Power supply system, method for controlling the same, and program thereof

Abstract

To provide a power supply system of a microgrid capable of surely determining a ground fault during independent operation.SOLUTION: A power supply system includes: a non-fundamental wave component injection unit that is connected to a power system via a circuit breaker and injects a non-fundamental wave component indicating a current and / or a voltage having a frequency different from that of a fundamental wave into a bus to which AC power having a predetermined frequency is supplied; a first measurement unit that is provided in a power line that electrically connects the bus and a load and into which the non-fundamental wave component is shunted and measures a zero phase current or a zero phase voltage including the non-fundamental wave component; a ground fault determination unit that determines a ground fault based on the zero phase current or the zero phase voltage measured by the first measurement unit in a state where the circuit breaker is opened; and a protection relay drive unit that opens a load circuit breaker that is the circuit breaker that opens and closes the power line in order to protect the load when the ground fault determination unit determines the ground fault.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, regional microgrid power supply systems have been studied, with the aim of utilizing renewable energy and improving power resilience in the event of a disaster. These systems operate in conjunction with the power grid during normal times and independently in the event of an emergency such as a disaster.

[0003] As shown in Patent Document 1, for example, this type of power supply system includes an intermediate harmonic current injection device that injects a current having a frequency that is a non-integer multiple of the fundamental wave of the power system into consumer equipment having distributed power sources, and a grid outage detection processing device that monitors and detects power system outages based on the measurement results of the intermediate harmonic voltage and current of the power system at the power receiving point of the consumer equipment, and disconnects the distributed power source from the power system when a power system outage is detected.As a result, the grid outage detection processing device detects a power system outage based on the intermediate harmonic voltage and current, making it possible to prevent islanding of the power supply system. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3367371 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the above-mentioned power supply system operates in an isolated mode, the capacity of the distributed power source is smaller than that of the power grid, so the ground fault current that flows in the event of a ground fault is reduced. In particular, as renewable energy generation becomes the main power source in the future, it is expected that the ground fault current in the isolated mode of the microgrid will decrease. As a result, it will become more difficult to detect ground faults in the isolated mode of the microgrid, making it difficult to protect the power supply system from ground faults.

[0006] Therefore, the present invention has been made in consideration of the above problems, and its main object is to provide a microgrid power supply system that can reliably determine a ground fault during isolated operation. [Means for solving the problem]

[0007] That is, the power supply system of the present invention is a power supply system that switches between grid-connected operation and stand-alone operation with respect to a power grid depending on the open / close state of a circuit breaker interposed between the power system and the system, and is characterized by comprising: a non-fundamental wave component injection unit that injects non-fundamental wave components indicating current and / or voltage of a frequency different from the fundamental wave into a bus that is connected to the power grid via the circuit breaker and to which AC power of a predetermined frequency is supplied; a first measurement unit that is provided on a power line that electrically connects the bus and the load and to which the non-fundamental wave components are branched, and that measures the zero-phase current or zero-phase voltage including the non-fundamental wave component; a ground fault determination unit that determines a ground fault based on the zero-phase current or the zero-phase voltage measured by the first measurement unit when the circuit breaker is open; and a protection relay drive unit that, when the ground fault determination unit determines a ground fault, opens a load circuit breaker that opens and closes the power line to protect the load.

[0008] In such a power supply system, the first measurement unit measures the zero-phase current or zero-phase current including the non-fundamental wave component injected by the non-fundamental wave component injection unit, so the first measurement unit does not need to measure the ground-fault current when a ground fault occurs. The ground-fault determination unit determines a ground fault based on the zero-phase current or zero-phase voltage including the non-fundamental wave component measured by the first measurement unit, so it can reliably determine a ground fault regardless of the magnitude of the ground-fault current during isolated operation. As a result, by identifying the location of the ground fault and quickly removing it, it is possible to prevent a power outage across the entire microgrid. Furthermore, since measures to increase the ground fault current are not required, increases in costs when building a microgrid can be suppressed.

[0009] A specific aspect for determining a ground fault includes a non-fundamental wave component calculation unit that calculates a non-fundamental wave current or a non-fundamental wave voltage corresponding to the frequency of the non-fundamental wave component from the zero-phase current or the zero-phase voltage measured by the first measurement unit, and an impedance calculation unit that calculates an impedance based on the non-fundamental wave current or the non-fundamental wave voltage calculated by the non-fundamental wave component calculation unit, and the ground fault determination unit determines that a ground fault has occurred when the impedance calculated by the impedance calculation unit is equal to or less than a set value.

[0010] With this configuration, the ground fault judgment unit judges a ground fault based on the impedance calculated based on the zero-phase current or zero-phase voltage including non-fundamental wave components, so the ground fault judgment unit can judge a ground fault regardless of the magnitude of the ground fault current.

[0011] It is preferable that the system further comprises a second measurement unit provided on the bus or the power line for measuring a current or voltage including the non-fundamental wave component, and a short circuit determination unit for determining a short circuit based on the current or voltage measured by the second measurement unit and a setting value, and when the short circuit determination unit determines that a short circuit has occurred, the protection relay driving unit opens the load breaker to protect the load.

[0012] With this configuration, the second measurement unit measures the current or voltage including the non-fundamental component injected by the non-fundamental component injection unit, so the second measurement unit does not need to measure the short-circuit current when a short circuit occurs. The short-circuit determination unit determines a short circuit based on the current or voltage including the non-fundamental component measured by the second measurement unit, so it can reliably determine a short circuit regardless of the magnitude of the short-circuit current during isolated operation. As a result, by identifying the location of the short circuit and quickly removing it, it is possible to prevent a power outage across the entire microgrid.

[0013] When the circuit breaker is closed, an isolated operation judgment unit judges whether the load is in isolated operation based on the current or the voltage measured by the second measurement unit and a setting value that is larger than the setting value used by the short circuit judgment unit, and when the isolated operation judgment unit judges whether the load is in isolated operation, the protective relay driving unit preferably opens a interconnection point circuit breaker that opens and closes the electrical connection between the load and a distributed power source, which is a power source that supplies power to the bus bar separately from the power system.

[0014] With this configuration, one power supply system is equipped with an islanding operation determination unit, a short circuit determination unit, and a ground fault determination unit, so that the single power supply system can determine islanding operation, a short circuit, and a ground fault all at once. Specifically, when the power supply system operates in interconnection with the power grid, the islanding operation determination unit and the short circuit determination unit determine islanding operation and a short circuit, respectively, and when the power supply system operates in independent operation, the short circuit determination unit and the ground fault determination unit determine a short circuit and a ground fault, respectively. Therefore, since the single power supply system can determine a ground fault, a short circuit, and islanding operation, the cost of the power supply system can be further reduced.

[0015] The power supply system may further include a ground injection unit that is provided on a ground line having one end electrically connected to the bus bar and the other end grounded, and that injects a current into the ground side of the ground line, and the first measurement unit may measure a zero-phase current or a zero-phase voltage that includes the current injected by the ground injection unit and the non-fundamental wave component.

[0016] With this configuration, the ground injection unit injects current into the ground side of the ground wire, so that the current injected into the ground fault circuit in the event of a ground fault increases by the amount of the current injected by the ground injection unit in addition to the non-fundamental wave component. Therefore, the zero-phase sequence current or zero-phase sequence voltage when the ground fault determination unit determines whether a ground fault has occurred increases, allowing the ground fault determination unit to accurately determine whether a ground fault has occurred.

[0017] The frequency of the current injected by the ground injection unit may be different from the predetermined frequency and the frequency of the non-fundamental wave component.

[0018] With this configuration, the frequency of the current injected by the ground injection unit is different from the predetermined frequency of the AC power supplied to the bus and the frequency of the non-fundamental wave component, so that the current injected by the ground injection unit can be prevented from interfering with the non-fundamental wave component or the AC power.

[0019] A control method for a power supply system that switches between grid-connected operation and standalone operation depending on the open / close state of a circuit breaker between the power system and the system, includes injecting a non-fundamental wave component, which is a frequency different from the fundamental wave, into a bus that is connected to the power system via the circuit breaker and to which AC power of a predetermined frequency is supplied, measuring a zero-phase current or zero-phase voltage including the non-fundamental wave component and that is provided on a power line that electrically connects the bus and the load and through which the non-fundamental wave component is branched, and determining whether a ground fault has occurred based on the zero-phase current or zero-phase voltage measured by the first measurement unit when the circuit breaker is open, and if a ground fault has been determined, opening a load circuit breaker, which is a circuit breaker that opens and closes the power line to protect the load. Another example is a program used in a power supply system that switches between grid-connected operation and standalone operation depending on the open / close state of a circuit breaker between the power supply system and the power grid, the program including: a non-fundamental wave component injection unit that injects non-fundamental wave components, which have a frequency different from the fundamental wave, into a bus that is connected to the power grid via the circuit breaker and to which AC power of a predetermined frequency is supplied; and a first measurement unit that is provided on a power line that electrically connects the bus and the load and to which the non-fundamental wave components are branched and that measures the zero-phase current or zero-phase voltage including the non-fundamental wave component, and causes a computer to function as a ground fault determination unit that determines a ground fault based on the zero-phase current or the zero-phase voltage measured by the first measurement unit when the circuit breaker is open; and a protective relay drive unit that opens a load circuit breaker, which is a circuit breaker that opens and closes the power line to protect the load, when the ground fault determination unit determines a ground fault.

[0020] With this configuration, it is possible to obtain the same effects as the above-described power supply system. [Effects of the Invention]

[0021] According to the present invention configured in this way, it is possible to provide a microgrid power supply system that can reliably determine a ground fault during isolated operation. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram showing the configuration of a power supply system according to an embodiment of the present invention; [Figure 2] 3A and 3B are schematic diagrams illustrating measurement of a zero-phase sequence current and a zero-phase sequence voltage of the power supply system according to the embodiment. [Figure 3] FIG. 2 is a diagram showing functional blocks of a protection relay device according to the embodiment. [Figure 4] 4 is a flowchart of a ground fault determination process during independent operation in the embodiment. [Figure 5] 4 is a flowchart of a short circuit determination during independent operation in the embodiment. [Figure 6] 4 is a flowchart of a short circuit determination and an islanding operation determination during interconnected operation with the power grid in the embodiment. [Figure 7] FIG. 10 is a schematic diagram illustrating measurement of a zero-phase current and a zero-phase voltage of a power supply system according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] An embodiment of a power supply system according to the present invention will be described below with reference to the drawings. Note that, for ease of understanding, some parts may be omitted or exaggerated in schematic form in all of the drawings shown below. Identical components are designated by the same reference numerals, and their descriptions will be omitted where appropriate.

[0024] <System configuration> The power supply system 100 in this embodiment constitutes a so-called microgrid that switches between interconnected operation with the power system G and independent operation depending on the open / close state of a circuit breaker C1 interposed between the power system G and the power system G. In this embodiment, independent operation refers to a state in which the bus B and the power system G are electrically disconnected and power is supplied to the load L from a distributed power source D, such as a DC power supply. Furthermore, interconnected operation with the power system G refers to a state in which the power system G and the bus B are electrically connected and power is supplied from the power system G to the load L.

[0025] Here, the bus B refers to an electric wire that is connected to the power system G via a circuit breaker C1 and that is supplied with AC power of a predetermined frequency, as shown in Fig. 1. In this embodiment, AC power of a fundamental wave is supplied to the bus B, but the frequency of the AC power supplied to the bus B is not limited to the fundamental wave.

[0026] In this embodiment, the power system G is configured with a non-rotating generator such as a renewable energy power generation device or other power source, but may also be a rotating generator. Also, although 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 limited.

[0027] 1, the power supply system 100 includes a power converter 20 that converts DC power from a distributed power source D into AC power, a non-fundamental wave component injection unit 30 that injects non-fundamental wave components that indicate current and / or voltage at frequencies different from the fundamental wave into a bus B, a first measurement unit 40 that is provided on a power line P1 that electrically connects the bus B and a load L and through which the non-fundamental wave components are diverted, a second measurement unit 50 that is provided on the bus B and the power line P1, and a protective relay device 60 that protects the load L when an abnormality such as a disaster is detected. Each unit will be described below.

[0028] The power converter 20 converts DC power supplied from a distributed power source D, such as a renewable energy power generation device or a power storage device, into AC power. The power converter 20 is, for example, a three-phase inverter. The AC power converted by the power converter 20 may be supplied to the bus B via an injection transformer T interposed between the power converter 20 and the bus B. In this embodiment, the power converter 20 and the distributed power source D are electrically connected or electrically disconnected depending on the open / close state of a tie-point circuit breaker C3, which opens and closes the electrical connection with the load L. Note that when the distributed power source D supplies AC power, the power supply system 100 does not need to include the power converter 20.

[0029] The non-fundamental wave component injection unit 30 injects a non-fundamental wave component into the bus B, thereby superimposing the non-fundamental wave component on the AC power supplied to the bus B. Specifically, the non-fundamental wave component injection unit 30 is a current injection device configured to be able to inject a current of any frequency into the bus B. The frequency of the non-fundamental wave in this embodiment is a so-called harmonic, which is a frequency higher than the frequency of the fundamental wave. When the non-fundamental wave component injection unit 30 injects the non-fundamental wave component into the bus B, AC power on which the non-fundamental wave component is superimposed is supplied from the bus B to the power line P1. Note that the frequency of the non-fundamental wave component injected by the non-fundamental wave component injection unit 30 may be an integer multiple of the fundamental frequency, or a non-integer multiple of the fundamental frequency.

[0030] The first measuring unit 40 is provided on the power line P1 and measures the zero-phase current and / or the zero-phase voltage including the non-fundamental wave component. Specifically, the first measuring unit 40 has a zero-phase current measuring unit 41 that measures the zero-phase current that flows through the power line P1 and includes the non-fundamental wave component, and a zero-phase voltage measuring unit 42 that measures the zero-phase voltage that flows through the power line P1 and includes the non-fundamental wave component. Here, the zero-phase current measuring unit 41 is, for example, but is not limited to, a zero-phase current transformer (ZCT). Furthermore, the zero-phase voltage measuring unit 42 is, for example, but is not limited to, a zero-phase voltage transformer (ZPD).

[0031] 2, when a ground fault occurs, the non-fundamental wave components injected by the non-fundamental wave component injection unit 30 flow from the power line P1 to the ground point of the power line P1, and the zero-phase-sequence current measurement unit 41 measures the zero-phase-sequence current flowing through the power line P1 at this time. The non-fundamental wave components flowing out from the ground point of the power line P1 flow through a ground fault circuit, which is a circuit that virtually connects the ground point of the power line P1 and the ground point of the zero-phase-sequence voltage measurement unit 42, and the zero-phase-sequence voltage measurement unit 42 measures the zero-phase-sequence voltage.

[0032] The second measurement unit 50 is provided on the bus B and / or the power line P1 and measures the current and / or voltage including non-fundamental wave components. Specifically, the second measurement unit 50 includes a second current measurement unit 51 provided on the power line P1 and measuring the current flowing through the power line P1 using, for example, a known current transformer, and a second voltage measurement unit 52 provided on the bus B and measuring the voltage of the bus B using, for example, a known voltage transformer. Here, the current measured by the second current measurement unit 51 has a non-fundamental wave component superimposed thereon, and the second current measurement unit 51 measures a current other than the zero-phase current. Furthermore, the voltage measured by the second voltage measurement unit 52 has a non-fundamental wave component superimposed thereon, and the second voltage measurement unit 52 measures a voltage other than the zero-phase voltage.

[0033] The protective relay device 60 detects an abnormality, such as a ground fault, a short circuit, and / or an islanding operation, and opens the load circuit breaker C2 and / or the tie-point circuit breaker C3 that open and close the power line P1 in the event of an abnormality. Specifically, the protective relay device 60 is composed of a dedicated or general-purpose computer equipped with a CPU, internal memory, an input / output interface, an A / D converter, etc., and an actuator that drives the load circuit breaker C2. More specifically, as shown in FIG. 3 , the protective relay device 60 causes the computer to function as a non-fundamental wave component calculation unit 61, an impedance calculation unit 62, a ground fault determination unit 63, a short circuit determination unit 64, and an islanding operation determination unit 65, and causes the actuator to function as a protective relay drive unit 66. Each unit of the protective relay device 60 will be described below.

[0034] The non-fundamental component calculation unit 61 samples the zero-phase current measured by the zero-phase current measurement unit 41, the zero-phase voltage measured by the zero-phase voltage measurement unit 42, the current measured by the second current measurement unit 51, and / or the voltage measured by the second voltage measurement unit 52 at predetermined time intervals to calculate the voltages measured by each measurement unit and the non-fundamental components contained in the currents. Here, the non-fundamental component calculation unit 61 calculates non-fundamental currents, which are currents constituting the non-fundamental components, from the currents measured by each current measurement unit, and calculates non-fundamental voltages, which are voltages constituting the non-fundamental components, from the voltages measured by each voltage measurement unit. Note that in this embodiment, the non-fundamental component calculation unit 61 calculates the non-fundamental currents and non-fundamental voltages by, for example, Fourier transform, but the calculation of the non-fundamental currents and non-fundamental voltages is not limited to Fourier transform.

[0035] Here, the non-fundamental wave that is the target of calculation by the non-fundamental wave component calculation unit 61 is the frequency of the non-fundamental wave current injected into the bus B by the non-fundamental wave component injection unit 30. Therefore, the non-fundamental wave component calculation unit 61 acquires the frequency of the non-fundamental wave current injected into the bus B from the non-fundamental wave component injection unit 30. Note that the physical quantity that the non-fundamental wave component calculation unit 61 acquires from the non-fundamental wave component injection unit 30 is not limited to the frequency of the non-fundamental wave current, and may be other parameters of the non-fundamental wave component, such as the order of the non-fundamental wave.

[0036] The impedance calculation section 62 calculates the impedance by dividing the non-fundamental wave voltage calculated by the non-fundamental wave component calculation section 61 by the non-fundamental wave current calculated by the non-fundamental wave component calculation section 61 .

[0037] As shown in FIG. 3(a), the ground fault determination unit 63 determines a ground fault based on the zero-phase-sequence current or zero-phase-sequence voltage measured by the first measurement unit 40 when the circuit breaker C1 is open (i.e., when the microgrid is operating independently). Specifically, the ground fault determination unit 63 compares a ground fault setting value, which is a setting value previously set for determining a ground fault, with the zero-phase-sequence impedance, which is an impedance calculated by the impedance calculation unit 62 based on the zero-phase-sequence current and zero-phase-sequence voltage. If the zero-phase-sequence impedance is equal to or less than the ground fault setting value, the ground fault determination unit 63 determines a ground fault. Furthermore, the ground fault determination unit 63 outputs an opening command signal to the protection relay driving unit 66 (described later) to command the load circuit breaker C2 to open. Note that multiple ground fault setting values ​​may be set.

[0038] As shown in FIGS. 3(a) and 3(b), the short circuit determination unit 64 determines a short circuit based on the current or voltage measured by the second measurement unit 50 when the circuit breaker C1 is open (i.e., the microgrid is operating independently) and / or when the circuit breaker C1 is closed (i.e., the microgrid is operating interconnected). Specifically, the short circuit determination unit 64 compares a short circuit setting value, which is a setting value previously set to determine a short circuit, with the impedance calculated by the impedance calculation unit 62 based on the current and voltage measured by the second measurement unit 50. If the impedance is equal to or less than the short circuit setting value, the short circuit determination unit 64 determines that a short circuit has occurred. Furthermore, the short circuit determination unit 64 outputs an open command signal to the protection relay driving unit 66, which will be described later. Note that multiple short circuit setting values ​​may be set.

[0039] As shown in FIG. 3(b), the islanding operation determination unit 65 determines whether islanding operation is occurring based on the current or voltage measured by the second measurement unit 50 when the circuit breaker C1 is closed (i.e., when the microgrid is in grid-connected operation). Specifically, the islanding operation determination unit 65 compares an islanding operation setting, which is a setting value previously set for determining whether islanding operation is occurring, with the impedance calculated by the impedance calculation unit 62 based on the current and voltage measured by the second measurement unit 50. If the impedance is equal to or greater than the islanding operation setting, the islanding operation determination unit 65 determines whether islanding operation is occurring. Furthermore, the islanding operation determination unit 65 outputs a stop command signal to a protection relay drive unit 66 (described later) to stop the power supply from the distributed power source D to the load L by opening the interconnection point circuit breaker C3.

[0040] In this embodiment, the islanding operation setting value is set to a value greater than the short circuit operation setting value. In addition, a plurality of islanding operation setting values ​​may be set.

[0041] The protection relay driving unit 66 opens the load breaker C2 upon receiving an opening command signal output by the ground fault determination unit 63, the short circuit determination unit 64, and / or the islanding operation determination unit 65. Here, the protection relay driving unit 66 is an actuator such as a motor.

[0042] <Power supply system control method> Next, a control method for the power supply system 100 in this embodiment will be described with reference to FIGS.

[0043] (a) Ground fault detection during isolated operation of a microgrid As shown in FIG. 4, during isolated operation of the microgrid, the non-fundamental wave component calculation unit 61 acquires the zero-phase current measured by the zero-phase current measurement unit 41 and the zero-phase voltage measured by the zero-phase voltage measurement unit 42 (S11).

[0044] Next, the non-fundamental wave component calculation unit 61 calculates a non-fundamental wave current from the zero-phase current measured by the zero-phase current measurement unit 41. Furthermore, the non-fundamental wave component calculation unit 61 calculates a non-fundamental wave voltage from the zero-phase voltage measured by the zero-phase voltage measurement unit 42 (S12).

[0045] Next, the impedance calculation unit 62 calculates the zero-phase impedance by dividing the non-fundamental wave voltage by the non-fundamental wave current (S13).

[0046] Then, the ground fault determination unit 63 compares the zero-phase impedance calculated by the impedance calculation unit 62 with the ground fault setting value (S14).

[0047] If the zero-phase impedance is equal to or less than the ground fault setting value, the ground fault determination unit 63 determines that a ground fault has occurred (S15). Then, the ground fault determination unit 63 outputs an opening command signal to the protection relay driving unit 66, and the protection relay driving unit 66 opens the load breaker C2 (S16).

[0048] On the other hand, if the zero-phase impedance is greater than the ground fault setting value, the ground fault determining unit 63 determines that a ground fault has not occurred, and the process returns to S11.

[0049] (b) Short circuit judgment during isolated operation of the microgrid As shown in FIG. 5, during the isolated operation of the microgrid, the non-fundamental wave component calculation unit 61 acquires the current measured by the second current measurement unit 51 and the voltage measured by the second voltage measurement unit 52 (S21).

[0050] Next, the non-fundamental wave component calculation unit 61 calculates a non-fundamental wave current from the current measured by the second current measurement unit 51. Furthermore, the non-fundamental wave component calculation unit 61 calculates a non-fundamental wave voltage from the voltage measured by the second voltage measurement unit 52 (S22).

[0051] Next, the impedance calculation unit 62 calculates the impedance by dividing the non-fundamental wave voltage by the non-fundamental wave current (S23).

[0052] Then, the short circuit determination unit 64 compares the impedance calculated by the impedance calculation unit 62 with the short circuit set value (S24).

[0053] If the impedance is equal to or less than the short circuit setting value, the short circuit determination unit 64 determines that a short circuit has occurred (S25). Then, the short circuit determination unit 64 outputs an opening command signal to the protection relay driving unit 66, and the protection relay driving unit 66 opens the load breaker C2 (S26).

[0054] On the other hand, if the impedance is greater than the short-circuit setting value, the short-circuit determination unit 64 determines that no short circuit has occurred and returns to S21. Note that the ground fault determination and short circuit determination during isolated operation of the microgrid may be performed simultaneously, or one of the ground fault determination or short circuit determination may be performed after the other is completed. Also, after a ground fault or short circuit is determined to have occurred and the load breaker C2 is opened, it is not necessary to perform the ground fault determination or short circuit determination.

[0055] (c) Judgment of short circuit and islanding operation during interconnected operation of microgrid As shown in FIG. 6, during interconnected operation of the microgrid, the non-fundamental wave component calculation unit 61 acquires the current measured by the second current measurement unit 51 and the voltage measured by the second voltage measurement unit 52 (S31).

[0056] Next, the non-fundamental wave component calculation unit 61 calculates a non-fundamental wave current from the current measured by the second current measurement unit 51. Furthermore, the non-fundamental wave component calculation unit 61 calculates a non-fundamental wave voltage from the voltage measured by the second voltage measurement unit 52 (S32).

[0057] Next, the impedance calculation unit 62 calculates the impedance by dividing the non-fundamental wave voltage by the non-fundamental wave current (S33).

[0058] Then, the islanding operation determination unit 65 compares the impedance calculated by the impedance calculation unit 62 with the islanding operation setting value (S34).

[0059] If the impedance is equal to or greater than the islanding operation setting value, the islanding operation determination unit 65 determines that the power supply system 100 is in islanding operation (S35). Then, the islanding operation determination unit 65 outputs a stop command signal to the protection relay drive unit 66, and the protection relay drive unit 66 opens the tie-point circuit breaker C3 (S36). This stops the power supply from the distributed power source D to the load L, and the power supply system 100 is prevented from islanding.

[0060] On the other hand, if the impedance is less than the islanding operation setting value, the short circuit determination unit 64 compares the impedance calculated by the impedance calculation unit 62 with the short circuit setting value (S37).

[0061] If the impedance is equal to or less than the short circuit setting value, the short circuit determination unit 64 determines that a short circuit has occurred (S38). Then, the short circuit determination unit 64 outputs an opening command signal to the protection relay driving unit 66, and the protection relay driving unit 66 opens the load breaker C2 (S39).

[0062] If the impedance is greater than the short-circuit setting value and less than the earth fault setting value, it is determined that neither a short circuit nor islanding has occurred, and the process returns to S31. Note that in Fig. 6, the islanding operation is determined first, and then a short circuit is determined, but the islanding operation may be determined after a short circuit is determined, or the islanding operation and short circuit determinations may be made simultaneously.

[0063] <Effects of this embodiment> In such a power supply system 100, the first measurement unit 40 measures the zero-phase-sequence current or zero-phase-sequence current including the non-fundamental wave component injected by the non-fundamental wave component injection unit 30, so the first measurement unit 40 does not need to measure the ground-fault current when a ground fault occurs. The ground fault determination unit 63 determines a ground fault based on the zero-phase-sequence current or zero-phase-sequence voltage including the non-fundamental wave component measured by the first measurement unit 40, so that a ground fault can be reliably determined during isolated operation regardless of the magnitude of the ground-fault current. As a result, by identifying the location of the ground fault and quickly removing it, it is possible to prevent a power outage in the entire microgrid. Furthermore, since the ground fault determination unit 63 can determine a ground fault regardless of the magnitude of the ground fault current, measures to increase the ground fault current are not required, which makes it possible to suppress increases in costs when building a microgrid.

[0064] In addition, since one protective relay device 60 includes a ground fault determination unit 63, a short circuit determination unit 64, and an islanding operation determination unit 65, it is possible to protect the load L from islanding operation, a short circuit, and a ground fault. Specifically, when the power supply system 100 performs interconnected operation with the power grid G, the short circuit determination unit 64 and the islanding operation determination unit 65 determine a short circuit and an islanding operation, respectively, and when the power supply system 100 performs isolated operation, the ground fault determination unit 63 and the short circuit determination unit 64 determine a ground fault and a short circuit, respectively. Therefore, since one protective relay device 60 can protect the load L from a ground fault, a short circuit, and an islanding operation, there is no need to provide a new device for detecting a ground fault, a short circuit, and / or an islanding operation, and the cost of the power supply system 100 can be further reduced.

[0065] <Other embodiments> The present invention is not limited to the above-described embodiment.

[0066] As shown in FIG. 7 , the power supply system 100 may further include a ground injection unit 70 that is provided on a ground line P2, one end of which is electrically connected to a bus line B and is grounded, and that injects a current into the ground side of the ground line P2. The ground injection unit 70 is a current injection device configured to be able to inject a current of any frequency into the ground side of the ground line P2. Here, the frequency of the current injected by the ground injection unit 70 is a frequency that is different from the predetermined frequency of the AC power supplied to the bus line B and the frequency of the non-fundamental wave component injected by the non-fundamental wave component injection unit 30, but is not limited to this. Note that, although the ground line P2 is provided in parallel with the power line P1 in FIG. 7 , the ground line P2 may also be provided in series with the power line P1.

[0067] 7, when a ground fault occurs during isolated operation of the microgrid, the non-fundamental wave components injected by the non-fundamental wave component injection unit 30 are measured by the zero-phase-sequence current measurement unit 41 and the zero-phase-sequence voltage measurement unit 42, as in the above embodiment. Also, the current injected by the ground injection unit 70 flows through a ground fault circuit, which is a circuit that virtually connects the ground point of the ground wire P2 and the ground point of the zero-phase-sequence voltage measurement unit 42. As a result, the current injected by the ground injection unit 70 and the voltage corresponding to that current are measured by the zero-phase-sequence current measurement unit 41 and the zero-phase-sequence voltage measurement unit 42, respectively.

[0068] With this configuration, the ground injection unit 70 injects a current into the ground side of the ground wire P2, so that the current injected into the ground circuit in the event of a ground fault increases by the amount of the non-fundamental wave component as well as the current injected by the ground injection unit 70. Therefore, the zero-phase sequence current or zero-phase sequence voltage when the ground fault determination unit 63 determines whether a ground fault has occurred increases, allowing the ground fault determination unit 63 to determine whether a ground fault has occurred with high accuracy.

[0069] In addition, since the frequency of the current injected by the ground injection unit 70 is different from the predetermined frequency of the AC power supplied to the bus B and the frequency of the non-fundamental wave component, it is possible to prevent the current injected by the ground injection unit 70 from interfering with the non-fundamental wave component or the AC power.

[0070] In this embodiment, the power supply system 100 may further include a control device (not shown) that commands the protective relay device 60 to perform control for independent operation based on the open / closed state of the circuit breaker C1. The control device referred to here may be, for example, an energy management system.

[0071] In the above embodiment, the protective relay device 60 is equipped with a ground fault judgment unit 63, a short circuit judgment unit 64, and an isolated operation judgment unit 65, but the ground fault judgment unit 63, the short circuit judgment unit 64, and / or the isolated operation judgment unit 65 may be provided in a computer separate from the protective relay device 60.

[0072] In the above embodiment, the power supply system 100 includes the ground fault determination unit 63, the short circuit determination unit 64, and the islanding operation determination unit 65, but the power supply system 100 only needs to include at least the ground fault determination unit 63. Even in this case, it is possible to provide a power supply system 100 that can reliably determine a ground fault during islanded operation of the microgrid.

[0073] In the above embodiment, the ground fault determination unit 63 determines a ground fault by comparing the zero-phase impedance with a ground fault setting value, but the physical quantity is not limited to impedance as long as it is a physical quantity obtained from the non-fundamental wave components of the voltage and current and changes due to a ground fault. For example, the ground fault determination unit 63 may determine a ground fault by using, for example, admittance calculated from the non-fundamental wave components of the voltage and current and comparing the admittance with a preset setting value.

[0074] 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]

[0075] 100 Power Supply System 20 Power Converter 30...Non-fundamental wave component injection part 40...1st measurement section 50...Second measurement section 60 Protective relay device 61...Non-fundamental wave component calculation unit 62 Impedance calculation unit 63 Ground fault detection section 64 Short circuit detection section 65 Isolated operation decision unit 66 Protection relay driver 70 Ground injection section G...Electric power system L...Load B...Bus bar P1 Power line P2...Ground wire

Claims

1. A power supply system that switches between grid-connected operation with a power grid and standalone operation depending on the open / close state of a circuit breaker interposed between the power supply system and the power grid, a non-fundamental wave component injection unit that injects a non-fundamental wave component indicating a current and / or a voltage having a frequency different from that of a fundamental wave into a bus that is connected to the power system via the circuit breaker and to which AC power of a predetermined frequency is supplied; a first measurement unit that is provided on a power line electrically connecting the bus and the load to which the non-fundamental wave component is shunted, and that measures a zero-phase current or a zero-phase voltage including the non-fundamental wave component; a ground fault determination unit that determines a ground fault based on the zero-phase sequence current or the zero-phase sequence voltage measured by the first measurement unit while the circuit breaker is open; a protection relay driving unit that opens a load circuit breaker, which is a circuit breaker that opens and closes the power line to protect the load, when the ground fault determination unit determines that a ground fault has occurred.

2. a non-fundamental wave component calculation unit that calculates a non-fundamental wave current or a non-fundamental wave voltage corresponding to a frequency of the non-fundamental wave component from the zero-phase-sequence current or the zero-phase-sequence voltage measured by the first measurement unit; an impedance calculation unit that calculates an impedance based on the non-fundamental current or the non-fundamental voltage calculated by the non-fundamental wave component calculation unit, 2. The power supply system according to claim 1, wherein the ground fault determination unit determines that a ground fault has occurred when the impedance calculated by the impedance calculation unit is equal to or less than a set value.

3. a second measurement unit provided on the bus or the power line, the second measurement unit measuring the current or voltage including the non-fundamental wave component; a short circuit determination unit that determines whether a short circuit has occurred based on the current or the voltage measured by the second measurement unit and a setting value, The power supply system according to claim 1 , wherein when the short circuit determination unit determines that a short circuit has occurred, the protection relay driving unit opens the load breaker to protect the load.

4. an islanding operation determination unit that determines whether or not an islanding operation is occurring based on the current or the voltage measured by the second measurement unit and a setting value that is greater than the setting value used by the short circuit determination unit when the circuit breaker is closed; 4. The power supply system according to claim 3, wherein, when the islanding operation determination unit determines that an islanding operation is occurring, the protection relay drive unit opens a grid-connection point circuit breaker that opens and closes an electrical connection between the load and a distributed power source that is a power source that supplies power to the bus bar separately from the power grid.

5. a ground injection unit provided on a ground line whose one end is electrically connected to the bus bar and whose other end is grounded, for injecting a current into the ground side of the ground line; 5. The power supply system according to claim 1, wherein the first measurement unit measures a zero-phase sequence current or a zero-phase sequence voltage including the current injected by the ground injection unit and the non-fundamental wave component.

6. 6. The power supply system according to claim 5, wherein the frequency of the current injected by the ground injection unit is different from the predetermined frequency and the frequency of the non-fundamental wave component.

7. A control method for a power supply system that switches between grid-connected operation with a power grid and standalone operation depending on the open / close state of a circuit breaker interposed between the power supply system and the power grid, comprising: injecting a non-fundamental wave component representing a current and / or a voltage having a frequency different from that of a fundamental wave into a bus that is connected to the power system via the circuit breaker and to which AC power of a predetermined frequency is supplied; a zero-phase-sequence current detector that electrically connects the bus and the load and is provided on a power line through which the non-fundamental wave component is shunted, and that measures a zero-phase-sequence current or a zero-phase-sequence voltage including the non-fundamental wave component; determining a ground fault based on the zero-phase-sequence current or the zero-phase-sequence voltage measured by the first measurement unit while the circuit breaker is open; A control method for a power supply system, which, when a ground fault is determined, opens a load breaker, which is a breaker that opens and closes the power line to protect the load.

8. A program used in a power supply system that switches between grid-connected operation with a power grid and standalone operation depending on the open / close state of a circuit breaker interposed between the power supply system and the power grid, a non-fundamental wave component injection unit that injects non-fundamental wave components indicating current and / or voltage having a frequency different from that of a fundamental wave into a bus that is connected to the power system via the circuit breaker and to which AC power of a predetermined frequency is supplied; a first measurement unit that is provided on a power line electrically connecting the bus and the load to which the non-fundamental wave component is branched, and that measures a zero-phase current or a zero-phase voltage including the non-fundamental wave component, a function as a ground fault determination unit that determines a ground fault based on the zero-phase sequence current or the zero-phase sequence voltage measured by the first measurement unit when the circuit breaker is open; A power supply system program that causes a computer to function as a protective relay driver that opens a load circuit breaker, which is a circuit breaker that opens and closes the power line to protect the load, when the ground fault determination unit determines that a ground fault has occurred.

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