Power supply system, and control method of power supply system

Abstract

To provide a highly reliable power supply system capable of suppressing over-voltage due to harmonic voltage regardless of a load to be connected, and a control method of the power supply system.SOLUTION: A power supply system includes: an energy storage device; a DC-AC converter for converting DC output of the energy storage device into AC output; and a control part (60) for controlling the DC-AC converter. The control part (60) includes: a harmonic current detection part (61) for detecting magnitude of harmonic current included in current; a harmonic compensation control part (62) for controlling the DC-AC converter in accordance with the magnitude of the harmonic current and operating harmonic voltage included in AC output; a reactive power acquisition part (63) for acquiring a phase of reactive power of AC output; and a harmonic compensation command part (64) for stopping operation of the harmonic compensation control part (62) when reactive power is phase advancing.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a power supply system and a control method for the power supply system.

Background Art

[0002] A power supply system applied to a power grid, a microgrid, etc. includes an energy storage device and a converter that converts the DC output of this energy storage device into an AC output and outputs it to a load. As such a power supply system, one provided with a harmonic compensation control unit for suppressing harmonics at the connection point to which the above load is connected is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a power supply system provided with a harmonic compensation control unit, depending on the characteristics of the load connected to the connection point, harmonics may not be suppressed, and conversely, the harmonic voltage may be increased by the operation of the harmonic compensation control unit. As a result, in a conventional power supply system, there has been a risk of overvoltage occurring and the reliability of the power supply system deteriorating.

[0005] The present disclosure has been made in view of the above problems, and an object thereof is to provide a highly reliable power supply system and a control method for the power supply system that can suppress overvoltage caused by harmonic voltage regardless of the connected load.

Means for Solving the Problems

[0006] To solve the above problems, a power supply system according to an aspect of the present disclosure includes an energy storage device, a converter that converts the DC output of the energy storage device into an AC output and outputs it to a load, a current measuring device that measures the current of the AC output, a voltage measuring device that measures the voltage of the AC output, and a control unit that controls the converter. The control unit includes a harmonic current detection unit that detects the magnitude of the harmonic current included in the current, a harmonic compensation control unit that controls the converter according to the magnitude of the harmonic current to manipulate the harmonic voltage included in the AC output, a reactive power acquisition unit that acquires the phase of the reactive power of the AC output, and a harmonic compensation command unit that stops the operation of the harmonic compensation control unit when the reactive power is in the leading phase.

[0007] Further, a control method for a power supply system according to an aspect of the present disclosure is a control method for a power supply system including an energy storage device, a converter that converts the DC output of the energy storage device into an AC output and outputs it to a load, a harmonic current detection unit that detects the magnitude of the harmonic current included in the current of the AC output, a harmonic compensation control unit that controls the converter according to the magnitude of the harmonic current to manipulate the harmonic voltage included in the AC output, and a reactive power acquisition unit that acquires the phase of the reactive power of the AC output. The control method includes a detection step of detecting the magnitude of the harmonic current, an acquisition step of acquiring the phase of the reactive power of the AC output, and a stop step of stopping the operation of the harmonic compensation control unit when the reactive power is in the leading phase.

Advantages of the Invention

[0008] According to one aspect of the present disclosure, it is possible to provide a highly reliable power supply system and a control method for the power supply system that can suppress overvoltage caused by harmonic voltage regardless of the connected load.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Embodiments for Carrying Out the Invention

[0010] 〔Embodiment〕 Hereinafter, an embodiment of the present invention will be described in detail.

[0011] <Configuration of the power system 100 to which the power supply system 1 is applied> FIG. 1 is a schematic configuration diagram showing the power supply system 1 according to the embodiment of the present disclosure. FIG. 1 shows the entirety of the power system 100 to which the power supply system 1 is applied. The power supply system 1 is a system capable of storing electric power, including the energy storage device 10. The AC power (AC output) output by the power supply system 1 is supplied to a plurality of feeders 90 connected to the connection point RT.

[0012] Each feeder 90 is composed of a breaker 91 and a load 92. In each feeder 90, when a short-circuit accident occurs in the feeder 90, the breaker 91 detects the continuation of overcurrent for a predetermined time and trips, disconnecting the feeder 90 from the power system 100. The load 92 can be a non-linear load, for example, an R load, an RL load, an RC load, a C load, or a rectifier load.

[0013] Although not shown in FIG. 1, a power generation system using natural energy such as a solar power generation system or a wind power generation system may be arranged in parallel with the power supply system 1 in the power system 100. Alternatively, a power generation system using fuel such as a diesel generator or a cogeneration system may be arranged in parallel with the power supply system 1. The power supply system 1 can be applied as at least a backup for the output of these power generation systems. In that sense, the power supply system 1 is also an uninterruptible power supply (UPS).

[0014] As a specific example of the power system 100, an isolated power system in an island or a mountainous area (for example, a power system of a microgrid) can be cited. If a power generation system using natural energy is used in such a power system, the power supply system 1 equipped with the energy storage device 10 is applied, so that the smoothing of the power supply using natural energy can be achieved. Alternatively, if a power generation system using fuel is used in such a power system 100, the power supply system 1 can also be adopted as a backup power supply in case of a failure of the power generation system.

[0015] However, the specific example of the power system 100 is not limited to an isolated power system in an island or a mountainous area, and it may be a power system in a factory that uses a power generation system using natural energy or other power generation systems. Even in the power system in the factory, the effects and actions of the present exemplary embodiment are similarly achieved.

[0016] When the power supply system 1 according to the embodiment supplies power to the power system 100, even when a short-circuit accident occurs in the feeder 90, it operates so as to continue supplying power to the power system 100 without stopping the operation as much as possible. In the following description, for easy understanding, it is described as if only the power supply system 1 supplies power to the power system 100. However, if the power supply system 1 supplies power to the power system 100, even when operating in parallel with other power generation systems, the operation of the power supply system 1 is the same.

[0017] <Configuration of the power supply system 1> As shown in FIG. 1, the power supply system 1 includes an energy storage device 10, a DC-AC converter 20 (converter), an ammeter 30, a coupling reactor 40, a voltmeter 50, and a control unit 60.

[0018] As will be described later, the power supply system 1 constitutes a self - contained BESS (Battery Energy Storage System) equipped with a harmonic compensation control unit for suppressing harmonic voltages. That is, in the power supply system 1, even when harmonics are generated in the power grid 100 due to the influence of the non - linear load or the like, the adverse effects such as harmonic voltages on the power grid 100 can be suppressed by appropriately compensating for the harmonics as will be described in detail later.

[0019] The energy storage device 10 is a device that holds the input power as energy inside and outputs the held energy as DC power (DC output) as needed. The energy storage device 10 can be a device equipped with a secondary battery such as a lithium - ion battery, a NaS (sodium - sulfur) battery, a redox flow battery, or a lead - acid battery.

[0020] However, the energy storage device 10 is not limited to a device equipped with a secondary battery. As the energy storage device 10, any unit having a function of storing electrical energy, such as a capacitor, a superconducting power storage unit, a flywheel - type power storage unit, or a compressed - air - type power storage unit, can be used. Note that the fact that the energy storage device 10 is a device that outputs DC power is a concept that includes the case where the power once output as AC power inside is converted to DC power by a rectifier circuit, a converter, or the like and then output.

[0021] The DC - AC converter 20 is a device that converts the DC power (DC output) output from the energy storage device 10 into AC power (AC output). The DC - AC converter 20 converts the DC power into AC power with the required voltage and frequency used by the power grid 100 according to a PWM (Pulse Width Modulation) signal as an output command from the control unit 60.

[0022] The ammeter 30 measures the current of the AC power (AC output) output by the power supply system 1 and transmits the information to the control unit 60. Further, the voltmeter 50 measures the voltage of the AC power (AC output) output by the power supply system 1 via the series reactor 40 and transmits the information to the control unit 60. Note that the series reactor 40 may be configured to contribute to suppression of higher-order harmonics.

[0023] <Configuration of Control Unit 60> Next, with reference to FIGS. 2 and 3 as well, the configuration and operation of the control unit 60 will be specifically described. FIG. 2 is a block diagram showing a specific configuration of the control unit shown in FIG. 1. FIG. 3 is a diagram showing the control logic of the above control unit.

[0024] As shown in FIG. 2, the control unit 60 includes a harmonic current detection unit 61 that detects the magnitude of the harmonic current included in the current of the AC output, a harmonic compensation control unit 62 that controls the DC-AC converter 20 according to the magnitude of the harmonic current to manipulate the harmonic voltage included in the AC output, a reactive power acquisition unit 63 that acquires the phase of the reactive power of the AC output, and a harmonic compensation command unit 64 that outputs a harmonic compensation command created based on the magnitude of the harmonic current and the phase of the reactive power to the harmonic compensation control unit 62.

[0025] In FIG. 3, the harmonic current detection unit 61 includes a BPF (band-pass filter) 61A that detects the magnitude of the harmonic current of one order n based on the measurement result of the ammeter 30. The BPF 61A outputs a signal corresponding to the magnitude of the detected harmonic current to the harmonic signal generator 62A provided in the harmonic compensation control unit 62 and the harmonic compensation command unit 64.

[0026] As shown in FIG. 3, the reactive power acquisition unit 63 receives the measurement result of the current from the current measuring device 30 and the measurement result of the voltage from the voltage measuring device 50. Then, based on the input measurement results of the current and the voltage, the reactive power acquisition unit 63 determines whether the phase of the reactive power of the AC output is leading, and outputs the result to the harmonic compensation command unit 64. That is, the reactive power acquisition unit 63 outputs a polarity notification signal indicating whether the reactive power is leading with respect to the harmonic current to the harmonic compensation command unit 64.

[0027] The harmonic compensation control unit 62 includes the harmonic signal generator 62A, a multiplier 62B, and an adder 62C that are sequentially connected to the harmonic signal generator 62A. The harmonic signal generator 62A calculates a harmonic compensation voltage (control amount) signal for compensating (suppressing) the harmonic voltage of the order n according to the magnitude of the harmonic current from the BPF 61A and the value (jnωL) of the circuit impedance of the order n. The harmonic signal generator 62A outputs the obtained harmonic compensation voltage to the multiplier 62B.

[0028] An ON signal with a value of "1" or an OFF signal with a value of "0" is input to the multiplier 62B as a harmonic compensation command from the harmonic compensation command unit 64. Then, the multiplier 62B outputs the multiplication result of the harmonic compensation command and the harmonic compensation voltage to the adder 62C. That is, when the ON signal is input, the multiplier 62B outputs the harmonic compensation voltage as the control amount to the adder 62C, and when the OFF signal is input, the multiplier 62B outputs a value of "0" to the adder 62C without outputting the harmonic compensation voltage.

[0029] The multiplication result (harmonic wave) from the multiplier 62B and the fundamental voltage (fundamental wave) from the functional block of the fundamental wave AVR 65 are input to the adder 62C, and these multiplication result and the fundamental voltage are added. Then, the adder 62C outputs the addition result to the functional block of the PWM 66 that outputs the PWM signal to the DC-AC converter 20.

[0030] The functional block of PWM66 creates a PWM signal based on the input addition result and outputs it to the DC-AC converter 20. The DC-AC converter 20 converts the DC power from the secondary battery 10A into AC power with the required voltage and frequency according to the input PWM signal. Also, when the harmonic compensation voltage is reflected in the PWM signal (when the above harmonic compensation command is an ON signal), the DC-AC converter 20 outputs, as the voltage of the converted AC power, a voltage that suppresses the harmonic distortion at the connection point RT by the above harmonic compensation voltage.

[0031] That is, in the harmonic compensation control unit 62, the functional block of PWM66 controls the DC-AC converter 20 so that the output of the waveforms of the above harmonic and the fundamental wave added by the adder 62C can be obtained. Thereby, the DC-AC converter 20 outputs a harmonic compensation voltage for controlling the voltage of the series reactor 40 so as to suppress the harmonic distortion at the connection point RT, and the harmonic distortion is suppressed.

[0032] The harmonic compensation command unit 64 inputs the magnitude of the harmonic current from the BPF61A and the polarity notification signal from the reactive power acquisition unit 63. Then, based on the magnitude of these harmonic currents and the polarity notification signal, the harmonic compensation command unit 64 determines whether to operate the harmonic compensation control unit 62 or not, and generates a harmonic compensation command.

[0033] Specifically, when the reactive power is in the leading phase, the harmonic compensation command unit 64 generates an OFF signal as the harmonic compensation command and stops the operation of the harmonic compensation control unit 62. Also, when the reactive power is not in the leading phase, if the magnitude of the harmonic current is equal to or greater than a predetermined current setting value, the harmonic compensation command unit 64 generates an ON signal as the harmonic compensation command and operates the harmonic compensation control unit 62.

[0034] On the other hand, when the reactive power is not leading and the magnitude of the harmonic current is less than the current set value, the harmonic compensation command unit 64 generates an OFF signal as a harmonic compensation command to stop the operation of the harmonic compensation control unit 62. That is, the output from the harmonic compensation control unit 62 is set to 0, and the harmonic compensation voltage is not generated in the DC-AC converter 20.

[0035] <Detailed Configuration of Harmonic Compensation Command Unit 64> Here, with reference to FIGS. 4 to 6, the detailed configuration and operation of the harmonic compensation command unit 64 will be specifically described. FIG. 4 is a diagram showing the specific configuration of the harmonic compensation command unit 64 shown in FIG. 2. FIG. 5 is a table showing the relationship between the type of load shown in FIG. 1, the reactive power, and the harmonic current. FIG. 6 is a table showing the relationship between the type of the load and the harmonic compensation command.

[0036] As shown in FIG. 4, the harmonic compensation command unit 64 includes a function block of current determination 64A that determines the magnitude of the harmonic current by determining whether the magnitude of the harmonic current is equal to or greater than the current set value, and a function block of ON / OFF delay 64B that is connected to the current determination 64A and delays the determination result of the current determination 64A.

[0037] In addition, the harmonic compensation command unit 64 includes a function block of power determination 64C that determines the phase of the reactive power by determining whether the reactive power is 0 or more, and a function block of ON / OFF delay 64D that is connected to the power determination 64C and delays the determination result of the power determination 64C.

[0038] Furthermore, the harmonic compensation command unit 64 includes an AND circuit 64E that obtains the AND result of the determination results from the function blocks of ON / OFF delays 64B and 64D. Then, based on the AND result, the AND circuit 64E generates an ON signal or an OFF signal as a harmonic compensation command and outputs it to the multiplier 62B.

[0039] Specifically, as shown in FIG. 5, when the load 92 is a no-load, R-load, or rectifier load, the reactive power is approximately 0. If the reactive power is approximately 0, the functional block of the power discrimination 64C outputs an ON signal with a value of "1". Also, when the load 92 is an RL load, the reactive power is +Q (lagging) and is a non-negative value of 0 or more. If the reactive power is not a non-negative value, that is, if it is not a leading reactive power, the functional block of the power discrimination 64C outputs an ON signal with a value of "1".

[0040] Also, when the load 92 is an RC load, the reactive power is -Q (leading) and is less than 0. If the reactive power is a negative value, that is, if it is a leading reactive power, the functional block of the power discrimination 64C outputs an OFF signal with a value of "0". In this way, the functional block of the power discrimination 64C outputs an ON signal or an OFF signal according to the reactive power.

[0041] When the load 92 is a no-load, R-load, RL load, or RC load, the normal harmonic current is not large. If the magnitude of the harmonic current is less than the above current setting value, the functional block of the current discrimination 64A outputs an OFF signal with a value of "0". Also, when the load 92 is a rectifier load, the normal harmonic current is large. If the magnitude of the harmonic current is equal to or greater than the above current setting value, the functional block of the current discrimination 64A outputs an ON signal with a value of "1". In this way, the functional block of the current discrimination 64A outputs an ON signal or an OFF signal according to the magnitude of the harmonic current.

[0042] The functional block of the ON·OFF delay 64B delays the ON signal or OFF signal from the functional block of the current discrimination 64A by a predetermined period (for example, 50 msec to 100 msec) and outputs it to the AND circuit 64E. This delay for this predetermined period is for preventing hunting in the discrimination of the harmonic current. Also, the functional block of the ON·OFF delay 64D delays the ON signal or OFF signal from the functional block of the power discrimination 64C by a predetermined period (for example, 50 msec to 100 msec) and outputs it to the AND circuit 64E. This delay for this predetermined period is for preventing hunting in the discrimination of the harmonic current.

[0043] As shown in FIG. 6, the AND circuit 64E creates an ON signal with a value of "1" or an OFF signal with a value of "0" as a harmonic compensation command in accordance with the ON signal with a value of "1" or the OFF signal with a value of "0" from each functional block of the ON / OFF delays 64B and 64D. That is, when the load 92 is a no-load, R-load, RL-load, or RC-load, the AND circuit 64E outputs an OFF-signal harmonic compensation command to stop the operation of the harmonic compensation control unit 62. Further, when the load 92 is a rectifier load, the AND circuit 64E outputs an ON-signal harmonic compensation command to operate the harmonic compensation control unit 62.

[0044] As described above, in the power supply system 1 of the present embodiment, since the presence or absence of the operation of the harmonic compensation control unit 62 is determined according to the type of the load 92, it becomes possible to appropriately compensate for harmonics corresponding to the load 92, and it becomes possible to appropriately suppress the adverse effect of the harmonic voltage on the power system 100.

[0045] In the above description, the configuration in which the harmonic current detection unit 61 includes the BPF 61A that detects the magnitude of the harmonic current of one order and detects the magnitude of the harmonic current of the one order has been described. However, the present embodiment is not limited to this, and the harmonic current detection unit 61 may have a configuration that detects the magnitudes of harmonic currents of a plurality of orders (for example, 5th, 7th, 11th, 13th).

[0046] As described above, when detecting the magnitudes of harmonic currents of a plurality of orders, in the harmonic current detection unit 61, by providing a plurality of BPFs respectively corresponding to the frequencies of the plurality of orders, the harmonic current detection unit 61 may detect the magnitude of the harmonic current for each of the harmonic currents of the plurality of orders. Further, the harmonic compensation command unit 64 may operate the harmonic compensation control unit 62 if the magnitude of any one of the harmonic currents of the plurality of orders is equal to or greater than a predetermined current setting value determined for the harmonic current of that order.

[0047] Specifically, in the harmonic compensation command unit 64, for each of a plurality of orders, a function block of current discrimination 64A, a function block of ON / OFF delay 64B, a function block of power discrimination 64C, a function block of ON / OFF delay 64D, and an AND circuit 64E are provided. Further, an OR circuit for obtaining the OR result of the AND results of the plurality of AND circuits 64E is installed, and an ON signal with a value of "1" or an OFF signal with a value of "0" as a harmonic compensation command may be created based on the OR result of the OR circuit.

[0048] In addition to the above description, for each of a plurality of orders, a function block of current discrimination 64A and a function block of ON / OFF delay 64B are provided, and an OR circuit for current discrimination for obtaining the OR result of the function blocks of the plurality of ON / OFF delays 64B is installed. Further, a set of function blocks of power discrimination 64C and ON / OFF delay 64D common to a plurality of orders are provided, and an AND circuit for obtaining the AND result with the OR circuit for current discrimination is installed, and an ON signal with a value of "1" or an OFF signal with a value of "0" as a harmonic compensation command may be created based on the AND result of the AND circuit.

[0049] In this way, when detecting the magnitude of harmonic current for each of a plurality of orders and operating the harmonic compensation control unit 62 if the magnitude of any harmonic current is equal to or greater than the above current setting value determined for the harmonic current of that order, regardless of the connected load 92, the harmonic voltage of the order to be compensated for harmonics can be more reliably suppressed.

[0050] <Operation of Power System 1> Subsequently, the operation of the power system 1 will be described. First, the basic operation of the power system 1 will be described. As described above, in the power system 1 of the present embodiment, when supplying the power of the energy storage device 10 to the load 92, the harmonic current detection unit 61 performs a detection process of detecting the magnitude of the harmonic current included in the current of the AC output to the load 92 based on the measurement result of the current measuring instrument 30.

[0051] Next, the reactive power acquisition unit 63 performs an acquisition process of acquiring the phase of the reactive power of the AC output based on the measurement result of the voltmeter 50. Then, when notified from the reactive power acquisition unit 63 that the reactive power is in the leading phase, the harmonic compensation command unit 64 performs a stop process of stopping the operation of the harmonic compensation control unit 62.

[0052] <Operation when RC load is connected> Next, in the conventional power system, the operation when an RC load is connected as a load, where there is a possibility that harmonics cannot be appropriately compensated, will be described.

[0053] [Operation in comparative example] First, with reference to FIGS. 7 to 10, the operation when an RC load is connected as load 92 in the comparative example will be specifically described. FIG. 7 is a diagram showing a specific example of the control logic of the comparative example. FIG. 8 is a diagram for explaining a specific example of the harmonic compensation operation in the comparative example. FIG. 9 is a waveform diagram showing a specific example of the operation waveform in the comparative example. FIG. 10 is a diagram showing an example of the result of performing a fast Fourier transform on the connection point voltage in the comparative example to show the magnitude of the voltage component at each frequency.

[0054] As shown in FIG. 7, in the comparative example, the DC output from the secondary battery 100A is converted to an AC output via the DC-AC converter 120 and supplied to the RC load 90A connected to the connection reactor 40 and the connection point RT. In the comparative example, the ammeter 130 and the BPF 161A are used to detect the magnitude of the harmonic current Ih included in the current of the AC output, and the harmonic compensation voltage Vhc (= jnωL·Ih) is calculated by the harmonic signal generator 162A and output to the adder 162C.

[0055] Incidentally, when the voltage of the AC output is Vh and the impedance including the connection reactor 140 and the RC load 90A is Zhs, the harmonic current Ih is, as shown in FIG. 7, a value obtained by dividing the voltage Vh of the AC output by the impedance Zhs as seen from the DC-AC converter 120 side.

[0056] In the comparative example, the harmonic compensation voltage Vhc, which is the control amount of harmonic compensation, and the fundamental voltage from the functional block of the fundamental wave AVR165 are added by the adder 162C and output to the functional block of the PWM166. Then, in the comparative example, the functional block of the PWM166 creates a PWM signal based on the addition result from the adder 162C and outputs it to the DC-AC converter 120. As a result, in the comparative example, even when the RC load 90A is connected to the connection point RT, the control operation of harmonic compensation is performed based on the magnitude of the detected harmonic current Ih.

[0057] In the comparative example, as shown in FIG. 8, depending on whether the impedance Zhs is capacitive or inductive, the harmonic compensation may not be appropriately performed, and instead, the distortion of the harmonic voltage may be increased.

[0058] That is, as shown in FIG. 8, when the impedance Zhs is capacitive, the harmonic compensation voltage Vhc has a polarity opposite to that of the voltage Vh of the AC output and acts to compensate (suppress) the harmonic voltage included in the voltage Vh. Note that the case where the impedance Zhs is capacitive means a state where the harmonic to be controlled has a lower frequency than the LC resonance point of the power system.

[0059] On the other hand, when the impedance Zhs is inductive, the harmonic compensation voltage Vhc has the same polarity as the voltage Vh of the AC output and acts to expand the harmonic voltage included in the voltage Vh. Note that the case where the impedance Zhs is inductive means a state where the harmonic to be controlled has a higher frequency than the LC resonance point of the power system.

[0060] Thus, in the comparative example, since the control operation of harmonic compensation based on the magnitude of the harmonic current is always performed, the harmonic voltage may be increased to cause an overvoltage, which may damage the DC-AC converter 120 and reduce the reliability of the power system.

[0061] Specifically, in the comparative example, when the impedance Zhs is inductive and the control operation of harmonic compensation is performed, for example, as shown between time point T11 and time point T12 in FIG. 9, both the bus voltage and the bus current supplied to the RC load 90A increase. That is, as shown in the enlarged view of part A in FIG. 9, the distortion in the bus voltage of each phase of the three-phase and the bus current of each phase of the three-phase becomes large respectively.

[0062] Also, as shown in FIG. 10, in the comparative example, with respect to the above bus voltage, the 5th harmonic voltage (300 Hz) becomes a value that is very enlarged to 48.7% with respect to the fundamental wave. Also, in the comparative example, the value of THD (total harmonic distortion rate) also becomes a very high value of 58.83%.

[0063] [Operation in this embodiment] Next, with reference to FIGS. 11 to 13, the operation when the same RC load as in the case of FIG. 9 of the comparative example is connected as the load 92 in the power supply system 1 of this embodiment will be specifically described. FIG. 11 is a diagram for explaining a specific example of the harmonic compensation operation in the power supply system 1. FIG. 12 is a diagram for explaining a specific example of the harmonic compensation operation in the power supply system 1. FIG. 13 is a diagram showing an example of the result of performing a fast Fourier transform on the bus voltage in the power supply system 1 and showing the magnitudes of the voltage components at each frequency.

[0064] In this embodiment, when the RC load is connected as the load 92, as shown in FIG. 6, the harmonic compensation command unit 64 outputs an OFF signal with a value of "0" as a harmonic compensation command to the multiplier 62B. Therefore, in this embodiment, the operation of the harmonic compensation control unit 62 is stopped.

[0065] Specifically, when the load 92 (RC load) is connected at time point T0 in FIG. 11, the active power P [W] increases. On the other hand, the reactive power Q [Var] becomes less than or equal to 0, for example, less than the power setting value SH1 of -10 [Var]. Therefore, the phase of the reactive power Q [Var] becomes leading, and regardless of the magnitude of the harmonic current, the harmonic compensation command becomes an OFF signal and the harmonic compensation control unit 62 is not operated.

[0066] As a result, in this embodiment, for example, as shown between time point T1 and time point T2 in FIG. 11, the tie point voltage and tie point current supplied to the load 92 (RC load) do not change (increase). That is, as shown in the enlarged view of part B in FIG. 11, there is no distortion in the tie point voltage of each of the three phases and the tie point current of each of the three phases.

[0067] As shown in FIG. 12, although the magnitude of the 5th harmonic voltage and the magnitude of the 7th harmonic voltage increase slightly after the time point T0 as shown in the graphs V5 and V7 in FIG. 12, respectively, they fall within a very small value less than the voltage value SH2 of 10 [V]. Therefore, the value of the harmonic compensation command is maintained as an OFF signal with a value of "0" even after passing through the time point T0.

[0068] Also, as shown in FIG. 13, in this embodiment, the 5th (300 Hz) harmonic voltage of the tie point voltage becomes a very small value of 0.6664% with respect to the fundamental wave. Also, in this embodiment, the value of THD (total harmonic distortion rate) also becomes a very low value of 1.19%.

[0069] <Operation when changing load conditions> Next, with reference to FIGS. 14 to 17 as well, the operation when the type of the load 92 is sequentially changed to change the load conditions in the power supply system 1 of this embodiment will be described. FIG. 14 is a table showing an example of changing the load conditions in the power supply system 1. FIG. 15 is a diagram for explaining a specific example of the harmonic compensation operation when the load conditions are changed in accordance with FIG. 14 in the power supply system 1. FIG. 16 is a diagram for explaining a specific example of the harmonic compensation operation after the time point T25 in FIG. 15 in the power supply system 1. FIG. 17 is a diagram showing an example of the result of performing a fast Fourier transform on the tie point voltage when the load conditions in FIG. 14 are changed in the power supply system 1 and showing the magnitude of the voltage components at each frequency.

[0070] In this embodiment, the operation when the load 92 is sequentially switched in the order of switching numbers I to IV under the load conditions shown in FIG. 14, for example, will be specifically described.

[0071] In this embodiment, when the DC-AC converter 20 starts AC output at time point T20 in FIG. 15, the interconnection point voltage rises to a predetermined voltage. Thereafter, in this embodiment, when an R load is connected as load 92 from a no-load state at time point T21 in FIG. 15 (switching I), an interconnection point current starts to flow and the active power P becomes positive. The reactive power Q is maintained at a value that is substantially 0. That is, this reactive power Q is a value equal to or greater than the power set value SH1 (for example, -10 [Var]). The harmonic current included in the interconnection point current is very small and is less than the above current set value, so the harmonic compensation command is maintained by an OFF signal.

[0072] Note that the magnitude of the 5th harmonic voltage and the magnitude of the 7th harmonic voltage become values less than the voltage value SH2 of, for example, 10 [V], corresponding to the current set value, as shown by graphs V5 and V7 in FIG. 15, respectively.

[0073] Next, when the R load is switched to an RL load and connected as load 92 at time point T22 in FIG. 15 (switching II), the active power P slightly decreases. Also, a lagging reactive power Q is generated and the reactive power Q is a positive value. The harmonic current included in the interconnection point current is very small and is less than the above current set value, so the harmonic compensation command is maintained by an OFF signal. For this reason, the harmonic compensation command is maintained by an OFF signal. Also, the 5th harmonic voltage and the 7th harmonic voltage vary slightly after the above time point T22 as shown by graphs V5 and V7 in FIG. 15, respectively, but are maintained at values less than the above voltage value SH2.

[0074] Next, when the RL load is switched to the RC load and connected as load 92 at time point T23 in FIG. 15 (switching III), the active power P stabilizes after slightly fluctuating. Also, the reactive power Q becomes a negative value less than the power setting value SH1 and smaller than 0. That is, it is determined that the reactive power is in the leading phase, and regardless of the magnitude of the harmonic current included in the tie-point current, the harmonic compensation command is maintained as an OFF signal. Also, as shown in graphs V5 and V7 in FIG. 15, the magnitudes of the 5th harmonic voltage and the 7th harmonic voltage become slightly larger after time point T23, but are maintained at values less than the voltage value SH2.

[0075] Next, when the RC load is switched to the rectifier load and connected as load 92 at time point T24 in FIG. 15 (switching IV), the active power P is maintained at a slightly smaller value after time point T24. Also, lagging reactive power Q occurs, and the reactive power Q is a positive value. Since the non-linearity of the rectifier load is large and the magnitude of the harmonic current included in the tie-point current becomes equal to or greater than the current setting value, the harmonic compensation command is switched from the OFF signal to the ON signal at time point T25. Thereby, the operation of the harmonic compensation control unit 62 is performed. As shown in graphs V5 and V7 in FIG. 15, the magnitudes of the 5th harmonic voltage and the 7th harmonic voltage increase after time point T24.

[0076] Also, although the tie-point voltage becomes slightly smaller, when the harmonic compensation operation is performed at time point T25, it returns to the predetermined voltage. Also, the tie-point current becomes slightly smaller and then slightly larger and stabilizes at time point T25.

[0077] As described above, in the power supply system 1 of the present embodiment, the operation of the harmonic compensation control unit is implemented or stopped according to the type of load connected to the tie point RT.

[0078] In addition, in the power supply system 1 of the present embodiment, when the harmonic compensation operation is performed, both the interconnection point voltage and the interconnection point current become waveforms with suppressed distortion generation, as shown in the graph of FIG. 16. Further, since the distortion of the harmonic voltage is suppressed by the harmonic compensation operation, as shown in FIG. 17, the 5th harmonic voltage (300 Hz) of the interconnection point voltage is reduced to 1.006% with respect to the fundamental wave. Also, in the present embodiment, the value of THD (total harmonic distortion rate) is also as low as 4.99%.

[0079] In the power supply system 1 of the present embodiment configured as described above, and its control method, the control unit 60 includes a harmonic current detection unit 61 that detects the magnitude of the harmonic current included in the current, a harmonic compensation control unit 62 that controls the DC-AC converter 20 according to the magnitude of the harmonic current to manipulate the harmonic voltage included in the AC output, a reactive power acquisition unit 63 that acquires the phase of the reactive power of the AC output, and a harmonic compensation command unit 64 that stops the operation of the harmonic compensation control unit 62 when the reactive power is in the leading phase. Thereby, in the present embodiment, as illustrated in FIG. 15, a highly reliable power supply system 1 that can suppress overvoltage caused by harmonic voltage can be configured regardless of the connected load 92.

[0080] Also, in the present embodiment, when the reactive power is not in the leading phase, the harmonic compensation command unit 64 operates the harmonic compensation control unit 62 if the magnitude of the harmonic current is equal to or greater than the current set value, and stops the operation of the harmonic compensation control unit 62 if the magnitude of the harmonic current is less than the current set value. Thereby, in the present embodiment, regardless of the connected load 92, the harmonic compensation control unit 62 can be surely made to operate appropriately, and overvoltage caused by harmonic voltage can be surely suppressed.

[0081] Also, in the description of the above embodiment, it was described that the control of each phase is not particularly distinguished for each phase and is executed by collective control. In this case, the control unit may execute control by adopting, as the voltage measurement value and the current measurement value, the minimum value among the phases for the voltage and the maximum value among the phases for the current. Alternatively, the three-phase instantaneous effective value (the square root of the mean of the squares of the instantaneous voltage values of each phase) may be adopted as the current measurement value. However, the control of each phase may be performed separately by the control unit for each phase. In this case, the current set value may be determined collectively or may be determined for each phase.

[0082] 〔Example of realization by software〕 Each functional block of the power supply system 1 (particularly, the control unit 60) may be realized by a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like, or may be realized by software.

[0083] In the latter case, the power supply system 1 includes a computer that executes instructions of a program that is software for realizing each function. This computer includes, for example, at least one processor (control device) and at least one computer-readable recording medium that stores the above program. Then, in the above computer, when the above processor reads and executes the above program from the above recording medium, the object of the present invention is achieved. As the above processor, for example, a CPU (Central Processing Unit) can be used.

[0084] As the above-mentioned recording medium, "non-transitory tangible media" such as ROM (Read Only Memory), tapes, disks, cards, semiconductor memories, programmable logic circuits, etc. can be used. Further, it may further include a RAM (Random Access Memory) for expanding the above program. Further, the above program may be supplied to the above computer via any transmission medium (communication network, broadcast wave, etc.) capable of transmitting the program. Note that one aspect of the present invention can also be realized in the form of a data signal embedded in a carrier wave, in which the above program is embodied by electronic transmission.

[0085] 〔Summary〕 In order to solve the above problems, a power supply system according to one aspect of the present disclosure includes an energy storage device, a converter that converts the DC output of the energy storage device into an AC output and outputs it to a load, an ammeter that measures the current of the AC output, a voltmeter that measures the voltage of the AC output, and a control unit that controls the converter. The control unit includes a harmonic current detection unit that detects the magnitude of the harmonic current included in the current, a harmonic compensation control unit that controls the converter according to the magnitude of the harmonic current to manipulate the harmonic voltage included in the AC output, a reactive power acquisition unit that acquires the phase of the reactive power of the AC output, and a harmonic compensation command unit that stops the operation of the harmonic compensation control unit when the reactive power is in the leading phase.

[0086] According to the above configuration, a highly reliable power supply system capable of suppressing overvoltage caused by harmonic voltage can be provided regardless of the connected load.

[0087] In the power supply system according to the above aspect, when the reactive power is not in the leading phase, the harmonic compensation command unit may operate the harmonic compensation control unit if the magnitude of the harmonic current is equal to or greater than a current set value, and stop the operation of the harmonic compensation control unit if the magnitude of the harmonic current is less than the current set value.

[0088] According to the above configuration, regardless of the connected load, the harmonic compensation control unit can be surely made to operate appropriately, and the overvoltage caused by the harmonic voltage can be surely suppressed.

[0089] In the power supply system according to the above aspect, the harmonic current detection unit detects the magnitude of the harmonic current for each of a plurality of orders of harmonic currents, and the harmonic compensation command unit, among the plurality of orders of the harmonic currents, if the magnitude of any of the harmonic currents is equal to or greater than a current set value determined for the harmonic current of that order, the harmonic compensation control unit may be operated.

[0090] According to the above configuration, regardless of the connected load, the harmonic voltage of the order to be compensated for harmonics can be more surely suppressed.

[0091] Further, a control method for a power supply system according to an aspect of the present disclosure includes an energy storage device, a converter that converts the DC output of the energy storage device into an AC output and outputs it to a load, a harmonic current detection unit that detects the magnitude of the harmonic current included in the current of the AC output, a harmonic compensation control unit that controls the converter according to the magnitude of the harmonic current to manipulate the harmonic voltage included in the AC output, and a reactive power acquisition unit that acquires the phase of the reactive power of the AC output, and is a control method for a power supply system including a detection step of detecting the magnitude of the harmonic current, an acquisition step of acquiring the phase of the reactive power of the AC output, and a stop step of stopping the operation of the harmonic compensation control unit when the reactive power is in the leading phase.

[0092] According to the above configuration, a control method for a power supply system with excellent reliability that can suppress the overvoltage caused by the harmonic voltage regardless of the connected load can be provided.

[0093] The present disclosure is not limited to the above-described embodiments, various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining the technical means disclosed in the embodiments are also included in the technical scope of the present disclosure.

Description of Reference Numerals

[0094] 1 Power supply system 10 Energy storage device 20 DC-AC converter (converter) 30 Ammeter 50 Voltmeter 60 Control unit 61 Harmonic current detection unit 62 Harmonic compensation control unit 63 Reactive power acquisition unit 64 Harmonic compensation command unit

Claims

1. An energy storage device, a converter that converts the DC output of the energy storage device into an AC output and outputs it to a load, a current measuring device that measures the current of the AC output, a voltage measuring device that measures the voltage of the AC output, and a control unit that controls the converter, wherein the control unit includes a harmonic current detection unit that detects the magnitude of the harmonic current included in the current, a harmonic compensation control unit that controls the converter according to the magnitude of the harmonic current to manipulate the harmonic voltage included in the AC output, a reactive power acquisition unit that acquires the phase of the reactive power of the AC output, and a harmonic compensation command unit that stops the operation of the harmonic compensation control unit when the reactive power is in the leading phase, a power supply system.

2. When the reactive power is not in the leading phase, the harmonic compensation command unit operates the harmonic compensation control unit if the magnitude of the harmonic current is equal to or greater than a current set value, and stops the operation of the harmonic compensation control unit if the magnitude of the harmonic current is less than the current set value. The power supply system according to claim 1.

3. The harmonic current detection unit detects the magnitude of the harmonic current for each of a plurality of orders of harmonic currents, and the harmonic compensation command unit operates the harmonic compensation control unit if the magnitude of any one of the plurality of orders of harmonic currents is equal to or greater than a current set value determined for the harmonic current of that order. The power supply system according to claim 2.

4. An energy storage device, a converter that converts the DC output of the energy storage device into an AC output and outputs it to a load, a harmonic current detection unit that detects the magnitude of the harmonic current included in the current of the AC output, a harmonic compensation control unit that controls the converter according to the magnitude of the harmonic current to manipulate the harmonic voltage included in the AC output, and a reactive power acquisition unit that acquires the phase of the reactive power of the AC output. A control method for a power supply system, including a detection step of detecting the magnitude of the harmonic current, an acquisition step of acquiring the phase of the reactive power of the AC output, and a stop step of stopping the operation of the harmonic compensation control unit when the reactive power is in the leading phase. A control method for a power supply system.

Images