JP7564461B2 - Power supply system and method for controlling the power supply system - Google Patents

Description

The present invention relates to a power supply system and a method for controlling a power supply system.

In conventional power supply systems, as shown in Patent Document 1, for example, during normal operation, power is supplied from the power supply system to the load via a power line. During an abnormal operation, a circuit breaker installed on the power line is opened to cut off the power supply from the power supply system to the load, and the inverter supplies power to the load, thereby compensating for the load voltage. After that, when the system voltage, which is the voltage of the power supply system, is restored, the circuit breaker is closed and power is again supplied from the power supply system to the load.

JP 2019-140781 A

In the above power supply system, in order to continue supplying voltage to the load, the inverter supplies power to the load so that the load voltage is the rated voltage. In other words, the inverter compensates for the drop in system voltage. Therefore, when the system voltage drops and the circuit breaker is turned on, the inverter compensates for the drop in system voltage, causing a potential difference in the circuit breaker. As a result, a short-circuit current is generated from the inverter in the power line where the circuit breaker is installed, which may damage the inverter.

The present invention was made in consideration of the above problems, and its main objective is to prevent the inverter from being damaged by a short circuit current generated from the inverter when the system voltage changes and the circuit breaker is closed.

That is, the power supply system of the present invention includes a mechanical switch that is provided on a power line for supplying power from a power supply system to a load and opens and closes the power line, a power converter that is provided on the power line and converts DC power to AC power to supply the load, a switch current measuring unit that measures a switch current that is a current flowing through the mechanical switch, and a control unit that controls the mechanical switch and the power converter, wherein when an abnormality occurs in the power supply system, the control unit opens the mechanical switch and the power converter performs compensation control to compensate for the voltage of the load, and after the power supply system is restored and the mechanical switch is closed, controls a converter current that is a current output by the power converter based on a switch current target value that is a target value for the switch current and the switch current.
Moreover, a control method for a power supply system according to the present invention is a control method for a power supply system that supplies power from a power supply system to a load when the power supply system is normal, cuts off power supply from the power supply system to the load when an abnormality occurs in the power supply system, compensates for a voltage of the load, and then restores power to the power supply system, the power supply system being provided on a power line for supplying power from the power supply system to the load, and including: a mechanical switch that opens and closes the power line; a switch current measuring unit that measures a switch current that is a current flowing through the mechanical switch; and a power converter that is provided on the power line and converts DC power to AC power to supply power to the load, and is characterized in that when an abnormality occurs in the power supply system, the mechanical switch is opened, and the power converter compensates for the voltage of the load, and after the power supply system is restored and the mechanical switch is closed, a converter current that is a current output by the power converter is controlled based on a switch current target value that is a target value of the switch current and the switch current.

In this configuration, the switch current measuring unit measures the current flowing through the mechanical switch, and after the power system is restored and the mechanical switch is turned on, the control unit controls the converter current based on the switch current target value and the switch current, so that the current supplied from the power converter to the mechanical switch is controlled. Therefore, even if the system voltage changes and a potential difference occurs between a voltage command value such as the rated voltage and the system voltage, the converter current can be controlled to prevent a short circuit current from occurring from the power converter, thereby preventing damage to the power converter.

It is preferable that the control unit gradually transitions the switch current target value from 0 to the current of the load once the mechanical switch has been turned on.

With this configuration, once the closing of the mechanical switch is completed, the control unit shifts the switch current target value from 0 to the load current and controls the converter current based on the switch current target value and the switch current, so that the switch current is controlled to be equal to the load current. Therefore, even if the system voltage changes, the switch current and the load current are controlled to be equal, so that when the closing of the mechanical switch is completed, the current flowing through the circuit formed by the power converter and the mechanical switch is 0. As a result, the current from the power supply system flows through the mechanical switch to the load, and no potential difference is generated between the power supply system and the load even if the system voltage changes, so that no short-circuit current is generated from the power converter and damage to the power converter can be prevented.
Furthermore, since the control unit gradually shifts the switch current target value to the current of the load, the power supply to the load can be smoothly switched from the power converter to the power supply system.

The device further includes a converter current measurement unit that measures the converter current, and the control unit shifts a converter current target value, which is a target value of the converter current, to 0 based on the converter current from the point in time when the mechanical switch is turned on.

In this configuration, the control unit calculates the converter current target value based on the converter current and shifts the converter current target value to zero, so that the current supplied from the power converter to the mechanical switch becomes zero and the switch current becomes equal to the load current. Therefore, the control unit can control the converter current without measuring the switch current, making control easier.

It is desirable that the control unit controls the power converter so that the voltage that the power converter compensates for the mechanical switch is set to zero when the power supply system is restored and before the closing of the mechanical switch is completed, and controls the converter current based on the switch current target value and the switch current after the closing of the mechanical switch is completed.

With this configuration, before closing of the mechanical switch is completed, the voltage that the power converter compensates for the mechanical switch is controlled to 0. As a result, even if the system voltage changes and before closing of the mechanical switch is completed, the power converter does not compensate the mechanical switch for the system voltage change, so that it is possible to prevent a potential difference from occurring in the mechanical switch and to further suppress overcurrent in the mechanical switch.
Furthermore, after the mechanical switch has been turned on, the control unit controls the converter current based on the switch current target value and the switch current. Therefore, even if the system voltage changes and a potential difference occurs between a voltage command value, such as a rated voltage, and the system voltage, the converter current can be controlled to prevent a short circuit current from occurring from the power converter, thereby preventing damage to the power converter.

With this configuration, the present invention can prevent damage to the power converter caused by a short circuit current generated from the power converter when the system voltage changes and the mechanical switch is turned on.

1 is a schematic diagram showing a configuration of a power supply system according to an embodiment of the present invention; 2 is a block diagram of a control unit of the power supply system according to the embodiment. FIG. FIG. 4 is a block diagram showing generation of a switch current target value in the present embodiment. 5 is a graph showing a change over time in a switch current target value in the present embodiment. 4 is an experimental example showing a simulation result of the power supply system according to the present embodiment. 13 is an experimental example showing a simulation result of a power supply system in a conventional example. FIG. 13 is a block diagram of a control unit of a power supply system according to another embodiment. 13 is a graph showing a change over time in a converter current target value in another embodiment. 13 is an experimental example showing a simulation result of a power supply system according to another embodiment.

Below, an embodiment of the power supply system according to the present invention will be described with reference to the drawings. Note that in any of the drawings shown below, some parts may be omitted or exaggerated and illustrated as schematics in order to make the drawings easier to understand. Identical components will be given the same reference numerals and descriptions thereof will be omitted as appropriate.

1. Device configuration
As shown in Fig. 1, the power supply system 100 in this embodiment is provided between a power supply system 10 and a load 20. This power supply system 100 supplies power from the power supply system 10 to the load 20 when the power supply system 10 is normal. Furthermore, when an abnormality occurs in the power supply system 10 due to a short circuit accident or the like in the power supply system 10, the power supply system 100 cuts off the power supply from the power supply system 10 to the load 20 and supplies power from the power storage unit 4 to the load 20. Thereafter, when the power supply system 10 recovers, the power supply system 100 resumes the power supply from the power supply system 10 to the load 20. Note that although the power supply system 100 in this embodiment is one-phase, it may be three-phase, and the number of phases is not particularly limited.

Specifically, the power supply system 100 includes a mechanical switch 3 that switches the power supply from the power supply system 10 to the load 20 by opening and closing, a power converter 5 that converts DC power into AC power and supplies the power to a power line L1, a system voltage measurement unit 7 that measures a system voltage V _S that is the voltage of the power supply system 10, a current measurement unit 8 that measures a current flowing through the power supply system 100, and a control unit 9 that controls the mechanical switch 3 and the power converter 5.

The mechanical switch 3 is provided on the power line L1 for supplying power from the power supply system 10 to the load 20, and switches the power line L1 between open and closed by mechanical action. In order to more quickly cut off the power supply from the power supply system 10 to the load 20 in the event of an abnormality in the power supply system 10, the mechanical switch 3 is preferably provided on the load 20 side rather than the power supply system 10, but is not limited thereto.

In addition, in this embodiment, the mechanical switch 3 is opened and closed by a drive circuit (not shown). The drive circuit outputs a switch open completion signal to the control unit 9 when the mechanical switch 3 is opened, and outputs a switch on completion signal to the control unit 9 when the mechanical switch 3 is closed.

The power storage unit 4 is, for example, a power storage device such as a secondary battery (storage battery). The power storage unit 4 stores DC power, and when an abnormality is detected in the power supply system 10, the DC power stored in the power storage unit 4 is supplied to the power converter 5.

The power converter 5 is connected to the power line L1 in parallel with the mechanical switch 3. Specifically, the power converter 5 is connected to the power line L1 at connection points A and B (connection point A is located closer to the power supply system 10 than connection point B). As a result, a closed circuit C is formed by the mechanical switch 3, the power converter 5, and connection points A and B. The power converter 5 is connected to the power line L1 via the injection transformer T, and converts the DC power of the power storage unit 4 into AC power and supplies it to the power line L1.

An impedance element 6 that stabilizes the output of the power converter 5 is provided between the power converter 5 and the power line L1. Specifically, the impedance element 6 includes an interconnection reactor 61 that is connected to the power converter 5 and stabilizes the AC current, and a capacitor 62 that is connected to the interconnection reactor 61 and stabilizes the voltage.

The system voltage measurement unit 7 measures the system voltage V _S and outputs the system voltage V _S to the control unit 9. Specifically, the system voltage measurement unit 7 is located closer to the power supply system 10 than the connection point A. The system voltage measurement unit 7 may output the measured system voltage V _S to the control unit 9 as a measured value, or may output it to the control unit 9 as a signal.

The current measuring unit 8 measures the current flowing through the power supply system 100 and outputs the measured current to the control unit 9. Specifically, the current measuring unit 8 includes a switch current measuring unit 81 that measures a switch current I _SW that is a current flowing through the mechanical switch 3, a load current measuring unit 82 that measures a load current I _X that is a current flowing through the load 20, and a converter current measuring unit 83 that measures a converter current I _Inv that is a current flowing through the power converter 5. The current measuring unit 8 may output the measured current to the control unit 9 as a measured value, or may output the measured current to the control unit 9 as a signal.

More specifically, the switch current measuring unit 81 is provided in the closed circuit C, and in this embodiment, the switch current measuring unit 81 is provided in the power line L1 between the connection points A and B. Note that the switch current measuring unit 81 only needs to be able to measure the current flowing through the mechanical switch 3 in the closed circuit C, and may be provided, for example, on the closed circuit C between the connection points A and B and the power converter 5.

Furthermore, the load current measuring unit 82 is provided on the power line L1 closer to the load 20 than the connection point B. The converter current measuring unit 83 is provided on the output side of the power converter 5, and is provided on the closed circuit C between the connection points A, B and the power converter 5.

The control unit 9 controls the mechanical switch 3 and the power converter 5 when an abnormality occurs in the power supply system 10. When the system voltage V _S is outside a predetermined range, the control unit 9 determines that an abnormality occurs in the power supply system 10 and starts controlling the mechanical switch 3 and the power converter 5. The system voltage V _S being outside the predetermined range here refers to a case where the system voltage V _S is, for example, 20% or less or 107% or more of the rated voltage. In this embodiment, the control unit 9 performs PWM control to repeatedly turn on and off the power converter 5 and control the voltage output from the power converter 5, but the control method performed by the control unit 9 on the power converter 5 is not limited to PWM control. Hereinafter, the control operation of the control unit 9 when an abnormality occurs in the power supply system 10 will be described with reference to FIG. 2.

When an abnormality occurs in the power supply system 10, the control unit 9 opens the mechanical switch 3, and performs compensation control in which the power converter 5 compensates for the load 20. Specifically, the control unit 9 outputs a switch opening signal to open the mechanical switch 3 to the drive circuit, and controls the mechanical switch 3. The control unit 9 also outputs a compensation voltage _VSW that compensates for the load voltage based on the difference between a target value _Vref of the load voltage, which is set to the rated voltage, and the system voltage _VS , and controls the power converter 5. Furthermore, the control unit 9 outputs a reduced voltage _VL, which is a voltage that is reduced via the impedance element 6, based on the converter current _IInv , and controls the power converter 5.

After the system voltage V _S is restored, the control unit 9 turns on the mechanical switch 3. Specifically, the control unit 9 determines whether power has been restored to the power supply system 10 based on the system voltage V _S measured by the system voltage measurement unit 7. When the control unit 9 determines that power has been restored to the power supply system 10, the control unit 9 outputs a switch-on signal to the drive circuit to turn on the mechanical switch 3, and the drive circuit turns on the mechanical switch 3. Note that the restoration of the system voltage V _S here refers to the state in which the system voltage V _S remains equal to the rated voltage for a certain period of time.

Thus, after the system voltage _VS is restored and the mechanical switch 3 is turned on, the control unit 9 controls the converter current I _Inv , which is a current output by the power converter 5, based on the switch current target value I _ref1 , which is a target value of the switch current I _SW , and the switch current I _SW . Specifically, the control unit 9 performs dq conversion of the switch current target value I _ref1 and the switch current I _SW based on the phase of the switch current target value I _ref1 , the switch current I _SW , and the target value V _ref of the load voltage. The control unit 9 performs PI control of the converter current I Inv by setting the difference between the dq converted switch current target value I _ref1 and the switch current I _SW as the converter current I _Inv . The control unit 9 converts _{the PI controlled converter current I Inv into} a three-phase coordinate system based on the phase of the target value V _ref of the load voltage, and controls the converter current I _Inv . The control of the converter current I _Inv is not limited to PI control, but may be other control such as PID control.

In this embodiment, the control unit 9 gradually shifts the switch current target value _Iref1 from 0 to the load current _Ix from the time point when the closing of the mechanical switch 3 is completed. Specifically, as shown in FIG. 3, the control unit 9 outputs a current shift trigger, which is the time point when the switch current target value _Iref1 is shifted from 0, at the time point when the closing of the mechanical switch 3 is completed. The control unit 9 outputs a ramp signal of the switch current target value _Iref1 based on the current shift trigger. Then, the control unit 9 generates a ramp function that gradually shifts the switch current target value _Iref1 from 0 to the load current _Ix based on the load current _Ix and the ramp signal of the switch current target value Iref1. Note that, as shown in FIG. 3, the control unit 9 may output a ramp signal based on the current shift trigger and _a switch closing completion signal.

The control unit 9 outputs the switch current target value _Iref1 based on the ramp function thus generated. Specifically, as shown in FIG. 4, the control unit 9 controls the switch current target value _Iref1 to be 0 from when it is determined that the system voltage _Vs is restored (time t0) until the current shift trigger is output (time t4). From time t4, the control unit 9 gradually shifts the switch current target value _Iref1 from 0 to the load current _Ix . When the switch current target value _Iref1 and the load current _Ix become equal, the difference between the switch current target value _Iref1 and the switch current _Isw becomes 0, and the converter current _Iinv becomes 0. Thereafter, when the system voltage _Vs is restored and the closing of the mechanical switch 3 is completed, the control unit 9 stops the power converter 5.

Here, time t4 may be any time that it can be determined that the closing of the mechanical switch 3 is completed. For example, as shown in Fig. 4, time t4 may be a time when a predetermined time has elapsed from any of the following times: the time when the control unit 9 determines that the system voltage _VS has been restored (time t0), the time when the control unit 9 outputs a switch-on signal (time t1), the time when the switch current measuring unit 81 measures the switch current _ISW (time t2), and the time when the drive circuit outputs a switch-on completion signal (time t3).

2. Experimental Example
An experimental example showing a simulation result of the control unit 9 performing the above-mentioned control and an experimental example showing a simulation result of the conventional control are shown in Fig. 5 and Fig. 6. In Fig. 5 and Fig. 6, the horizontal axis represents time, and the vertical axis represents the system voltage, the system voltage effective value, the switch current, the load voltage, the load current, the converter voltage, and the converter current.

As shown in Fig. 5, after it is determined that the system voltage V _S has been restored and, for example, the system voltage V _S has dropped by 10%, the mechanical switch 3 is turned on (time s1). When the turning on of the mechanical switch 3 is completed and a current transfer trigger is output (time s2), the control unit 9 controls the converter current I _Inv based on the switch current target value I _ref1 and the switch current I _SW . As a result, after time s2, the switch current target value I _ref1 gradually transitions from 0 to the load current I _X , so that the switch current I _SW gradually transitions to the load current I _X and eventually becomes equal to the load current I _X , and the converter current I _Inv converges to 0. As a result, the switch current I _SW and the load current I _X do not diverge.

6, in the conventional control, when the mechanical switch 3 is closed (at time s1) after the system voltage V _S drops, the power converter 5 outputs to compensate for the drop in the system voltage V _S , which generates a potential difference in the mechanical switch 3. As a result, an overcurrent flows through the mechanical switch 3 and the power converter 5, the switch current I _SW , the load current I _X , and the converter current I _Inv diverge, and the mechanical switch 3 and the power converter 5 may be damaged.

3. Effects of this embodiment
According to this embodiment,
The switch current measuring unit 81 measures the current flowing through the mechanical switch 3, and the control unit 9 controls the converter current I _Inv based on the switch current target value I _ref1 and the switch current I _SW after the power supply system 10 is restored and the mechanical switch 3 is turned on, so that the current supplied from the power converter 5 to the mechanical switch 3 is controlled. Therefore, even if the system voltage _VS changes and a potential difference occurs between a voltage command value such as a rated voltage and the system voltage _VS , the converter current I _Inv is controlled to prevent a short circuit current from occurring from the power converter 5, thereby preventing damage to the power converter 5.

In particular, according to this embodiment, from the time when the closing of the mechanical switch 3 is completed, the control unit 9 shifts the switch current target value I _ref1 from 0 to the load current I _X and controls the converter current I _Inv based on the switch current target value I _ref1 and the switch current I _SW , so that the switch current I _SW is controlled to be equal to the load current I _X. Therefore, even if the system voltage V _S changes, the switch current I _SW and the load current I _X are controlled to be equal, so that when the closing of the mechanical switch 3 is completed, the current flowing through the circuit formed by the power converter 5 and the mechanical switch 3 becomes 0. As a result, the current from the power supply system 10 flows through the mechanical switch 3 to the load, and even if the system voltage V _S changes, no potential difference is generated between the power supply system 10 and the load 20, so that no short-circuit current is generated from the power converter 5 and damage to the power converter 5 can be prevented.
Furthermore, since the control unit 9 gradually shifts the switch current target value I _ref1 to the load current I _X , the power supply to the load 20 can be smoothly switched from the power converter 5 to the power supply system 10 .

4. Other embodiments
The present invention is not limited to the above-described embodiment.

In the above embodiment, the control unit 9 gradually shifts the switch current target value _Iref1 from 0 to the load current _IX from the time when the closing of the mechanical switch 3 is completed, but the configuration of the control unit 9 is not limited to this. For example, as shown in Fig. 7 and Fig. 8, the control unit 9 may shift the converter current target value _Iref2 , which is the target value of the converter current _IInv , to 0 based on the converter current _IInv from the time when the closing of the mechanical switch 3 is completed.

9 shows a simulation result in the case where the control unit 9 shifts the converter current target value I _ref2 to 0. After the control unit 9 determines that power has been restored (time s0) and the mechanical switch 3 is turned on (time s1), the control unit 9 outputs a current shift trigger (time s2). Then, after time s2, the control unit 9 gradually shifts the converter current target value I _ref2 from the converter current I _Inv to 0, so that the current supplied from the power converter 5 to the mechanical switch 3 becomes 0 and the switch current I _SW becomes equal to the load current I _X. Therefore, when the control unit 9 shifts the converter current target value I _ref2 to 0, the control unit 9 can control the converter current I _Inv without measuring the switch current I _SW , making the control easier.

In addition to the above embodiment, when the power supply system 10 is restored and before the closing of the mechanical switch 3 is completed, the control unit 9 may control the power converter 5 so that the voltage that the power converter 5 compensates for the power line L1 is set to 0, and after the closing of the mechanical switch 3 is completed, the control unit 9 may control the converter current I _Inv based on the switch current target value I _ref1 and the switch current I _SW . In this case, before the closing of the mechanical switch 3 is completed, the voltage that the power converter 5 compensates for the mechanical switch 3 is controlled to 0. As a result, even if the system voltage V _S changes and before the closing of the mechanical switch 3 is completed, the power converter 5 does not compensate the mechanical switch 3 for the system voltage V _S of the change, so that it is possible to prevent a potential difference from occurring in the mechanical switch 3 and to further suppress an overcurrent in the mechanical switch 3.

It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the invention.

REFERENCE SIGNS LIST 100: Power supply system 10: Power supply system 20: Load 3: Mechanical switch 4: Power storage unit 5: Power converter 6: Impedance element 7: System voltage measurement unit 8: Current measurement unit 81: Switch current measurement unit 82: Load current measurement unit 83: Converter current measurement unit 9: Control unit L1: Power line

Claims (5)

a mechanical switch provided on a power line for supplying power from a power supply system to a load, the mechanical switch opening and closing the power line;
a power converter provided on the power line for converting DC power into AC power and supplying the AC power to the load;
a switch current measuring unit for measuring a switch current that is a current flowing through the mechanical switch;
a control unit for controlling the mechanical switch and the power converter,
The control unit is
When an abnormality occurs in the power supply system, the mechanical switch is opened, and the power converter performs compensation control to compensate for a voltage of the load;
a power supply system that controls a converter current, which is a current output by the power converter, based on a switch current target value, which is a target value of the switch current, and the switch current, after the power supply system is restored and the mechanical switch is turned on. The power supply system according to claim 1, wherein the control unit gradually shifts the switch current target value from 0 to the current of the load from the point in time when the mechanical switch is turned on. A converter current measuring unit for measuring the converter current is further provided.
The power supply system according to claim 1 , wherein the control unit transitions a converter current target value, which is a target value of the converter current, to 0 based on the converter current from a point in time when closing of the mechanical switch is completed. The power supply system according to any one of claims 1 to 3, wherein the control unit controls the power converter so that the voltage compensated by the power converter to the mechanical switch is set to 0 before the closing of the mechanical switch is completed when the power supply system is restored, and controls the converter current based on the switch current target value and the switch current after the closing of the mechanical switch is completed. A control method for a power supply system, which supplies power from a power supply system to a load when the power supply system is normal, cuts off power supply from the power supply system to the load when an abnormality occurs in the power supply system, compensates for a voltage of the load, and then restores power to the power supply system,
The power supply system includes:
a mechanical switch provided on a power line for supplying power from the power supply system to the load, the mechanical switch opening and closing the power line;
a switch current measuring unit for measuring a switch current that is a current flowing through the mechanical switch;
a power converter that is provided on the power line and converts DC power into AC power to supply the power to the load,
When an abnormality occurs in the power supply system, the mechanical switch is opened and the power converter compensates for the voltage of the load;
A power supply system control method comprising: controlling a converter current, which is a current output by the power converter, based on a switch current target value, which is a target value of the switch current, and the switch current, after the power supply system is restored and the mechanical switch is turned on.