Power supply system and method for controlling the power supply system

Abstract

To provide an electrical power system having a configuration simplified by integrating a device for assisting opening of a breaker and a device for compensating a voltage of a load after opening of the breaker.SOLUTION: An electrical power system comprises: a mechanical switch 3 that is provided in an electric power line L1 for supplying electric power from an electric power system 10 to a load 20, and opens and close the electric power line L1; a switch controller 91 for controlling the mechanical switch 3; a power converter 8 that is connected to the electric power line L1 and coverts direct-current power of a capacitor 7 into alternating-current power and supplies the alternating-current power to the electric power line L1; a power converter controller 92 for controlling the power converter 8; and an abnormality detector 6 that when an abnormality of the power electric power system 10 is detected, outputs an open instruction C for the mechanical switch 3 to the switch controller 91. The power converter controller 92 performs current interruption control in response to the output of the open instruction C. In the current interruption control, the power converter 8 is subjected to feedback control in a manner that the current flowing to the mechanical switch 3 becomes zero. After the current interruption control, the power converter controller 92 performs voltage compensation control that controls the power converter 8 to compensate the voltage of the load 20.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power supply system and a method for controlling a power supply system. [Background technology]

[0002] In a conventional power supply system, when an abnormality occurs in the power system, a circuit breaker installed in a power line for supplying power from the power system to the load is opened to cut off the power supply from the power system to the load. After the power system has been cut off from the load, a distributed power source connected to the load side supplies power to the load, thereby compensating for the voltage of the load.

[0003] In this type of power supply system, for example, as shown in Patent Document 1, a power supply system further including a commutation circuit connected in parallel with the circuit breaker has been proposed to assist in opening the circuit breaker. In this power supply system, when an abnormality in the power system is detected, the circuit breaker is opened and the commutation circuit is turned on at the same time, and the commutation circuit superimposes a harmonic current on the fault current flowing through the circuit breaker to form a current zero point of the fault current. As a result, the current zero point is forcibly formed, so that the circuit breaker is opened in a short time and the load is disconnected from the power system. After that, the distributed power source supplies power to the load and compensates for the load voltage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-264932 A Summary of the Invention [Problem to be solved by the invention]

[0005] Here, in the above power supply system, a commutation circuit is used to assist in opening the circuit breaker, while a distributed power supply is used to compensate for the load voltage after the circuit breaker is opened. In other words, in this type of power supply system, the device that assists in opening the circuit breaker and the device that compensates for the load voltage after the circuit breaker is opened are different, which makes the power supply system configuration complicated.

[0006] Therefore, the present invention has been made in consideration of the above problems, and has as its main object to simplify the configuration of the power supply system by combining a device that assists in opening the circuit breaker and a device that compensates for the load voltage after the circuit breaker is opened in one device. [Means for solving the problem]

[0007] That is, the power supply system of the present invention is provided on a power line for supplying power from a power system to a load, and includes a mechanical switch for opening and closing the power line, a switch control unit for controlling the mechanical switch, a power converter connected to the power line and converting DC power from a power storage unit into AC power and supplying the power to the power line, a power converter control unit for controlling the power converter, and an abnormality detection unit for outputting an opening command for the mechanical switch to the switch control unit when an abnormality in the power system is detected, and the power converter control unit performs current interruption control that feedback controls the power converter so as to reduce the current flowing through the mechanical switch to zero in response to the output of the opening command, and performs voltage compensation control after the current interruption control that controls the power converter to compensate for the voltage of the load.

[0008] In such a power supply system, in current interruption control, the power converter controlled by the power converter control unit supplies power to the power line so as to make the current flowing through the mechanical switch zero. In addition, in voltage compensation control, the power converter controlled by the power converter control unit supplies power to the power line so as to compensate for the voltage of the load. In other words, the power converter serves as a common device for supplying power to assist in opening the mechanical switch and a device for supplying power to compensate for the voltage of the load, thereby simplifying the configuration of the power supply system. In addition, since the power converter control unit feedback controls the power converter so as to make the current flowing through the mechanical switch zero, the current zero point of the current flowing through the mechanical switch is forcibly formed. Therefore, the mechanical switch can be opened more quickly, and the load can be disconnected from the power system more quickly.

[0009] It is preferable that the power converter control unit further includes a switch current measuring unit that measures the current flowing through the mechanical switch and outputs the measured value to the power converter control unit, and the power converter control unit proportionally controls the power converter based on the deviation between a command value for setting the current flowing through the mechanical switch to zero and the measured value. This power converter control unit performs proportional control according to the deviation between the command value that reduces the current flowing through the mechanical switch to zero and the measured value, making it possible to forcibly form a zero current point for the current flowing through the mechanical switch and open the mechanical switch in a shorter time.

[0010] It is desirable that the power converter control unit further includes a limiter unit that calculates a voltage target value, which is a target value of the voltage in the power converter, so as to set the current flowing through the mechanical switch to zero, and limits the voltage target value within a predetermined range. With this power converter control unit, the limiter unit limits the voltage target value within a predetermined range, so that when supplying power from the power converter to a power line, it is possible to prevent excessive power from being supplied to the power line, and to prevent overcurrent in the power converter.

[0011] When the opening of the mechanical switch is completed, the switch control unit outputs an opening completion signal indicating that the opening of the mechanical switch is completed to the power converter control unit, and the power converter control unit switches from the current interruption control to the voltage compensation control upon receiving the output of the opening completion signal. In this configuration, the load is completely disconnected from the power grid by the output of the disconnection completion signal, and in this state, the power converter control unit switches from current interruption control to voltage compensation control. Then, the power converter control unit performs voltage compensation control and the power converter supplies power to the load, so that the voltage of the load can be reliably compensated.

[0012] The power converter control unit may switch from the current interruption control to the voltage compensation control after a predetermined time has elapsed since the opening command was output. With this configuration, since the control is switched to the voltage compensation control after a predetermined time has elapsed since the opening command is output, the voltage compensation control can be reliably started even if a problem occurs in the opening completion signal from the switch control unit. For example, even if the switch control unit fails and the opening completion signal is not output, or if there is a delay between the opening completion signal being output and reaching the power converter control unit, the power converter control unit can switch from the current cutoff control to the voltage compensation control after a predetermined time has elapsed since the opening command was output.

[0013] Furthermore, 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 system to a load when the power system is normal, cuts off the power supply from the power system to the load when the power system is abnormal, and supplies power from a power storage unit to the load, the power supply system including a mechanical switch that is provided on a power line for supplying power from the power system to the load and opens and closes the power line, and a power converter that is connected to the power line and converts DC power from the power storage unit to AC power and supplies the AC power to the power line, and is characterized in that when an abnormality in the power system is detected, an opening command for the mechanical switch is output, and in response to the output of the opening command, current interruption control is performed to feedback control the power converter so as to reduce the current flowing through the mechanical switch to zero, and after the current interruption control, voltage compensation control is performed to control the power converter to compensate for the voltage of the load. Effect of the Invention

[0014] According to the present invention configured in this manner, the device that assists in opening the circuit breaker and the device that compensates for the load voltage after the circuit breaker is opened can be combined into a single device, thereby simplifying the configuration of the power supply system. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing a configuration of a power supply system according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a schematic diagram showing a control block in the embodiment. [Diagram 3] 5 is a schematic diagram showing conditions of a limiter section in the embodiment. FIG. [Figure 4] 4 is a timing chart illustrating a current cutoff control and a voltage compensation control in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] An embodiment of a power supply system according to the present invention will be described below with reference to the drawings. Note that in any of the drawings shown below, some parts may be omitted or exaggerated and illustrated in a schematic manner for ease of understanding. Identical components are given the same reference numerals and descriptions thereof will be omitted as appropriate.

[0017] <1.Device configuration> 1, a power supply system 100 in this embodiment is provided between a power system 10 and a load 20, and constitutes a three-phase circuit. This power supply system 100 supplies power from the power system 10 to the load 20 when the power system 10 is normal, and when an abnormality occurs in the power system 10 due to a short circuit accident or the like in the power system 10, the power supply system 100 cuts off the power supply from the power system 10 to the load 20 and supplies power from the power storage unit 7 to the load 20. Note that while the power supply system 100 in this embodiment is a three-phase circuit, it may be a single-phase circuit, and the number of phases is not particularly limited.

[0018] Specifically, the power supply system 100 includes a mechanical switch 3 that switches the power supply from the power system 10 to the load 20 by opening and closing, a voltage measurement unit 4 that measures the voltage generated in the power system 10, a switch current measurement unit 5 that measures the current flowing through the mechanical switch 3, an abnormality detection unit 6 that detects abnormalities in the power system 10, a power converter 8 that converts DC power from a power storage unit 7 to AC power and supplies it to a power line L1, and a control device 9 that controls the mechanical switch 3 and the power converter 8.

[0019] The mechanical switch 3 is provided on a power line L1 for supplying power from the power system 10 to the load 20, and switches between opening and closing the power line L1 by mechanical operation. The mechanical switch 3 switches between connection and disconnection between terminals, thereby switching between supplying and cutting off the power supply from the power system 10 to the load 20. In the event of an abnormality in the power system 10, the mechanical switch 3 is preferably provided on the load 20 side rather than the power system 10 in order to more quickly cut off the power supply from the power system 10 to the load 20, but is not limited to this.

[0020] The voltage measuring unit 4 measures the voltage occurring in the power system 10 and outputs the measured voltage to the abnormality detecting unit 6. Specifically, as shown in Fig. 1, the voltage measuring unit 4 is connected to the power line L1 via a system transformer 41, and measures the voltage on the power system 10 side rather than the mechanical switch 3 so that the voltage of the power system 10 can be measured more quickly.

[0021] The switch current measuring unit 5 measures the current flowing through the mechanical switch 3 and outputs the measured value I to the control device 9. Specifically, as shown in Fig. 1, the switch current measuring unit 5 is provided on the power line L1 and measures the current on the power system 10 side of the mechanical switch 3. More specifically, as shown in Fig. 1, the switch current measuring unit 5 is provided between the connection point of the power converter 8 and the power line L1, and is connected in series to the mechanical switch 3 and in parallel to the power converter 8.

[0022] The abnormality detection unit 6 outputs an opening command C to open the mechanical switch 3 when an abnormality in the power system 10 is detected. In this embodiment, the abnormality detection unit 6 detects an abnormality in the power system 10 based on the voltage measured by the voltage measurement unit 4. Specifically, the abnormality detection unit 6 determines that an abnormality has occurred in the power system 10 when the system voltage is below a set value over multiple cycles. Note that the set value in this embodiment is a voltage value for detecting a momentary sag or a power outage.

[0023] The power storage unit 7 is, for example, a power storage device such as a secondary battery (storage battery). The power storage unit 7 stores DC power. When an abnormality in the power system 10 is detected, the DC power stored in the power storage unit 7 is supplied to the power converter 8.

[0024] The power converter 8 is connected to the power line L1 via the injection transformer T, and converts the DC power of the power storage unit 7 into AC power and supplies the AC power to the power line L1. Specifically, the power converter 8 is connected in parallel with the mechanical switch 3 on the power line L1, as shown in FIG.

[0025] Moreover, the specific configuration of the power converter 8 includes an inverter 81 that converts DC power from the power storage unit 7 into AC power, an interconnection reactor 82 that is connected in series to the output side of the inverter 81 and stabilizes the AC current, and a capacitor 83 that is connected to the interconnection reactor 82 and stabilizes the voltage. Note that the interconnection reactor 82 and the capacitor 83 may be connected to the input side of the inverter 81 in order to rectify the DC power of the power storage unit 7.

[0026] The control device 9 controls the mechanical switch 3 and the power converter 8 when an abnormality occurs in the power system 10. The control device 9 includes a switch control unit 91 that controls the mechanical switch 3, and a power converter control unit 92 that controls the power converter 8.

[0027] The switch control unit 91 controls switching between on and off of the mechanical switch 3. In this embodiment, the switch control unit 91 receives an opening command C output by the abnormality detection unit 6 and controls to open the mechanical switch 3. When the opening of the mechanical switch 3 is completed, the switch control unit 91 outputs an opening completion signal S indicating the completion of opening of the mechanical switch 3 to the power converter control unit 92.

[0028] Then, in response to the opening command C output by the abnormality detection unit 6, the power converter control unit 92 performs current cut-off control to feedback control the power converter 8 so as to make the current flowing through the mechanical switch 3 zero, and after the current cut-off control, performs voltage compensation control to control the power converter 8 so as to compensate for the voltage of the load 20. Specifically, as shown in Fig. 2, the power converter control unit 92 includes a current cut-off control unit 921 that performs current cut-off control, a limiter unit 922 that limits the control by the current cut-off control unit 921 to within a predetermined range, a voltage compensation control unit 923 that performs voltage compensation control, and an output control unit 924 that controls the power converter 8 based on the output by the current cut-off control unit 921 or the voltage compensation control unit 923.

[0029] The current cut-off control unit 921 performs current cut-off control by feedback controlling the power converter 8 so as to set the current flowing through the mechanical switch 3 to zero in response to the output of the opening command C. In this embodiment, as shown in Fig. 2, the current cut-off control unit 921 performs proportional control using a proportional gain Kp based on the deviation ΔI between the measurement value I output by the switch current measuring unit 5 and a command value Iref for setting the current flowing through the mechanical switch 3 to zero, and calculates a voltage target value Vout which is a target value for the voltage in the power converter 8. Note that in this embodiment, the proportional gain Kp satisfies equation (1). Kp ≥ V 2 / S (V: rated voltage, S: rated capacity of power converter 8) (1)

[0030] The limiter unit 922 is provided in the current interruption control unit 921, and controls the voltage target value Vout so that it is within the range of the maximum voltage Vmax expressed by equation (2). The limiter unit 922 compares the voltage target value Vout with the maximum voltage Vmax, and if the voltage target value Vout is within the range of the maximum voltage Vmax, the limiter unit 922 outputs the voltage target value Vout to the output control unit 924. On the other hand, if the voltage target value Vout exceeds the range of the maximum voltage Vmax, the limiter unit 922 outputs the maximum voltage Vmax to the output control unit 924. The impedance Z is composed of an interconnection reactor 82, a capacitor 83, and an injection transformer T, as shown in FIG. 3. Vmax = Imax × Z (Imax: maximum current, Z: impedance) (2)

[0031] The voltage compensation control unit 923 controls the power converter 8 so as to compensate for the voltage of the load 20 that has dropped due to the current interruption control. Specifically, as shown in Fig. 2, the voltage compensation control unit 923 calculates a voltage compensation value for compensating for the voltage of the load 20 based on the deviation between the voltage V measured by the voltage measurement unit 4 and the voltage command value Vref, and performs feedback control of the power converter 8.

[0032] The output control unit 924 receives the output from the current interruption control unit 921 or the voltage compensation control unit 923, and controls the power converter 8 so that a predetermined voltage is generated. Specifically, the output control unit 924 controls the power converter 8 based on the voltage target value Vout or the maximum voltage Vmax calculated by the current interruption control unit 921. In addition, the output control unit 924 controls the power converter 8 based on the voltage compensation value calculated by the voltage compensation control unit 923.

[0033] Furthermore, upon receiving the opening completion signal S, the output control unit 924 outputs a switching signal for switching from current cut-off control to voltage compensation control to the current cut-off control unit 921 and the voltage compensation control unit 923. On the other hand, if a predetermined time has elapsed since the output of the opening command C before the output control unit 924 receives the opening completion signal S, the output control unit 924 outputs a switching signal to the current cut-off control unit 921 and the voltage compensation control unit 923. Note that the predetermined time here refers to, for example, a time of 2 ms from the output of the opening command C, but is not limited to this value.

[0034] 2. Power supply system control operation Next, the control operation of the power supply system 100 will be described.

[0035] (1) Power grid 10 in normal operation The voltage measurement unit 4 constantly measures the voltage of the power system 10, and inputs the measured voltage to the abnormality detection unit 6. The abnormality detection unit 6 compares the voltage measured by the voltage measurement unit 4 with a predetermined setting value.

[0036] When the power system 10 is normal, the voltage measured by the voltage measuring unit 4 is equal to or higher than the set value, and the mechanical switch 3 is closed. This causes AC power to be supplied from the power system 10 to the load 20.

[0037] (2) Abnormality in power grid 10 When an abnormality occurs in the power system 10, the voltage measured by the voltage measuring unit 4 is less than the set value. At this time, the abnormality detecting unit 6 outputs an opening command C to the control device 9 to command the mechanical switch 3 to be opened.

[0038] In response to the opening command C, the power converter control unit 92 performs current interruption control on the power converter 8, and the power converter 8 converts the DC power from the power storage unit 7 into AC power and supplies it to the power line L1. This AC power is supplied so that the current flowing through the mechanical switch 3 is set to zero, so that a current zero point is forcibly formed in the current flowing through the mechanical switch 3. When the current zero point is formed, the switch control unit 91 opens the mechanical switch 3 via a drive circuit (not shown).

[0039] When the mechanical switch 3 is opened and the switch control unit 91 outputs an opening completion signal S, the output control unit 924 outputs a switching signal for switching from current cut-off control to voltage compensation control to the current cut-off control unit 921 and the voltage compensation control unit 923. Note that if a predetermined time has elapsed since the output of the opening command C before the opening completion signal S is output, the output control unit 924 forcibly outputs the switching signal.

[0040] Upon receiving the switching signal from the output control unit 924, the current interruption control unit 921 ends the current interruption control. Meanwhile, the voltage compensation control unit 923 controls the power converter 8 to compensate for the voltage of the load 20 that has dropped due to the current interruption control. As a result, as shown in Fig. 4, the voltage of the load 20 drops initially when switching from the current interruption control to the voltage compensation control, but the voltage compensation control causes the power converter 8 to supply the voltage equivalent to the drop to the load 20. Then, after the voltage of the load 20 is compensated for, the voltage of the power grid 10 recovers.

[0041] <Effects of this embodiment> According to this embodiment, the power converter 8 supplies power to the mechanical switch 3 and the load 20 under the control of the power converter control unit 92, so that the power converter 8 can serve both as a device for assisting in the opening of the mechanical switch 3 and a device for compensating for the voltage of the load 20 after the mechanical switch 3 is opened.

[0042] Furthermore, since the power converter control unit 92 performs feedback control of the power converter 8 so as to make the current flowing through the mechanical switch 3 zero during current interruption control, it is possible to forcibly form a current zero point in the current flowing through the mechanical switch 3. As a result, it is possible to open the mechanical switch 3 more quickly, and therefore possible to interrupt the power supply from the power system 10 to the load 20 more quickly.

[0043] <Other embodiments> The present invention is not limited to the above-described embodiment.

[0044] Although the abnormality detection unit 6 in the present embodiment detects an abnormality in the power system 10 based on a change in the system voltage, the detection of an abnormality is not limited to this. For example, the abnormality detection unit 6 may detect an abnormality in the power system 10 based on a change in the current or frequency in the power system 10. Accordingly, the setting value of the abnormality detection unit 6 is not limited to the voltage value of the power system 10, but may be the current value or frequency in the power system 10.

[0045] In the present embodiment, the output control unit 924 forcibly switches from current interruption control to voltage compensation control when a predetermined time has elapsed since the opening command C was output prior to the output of the opening completion signal S, but the time when the opening command C was output does not have to be the starting point. For example, the output control unit 924 may forcibly switch from current interruption control to voltage compensation control after a predetermined time has elapsed from the starting point, which may be any one of the time when an abnormality in the power system 10 is detected, the time when the current interruption control unit 921 starts control, or the time when the measured value I of the current flowing through the mechanical switch 3 becomes 0.

[0046] In the present embodiment, the power supplied from the power system 10 to the load 20 is AC power, but the power supplied from the power system 10 to the load 20 may be DC power.

[0047] Furthermore, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0048] 100 Power Supply System 10...Electric power system 20 Load 3. Mechanical Switch 4. Voltage measurement section 5 Switch current measurement section 6. Abnormality detection section 7. Storage unit 8. Power Converter 9. Control device 91 Switch control section 92 Power converter control section L1...power line C...Open command S...Opening completion signal

Claims

1. a mechanical switch provided on a power line for supplying power from a power system to a load, the mechanical switch opening and closing the power line; a switch control unit that controls the mechanical switch; a power converter connected to the power line, converting DC power from the power storage unit into AC power and supplying the AC power to the power line; a power converter control unit that controls the power converter; an abnormality detection unit that outputs an open command for the mechanical switch to the switch control unit when an abnormality in the power system is detected; a switch current measuring unit that measures a current flowing through the mechanical switch and outputs the measured value to the power converter control unit; the power converter control unit performs current interruption control by feedback controlling the power converter so as to set the current flowing through the mechanical switch to zero in response to the output of the opening command, and after the current interruption control, performs voltage compensation control by controlling the power converter so as to compensate for the voltage of the load; In the current interruption control, proportional control using a proportional gain is performed on the power converter based on a deviation between a command value for making the current flowing through the mechanical switch zero and the measured value.

2. the power converter control unit calculates a voltage target value that is a target value of a voltage in the power converter so as to set a current flowing through the mechanical switch to zero; The power supply system according to claim 1 , further comprising a limiter section that limits the target voltage value to within a predetermined range.

3. when the opening of the mechanical switch is completed, the switch control unit outputs an opening completion signal indicating the completion of the opening of the mechanical switch to the power converter control unit; 3. The power supply system according to claim 1, wherein the power converter control unit switches from the current cut-off control to the voltage compensation control upon receiving the output of the opening completion signal.

4. The power supply system according to claim 3 , wherein the power converter control unit switches from the current cut-off control to the voltage compensation control after a predetermined time has elapsed since receiving the opening command.

5. A control method for a power supply system that supplies power from a power system to a load when the power system is normal, and cuts off power supply from the power system to the load when an abnormality occurs in the power system, and supplies power from a power storage unit to the load, comprising: the power supply system includes a mechanical switch provided on a power line for supplying power from the power grid to the load, the mechanical switch opening and closing the power line; a power converter connected to the power line, converting DC power from the power storage unit into AC power and supplying the AC power to the power line; a switch current measuring unit that measures a current flowing through the mechanical switch, When an abnormality in the power system is detected, an opening command for the mechanical switch is output. In response to the output of the opening command, a current interruption control is performed in which the power converter is feedback-controlled so as to make the current flowing through the mechanical switch zero, and after the current interruption control, a voltage compensation control is performed in which the power converter is controlled so as to compensate for the voltage of the load; a control method for a power supply system, wherein, in the current interruption control, proportional control using a proportional gain is performed on the power converter based on a deviation between a command value for making the current flowing through the mechanical switch zero and the measured value measured by the switch current measuring unit.

Images