cost can be suppressed. As described above, according to the first embodiment, the power factor control within the maximum allowable current designed in consideration of the cost is realized (apparent power limitation), and the power factor control within the rated active power is realized. Can (active power limit).

  FIG. 6 is a diagram illustrating a configuration example of the output measuring unit 28 and the output limiting unit 29 according to Embodiment 2 of the present invention. The output measurement unit 28 includes an output active power calculation unit 281, an output apparent power calculation unit 282, an output effective current calculation unit 283, and an output apparent current calculation unit 284. The output limiting unit 29 includes an active power excess determination unit 291, an apparent power excess determination unit 292, an OR circuit 293, an active current excess determination unit 294, and an apparent current excess determination unit 295.

  The processing contents of the output active power calculation unit 281 and the output apparent power calculation unit 282 are the same as described in FIG. The output active current calculation unit 283 calculates the output effective current value IP (effective value) by dividing the output active power value P calculated by the output active power calculation unit 281 by the effective voltage value Vrms. The output active current calculation unit 283 outputs the calculated output effective current value IP to the active current excess determination unit 294. The output apparent current calculation unit 284 divides the output apparent power value S calculated by the output apparent power calculation unit 282 by the effective voltage value Vrms to calculate an output apparent current value IS (effective value). The output apparent current calculation unit 284 outputs the calculated output apparent current value IS to the apparent current excess determination unit 295.

  The processing contents of the active power excess determination unit 291 and the apparent power excess determination unit 292 are the same as described in FIG. The effective current excess determination unit 294 determines whether or not the output effective current value IP input from the output effective current calculation unit 283 exceeds the effective current limit value IPlim. When it exceeds, a high level signal is output to the OR circuit 293, and when it does not exceed, a low level signal is output to the OR circuit 293. The apparent current excess determination unit 295 determines whether or not the output apparent current value IS input from the output apparent current calculation unit 284 exceeds the apparent current limit value ISlim. When it exceeds, a high level signal is output to the OR circuit 293, and when it does not exceed, a low level signal is output to the OR circuit 293.

  The OR circuit 293 receives a signal input from the active power excess determination unit 291, a signal input from the apparent power excess determination unit 292, a signal input from the active current excess determination unit 294, and an input from the apparent current excess determination unit 295. If the result of the operation is high level, a suppression signal is issued to the converter drive control unit 23. When the calculation result is at a low level, no suppression signal is issued.

  FIG. 7 is a diagram for explaining the relationship between the output power value of the power conversion device 2, the active power limit value, and the apparent power limit value according to the second embodiment. When the system voltage becomes insufficient with respect to the nominal voltage, the output current increases in order to maintain the active power output from the power converter 2 to the system 3 in the same state as before the voltage shortage. Thereby, even when operating within the range of the effective power limit value and the apparent power limit value, the current stress on the circuit element may increase unexpectedly.

  Therefore, in the second embodiment, an excess determination using the effective current value limit value and an excess determination using the apparent current limit value are added to the excess determination according to the first embodiment.

  As described above, in the second embodiment, by adding the excess determination using the effective current limit value and the excess determination using the apparent current limit value, the current exceeding the allowable range flows to the circuit element. It can prevent more reliably.

  In the second embodiment, the configuration in which the excess determination using the effective current value limit value and the excess determination using the apparent current limit value are added has been described. However, the excess determination using the effective current limit value is performed. A configuration in which only an excess determination using the apparent current limit value is added may be omitted. Since the apparent current is the actual current that flows through the circuit element, if the current tolerance is designed in accordance with the allowable apparent current and an excess judgment is made using the apparent current limit value, the circuit element is surely protected from the current. Can do.

  The power balance response time of the power balance control 241 of the inverter drive control unit 24 described above is set slower than the response time of the current control 242 to 247 to the inverter 22 by the control unit 24 in order to prevent system hunting. Sometimes.

  FIG. 8 is a diagram for explaining the output power limiting process when the power control by the converter drive control unit 23 is slower in response than the current control by the inverter drive control unit 24. Referring to FIG. 8, consider a case where the set power factor changes suddenly. In the example shown in FIG. 8, the set power factor (t0) at time t0 is cosφt0 = 1.0, and the set power factor (t1) at time t1 is cosφt1 = 0.8, which has changed from time t0 to time t1. The power factor suddenly drops at the moment.

  The sudden change in the power factor occurs when a command that requires a sudden change in the power factor is received by external communication, a preset characteristic that changes the power factor according to the output power of the power converter 2, and the like. As shown in FIG. 8, at time t1, reactive power components are superimposed according to the power factor change, and the output power (apparent power) once exceeds the apparent power limit. After that, the output power (apparent power) falls within the range of the apparent power limitation due to the output limitation by the output limiting unit 29 and the converter drive control unit 23.

  Since the response time of the power balance control 241 of the inverter drive control unit 24 is slower than the response time of the reactive current superimposition in the current control 242 to 247 to the inverter 22, it is transiently generated in the inverter 22 from time t 1 to time t 2. A current exceeding the apparent current limit value flows. In the following, an example will be described in which measures for a sudden power factor change are introduced so as not to generate a transient over-limit current when the set power factor suddenly changes. It should be noted that preventing a sudden power factor change (reactive power change) also has an effect of preventing the system 3 from becoming unhealthy. Hereinafter, three examples will be described as configuration examples for suppressing the power factor sudden change.

Example 1
FIG. 9 is a diagram for explaining the configuration of the power conversion device 2 according to the first embodiment. The power conversion device 2 according to the first embodiment has a configuration in which a power factor change restriction unit 251 is added to the configuration of the power conversion device 2 illustrated in FIG. 1. The power factor change limiting unit 251 is provided between the output power factor setting unit 25 and the reactive current command unit 243. The power factor change limiting unit 251 controls the change amount Δcosφ per unit time of the power factor cosφ set by the output power factor setting unit 25 so that it falls within a predetermined power factor change amount. The power factor change restriction unit 251 sets the power factor cos φ ′ after the sudden change restriction in the reactive current command unit 243.

  FIGS. 10A to 10B are diagrams illustrating an example of the power factor change before the sudden change restriction and the power factor change after the sudden change restriction. FIG. 10A compares the change in the set power factor cosφ with that before the limit by the moving average process using the buffer by the power factor change limiting unit 251 or the smoothing process using the low-pass filter without using the buffer. It shows an example that is relaxed. FIG. 10B shows an example in which the power factor change limiting unit 251 changes the set power factor cos φ with a step width corresponding to the limit value of the power factor change amount Δcos φ per unit time.

  FIG. 11 is a flowchart illustrating the flow of the power factor change process according to the first embodiment. In FIG. 11, “delay” in the power factor cos φ is treated as positive and “advance” is treated as negative for simplicity of explanation. Further, the power factor change amount Δcosφ that becomes the limit value is treated as a positive absolute value. Hereinafter, the current set power factor is -0.8 (advanced power factor), the post-restricted set power factor (previous set power factor) is 0.8 (delayed power factor), and the power factor change amount Δcosφ is 0.05. Consider an example.

  In FIG. 11, the power factor change limiting unit 251 determines whether or not the current set power factor is zero or more (S10). That is, it is determined whether or not the current set power factor is a delayed power factor. When the current set power factor is zero or more (Y in S10), the power factor change limiting unit 251 calculates the current set power factor reference value deviation by subtracting the current set power factor from 1 (S11). When the current set power factor is less than zero (N in S10), the power factor change limiting unit 251 calculates the current set power factor reference value deviation by subtracting the current set power factor from −1 (S12). . In this example, since the current set power factor is −0.8, the current set power factor reference value deviation is −1 − (− 0.8) = − 0.2.

  Next, the power factor change restriction unit 251 determines whether or not the post-restriction set power factor is zero or more (S13). That is, it is determined whether the post-restriction set power factor is a delayed power factor. When the post-restriction set power factor is zero or more (Y in S13), the power factor change restriction unit 251 calculates the post-restriction set power factor reference value deviation by subtracting the post-restriction set power factor from 1 (S14). When the post-restriction set power factor is less than zero (N in S13), the power factor change restriction unit 251 calculates the post-restriction set power factor reference value deviation by subtracting the post-restriction set power factor from -1 (S15). . In the first stage of this example, the post-restriction set power factor is 0.8, so the post-restriction set power factor reference value deviation is 1-0.8 = 0.2.

  Next, the power factor change limiting unit 251 calculates a power factor fluctuation deviation by subtracting the post-restricted set power factor reference value deviation from the current set power factor reference value deviation (S16). In the first stage of this example, −0.2−0.2 = −0.4.

  Next, the power factor change limiting unit 251 determines whether or not the power factor variation deviation is larger than Δcosφ (S17). If larger (Y in S17), the power factor change limiting unit 251 sets Δcosφ to the power factor fluctuation deviation limit value (S19). If not large (N in S17), the power factor change limiting unit 251 determines whether or not the power factor variation deviation is smaller than -Δcosφ (S18). If it is smaller (Y in S18), the power factor change limiting unit 251 sets -Δcosφ as the power factor variation deviation limit value (S20). If not smaller (N in S18), the power factor change limiting unit 251 sets the power factor fluctuation deviation to the power factor fluctuation deviation limit value (S21). In the first stage of this example, since the relationship is 0.4 <−0.05, −0.05 is set as the power factor variation deviation limit value.

  Next, the power factor change limiting unit 251 determines whether or not the value obtained by adding the power factor variation deviation limit value to the post-limit setting power factor reference value deviation is zero or more (S22). When it is zero or more (Y in S22), the power factor change limiting unit 251 subtracts the value from 1 to calculate a new post-limit setting power factor (S23). When it is less than zero (N in S22), the power factor change limiting unit 251 calculates a new post-limit setting power factor by subtracting the value from −1 (S24). In the first stage of this example, the relationship is 0.2 + (− 0.05) ≧ 0, so the new post-restriction set power factor is 1−0.15 = 0.85.

  The power factor change limiting unit 251 sets a new post-limit setting power factor in the reactive current command unit 243 (S25). At the same time, the power factor change restriction unit 251 determines whether or not the new post-restriction set power factor has reached the current set power factor (S26). When it reaches (Y of S26), this power factor change process is complete | finished. If not reached (N in S26), the process proceeds to step S10 and the process is continued.

  Thus, by using the power factor reference value deviation based on the power factor 1, the power factor value can be expressed by a continuous linear relationship based on the power factor 1. Therefore, a power factor change that crosses 1 can be processed uniformly. Similarly, when using the moving average or the low-pass filter described above, the power factor reference value deviation based on the power factor 1 is used to represent the power factor value in a continuous linear relationship based on the power factor 1. Can do. A filter process may be performed on the power factor reference value deviation, and the power factor reference value deviation after the filter process may be converted into a power factor value.

(Example 2)
FIG. 12 is a diagram for explaining the configuration of the power conversion device 2 according to the second embodiment. The power conversion device 2 according to the second embodiment has a configuration in which a reactive current command value change limiting unit 248 is added to the configuration of the power conversion device 2 illustrated in FIG. 1. The reactive current command value change limiting unit 248 is provided between the reactive current command unit 243 and the reactive instantaneous current command unit 244. The reactive current command value change limiting unit 248 controls the amount of change ΔIp per unit time of the peak value Ip of the reactive current command value generated by the reactive current command unit 243 to be within a predetermined reactive current command value change amount. . The reactive current command value change limiting unit 248 sets the peak value Ip ′ of the reactive current command value after the sudden change limitation in the reactive instantaneous current command unit 244.

  FIGS. 13A to 13C are diagrams illustrating an example of a change in the reactive current command value before the sudden change restriction and a change in the reactive current command value after the sudden change restriction. FIGS. 13A to 13C show an example in which the power factor cos φ is changed from 1.0 to 0.8 with an apparent current of 10 A.

  FIG. 13A shows that the reactive current command value change limiting unit 248 changes the reactive current command value before the limit by moving average processing using a buffer or smoothing processing using a low-pass filter without using a buffer. An example in which the comparison is moderated is shown. FIG. 13B shows an example in which the reactive current command value change limiting unit 248 changes the reactive current command value with a step width corresponding to the limit value of the reactive current command value change amount per unit time. FIG.13 (c) has shown the change of the active current command value at the time of the change of the reactive current command value shown to Fig.13 (a), (b).

(Example 3)
FIG. 14 is a diagram for explaining the configuration of the reactive current command unit 243 of the power converter 2 according to the third embodiment. The reactive current command unit 243 according to the third embodiment includes a tangent conversion unit 243a, a reactive current ratio change limiting unit 243b, and a reactive current command value generation unit 2243c. The tangent conversion unit 243a performs tangent conversion on the power factor cosφ set by the output power factor setting unit 25, and generates a reactive current ratio tanφ indicating a ratio of reactive current to effective current.

  The reactive current ratio change limiting unit 243b controls the amount of change Δtanφ per unit time of the generated reactive current ratio tanφ to be within a predetermined reactive current ratio change amount. The reactive current ratio change limiting unit 243b sets the reactive current ratio tanφ ′ after the sudden change limitation in the reactive current command value generation unit 243c. The reactive current command value generation unit 243c generates a reactive current command value peak value Iq = Ip based on the set reactive current ratio tanφ ′ and the active current command value peak value Ip input from the power balance control unit 241. Generate tanφ ′. The generated reactive current command value peak value Iq = Ip · tanφ ′ is output to the reactive instantaneous current command unit 244.

  FIGS. 15A and 15B are diagrams illustrating an example of the reactive current ratio change before the sudden change restriction and the reactive current ratio change after the sudden change restriction. FIG. 15A shows that the reactive current ratio change limiting unit 243b compares the change in the reactive current ratio tanφ with that before the limit by moving average processing using a buffer or smoothing processing using a low-pass filter without using a buffer. And the example that is loose. FIG. 15B shows an example in which the reactive current ratio change limiting unit 243b changes the reactive current ratio tanφ with a step width corresponding to the limit value of the reactive current ratio change amount Δtanφ per unit time.

  FIG. 16 is a flowchart illustrating the flow of the power factor change process according to the third embodiment. In FIG. 16, “delay” in the power factor cos φ and reactive current ratio tan φ is treated as positive and “advance” is treated as negative for the sake of simplicity. Further, the reactive current ratio change amount Δtanφ that becomes the limit value is treated as a positive absolute value. Hereinafter, an example in which the current set power factor is −0.8 (advanced power factor), the previous set power factor is 0.8 (lag power factor), and the reactive current ratio change amount Δtanφ is 0.3 is considered.

  In FIG. 16, the tangent conversion unit 243a calculates the current reactive current ratio tanφ with respect to the current set power factor cosφ (S30). In the present example, the current reactive current ratio tanφ is −0.75.

  Next, the reactive current ratio change limiting unit 243b determines whether or not the absolute value of the difference between the current reactive current ratio and the post-restricted reactive current ratio (previous reactive current ratio) is greater than Δtanφ (S31). If not (N in S31), the reactive current ratio change limiting unit 243b sets the current reactive current ratio to the post-restricted reactive current ratio (S32). If it is larger (Y in S31), the reactive current ratio change limiting unit 243b sets whether or not the current reactive current ratio is larger than the post-restricted reactive current ratio (S33). If larger (Y in S33), the reactive current ratio change limiting unit 243b sets a value obtained by adding Δtanφ to the post-restricted reactive current ratio as a new post-restricted reactive current ratio (S34). If not (N in S33), the reactive current ratio change limiting unit 243b sets a value obtained by subtracting Δtanφ from the post-restricted reactive current ratio as a new post-restricted reactive current ratio (S35).

  In the first stage of the present example, the current reactive current ratio-restricted reactive current ratio in step S31 is -1.5, and the new limited reactive current ratio in step S35 is -4.5 (power factor is 0.91). )

  The reactive current ratio change limiting unit 243b sets a new post-restriction reactive current ratio in the reactive current command value generation unit 2243c (S36). At the same time, the reactive current ratio change limiting unit 243b calculates a post-limit set power factor corresponding to the new post-limit reactive current ratio (S37), and whether or not the new post-limit set power factor has reached the current set power factor. (S38). If it has been reached (Y in S38), the power factor change process is terminated. If not reached (N in S38), the process proceeds to step 30 and the process is continued.

  According to the power factor change process according to Example 1-3 described above, it is possible to suppress the occurrence of a transient over-limit current when the set power factor suddenly changes. As a result, it is possible to avoid a situation in which excessive current stress is applied to the circuit elements. Further, by making the power factor (reactive power) change moderate, it is possible to prevent the system 3 from becoming unhealthy.

  FIG. 17 is a table summarizing the individual effects of Example 1-3. In terms of design easiness, the filter target of the second embodiment is the reactive current command value Iq, so the second embodiment is the easiest. The filter target of the first embodiment is the power factor cosφ, and the filter target of the third embodiment is the reactive current ratio tanφ. Compared with each other, the design of the third embodiment is easier.

  FIG. 18 is a diagram for explaining the linearity of the power factor when the power factor is changed in Example 1-3. 18A shows an example of power factor change in the first embodiment, and FIG. 18B shows an example of power factor change in the second and third embodiments. As shown in FIG. 18A, in the first embodiment, the power factor change has linearity (linearity). Therefore, when the response time with respect to the change between desired power factors is specified by a standard or the like, there is an advantage that the design is easy. For example, when the power factor changes from 1.0 to 0.9 and when the power factor changes from 0.9 to 0.8, the response time is the same because the power factor deviation is the same. In the first embodiment, the change in the injecting / withdrawing reactive energy is non-linear.

As shown in FIG. 18B, in Examples 2 and 3, the power factor change is a curve represented by cos (arctanX) = 1 / √ (1 + X ² ). In Examples 2 and 3, the amount of change (inclination) of the reactive current amount is linear. Therefore, when the amount of change in reactive power per unit time is defined from the influence on the system 3, etc., there is an advantage that the design is easy. In Examples 2 and 3, the power factor change is non-linear.

  Returning to FIG. In the power factor followability when the effective current command value Ip changes, the first and third embodiments are superior to the second embodiment. Here, the active power is rated at 80%, the power factor, reactive current command value, and reactive current ratio are limited, the instantaneous power factor after limiting is 0.8, and then the active power suddenly changes to 40% think of.

  In the first and third embodiments, the reactive current command Iq = Ip · tanφ ′, so that the reactive current command value Iq is halved according to the active power command value Ip. Since the reactive current ratio tan φ ′ after the limit remains unchanged corresponding to the power factor cos φ ′ = 0.8 after the limit, the set power factor at the final current command value Ip + Iq remains 0.8. That is, it operates so as to maintain the set power factor by instantaneously following the change in active power. Therefore, Examples 1 and 3 are suitable for a power conditioner when one natural energy power source such as a solar battery is present independently. In the case of such a natural energy power source, the active power is likely to change, so it is important to maintain the power factor with respect to the change in active power.

In Example 2, since the reactive current command value Iq ′ after restriction is Iq ′ = LPF (Ip · tanφ), instantaneously, Ip = 40% rating, Iq ′ = 60% rating, power factor = 0.55 = Ip / √ (Iq ′ ² + Ip ² ). However, a large deviation can be suppressed by selecting an appropriate filter constant. Example 2 is the easiest to design, but the accuracy of maintaining a constant power factor with respect to changes in active power is relatively low. Therefore, Example 2 is suitable for a power conditioner of a storage battery parallel power supply such as a solar battery and a storage battery of a natural energy power supply. In the case of a storage battery parallel power supply, since the change in active power is unlikely to occur, the demand for maintaining the power factor against the change in active power is reduced.

  The present invention has been described based on the embodiments. The embodiments are exemplifications, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. .

  For example, in the above-described embodiment, the power conversion device 2 includes the DC-DC converter 21. However, when the DC power supply 1 has an output adjustment function, the DC-DC converter 21 of the power conversion device 2 is omitted. The configuration may be such that the DC power supply 1 is notified of the suppression command.

  The embodiment may be specified by the following items.

[Item 1]
An inverter (23) for converting DC power output from the DC power source (1) into AC power and supplying the AC power to the system (3);
A control circuit (24) for controlling active power output from the inverter (23) and reactive power output from the inverter (23), and a power converter (2) comprising:
When the active power exceeds a predetermined active power limit value and when the apparent power exceeds a predetermined apparent power limit value, the control circuit (24, 29) satisfies the inverter. Controlling the output power of (23) to be less than or equal to the active power limit value and the apparent power limit value;
The power converter device (2) characterized by the above-mentioned.
According to this, it is possible to realize a highly reliable circuit design while suppressing the cost regarding the current resistance.
[Item 2]
A DC-DC converter (21) that is interposed between the DC power source (1) and the inverter (22), adjusts the voltage of DC power output from the DC power source (1), and supplies the voltage to the inverter (22). And further comprising
The control circuit (23, 24, 29) is configured to control the DC-DC converter (21),
The control circuit (23, 24, 29) satisfies at least one of when the active power exceeds the predetermined active power limit value and when the apparent power exceeds the predetermined apparent power limit value. The power converter (2) according to item 1, wherein control is performed so as to suppress power input from the DC-DC converter (21) to the inverter (22).
According to this, when the output power of the inverter (22) exceeds at least one of the predetermined active power limit value and the predetermined apparent power limit value, the input power to the inverter (22) by the DC-DC converter (21). Can be squeezed.
[Item 3]
The control circuit (23, 24, 29) is configured such that the active power exceeds the predetermined active power limit value, the apparent power exceeds the predetermined apparent power limit value, and the inverter (22). When the apparent current output from the inverter exceeds a predetermined apparent current limit value, the output power of the inverter (22) is suppressed below the active power limit value and the apparent power limit value when at least one of them is satisfied. And the power converter device (2) of item 1 or 2 characterized by controlling so that the output current of the said inverter (22) may be suppressed below the said apparent power limit value.
According to this, it is possible to realize a circuit design with higher reliability while suppressing the cost regarding current resistance.
[Item 4]
The control circuit (23, 24, 29) is configured to be able to control the power factor of the output power of the inverter (22),
The control circuit (23, 24, 29), when changing the power factor of the output power of the inverter (22), from the reactive current according to the power factor before the change, the invalidity according to the power factor after the change 4. The power converter (2) according to any one of items 1 to 3, wherein the power converter is gradually changed to a current.
According to this, it is possible to suppress the output power of the power conversion device (2) from instantaneously exceeding the apparent power limit value when the power factor changes suddenly.
[Item 5]
5. The power conversion device according to any one of items 1 to 4, further comprising a power factor change limiting unit (251) that limits a change amount of the power factor per unit time to a predetermined power factor change amount (251). 2).
According to this, the change in the current command value can be moderated while ensuring the linearity of the power factor when the power factor is changed and the followability of the power factor when the active power is changed.
[Item 6]
The said control circuit (23, 24, 29) restrict | limits the variation | change_quantity per unit time of a reactive current to predetermined variation | change_quantity, The power converter device in any one of the items 1 to 4 characterized by the above-mentioned (2). ).
According to this, it is possible to moderate the change in the current command value with a relatively easy design.
[Item 7]
The control circuit (23, 24, 29) limits the amount of change per unit time of the ratio of reactive current to active current to a predetermined ratio change amount, according to any one of items 1 to 4. Power converter (2).
According to this, the change of the current command value can be moderated while ensuring the followability of the power factor when the active power changes.

  DESCRIPTION OF SYMBOLS 1 DC power supply, 2 Power converter device, 3 systems, 21 DC-DC converter, 22 Inverter, 23 Converter drive control part, 24 Inverter drive control part, 241 Power balance control part, 242 Effective instantaneous current command part, 243 Invalid current command Unit, 243a tangent conversion unit, 243b reactive current ratio change limiting unit, 243c reactive current command value generation unit 2, 244 reactive instantaneous current command unit, 245 addition unit, 246 subtraction unit, 247 drive unit, 248 reactive current command value change limit Unit, 25 output power factor setting unit, 26 output current detection unit, 27 system voltage detection unit, 28 output measurement unit, 281 output active power calculation unit, 282 output apparent power calculation unit, 283 output effective current calculation unit, 284 output apparent Current calculation unit, 29 output limiting unit, 291 active power Over determination unit, 292 apparent power exceeds the determination unit, 293 OR circuit 294 active current excess determination unit, 295 apparent current exceedance determination unit, 251 power factor change restriction unit.

Claims (7)

An inverter that converts DC power output from the DC power source into AC power and supplies the AC power to the system;
A control circuit that controls active power output from the inverter and reactive power output from the inverter, and a power conversion device comprising:
The control circuit, when the active power exceeds a predetermined active power limit value, and when the apparent power exceeds a predetermined apparent power limit value, when satisfying at least one of the output power of the inverter, Control to suppress below the effective power limit value and the apparent power limit value,
The power converter characterized by the above-mentioned. A DC-DC converter that is interposed between the DC power supply and the inverter and adjusts the voltage of DC power output from the DC power supply and supplies the DC power to the inverter;
The control circuit is configured to control the DC-DC converter,
When the active power exceeds the predetermined active power limit value and when the apparent power exceeds the predetermined apparent power limit value, the control circuit satisfies the DC-DC The power conversion device according to claim 1, wherein control is performed so as to suppress power input from the converter to the inverter.   The control circuit is configured such that when the active power exceeds the predetermined active power limit value, the apparent power exceeds the predetermined apparent power limit value, and the apparent current output from the inverter is a predetermined apparent current. When at least one of the limit value is exceeded, the output power of the inverter is suppressed below the active power limit value and the apparent power limit value, and the output current of the inverter is reduced to the apparent power limit value The power conversion device according to claim 1, wherein control is performed so as to suppress the following. The control circuit is configured to be able to control the power factor of the output power of the inverter,
When changing the power factor of the output power of the inverter, the control circuit gradually changes from a reactive current corresponding to the power factor before the change to a reactive current corresponding to the power factor after the change. The power converter according to any one of claims 1 to 3.   The power converter according to any one of claims 1 to 4, further comprising a power factor change limiting unit that limits a change amount of the power factor per unit time to a predetermined power factor change amount.   5. The power converter according to claim 1, wherein the control circuit limits a change amount of the reactive current per unit time to a predetermined change amount. 6.   5. The power conversion device according to claim 1, wherein the control circuit limits a change amount per unit time of a ratio of the reactive current to the effective current to a predetermined ratio change amount. 6.

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