JP7183713B2 - POWER CONVERTER, POWER SUPPLY SYSTEM, AND CONTROL METHOD FOR POWER CONVERTER - Google Patents

Description

The present invention relates to a power conversion device, a power supply system, and a control method for a power conversion device.

The power converter (power conditioner) is provided with an islanding detection function in order to detect the power failure and disconnect itself from the commercial power system at the time of power failure in the commercial power system (from the Japan Electrical Manufacturers' Association JEM1498 ). On the other hand, it is also considered that when the voltage of the commercial power system is rising, the power conversion device suppresses the voltage rise by increasing the leading reactive power to the commercial power system as seen from the self. Since islanding detection must be performed quickly, it is performed repeatedly in a short period of time. On the other hand, voltage rise suppression is performed in a relatively long cycle. If the suppression of the voltage rise is performed at the same time as the detection of the islanding operation, there is a possibility that the control of the two will interfere with each other and the operation will not be performed normally. Therefore, when there is a risk of such interference, it has been proposed to perform control to temporarily stop the power converter (see, for example, Patent Document 1).

JP 2015-180123 A

However, if the power converter is stopped even for a short period of time, power generation efficiency will deteriorate. In view of such a problem, an object of the present invention is to suppress mutual interference between islanding detection and voltage fluctuation suppression while avoiding stoppage.

The present disclosure includes the following inventions. However, the present invention is defined by the claims.

A power conversion device according to an expression of the present invention is a power conversion device that is interconnected with a commercial power system, is provided between an AC electric line connected to the commercial power system and a DC power supply, and converts DC to AC or its A power conversion unit that performs reverse power conversion, and a first calculation that controls the switching operation of the power conversion unit and obtains a first reactive power to be injected for islanding detection based on the AC voltage of the AC circuit. and a control unit including a second calculation unit that obtains active power and second reactive power for suppressing voltage fluctuation of the AC electric circuit, wherein the first calculation unit interferes with the second reactive power When the first reactive power is to be injected, the controller injects the first reactive power while holding the current value of the second reactive power constant.

Further, a power supply system according to an aspect of the present invention is a power supply system comprising a DC power supply and a power conversion device connected to the DC power supply and interconnected with a commercial power system, wherein the power conversion device is , a power conversion unit provided between an AC electric line connected to the commercial power system and the DC power supply for performing power conversion from DC to AC or vice versa, and controlling the switching operation of the power conversion unit, the AC electric line Based on the AC voltage, a first calculation unit for obtaining the first reactive power to be injected for islanding detection, and a second for obtaining active power and second reactive power for suppressing voltage fluctuation of the AC electric circuit a controller including a calculator, wherein when the first calculator tries to inject the first reactive power that interferes with the second reactive power, the controller controls the second reactive power The first reactive power is injected while the current value of is held constant.

Further, a method for controlling a power conversion device according to an expression of the present invention includes a power conversion unit provided between an AC electric line connected to a commercial power system and a DC power supply, and performing power conversion from DC to AC or vice versa. A control method for a power conversion device, comprising: controlling the switching operation of the power conversion unit; and determining first reactive power to be injected for islanding detection based on the AC voltage of the AC circuit. , Also, when the active power and the second reactive power for suppressing voltage fluctuation of the AC electric circuit are obtained, and the first computing unit tries to inject the first reactive power that interferes with the second reactive power , injecting said first reactive power while holding the current value of said second reactive power constant.

ADVANTAGE OF THE INVENTION According to this invention, mutual interference of islanding detection and voltage fluctuation suppression can be suppressed, avoiding a stop of a power converter device.

FIG. 1 is a circuit diagram showing an example of a power conversion device and its input/output circuits. FIG. 2 is a control block diagram showing control functions in the control unit. FIG. 3 is a flowchart showing a first example of control for voltage fluctuation (rise) suppression. FIG. 4 is a flow chart showing a second example of control for voltage fluctuation (rise) suppression. FIG. 5 is a flowchart showing a third example of control for voltage fluctuation (drop) suppression. FIG. 6 is a flowchart showing a fourth example of control for voltage fluctuation (drop) suppression.

[Summary of Embodiment]
SUMMARY OF THE INVENTION Embodiments of the invention include at least the following.

(1) The present disclosure is a power conversion device interconnected with a commercial power system, which is provided between an AC electric circuit connected to the commercial power system and a DC power supply, and performs power conversion from DC to AC or vice versa. a power conversion unit that controls the switching operation of the power conversion unit to determine the first reactive power to be injected for islanding detection based on the AC voltage of the AC electric circuit; and a control unit including a second calculation unit that obtains active power and second reactive power for suppressing voltage fluctuations in an AC electric circuit, wherein the first calculation unit interferes with the second reactive power. The control unit is a power converter that, when injecting reactive power, injects the first reactive power while maintaining a current value of the second reactive power constant.

In such a power conversion device, if the islanding operation detection operation is performed at the same time that the voltage fluctuation suppression operation is performed by the control unit, the first reactive power interferes with the second reactive power. There is Therefore, in such a case, the control unit injects the first reactive power while keeping the current value of the second reactive power constant. This suppresses the voltage fluctuation suppression function, avoids interference between the function and the islanding detection function, and allows islanding detection to be performed while the power converter is in operation.

(2) In addition, in the power conversion device of (1), one of the amount of change from the previous value of the first reactive power and the amount of change from the previous value of the second reactive power is If the change amount is in the advancing direction and the other amount of change is in the lagging direction, the control unit may inject the first reactive power while maintaining the current value of the second reactive power constant. good.
In such cases, the first reactive power interferes with the second reactive power. Therefore, in such a case, the control unit can keep the voltage fluctuation suppression function in a constant state and perform islanding detection.

(3) In addition, in the power conversion device of (1), when the change amount from the previous value of the first reactive power is a value other than 0, the current value of the second reactive power may be held constant.
As a result, not only when the first reactive power interferes with the second reactive power, but also when it does not interfere, the control unit can keep the voltage fluctuation suppression function in a constant state and perform islanding detection. can.

(4) In the power converter according to any one of (1) to (3) above, when power is supplied from the DC power supply to the AC electric circuit, the second reactive power is phase-leading reactive power, When the first computation unit attempts to inject the first reactive power that interferes with the second reactive power, the control unit maintains the current value of the second reactive power constant and the active power may be reduced.
As a result, in the case of power conversion in which power is supplied from a DC power supply to an AC electric line, a voltage rise in the AC electric line can be suppressed by reducing the effective power.

(5) In addition, in the power converter according to any one of the above (1) to (3), when charging power is supplied from the AC circuit to the DC power supply, which is a storage battery, the second reactive power is lagging phase. is reactive power, and when the first computing unit attempts to inject the first reactive power that interferes with the second reactive power, the control unit keeps the current value of the second reactive power constant. The effective power may be reduced while maintaining.
As a result, in the case of power conversion in which charging power is supplied from an AC electric circuit to a DC power supply, a voltage drop in the AC electric circuit can be suppressed by reducing the effective power.

(6) On the other hand, the present disclosure is a power supply system having a DC power supply and a power conversion device connected to the DC power supply and interconnected with a commercial power system, wherein the power conversion device is connected to the commercial power A power conversion unit provided between an AC electric line connected to a system and the DC power supply for converting power from DC to AC or vice versa, and a switching operation of the power conversion unit to control the AC voltage of the AC electric line. Based on, a first calculation unit for obtaining a first reactive power to be injected for islanding detection, and a second calculation unit for obtaining an active power and a second reactive power for suppressing voltage fluctuation of the AC electric circuit and a control unit, wherein when the first computing unit attempts to inject the first reactive power that interferes with the second reactive power, the control unit calculates the current value of the second reactive power. A power system for injecting the first reactive power while holding it constant.

In such a power conversion device of a power supply system, when an islanding operation detection operation is performed at the same time that the voltage fluctuation suppression operation is performed by the control unit, the first reactive power becomes the second reactive power. Interference may occur. Therefore, in such a case, the control unit injects the first reactive power while keeping the current value of the second reactive power constant. This suppresses the voltage fluctuation suppression function, avoids interference between the function and the islanding detection function, and allows islanding detection to be performed while the power converter is in operation.

(7) In addition, the present disclosure is provided between an AC electric line connected to a commercial power system and a DC power supply, and has a power conversion unit that performs power conversion from DC to AC or vice versa. A method for controlling a switching operation of the power conversion unit, obtaining a first reactive power to be injected for islanding detection based on an AC voltage of the AC electric circuit, and determining a voltage of the AC electric circuit. When the active power and the second reactive power for suppressing fluctuation are obtained, and the first computing unit tries to inject the first reactive power that interferes with the second reactive power, the second reactive power This is a control method for a power conversion device, in which the first reactive power is injected while a current value is kept constant.

In such a method for controlling a power conversion device, if the islanding detection operation is performed at the same time that the voltage fluctuation suppression operation is performed, the first reactive power interferes with the second reactive power. There is Therefore, in such a case, the current value of the second reactive power is kept constant and the first reactive power is injected. This suppresses the voltage fluctuation suppression function, avoids interference between the function and the islanding detection function, and allows islanding detection to be performed while the power converter is in operation.

[Details of embodiment]
DESCRIPTION OF THE PREFERRED EMBODIMENTS A power conversion device and a control method thereof according to an embodiment of the present invention will be described below with reference to the drawings.

<<Configuration example of power converter>>
FIG. 1 is a circuit diagram showing an example of a power conversion device 100 and its input/output circuits. First, describing the main circuit elements, the power conversion device 100 includes a DC/DC converter 1 and an inverter 2 as a power conversion section 50 . A DC power supply 3 (for example, a storage battery, a photovoltaic panel, etc.) is connected to the DC side (left side of the drawing) of the power converter 100 . An AC electric circuit 4 is connected to the AC side (right side in the drawing) of the power converter 100 .
Note that the DC power supply 3 and the power converter 100 constitute a power supply system.

The two wires of the AC electric circuit 4 are usually single-phase three-wire voltage wires (U wire and W wire). In practice, a neutral line (O line) with an intermediate potential (0 V) is often created in the power conversion device 100 and connected to the single-phase, three-line commercial power system 7 in three lines. Illustrated.
A consumer's load 5 is connected to the AC electric line 4 . In addition, the AC electric line 4 is provided with an interconnection relay 6 . The interconnection relay 6 is connected to the commercial power system 7 .

Here, the simplest example in which there is only one DC system from the DC power supply 3 to the DC/DC converter 1 is shown, but the present invention is not limited to this. A circuit configuration connected in parallel may be used.

A DC side capacitor 9 is provided between the DC power supply 3 and the DC/DC converter 1 . The DC/DC converter 1 is configured by connecting a DC reactor 10, a low-side switching element Q1, and a high-side switching element Q2 as shown. Diodes d1 and d2 are connected in anti-parallel to the switching elements Q1 and Q2, respectively. The DC/DC converter 1 can operate as a step-up chopper or in the opposite direction as a step-down chopper.

The illustrated switching elements Q1 and Q2 are IGBTs (Insulated Gate Bipolar Transistors). The same applies to the other switching elements Q3-Q6. However, switching elements such as MOS-FETs (Metal-Oxide-Semiconductor Field-Effect Transistors) can be used instead of IGBTs.

An intermediate capacitor 11 is provided between the two lines of the DC bus 8 . An inverter 2 is connected to the DC bus 8 . The inverter 2 includes switching elements Q3, Q4, Q5, and Q6 forming a bridge circuit. Diodes d3, d4, d5 and d6 are connected in antiparallel to the switching elements Q3, Q4, Q5 and Q6, respectively. An AC reactor 12 and an AC side capacitor 13 are provided on the AC side of the inverter 2 .

As for elements related to measurement and control, first, the voltage sensor 14 detects the voltage across the DC side capacitor 9 and sends the detection output to the control section 20 . Current sensor 15 detects the current flowing through DC/DC converter 1 and sends the detection output to control unit 20 . The voltage sensor 16 detects the voltage between the two lines of the DC bus 8 and sends the detected output to the controller 20 . The current sensor 17 detects the current flowing through the AC reactor 12 and sends the detection output to the controller 20 . The voltage sensor 18 detects the voltage between the two lines of the AC electric circuit 4 and sends the detected output to the control section 20 .

The control unit 20 controls the switching elements Q1 to Q6 based on the detection output from each sensor. Also, the control unit 20 controls opening and closing of the interconnection relay 6 . During normal operation of the power converter 100, the interconnection relay 6 is closed. The control unit 20 opens the interconnection relay 6 when detecting that the commercial power system 7 has lost power and the power conversion device 100 has entered an isolated operation state.
The control unit 20 includes, for example, a computer, and the computer executes software (computer program) to realize necessary control functions. The software is stored in a storage device (not shown) of control unit 20 .

The power conversion device 100 is bi-directional, and in addition to power conversion from DC to AC, if the DC power supply 3 is a storage battery, power conversion from AC to DC is performed to charge the storage battery. can also

《Example of normal control》
During normal operation, as described above, the control unit 20 can perform grid-connected operation of the power conversion device 100 by controlling the switching elements Q1 to Q6 based on the detection output from each sensor.

When the power conversion device 100 is provided between the commercial power system 7 and the DC power supply 3 having a voltage lower than the peak value of the absolute value of the AC voltage, one example of preferred known control is AC half-cycle Among them, one of the DC/DC converter 1 and the inverter 2 is made to perform switching operation according to the phase of the alternating current, and the other is made to rest. Then, the control unit 20 controls the voltage of the AC power, the current flowing through the AC reactor 12, the voltage change due to the impedance of the AC reactor 12, the reactive current flowing through the intermediate capacitor 11 and the AC side capacitor 13, and the voltage of the DC power. Then, the current command value of the DC/DC converter 1 is set so as to be synchronized with the current of the AC power. Further, as the voltage of the AC power, a voltage obtained by supplementing the phase of the fundamental wave extracted based on the AC voltage detection value of the commercial power system 7 in consideration of the detection and control system delays can be used.

In such a power conversion device 100, the control unit 20 causes one of the DC/DC converter 1 and the inverter 2 to perform a switching operation according to the phase of the alternating current within the half cycle of the alternating current, and sets the period during which the other is stopped. A "minimum switching conversion scheme" can be implemented that In order to realize this method with high conversion efficiency, the voltage of the AC power, the current flowing through the AC reactor 12, the voltage change due to the impedance of the AC reactor 12, the reactive current flowing through the intermediate capacitor 11 and the AC side capacitor 13, and the DC power , the controller 20 sets the current command value of the DC/DC converter 1 so as to synchronize with the current of the AC power.

Then, as the voltage of the AC power, the phase is supplemented to the fundamental wave extracted based on the AC voltage detection value of the commercial power system 7 (the AC voltage detected by the voltage sensor 18) in consideration of the detection and control system delays. By using the voltage, it is possible to suppress the delay in control of the voltage phase, eliminate the influence of the disturbance of the system voltage of the commercial power system 7, and obtain a stable alternating current with little distortion.

Specifically, the output current command value to the load 5 is Ia*, the capacitance of the AC side capacitor 13 is Ca, the AC voltage of the AC circuit 4 is Va, the voltage on the DC power supply 3 side is V _DC , and the Laplace operator be s. In this case, the control unit 20 sets the AC output current command value Iinv* to flow to the current sensor 17 as
Iinv*=Ia*+sCaVa (1)
set to

Furthermore, when the impedance of the AC reactor 12 is Za, the control unit 20 sets the AC output voltage command value Vinv* at the output end of the inverter 2 (the interconnection point between the inverter 2 and the AC reactor 12) to
Vinv*=Va+ZaIinv* (2)
set to

In addition, the control unit 20 sets the larger of the absolute values of the voltage V _DC and the AC output voltage command value Vinv* as the output voltage command value Vo* of the DC/DC converter 1, and the intermediate capacitor 11 When the capacitance is C, the current command value Iin* of the DC/DC converter 1 is
Iin*={(Iinv**Vinv*)+(sC Vo*)*Vo*}/V _DC
... (3)
set to Then, the AC voltage Va is expressed as follows, where _{Va_rms} is the effective value and ωt is the phase of the timing for commanding the switching operation.
Va=√2 _{Va_rms} ×sin(ωt) (4)
can be

According to the above control, the current command value Iin* of the DC/DC converter 1 is the voltage of the AC power, the voltage change due to the current flowing through the AC reactor 12 and the impedance of the AC reactor 12, the intermediate capacitor 11 and the AC side capacitor The reactive current flowing through 13 and the voltage of the DC power are all reflected. Therefore, even when the voltage of the DC power supply 3 or the AC output current changes, it is possible to always output power synchronized with the AC output current.

By such control of the minimum switching conversion method, the DC/DC converter 1 and the inverter 2 can perform DC/AC conversion with the minimum required number of high-frequency switching. As a result, the switching loss of the semiconductor switching element and the iron loss of the AC and DC reactors are greatly reduced, and high conversion efficiency can be obtained. Furthermore, by setting the system voltage Va in this manner, a low-distortion alternating current can be obtained.

<<Functions of control unit including islanding detection and voltage rise suppression>>
FIG. 2 is a control block diagram showing control functions in the control unit 20. As shown in FIG. In the figure, the control unit 20 takes in the current detection value flowing through the AC reactor 12 (FIG. 1) from the current sensor 17 and the voltage detection value of the AC electric circuit 4 from the voltage sensor 18, respectively. Basically, the control unit 20 performs active power calculation according to the operation mode (B2) based on the control target (B1) according to the operation mode, and determines the current command value (B3). The current control section (B4) controls the switching operation of the power conversion section 50 based on this current command value.

Based on the voltage detection value detected by the voltage sensor 18, the control unit 20 calculates the system frequency (B5). Based on the calculated system frequency, the control unit 20 performs active detection (B7) and passive detection (B8) in the islanding detection unit (B6). Islanding operation is detected when a deviation of a frequency equal to or greater than a predetermined value is confirmed.

Based on the calculated system frequency (B5), the control unit 20 performs moving average calculation (B9), frequency deviation calculation (B10), and frequency feedback function reactive power calculation (B11). These moving average calculation (B9), frequency deviation calculation (B10), and frequency feedback function reactive power calculation (B11) function as a frequency feedback section (B12).

On the other hand, based on the voltage detection value, the control unit 20 performs fundamental wave voltage calculation (B13) and harmonic wave voltage calculation (B14), determines step injection occurrence conditions of reactive power (B15), and disables the step injection function. Power calculation (B16) is performed. These processes are the processes of the step injection part (B17).

The control unit 20 performs reactive power injection calculation for islanding detection based on the calculation result of the frequency feedback unit (B12) and the calculation result of the step injection unit (B17) (B18 (first calculation unit)). On the other hand, based on the voltage detection value, the control unit 20 calculates active power and reactive power for voltage rise suppression (B19 (second calculation unit)). The reactive power for islanding detection and the reactive power for voltage rise suppression are summed up in the reactive power injection calculation (B20). The active power for suppressing the voltage rise is subject to addition in the active power calculation (B2) according to the operation mode.

Further, based on the voltage detection value, the control unit 20 performs current control phase difference synchronization processing (B21) and provides a processed signal to the current control unit B4. A current detection signal is also provided to the current controller B4.

Here, it should be noted that the reactive power injection calculation for islanding detection (B18) and the active power/reactive power calculation for voltage rise suppression (B19) are connected in terms of calculation. Specifically, information on the reactive power for islanding detection (B18) is notified to the reactive power calculation for voltage rise suppression (B19), and when mutual interference occurs, the reactive power for voltage rise suppression is the current value. is kept constant. However, the active power for voltage rise suppression is not subject to such restrictions.

"others"
In the above description, it is assumed that the power converter 100 flows in reverse from the power converter 100 to the commercial power system 7. Conversely, when the DC power supply 3 is a storage battery, the power converter 100 is transferred from the commercial power system 7. A similar idea can be applied to the forward power flow charging the DC power supply 3 through the DC power supply. However, in the case of a forward power flow, the voltage drop is suppressed rather than the voltage rise is suppressed. Including rise and fall, it means suppression of voltage fluctuation.

<<Example of control for suppressing voltage fluctuation>>
(Reverse power flow from the power converter to the commercial power system (when considering the direction of reactive power))
<For control pattern 1>
For example, the reactive power for islanding detection is considered as the first reactive power, and the reactive power for voltage rise suppression is considered as the second reactive power. In this case, in the calculation process, regarding the amount of change from the previous value of the first reactive power and the amount of change from the previous value of the second reactive power, one amount of change is the leading direction and the other is the amount of change. If the quantity is lagging, the first reactive power interferes with the second reactive power. Therefore, the control unit 20 injects the first reactive power while keeping the current value of the second reactive power constant. As a result, the control unit 20 can maintain the voltage fluctuation suppression function in a constant state and perform islanding detection.

FIG. 3 is a flowchart showing a first example of control for voltage fluctuation (rise) suppression. In the figure, the control unit 20 determines whether or not the system voltage is equal to or higher than the threshold based on the detection output of the voltage sensor 18 (FIG. 1) (step S101). If the system voltage is equal to or higher than the threshold, control to lower the voltage is necessary, and if it is not equal to or higher than the threshold, control to lower the voltage is not necessary.
When the system voltage is equal to or higher than the threshold, the control unit 20 determines whether the power factor is greater than the lower limit based on the detection outputs of the voltage sensor 18 (FIG. 2) and the current sensor 17 (FIG. 2) ( step S102).

When the power factor is greater than the lower limit, the control unit 20 determines whether or not to inject lagging reactive power for islanding detection at this timing (step S103). If not injected, there is no risk of interference with the islanding detection, so the control unit 20 increases the leading reactive power while maintaining the active power (step S107). On the other hand, when the power factor is equal to or lower than the lower limit value in step S102, since no more reactive power can be injected, the active power is decreased and the leading reactive power is held at the current value (step S108). Also, when the lagging reactive power is injected in step S103, there is a risk of interfering with islanding detection, so the active power is reduced and the leading reactive power is held at the current value (step S108).

On the other hand, when the system voltage is lower than the threshold in step S101, there is no need to lower the voltage. Therefore, the control unit 20 determines whether or not the active power is being suppressed (step S104). If not suppressed, the control unit 20 determines whether or not phase-advance reactive power is being injected (step S105). If it is being injected, the control unit 20 determines whether or not to inject leading reactive power for islanding detection (step S106). In the case of not injecting, the control unit 20 reduces the leading reactive power while keeping the active power as it is (step S110). On the other hand, when the leading reactive power is not being injected in step S105, nothing needs to be done, so the active power and the leading reactive power are held (step S109). Further, when injecting the leading reactive power for islanding detection, the control unit 20 holds the active power and the leading reactive power (step S109).

Furthermore, when the active power is being suppressed in step S104, it is desired to return the active power preferentially, so the control unit 20 increases the active power and holds the leading reactive power at the current value (step S111). .

(Reverse power flow from the power converter to the commercial power system (when the direction of reactive power is not considered))
<For control pattern 2>
As described above, if the reactive power for islanding detection is considered as the first reactive power and the reactive power for suppressing voltage rise is considered as the second reactive power, and the direction of the reactive power is not considered, the control unit 20 , the current value of the second reactive power is held constant when the amount of change from the previous value of the first reactive power is a value other than zero. As a result, not only when the first reactive power interferes with the second reactive power, but also when it does not interfere, the control unit 20 keeps the voltage fluctuation suppression function in a constant state and performs islanding detection. can be done. In other words, the control is slightly rougher than control pattern 1.

FIG. 4 is a flow chart showing a second example of control for voltage fluctuation (rise) suppression. In the figure, the control unit 20 determines whether or not the system voltage is equal to or higher than the threshold based on the detection output of the voltage sensor 18 (FIG. 1) (step S201). If the system voltage is equal to or higher than the threshold, control to lower the voltage is necessary, and if it is not equal to or higher than the threshold, control to lower the voltage is not necessary.
When the system voltage is equal to or higher than the threshold, the control unit 20 determines whether the power factor is greater than the lower limit based on the detection outputs of the voltage sensor 18 (FIG. 2) and the current sensor 17 (FIG. 2) ( step S202).

When the power factor is greater than the lower limit, the control unit 20 determines whether or not to inject leading or lagging reactive power for islanding detection at this timing (step S203). If not injected, there is no risk of interference with the islanding detection, so the control unit 20 increases the leading reactive power while maintaining the active power (step S207). On the other hand, when the power factor is equal to or lower than the lower limit in step S202, since no more reactive power can be injected, the active power is reduced and the leading reactive power is held at the current value (step S208). Also, when leading or lagging reactive power is injected in step S203, since there is a risk of interfering with islanding detection, the active power is reduced and the leading reactive power is held at the current value (step S208).

On the other hand, when the system voltage is lower than the threshold in step S201, there is no need to lower the voltage. Therefore, the control unit 20 determines whether or not the active power is being suppressed (step S204). If not suppressed, the control unit 20 determines whether or not phase-advancing reactive power is being injected (step S205). If the injection is in progress, the control unit 20 determines whether or not to inject the leading or lagging reactive power for islanding detection (step S206). If not injected, the control unit 20 reduces the leading reactive power while keeping the active power (step S210). On the other hand, when the leading reactive power is not being injected in step S205, nothing needs to be done, so the active power and the leading reactive power are held (step S209). Also, when injecting the leading or lagging reactive power for islanding detection, the control unit 20 holds the active power and the leading reactive power (step S209).

Furthermore, when the active power is suppressed in step S204, it is desired to return the active power preferentially, so the control unit 20 increases the active power and holds the leading reactive power at the current value (step S211). .

(Forward power flow from the commercial power system to the power converter (when considering the direction of reactive power))
<For control pattern 1>
FIG. 5 is a flowchart showing a third example of control for voltage fluctuation (drop) suppression. In the figure, the control unit 20 determines whether or not the system voltage is equal to or less than a threshold based on the detection output of the voltage sensor 18 (FIG. 1) (step S301). If the system voltage is equal to or less than the threshold, control to raise the voltage is necessary, and if it is not equal to or less than the threshold, control to raise the voltage is not necessary.
If the system voltage is equal to or less than the threshold, the control unit 20 determines whether the power factor is greater than the lower limit based on the detection outputs of the voltage sensor 18 (FIG. 2) and the current sensor 17 (FIG. 2) ( step S302).

When the power factor is greater than the lower limit value, the control unit 20 determines whether or not to inject leading reactive power for islanding detection at this timing (step S303). If not injected, there is no risk of interference with islanding detection, so control unit 20 increases the lagging phase reactive power while maintaining the active power for charging (step S307). On the other hand, when the power factor is equal to or lower than the lower limit in step S302, since no more reactive power can be injected, the active power for charging is reduced and the lagging reactive power is held at the current value (step S308). Also, when the leading reactive power is injected in step S303, there is a risk of interfering with islanding detection, so the charging active power is reduced and the lagging reactive power is held at the current value (step S306).

On the other hand, when the system voltage is higher than the threshold in step S301, there is no need to raise the voltage. Therefore, the control unit 20 determines whether or not the effective power for charging is suppressed (step S304). If not suppressed, the control unit 20 determines whether or not the lagging reactive power is being injected (step S305). If it is being injected, the control unit 20 determines whether or not to inject the lagging reactive power for islanding detection (step S306). When not injecting, the controller 20 reduces the lagging reactive power while keeping the active power of charging as it is (step S310). On the other hand, when the lagging reactive power is not being injected in step S305, nothing needs to be done, so the active charging power and the lagging reactive power are held (step S309). Further, when injecting the lagging reactive power for islanding detection, the control unit 20 holds the charging active power and the lagging reactive power (step S309).

Furthermore, when the active power of charging is suppressed in step S304, the active power is preferentially returned, so the control unit 20 increases the active power of charging and holds the lagging reactive power at the current value. (Step S311).

(Forward power flow from the commercial power system to the power converter (when the direction of reactive power is not considered))
<For control pattern 2>
FIG. 6 is a flowchart showing a fourth example of control for voltage fluctuation (drop) suppression. In the figure, the control unit 20 determines whether or not the system voltage is equal to or less than the threshold based on the detection output of the voltage sensor 18 (FIG. 1) (step S401). If the system voltage is equal to or less than the threshold, control to raise the voltage is necessary, and if it is not equal to or less than the threshold, control to raise the voltage is not necessary.
If the system voltage is equal to or less than the threshold, the control unit 20 determines whether the power factor is greater than the lower limit based on the detection outputs of the voltage sensor 18 (FIG. 2) and the current sensor 17 (FIG. 2) ( step S402).

When the power factor is greater than the lower limit, the control unit 20 determines whether or not to inject leading or lagging reactive power for islanding detection at this timing (step S403). If not injected, there is no risk of interference with islanding detection, so control unit 20 increases the lagging reactive power while maintaining the active power for charging (step S407). On the other hand, when the power factor is equal to or lower than the lower limit in step S402, since no more reactive power can be injected, the charging active power is reduced and the lagging reactive power is held at the current value (step S406). Also, when the leading or lagging reactive power is injected in step S403, since there is a risk of interfering with islanding detection, the charging active power is reduced and the lagging reactive power is held at the current value (step S408). .

On the other hand, when the system voltage is higher than the threshold in step S401, there is no need to lower the voltage. Therefore, the control unit 20 determines whether or not the effective power for charging is suppressed (step S404). If not suppressed, the control unit 20 determines whether or not the lagging reactive power is being injected (step S405). If it is being injected, the control unit 20 determines whether or not to inject the leading or lagging reactive power for islanding detection (step S406). If not, the control unit 20 reduces the lagging reactive power while maintaining the active power of charging (step S410). On the other hand, when the lagging reactive power is not being injected in step S405, nothing needs to be done, so the control unit 20 holds the charging active power and the lagging reactive power (step S409). Also, when injecting leading or lagging reactive power for islanding detection, the controller 20 holds the charging active power and lagging reactive power (step S409).

Furthermore, when the reactive power is being suppressed in step S404, it is desired to return the active power preferentially, so the control unit 20 increases the charging active power and holds the lagging reactive power at the current value (step S411).

《Summary of Disclosure》
The control unit 20 of the power conversion device 100 according to the present disclosure controls the switching operation of the power conversion unit 50, and obtains the first reactive power to be injected for islanding detection based on the AC voltage of the AC electric circuit 4. A first calculation unit (B18) and a second calculation unit (B19) for obtaining the active power and the second reactive power for suppressing voltage fluctuation of the AC electric circuit 4, and the first calculation unit (B18) is the second When attempting to inject the first reactive power that interferes with the reactive power, the control unit 20 injects the first reactive power while holding the current value of the second reactive power constant.

In such a power conversion device, when the control unit 20 performs the operation of suppressing the voltage fluctuation and simultaneously performs the islanding detection operation, the first reactive power interferes with the second reactive power. Sometimes. Therefore, in such a case, the control unit 20 keeps the current value of the second reactive power constant and injects the first reactive power. This suppresses the voltage fluctuation suppression function, avoids interference between the function and the islanding detection function, and allows the islanding detection to be performed while the power converter 100 is in operation.

Specifically, for example, regarding the amount of change from the previous value of the first reactive power and the amount of change from the previous value of the second reactive power, one amount of change is in the advance direction and the other is the amount of change. is in the lagging direction, the first reactive power interferes with the second reactive power. Therefore, the control unit 20 injects the first reactive power while keeping the current value of the second reactive power constant. As a result, the control unit 20 can maintain the voltage fluctuation suppression function in a constant state and perform islanding detection.

Further, when the amount of change from the previous value of the first reactive power is a value other than 0, the control unit 20 may keep the current value of the second reactive power constant. As a result, not only when the first reactive power interferes with the second reactive power, but also when it does not interfere, the control unit 20 keeps the voltage fluctuation suppression function in a constant state and performs islanding detection. can be done.

Note that the present disclosure is also a power supply system having the DC power supply 3 and the power converter 100 . Further, the present disclosure is a control method for the power conversion device 100, which controls the switching operation of the power conversion unit 50, and based on the AC voltage of the AC electric circuit 4, should be injected for islanding detection. A first reactive power is obtained, an active power for suppressing voltage fluctuations in the AC electric circuit 4 and a second reactive power are obtained, and the first computing unit injects the first reactive power that interferes with the second reactive power. When about to do so, the first reactive power is injected while the current value of the second reactive power is held constant.

According to such a control method for a power conversion device, when an islanding operation detection operation is performed at the same time that a voltage fluctuation suppression operation is performed, the first reactive power interferes with the second reactive power. In such a case, the current value of the second reactive power is held constant and the first reactive power is injected. This suppresses the voltage fluctuation suppression function, avoids interference between the function and the islanding detection function, and allows the islanding detection to be performed while the power converter 100 is in operation.

《Supplement》
It should be noted that the embodiments disclosed this time should be considered as examples in all respects and not restrictive. The scope of the present invention is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope of equivalence to the scope of claims.

1 DC/DC Converter 2 Inverter 3 DC Power Supply 4 AC Circuit 5 Load 6 Interconnection Relay 7 Commercial Power System 8 DC Bus 9 DC Side Capacitor 10 DC Reactor 11 Intermediate Capacitor 12 AC Reactor 13 AC Side Capacitor 14 Voltage Sensor 15 Current Sensor 16 Voltage sensor 17 Current sensor 18 Voltage sensor 20 Control unit 50 Power conversion unit 100 Power conditioner d1, d2, d3, d4, d5, d6 Diodes Q1, Q2, Q3, Q4, Q5, Q6 Switching elements

Claims (7)

A power conversion device interconnected with a commercial power system,
A power conversion unit provided between an AC electric line connected to the commercial power system and a DC power supply and performing power conversion from DC to AC or vice versa;
a first computing unit that controls the switching operation of the power conversion unit and obtains a first reactive power to be injected for islanding detection based on the AC voltage of the AC electric circuit; and voltage fluctuation suppression of the AC electric circuit. a control unit including a second computing unit that determines the active power and the second reactive power for
with
When the first computing unit attempts to inject the first reactive power that interferes with the second reactive power, the control unit controls the current value of the second reactive power to be held constant. injecting a first reactive power;
Further, when the amount of change from the previous value of the first reactive power is a value other than 0, the control unit reduces the first reactive power while maintaining the current value of the second reactive power constant. A power conversion device that injects A power conversion device interconnected with a commercial power system,
A power conversion unit provided between an AC electric line connected to the commercial power system and a DC power supply and performing power conversion from DC to AC or vice versa;
a first computing unit that controls the switching operation of the power conversion unit and obtains a first reactive power to be injected for islanding detection based on the AC voltage of the AC electric circuit; and voltage fluctuation suppression of the AC electric circuit. a control unit including a second computing unit that determines the active power and the second reactive power for
with
When power is supplied from the DC power supply to the AC electric circuit, the second reactive power is phase-leading reactive power,
When the first computing unit attempts to inject the first reactive power that interferes with the second reactive power, the control unit controls the current value of the second reactive power to be held constant. A power converter that injects a first reactive power and reduces the active power. A power conversion device interconnected with a commercial power system,
A power conversion unit provided between an AC electric line connected to the commercial power system and a DC power supply and performing power conversion from DC to AC or vice versa;
a first computing unit that controls the switching operation of the power conversion unit and obtains a first reactive power to be injected for islanding detection based on the AC voltage of the AC electric circuit; and voltage fluctuation suppression of the AC electric circuit. a control unit including a second computing unit that determines the active power and the second reactive power for
with
When charging power is supplied from the AC circuit to the DC power supply, which is a storage battery, the second reactive power is lagging reactive power,
When the first computing unit attempts to inject the first reactive power that interferes with the second reactive power, the control unit controls the current value of the second reactive power to be held constant. A power converter that injects a first reactive power and reduces the active power. a DC power supply;
and a power conversion device according to any one of claims 1 to 3, which is connected to the DC power supply and interconnected with a commercial power system . A control method for a power conversion device having a power conversion unit that is provided between an AC electric line connected to a commercial power system and a DC power supply and performs power conversion from DC to AC or vice versa,
Controlling the switching operation of the power converter, obtaining first reactive power to be injected for islanding detection based on the AC voltage of the AC electric circuit, and calculating the effective power for suppressing voltage fluctuation of the AC electric circuit determining power and a second reactive power;
when trying to inject the first reactive power that interferes with the second reactive power, injecting the first reactive power while holding the current value of the second reactive power constant;
Furthermore, when the amount of change from the previous value of the first reactive power is a value other than 0, injecting the first reactive power while maintaining the current value of the second reactive power constant.
A control method for a power converter. A control method for a power conversion device having a power conversion unit that is provided between an AC electric line connected to a commercial power system and a DC power supply and performs power conversion from DC to AC or vice versa,
controlling the switching operation of the power conversion unit, obtaining first reactive power to be injected for islanding detection based on the AC voltage of the AC electric circuit, and determining the voltage of the AC electric circuit;
Obtaining the active power for suppressing fluctuation and the second reactive power, which is the leading reactive power when power is supplied from the DC power supply to the AC electric circuit,
When trying to inject the first reactive power that interferes with the second reactive power, the first reactive power is injected while the current value of the second reactive power is held constant, and the effective reduce power,
A control method for a power converter. A control method for a power conversion device having a power conversion unit that is provided between an AC electric line connected to a commercial power system and a DC power supply and performs power conversion from DC to AC or vice versa,
controlling the switching operation of the power conversion unit, obtaining first reactive power to be injected for islanding detection based on the AC voltage of the AC electric circuit, and determining the voltage of the AC electric circuit;
Obtaining the second reactive power, which is the lagging phase reactive power when charging power is supplied from the AC electric circuit to the DC power supply, which is a storage battery, from the active power for suppressing fluctuation,
When trying to inject the first reactive power that interferes with the second reactive power, the first reactive power is injected while the current value of the second reactive power is held constant, and the effective reduce power,
A control method for a power converter.

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