Power Conversion Equipment

Abstract

The power conversion device (50) includes a power converter (20) and a control device (10). The control device (10) generates a first voltage command value for the power converter (20) by simulating characteristics of a synchronous generator based on an AC voltage and an AC current in a power system (30), generates a first current command value for the power converter (20) based on the first voltage command value, and when no fault is detected in the power system (30), sets a limit value such that a second current range according to the limit value is smaller than a first current range according to the current capacity of the power converter (20), limits the first current command value within the second current range to generate a second current command value, generates a second voltage command value based on the second current command value, and generates a control signal for the power converter (20) based on the second voltage command value.

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device. [Background technology]

[0002] In recent years, many distributed power sources using renewable energy such as solar power generation facilities have been introduced into power systems. As a result, an increase in the rate of change of frequency (RoCoF), which indicates the magnitude of frequency change per unit time, has become an issue in the event of an accident such as a generator tripping. A frequency stabilization device stabilizes the power system by controlling the active power output from power sources such as solar power generation panels and storage batteries using a power converter and applying a pseudo inertial force to the power system.

[0003] For example, JP 2019-176584 A (Patent Document 1) discloses a control device for a distributed power source. This control device sets a virtual inertia for a power conversion device that connects a distributed power source to a power grid, calculates a virtual inertia value based on the specifications and operating state of the distributed power source, and sets the virtual inertia for the power conversion device based on either the calculated virtual inertia value or a required inertia value requested by a grid operator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-176584 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-mentioned power conversion device, during normal operation, it is operated so that active power can be output up to the upper limit. However, in this case, even if the power conversion device tries to increase the active power output to the power system in the event of a system accident (e.g., when a generator trips), the power conversion device does not have the capacity to do so. Therefore, the power conversion device cannot apply inertial force to the power system and cannot stabilize the system frequency.

[0006] An object in one aspect of the present disclosure is to provide a power conversion device that can supply active power to a power grid during normal operation, while providing inertial force when an accident occurs in the power grid. [Means for solving the problem]

[0007] A power conversion device according to an embodiment includes a power converter that performs power conversion between a DC circuit and a power system, and a control device that controls the power converter. The control device includes a generator simulation unit that generates a first voltage command value for the power converter by simulating characteristics of a synchronous generator based on an AC voltage and an AC current in the power system, a current command generation unit that generates a first current command value for the power converter based on the first voltage command value generated by the generator simulation unit, a setting unit that sets a limit value so that a second current range according to the limit value is smaller than a first current range according to a current capacity of the power converter when no fault is detected in the power system, a limiter that limits the first current command value within the second current range to generate a second current command value, a voltage command generation unit that generates the second voltage command value based on the second current command value, and a signal generation unit that generates a control signal for the power converter based on the second voltage command value.

[0008] A power conversion device according to another embodiment includes a power converter that performs power conversion between a DC circuit and a power system, and a control device that controls the power converter. The control device includes a generator simulation unit that generates a first voltage command value for the power converter by simulating characteristics of a synchronous generator based on an AC voltage and an AC current in the power system, a current command generation unit that generates a first current command value for the power converter based on the first voltage command value generated by the generator simulation unit, a limiter that generates a second current command value by limiting the first current command value within a current range according to the current capacity of the power converter, a voltage command generation unit that generates a second voltage command value based on the second current command value, and a signal generation unit that generates a control signal for the power converter based on the second voltage command value. When no fault is detected in the power system, the generator simulation unit generates the phase of the first voltage command value based on a second active power that is smaller than a first active power calculated based on the current capacity of the power converter. Effect of the Invention

[0009] According to the power conversion device according to the present disclosure, it is possible to supply active power to the power grid during normal operation, while providing an inertial force when an accident occurs in the power grid. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram for explaining an example of an overall configuration of a power conversion system. [Diagram 2] FIG. 2 is a diagram showing an example of a time change in active power output from a power converter. [Diagram 3] FIG. 2 is a diagram illustrating an example of a hardware configuration of a control device. [Figure 4] 4 is a block diagram showing an example of a functional configuration of a command generating unit according to the first embodiment. FIG. [Diagram 5] 4 is a block diagram showing an example of the configuration of a voltage amplitude generating unit; [Figure 6] 13 is a flowchart illustrating an example of processing by an accident detection unit and a setting unit. [Figure 7] FIG. 4 is a diagram showing an example of a change over time in active power output from the power converter according to the first embodiment. [Figure 8] FIG. 13 is a diagram illustrating an example of a configuration of a setting unit according to a modification of the first embodiment. [Figure 9] FIG. 13 is a diagram illustrating another example of the configuration of the setting unit according to the modification of the first embodiment. [Figure 10] FIG. 11 is a diagram showing an example of a change over time in active power output from a power converter according to a modification of the first embodiment. [Figure 11] FIG. 11 is a diagram showing another example of a change over time in active power output from the power converter according to the modification of the first embodiment. [Figure 12] FIG. 11 is a block diagram showing an example of a configuration of a command generating unit according to a second embodiment. [Figure 13] FIG. 13 is a block diagram showing an example of the configuration of a command generating unit according to a modification of the second embodiment. [Figure 14] 10 is a diagram for explaining the relationship between an active power command value and a power margin; FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the present embodiment will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[0012] Embodiment 1 <Overall composition> 1 is a diagram for explaining an example of the overall configuration of a power conversion system. The power conversion system 1000 includes a power system 30, a transformer 34, a DC circuit 40, a power conversion device 50, a current detector 91, and a voltage detector 93. The power conversion device 50 includes a control device 10 and a power converter 20.

[0013] The power converter 20 is a power converter that performs power conversion between the DC circuit 40 and the power system 30. Specifically, the power converter 20 is connected to the power system 30 via a transformer 34, converts DC power from the DC circuit 40 into AC power, and outputs the AC power to the power system 30.

[0014] The power converter 20 is, for example, a self-excited converter such as a two-level converter, a three-level converter, or a modular multilevel converter. The self-excited converter is a converter using self-extinguishing elements, and the magnitude and phase of the output voltage can be freely controlled. The self-excited converter can also exchange AC and DC power without a power source of a power system. The power system 30 is, for example, a three-phase AC system. The DC circuit 40 is, for example, a renewable energy power source such as a solar cell or a wind power generator, a power storage element, a DC transmission system, a DC terminal of another power converter, or the like.

[0015] The current detector 91 detects three-phase AC currents at the interconnection point 32 between the power system 30 and the power converter 20. Specifically, the current detector 91 detects a U-phase AC current Isysu, a V-phase AC current Isysv, and a W-phase AC current Isysw flowing between the interconnection point 32 and the transformer 34. The AC currents Isysu, Isysv, and Isysw (hereinafter collectively referred to as the “AC current Isys”) are input to the control device 10.

[0016] The voltage detector 93 detects three-phase AC voltages at the interconnection point 32 of the power system 30. Specifically, the voltage detector 93 detects a U-phase AC voltage Vsysu, a V-phase AC voltage Vsysv, and a W-phase AC voltage Vsysw at the interconnection point 32. The AC voltages Vsysu, Vsysv, and Vsysw (hereinafter collectively referred to as "AC voltage Vsys") are input to the control device 10.

[0017] The control device 10 is a device that controls the operation of the power converter 20. Specifically, the control device 10 includes a command generating unit 100 and a signal generating unit 200 as main functional components. Each function of the command generating unit 100 and the signal generating unit 200 is realized by a processing circuit. The processing circuit may be dedicated hardware, or may be a CPU (Central Processing Unit) that executes a program stored in the internal memory of the control device 10. When the processing circuit is dedicated hardware, the processing circuit is configured, for example, by a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), or a combination of these.

[0018] The command generating unit 100 mainly has a function of simulating the characteristics of a synchronous generator, and generates a phase θ of the voltage output from the power converter 20 (i.e., the phase of a voltage command value) and an amplitude V of the voltage (i.e., the amplitude of the voltage command value). The phase θ is a reference phase used for controlling the power converter 20. The command generating unit 100 will be described in detail later.

[0019] The signal generating unit 200 generates a control signal for the power converter 20 based on the voltage command value (i.e., the amplitude V and the phase θ) generated by the command generating unit 100, and outputs the control signal to the power converter 20. Specifically, the signal generating unit 200 includes a three-phase voltage generating unit 202 and a PWM control unit 204.

[0020] Based on the phase θ and the amplitude V, the three-phase voltage generating unit 202 generates three-phase sinusoidal voltages Vu*, Vv*, and Vw* by two-phase / three-phase conversion.

[0021] The PWM control unit 204 performs pulse width modulation on each of the three-phase sinusoidal voltages Vu*, Vv*, and Vw* to generate a control signal as a PWM signal. The PWM control unit 204 outputs the control signal to the power converter 20. Typically, the control signal is a gate control signal for controlling the on and off of each switching element included in the power converter 20.

[0022] The power conversion device 50 as described above has a function of simulating the characteristics of a synchronous generator, and adjusts the active power output to the power system 30 in order to stabilize the system frequency. Here, if the power conversion device 50 is configured to be able to output active power up to an upper limit determined by the hardware performance during normal operation when no fault occurs in the power system 30, a problem as shown in FIG. 2 occurs.

[0023] Fig. 2 is a diagram showing an example of a change over time in the active power output from the power converter. The horizontal axis of Fig. 2 represents time, and the vertical axis represents the output active power of the power converter 20. The direction in which active power is output from the power converter 20 to the power system 30 is defined as a positive direction, and the direction in which active power is input (i.e., absorbed) from the power system 30 to the power converter 20 is defined as a negative direction. In the example of Fig. 2, the DC circuit 40 is configured from a renewable energy power source that supplies power to the power converter 20.

[0024] 2 indicates an active power upper limit value defined by the upper limit value of the positive polarity of the current capacity (i.e., the allowable current) determined by the hardware performance of the power converter 20. The "lower limit value" in Fig. 2 indicates an active power lower limit value defined by the upper limit value of the negative polarity of the current capacity of the power converter 20 (i.e., the lower limit value of the current capacity).

[0025] 2, the power converter 20 continues to output active power at an upper limit value under normal circumstances. When a system accident occurs (e.g., a generator in the power system 30 trips) and the system frequency drops, the power converter 20 attempts to increase the active power output to the power system 30 in order to increase the system frequency, but is unable to increase the active power due to limitations in hardware performance. In other words, it is unable to impart a pseudo inertial force to the power system 30 and is unable to maintain the system frequency at a specified value. Therefore, it is preferable that the power converter 50 is configured to be able to increase the active power output when the system frequency drops.

[0026] Furthermore, when a system fault occurs (for example, a load in the power system 30 drops) and the system frequency increases, the power converter 20 reduces the active power output to the power system 30 in order to lower the system frequency. However, in the example of Fig. 2, the renewable energy power source serving as the DC circuit 40 cannot absorb active power. Therefore, it is necessary to appropriately set the lower limit of the active power output by the power conversion device 50.

[0027] The power conversion device 50 according to the present embodiment is configured to increase the effective power output to the power system 30 when the system frequency drops, thereby applying an inertial force. The specific configuration will be described later.

[0028] <Hardware configuration> Fig. 3 is a diagram showing an example of a hardware configuration of the control device 10. Fig. 3 shows an example of the control device 10 configured by a computer.

[0029] 3, the control device 10 includes one or more input converters 70, one or more sample-and-hold circuits 71, a multiplexer 72, an A / D converter 73, one or more central processing units (CPUs) 74, a random access memory (RAM) 75, a read-only memory (ROM) 76, one or more input / output interfaces 77, and an auxiliary storage device 78. The control device 10 includes a bus 79 that interconnects the components.

[0030] The input converter 70 has an auxiliary transformer for each input channel, and each auxiliary transformer converts the detection signals from the current detector 91 and the voltage detector 93 in FIG. 1 into signals of a voltage level suitable for subsequent signal processing.

[0031] A sample-and-hold circuit 71 is provided for each input converter 70. The sample-and-hold circuit 71 samples and holds a signal representing an electrical quantity received from the corresponding input converter 70 at a specified sampling frequency.

[0032] The multiplexer 72 sequentially selects the signals held in the multiple sample-and-hold circuits 71. The A / D converter 73 converts the signal selected by the multiplexer 72 into a digital value. Note that by providing multiple A / D converters 73, A / D conversion may be performed in parallel on detection signals of multiple input channels.

[0033] The CPU 74 controls the entire control device 10 and executes arithmetic processing according to a program. The RAM 75 as a volatile memory and the ROM 76 as a non-volatile memory are used as the main memory of the CPU 74. The ROM 76 stores programs and setting values ​​for signal processing. The auxiliary storage device 78 is a non-volatile memory with a larger capacity than the ROM 76, and stores programs, data on detected electric quantity values, and the like.

[0034] The input / output interface 77 is an interface circuit for communication between the CPU 74 and an external device.

[0035] Unlike the example of FIG. 3, at least a part of the control device 10 can be configured using circuits such as an FPGA and an ASIC.

[0036] <Command generator> Fig. 4 is a block diagram showing an example of a functional configuration of a command generating unit according to the first embodiment. With reference to Fig. 4, the command generating unit 100 includes a generator simulator 110, a fault detector 120, a setting unit 130, a current command generating unit 140, a current limiter 142, a voltage command generating unit 144, a coordinate converter 150, an AC power calculator 152, and a voltage amplitude generator 160. In Fig. 4, it is assumed that the DC circuit 40 is composed of a renewable energy power source.

[0037] The coordinate conversion unit 150 performs three-phase / two-phase conversion on the AC currents Isysu, Isysv, and Isysw using the phase θ to calculate the d-axis current Id and the q-axis current Iq. The coordinate conversion unit 150 also performs three-phase / two-phase conversion on the AC voltages Vsysu, Vsysv, and Vsysw using the phase θ to calculate the d-axis voltage Vd and the q-axis voltage Vq.

[0038] The AC power calculation unit 152 calculates active power P and reactive power Q at the interconnection point 32 based on the AC current Isys detected by the current detector 91 and the AC voltage Vsys detected by the voltage detector 93.

[0039] The voltage amplitude generating unit 160 generates an amplitude Vref of the voltage command value based on the d-axis voltage Vd, the q-axis voltage Vq, the reactive power Q, and the reactive power command value Qref. The amplitude Vref corresponds to the amplitude command value of the output voltage of the power converter 20.

[0040] 5 is a block diagram showing a configuration example of the voltage amplitude generation unit 160. With reference to FIG. 5, the voltage amplitude generation unit 160 includes a positive-phase voltage calculation unit 161, subtractors 162 and 163, a voltage adjustment unit 164, coordinate conversion units 165 and 167, and an adder 166.

[0041] The positive-sequence voltage calculation unit 161 calculates the positive-sequence voltage Vpos based on the d-axis voltage Vd and the q-axis voltage Vq. The subtractor 162 calculates the deviation ΔQ (=Qref-Q) between the reactive power command value Qref and the reactive power Q. The subtractor 162 calculates the deviation ΔVpos (=Vacref-Vpos) between the grid voltage command value Vacref and the positive-sequence voltage Vpos.

[0042] The voltage adjustment unit 164 selects either the automatic reactive power adjustment mode or the automatic voltage adjustment mode, and generates a voltage amplitude adjustment amount ΔVacref based on the selected mode. Specifically, when the automatic reactive power adjustment mode is selected, the voltage adjustment unit 164 generates a voltage amplitude adjustment amount ΔVacref by feedback control for making the deviation ΔQ equal to or less than a specified value (for example, 0). When the automatic voltage adjustment mode is selected, the voltage adjustment unit 164 generates a voltage amplitude adjustment amount ΔVacref by feedback control for making the deviation ΔVpos equal to or less than a specified value (for example, 0). The voltage adjustment unit 164 is composed of a PI controller, a first-order lag element, and the like.

[0043] The coordinate conversion unit 165 converts the d-axis component (i.e., the prescribed d-axis voltage command value Vdx) and the q-axis component (i.e., the prescribed q-axis voltage command value Vqx) of the prescribed voltage command value into an amplitude |Vx| and a phase φv. The prescribed d-axis voltage command value Vdx and the prescribed q-axis voltage command value Vqx are values ​​that are set in advance by a system operator or the like. The adder 166 adds the amplitude |Vx| and the voltage amplitude adjustment amount ΔVacref. The coordinate conversion unit 167 performs dq-axis conversion on the added value of the amplitude |Vx| and the voltage amplitude adjustment amount ΔVacref and the phase φv to generate the d-axis voltage amplitude Vdref (i.e., the d-axis component of the amplitude Vref) and the q-axis voltage amplitude Vqref (i.e., the q-axis component of the amplitude Vref).

[0044] 4 again, the generator simulation unit 110 generates a voltage command value V1* for the power converter 20 by simulating the characteristics of a synchronous generator based on the AC voltage Vsys and the AC current Isys in the power system 30. Specifically, the generator simulation unit 110 includes a subtractor 111, an integrator 112, an adder 113, an integrator 114, and a voltage command generation unit 115.

[0045] The subtractor 111 outputs the difference ΔP (=Pref−P) between the active power P and the active power command value Pref to the integrator 112. The active power command value Pref is a target value of the active power P, and is determined by a system operator.

[0046] The integrator 112 outputs the angular frequency deviation Δω by time-integrating the difference ΔP, which is the output value of the subtractor 111. This simulates the braking force of the synchronous generator in the control of the power converter 20. "M" of the integrator 112 is the inertia constant of the synchronous generator. The angular frequency deviation Δω corresponds to the difference between the angular frequency of the rotor in the virtual synchronous generator and the reference angular frequency ω0. The reference angular frequency ω0 is the angular frequency of the reference frequency of power in the power system 30 (for example, 50 Hz or 60 Hz).

[0047] The adder 113 adds the angular frequency deviation Δω and the reference angular frequency ω0 to output the angular frequency ω (=Δω+ω0). The integrator 114 calculates the phase θ by time-integrating the angular frequency ω. The voltage command generator 115 generates a voltage command value V1* based on the amplitude Vref and the phase θ.

[0048] The fault detection unit 120 detects a fault in the power system 30 based on the angular frequency deviation Δω. For example, when the angular frequency deviation Δω is equal to or greater than a set value, the fault detection unit 120 determines that a fault has occurred in the power system 30 (i.e., detects a system fault), and when the angular frequency deviation Δω is less than the set value, determines that no fault has occurred in the power system 30. The fault detection unit 120 outputs a signal Tr according to the detection result. For example, the value of the signal Tr indicates "1" when a system fault is detected, and indicates "0" when no system fault is detected.

[0049] However, the above detection method is merely an example, and other known detection methods may be used. For example, the fault detection unit 120 may detect a fault in the power system 30 based on the difference between the active power command value Pref and the active power P, or other signals in the generator simulation unit 110. The fault detection unit 120 may also detect a fault in the power system 30 based on the frequency fluctuation results of the AC voltage Vsys at the interconnection point 32.

[0050] The setting unit 130 sets a limit value for the current limiter 142. Specifically, the setting unit 130 includes a selector 131, a current calculator 132, and a subtractor 133.

[0051] The selector 131 outputs "Pmar" to the current calculation unit 132 when a system fault is not detected (i.e., when the value of the signal Tr is "0"), and outputs "0" to the current calculation unit 132 when a system fault is detected (i.e., when the value of the signal Tr is "1"). Pmar indicates the margin of active power output from the power converter 20 to the power system 30 (hereinafter also referred to as "power margin"). The power margin Pmar is a value that is determined in advance by the system operator.

[0052] When no grid fault is detected, the current calculation unit 132 calculates the current margin Imar required for the active power output of the power margin Pmar. Here, the upper limit value of the current capacity of the power converter 20 (i.e., the upper limit value of the positive polarity) is described as the "current capacity Ica". The subtractor 133 sets the subtracted value (i.e., Ica-Imar) obtained by subtracting the current margin Imar from the current capacity Ica (where Ica>0) of the power converter 20 to the upper limit value Imax indicating the upper limit value of the limit value of the current limiter 142.

[0053] On the other hand, when a grid fault is detected, the current calculation unit 132 outputs “0” to the subtractor 133. The subtractor 133 sets the current capacity Ica of the power converter 20 to the upper limit value Imax of the current limiter 142.

[0054] In addition, since the renewable energy power source serving as the DC circuit 40 cannot absorb active power, the setting unit 130 sets the lower limit value Imin indicating the lower limit value of the limit value of the current limiter 142 to zero.

[0055] As described above, when no fault is detected in the power system 30, the setting unit 130 sets the upper limit value Imax to a value obtained by subtracting the current margin Imar from the upper limit value of the current capacity (i.e., Ica), and sets the lower limit value Imin to "0." In this case, since the upper limit value Imax is smaller than the current capacity Ica, the current range R2 according to the limit value is smaller than the current range R1 according to the current capacity.

[0056] Furthermore, when a fault is detected in the power system 30, the setting unit 130 sets the upper limit value Imax to "Ica" and the lower limit value Imin to "0." In this case, the current capacity Ica and the upper limit value max are the same.

[0057] Fig. 6 is a flowchart showing an example of the processing of the fault detection unit and the setting unit. Referring to Fig. 6, the fault detection unit 120 judges whether or not a fault has been detected in the power system 30 (step S10). If a fault has been detected (YES in step S10), the setting unit 130 sets the current capacity Ica of the power converter 20 as the upper limit value Imax (step S12). In this case, the power margin Pmar is not taken into consideration. On the other hand, if no fault has been detected (NO in step S10), the setting unit 130 sets a value reflecting the power margin Pmar in the current capacity Ica (i.e., Ica-Imar) as the upper limit value Imax (step S14).

[0058] 4 again, the current command generating unit 140 generates a current command value I1* for the power converter 20 based on the voltage command value V1* generated by the generator simulation unit 110. Here, the relationship between the AC voltage Vsys at the interconnection point 32, the output voltage Vi of the power converter 20, the output current I of the power converter 20, and the leakage reactance X of the transformer 34 is expressed by the following equation (1).

[0059] I = (Vsys - Vi) / X ... (1) Therefore, the current command value I1* is calculated as "(Vsys-V1*) / X" using the formula (1).

[0060] The current limiter 142 limits the current command value I1* within a current range R2 to generate a current command value I2*. Specifically, the current limiter 142 outputs a value obtained by limiting the current command value I1* to a value equal to or greater than the lower limit value Imin and equal to or less than the upper limit value Imax as the current command value I2*. For example, when no grid fault is detected (i.e., when the lower limit value Imin is set to "0" and the upper limit value Imax is set to "Ica-Imar"), the current command value I2* is limited to a value equal to or greater than 0 and equal to or less than "Ica-Imar".

[0061] The voltage command generating unit 144 generates a voltage command value V2* for the power converter 20 based on the current command value I2*. Specifically, the voltage command generating unit 144 generates the voltage command value V2* (specifically, V2*=Vsys-(X×I2*)) by converting the current command value I2* using equation (1). The voltage command value V2* corresponds to a voltage command value having a phase θ and an amplitude V output from the command generating unit 100 in FIG. 1. Therefore, the signal generating unit 200 in FIG. 1 generates a control signal for the power converter 20 based on the voltage command value V2* generated by the command generating unit 100, and outputs the control signal to the power converter 20.

[0062] According to the above-described configuration of the command generating unit 100, the change over time of the active power output from the power converter 20 is as shown in FIG.

[0063] Fig. 7 is a diagram showing an example of a change over time in the active power output from the power converter according to the first embodiment. The horizontal axis of Fig. 7 represents time, and the vertical axis represents the output active power of power converter 20. The direction in which active power is output from power converter 20 to power system 30 is defined as a positive direction, and the direction in which active power is absorbed from power system 30 to power converter 20 is defined as a negative direction.

[0064] 7, before the occurrence of a fault in the power system 30, the power converter 20 outputs active power corresponding to the upper limit value in normal times (that is, active power corresponding to the current "Ica-Imar").

[0065] When a system fault occurs (for example, a generator in the power system 30 trips) and the system frequency drops, the power converter 20 increases the active power output to the power system 30 by Pmar in order to increase the system frequency, and outputs the active power corresponding to the upper limit value at the time of the fault (i.e., the active power corresponding to the current "Ica"). This makes it possible to impart a pseudo inertial force to the power system 30, thereby realizing stabilization of the system frequency.

[0066] On the other hand, when a system fault occurs (e.g., a load in the power system 30 drops) and the system frequency increases, the power converter 20 reduces the active power to the power system 30 in order to lower the system frequency, and outputs a lower limit value of active power (i.e., active power corresponding to a current of "0"). That is, the power converter 20 sets the active power output to zero. This allows the lower limit value of the active power output of the power converter 20 to be appropriately controlled.

[0067] <Modification> In the above-described first embodiment, an example in which the DC circuit 40 is configured with a renewable energy power source has been described, but in a modification of the first embodiment, an example in which the DC circuit 40 is configured with a power source (e.g., a power storage element) capable of transmitting and receiving power to and from the power converter 20 will be described. The power storage element differs from the renewable energy power source in that it is capable of supplying and absorbing active power. For example, the power storage element is a power storage device including, for example, an electric double layer capacitor or a storage battery such as a lithium ion battery.

[0068] In the following description, the DC circuit 40 is described as a power storage element, but the DC circuit 40 may be, for example, a DC power system including a DC transmission network or a DC terminal of another power conversion device. In the latter case, a BTB (Back To Back) system for connecting AC power systems having different rated frequencies is configured by linking two power converters.

[0069] Fig. 8 is a diagram illustrating an example of a configuration of a setting section according to a modification of embodiment 1. With reference to Fig. 8, setting section 130A has a configuration in which polarity inversion section 134 is added to setting section 130 in Fig. 4.

[0070] When no grid fault is detected, the subtractor 133 subtracts the current margin Imar from the current capacity Ica (where Ica>0) of the power converter 20, and sets the resulting value (i.e., Ica-Imar) as the upper limit value Imax of the current limiter 142. The subtractor 133 also outputs the subtracted value to the polarity reversal unit 134. The polarity reversal unit 134 sets the value obtained by reversing the polarity of the subtracted value (i.e., -Ica+Imar) as the lower limit value Imin of the current limiter 142.

[0071] When a grid fault is detected, the subtractor 133 sets the current capacity Ica of the power converter 20 to an upper limit value Imax of a current limiter 142. The subtractor 133 also outputs the current capacity Ica to the polarity inverter 134. The polarity inverter 134 sets a value obtained by inverting the polarity of the current capacity Ica (i.e., −Ica) to a lower limit value Imin of the current limiter 142.

[0072] As described above, when no system fault is detected, the setting unit 130A sets the value obtained by subtracting the current margin Imar from the upper limit value of the current capacity (i.e., Ica) as the upper limit value Imax, and sets the value obtained by adding the current margin Imar to the lower limit value of the current capacity (i.e., -Ica) as the lower limit value Imin.

[0073] On the other hand, when a grid fault is detected, the setting unit 130A sets the upper limit value of the current capacity (ie, Ica) as the upper limit value Imax, and sets the lower limit value of the current capacity (ie, −Ica) as the lower limit value Imin.

[0074] Fig. 9 is a diagram for explaining another example of the configuration of the setting unit according to the modification of embodiment 1. With reference to Fig. 9, setting unit 130B has a configuration in which selector 135, current calculation unit 136, subtractor 137, and polarity inversion unit 138 are added to setting unit 130 in Fig. 4.

[0075] The method for setting the upper limit value Imax of the current limiter 142 is similar to that described with reference to FIG.

[0076] The selector 135 outputs "Pmar2" to the current calculation unit 132 when a system fault is not detected (i.e., when the value of the signal Tr is "0"), and outputs "0" to the current calculation unit 132 when a system fault is detected (i.e., when the value of the signal Tr is "1"). Pmar2 indicates the margin of active power output from the power converter 20 to the DC circuit 40 (e.g., absorbed by the storage element). The power margin Pmar2 is a value that is determined in advance by the system operator. Typically, the power margin Pmar2 is a value different from the power margin Pmar of the active power output from the power converter 20 to the power system 30.

[0077] When no grid fault is detected, the current calculation unit 136 calculates a current margin Imar2 required for an active power output of the power margin Pmar2. The subtractor 137 outputs a subtraction value (i.e., Ica-Imar2) obtained by subtracting the current margin Imar2 from the current capacity Ica of the power converter 20 to the polarity reversal unit 138. The polarity reversal unit 138 sets a value obtained by inverting the polarity of the subtraction value (i.e., -Ica+Imar2) as the lower limit value Imin of the current limiter 142.

[0078] On the other hand, when a grid fault is detected, the current calculation unit 136 outputs “0” to the subtractor 137. The subtractor 137 outputs the current capacity Ica to the polarity inversion unit 138. The polarity inversion unit 138 sets the lower limit value Imin of the current limiter 142 to a value obtained by inverting the polarity of the current capacity Ica (i.e., −Ica).

[0079] As described above, when no system fault is detected, the setting unit 130B sets the value obtained by subtracting the current margin Imar from the upper limit value of the current capacity (i.e., Ica) as the upper limit value Imax, and sets the value obtained by adding the current margin Imar2 to the lower limit value of the current capacity (i.e., -Ica) as the lower limit value Imin.

[0080] On the other hand, when a grid fault is detected, the setting unit 130B sets the upper limit value of the current capacity (ie, Ica) as the upper limit value Imax, and sets the lower limit value of the current capacity (ie, −Ica) as the lower limit value Imin.

[0081] As described above, when no grid fault is detected, the upper limit value Imax is smaller than the upper limit value of the current capacity (i.e., Ica) and the lower limit value Imin is larger than the lower limit value of the current capacity (i.e., -Ica) according to the setting method of the setting units 130A and 130B. Therefore, the current range R2 according to the limit values ​​(i.e., the upper limit value Imax and the lower limit value Imin) is smaller than the current range R1 according to the current capacity of the power converter 20.

[0082] According to the configuration of the above modified example, the change over time of the active power output from the power converter 20 is as shown in FIG. 10 or FIG.

[0083] Fig. 10 is a diagram showing an example of a change over time in the active power output from the power converter according to the modification of the first embodiment. The horizontal axis of Fig. 10 is time, and the vertical axis is the output active power of the power converter 20. The direction in which active power is output from the power converter 20 to the power system 30 is defined as a positive direction, and the direction in which active power is absorbed by the power converter 20 from the power system 30 is defined as a negative direction. This also applies to Fig. 11 below. In the example of Fig. 10, the power converter 20 transmits active power to the power system 30 during normal operation.

[0084] Referring to FIG. 10, before the occurrence of a fault in the power system 30, the power converter 20 outputs active power corresponding to the upper limit value in normal times (that is, active power corresponding to the current "Ica-Imar").

[0085] When a system accident occurs and the system frequency drops, the power converter 20 increases the active power output to the power system 30 in order to increase the system frequency, and outputs the active power corresponding to the upper limit value at the time of the accident (i.e., the active power corresponding to the current "Ica"). On the other hand, when a system accident occurs and the system frequency increases, the power converter 20 reduces the active power to the power system 30 in order to lower the system frequency, and causes the storage element to absorb the active power corresponding to the lower limit value at the time of the accident (i.e., the active power corresponding to the current "-Ica").

[0086] Fig. 11 is a diagram showing another example of a change over time in the active power output from the power converter according to the modification of Embodiment 1. In the example of Fig. 11, the power converter 20 receives active power from the power system 30 during normal operation.

[0087] Referring to FIG. 11, before the occurrence of a fault in the power system 30, the power converter 20 absorbs active power corresponding to the lower limit value in normal times (that is, active power corresponding to the current "-Ica+Imar").

[0088] When a system accident occurs and the system frequency drops, the power converter 20 increases the active power output to the power system 30 in order to increase the system frequency, and outputs active power corresponding to the upper limit value during the accident (i.e., active power corresponding to the current "Ica"). On the other hand, when a system accident occurs and the system frequency increases, the power converter 20 causes the storage element to absorb the active power from the power system 30 (i.e., active power corresponding to the current "-Ica") in order to lower the system frequency.

[0089] As described above, according to the modified example, the power converter 20 outputs active power to the power grid 30 when the system frequency drops, and absorbs active power from the power grid 30 when the system frequency increases, thereby achieving stabilization of the system frequency.

[0090] <Advantages> According to the first embodiment, when the DC circuit 40 is configured with a power source that can only output active power but cannot absorb it (e.g., a renewable energy power source), during normal operation of the power conversion device 50, active power is supplied to the power system 30, and when an inertial force is required due to an accident or the like in the power system 30, an appropriate active power can be output to impart a pseudo inertial force.

[0091] Furthermore, when the DC circuit 40 is configured by a power source capable of both outputting and absorbing active power (for example, a power storage element, a DC transmission system, a DC terminal of another power converter, etc.), it is possible to ensure an active power margin for imparting an inertial force both when the power conversion device 50 is operating to transmit active power to the power system 30 during normal operation and when the power conversion device 50 is operating to receive active power from the power system 30. This allows the power conversion device 50 to supply active power to the power system 30 during normal operation, and to impart a pseudo inertial force by outputting or absorbing an appropriate active power when an inertial force is required due to an accident or the like in the power system 30.

[0092] Embodiment 2 In the first embodiment, a configuration has been described in which the active power margin is ensured by appropriately setting the limit value of the current limiter 142. In the second embodiment, a configuration will be described in which the generator simulator outputs a voltage command value V1* reflecting the active power margin.

[0093] Fig. 12 is a block diagram showing a configuration example of a command generating unit according to the second embodiment. With reference to Fig. 12, command generating unit 100A includes a generator simulator 110A, a fault detector 120, a current command generating unit 140, a current limiter 142, a voltage command generating unit 144, a coordinate converter 150, an AC power calculator 152, and a voltage amplitude generator 160. Detailed description of the same configuration as in Fig. 4 will not be repeated. Note that in Fig. 12, it is assumed that DC circuit 40 is composed of a renewable energy power source.

[0094] The generator simulation unit 110A includes a subtractor 111, an integrator 112, an adder 113, an integrator 114A, a voltage command generation unit 115, a phase calculation unit 116, and a limit setting unit 117. The functional configurations of the subtractor 111, the integrator 112, and the adder 113 are similar to the configurations in FIG.

[0095] The phase calculation unit 116 generates the phase θmarS based on the active power PmarS taking into account the active power margin (e.g., Pmar). For example, the active power PmarS is a value obtained by subtracting the power margin Pmar from the active power upper limit value (e.g., Pref). Here, the relationship between the active power PmarS, the AC voltage Vsys, the output voltage Vi of the power converter 20, the phase θmarS, and the leakage reactance X of the transformer 34 is expressed by the following equation (2).

[0096] PmarS={Vsys×Vi×sin(θmarS)} / X …(2) Therefore, the phase θmarS is calculated using equation (2).

[0097] When a system fault is detected (i.e., when the value of the signal Tr is "1"), the limit setting unit 117 sets the upper limit value of the integrator 114A to +∞ and the lower limit value to -∞. That is, the limit setting unit 117 does not limit the output value of the integrator 114A.

[0098] On the other hand, when a system fault is not detected (i.e., when the value of the signal Tr is "0"), the limit setting unit 117 sets both the upper limit value and the lower limit value to the phase θmarS. That is, the limit setting unit 117 limits the output value of the integrator 114A to "θmarS".

[0099] When the upper limit value and the lower limit value are not limited by the limit setting unit 117 (i.e., when a system fault is detected), the integrator 114A outputs the value obtained by integrating the angular frequency ω over time as the phase θ. On the other hand, when the upper limit value and the lower limit value are limited to "θmarS" by the limit setting unit 117 (i.e., when a system fault is not detected), the integrator 114A outputs "θmarS" as the phase θ regardless of the result of the time integration.

[0100] The voltage command generating unit 115 generates a voltage command value V1* based on the amplitude Vref and the phase θ. Specifically, when no grid fault is detected, the voltage command generating unit 115 sets the phase θmar calculated based on the active power PmarS as the phase θ of the voltage command value V1*. When a grid fault is detected, the voltage command generating unit 115 sets a value obtained by integrating the angular frequency ω over time as the phase θ of the voltage command value V1*.

[0101] The functional configurations of the current command generating unit 140, the current limiter 142, and the voltage command generating unit 144 are similar to those described in Fig. 4. However, the upper limit value Imax of the current limiter 142 is fixed to the current capacity Ica, and the lower limit value Imin is fixed to zero.

[0102] Fig. 13 is a block diagram showing a configuration example of a command generating unit according to a modification of the second embodiment. With reference to Fig. 13, a command generating unit 100B corresponds to a configuration in which the generator simulation unit 110A of the command generating unit 100A is replaced with a generator simulation unit 110B. Detailed description of the same configuration as in Fig. 12 will not be repeated. Note that in Fig. 13, it is assumed that the DC circuit 40 is composed of a renewable energy power source.

[0103] The generator simulation unit 110B includes subtractors 111A and 111B, an integrator 112, an adder 113, an integrator 114, a voltage command generation unit 115, and a selector 118. The functional configurations of the integrator 112, the adder 113, the integrator 114, and the voltage command generation unit 115 are similar to the functional configurations described in FIG.

[0104] The selector 118 outputs "Pmar" to the subtractor 111A when no system fault is detected (i.e., when the value of the signal Tr is "0"), and outputs "0" to the subtractor 111A when a fault is detected in the power system 30 (i.e., when the value of the signal Tr is "1").

[0105] When no system fault is detected (i.e., when the value of the signal Tr is “0”), the subtractor 111A outputs the difference ΔP1 between the active power command value Pref and the power margin Pmar (i.e., ΔP1=Pref−Pmar) to the subtractor 111B.

[0106] 14 is a diagram for explaining the relationship between the active power command value and the power margin. Referring to Fig. 14, the active power command value Pref corresponds to the active power upper limit value defined by the upper limit value of the positive polarity of the current capacity determined by the hardware performance of the power converter 20.

[0107] The active power PmarS corresponds to the upper limit of the active power in normal operation. For example, the active power PmarS corresponds to the active power corresponding to the current "Ica-Imar" described in the first embodiment. From this, it can be understood that the difference ΔP1 corresponds to the active power PmarS.

[0108] Referring again to FIG. 13, when a system fault is not detected, the subtractor 111B outputs the difference ΔP2 (i.e., ΔP2=PmarS-P) between the active power PmarS (i.e., the difference ΔP1) and the active power P to the integrator 112. The integrator 112 outputs the angular frequency deviation Δω by integrating the difference ΔP2 over time. The integrator 114 calculates the phase θ by integrating the angular frequency ω, which is the sum of the angular frequency deviation Δω and the reference angular frequency ω0 over time. The voltage command generation unit 115 generates a voltage command value V1* based on the amplitude Vref and the phase θ. In this way, the voltage command generation unit 115 sets the phase calculated based on the difference between the active power PmarS and the active power P as the phase θ of the voltage command value V1*.

[0109] The method of generating the phase θ when a system fault is detected is the same as that described with reference to FIG.

[0110] As described above, when no grid fault is detected, the generator simulator 110A generates the phase of the voltage command value V1* based on an active power (e.g., PmarS) that is smaller than the active power (e.g., active power command value Pref) calculated based on the current capacity of the power converter 20. This makes it possible to output the voltage command value V1* in which the active power margin is taken into consideration.

[0111] <Advantages> The second embodiment has the same advantages as the first embodiment.

[0112] Other embodiments. The configurations exemplified as the above-mentioned embodiments are examples of the configurations of the present disclosure, and may be combined with other known technologies, or may be modified, such as by omitting some parts, without departing from the scope of the present disclosure. In addition, the above-mentioned embodiments may be implemented by appropriately adopting the processes and configurations described in other embodiments.

[0113] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0114] 10 control device, 20 power converter, 30 power system, 32 interconnection point, 34 transformer, 40 DC circuit, 50 power conversion device, 70 input converter, 71 sample-and-hold circuit, 72 multiplexer, 73 A / D converter, 74 CPU, 75 RAM, 76 ROM, 77 input / output interface, 78 auxiliary storage device, 79 bus, 91 current detector, 93 voltage detector, 100, 100A, 100B command generator, 110, 110A, 110B generator simulation unit, 112, 114, 114A integrator, 115, 144 voltage command generator, 116 phase calculation unit, 117 limit setting unit, 118, 131, 135 selector, 120 fault detector, 130, 130A, 130B setting unit, 132, 136 Current calculation unit, 134, 138 polarity inversion unit, 140 current command generation unit, 142 current limiter, 150, 165, 167 coordinate conversion unit, 152 AC power calculation unit, 160 voltage amplitude generation unit, 161 positive sequence voltage calculation unit, 164 voltage adjustment unit, 200 signal generation unit, 202 three-phase voltage generation unit, 204 PWM control unit, 1000 power conversion system.

Claims

1. a power converter that performs power conversion between the DC circuit and the power grid; a control device for controlling the power converter, The control device a generator simulation unit that generates a first voltage command value for the power converter by simulating characteristics of a synchronous generator based on an AC voltage and an AC current in the power system; a current command generating unit that generates a first current command value for the power converter based on the first voltage command value generated by the generator simulation unit; a setting unit that sets the limit value so that a second current range according to the limit value is smaller than a first current range according to the current capacity of the power converter when no fault is detected in the power system; a limiter that limits the first current command value to within the second current range to generate a second current command value; a voltage command generating unit that generates a second voltage command value based on the second current command value; a signal generating unit that generates a control signal for the power converter based on the second voltage command value.

2. the DC circuit includes a power supply capable of supplying and receiving power to and from the power converter, 2. The power conversion device according to claim 1, wherein, when no fault is detected in the power system, the setting unit sets a value obtained by subtracting a margin from an upper limit value of the current capacity as the upper limit value of the limit value, and sets a value obtained by adding the margin to a lower limit value of the current capacity as the lower limit value of the limit value.

3. the DC circuit includes a power supply capable of supplying and receiving power to and from the power converter, 3. The power conversion device according to claim 2, wherein, when no fault is detected in the power system, the setting unit sets a value obtained by subtracting a first margin from an upper limit value of the current capacity as the upper limit value of the limit value, and sets a value obtained by adding a second margin to a lower limit value of the current capacity as the lower limit value of the limit value.

4. 4. The power conversion device according to claim 2, wherein, when a fault is detected in the power system, the setting unit sets an upper limit value of the current capacity as an upper limit value of the limit value, and sets a lower limit value of the current capacity as a lower limit value of the limit value.

5. the DC circuit includes a renewable energy power source that supplies power to the power converter; 2. The power conversion device according to claim 1, wherein, when no fault is detected in the power system, the setting unit sets a value obtained by subtracting a margin from the upper limit value of the current capacity as the upper limit value of the limit value, and sets the lower limit value of the limit value to zero.

6. the generator simulation unit calculates a first angular frequency by integrating, with respect to time, a difference between an active power calculated based on the AC voltage and the AC current and a target value of the active power; 4. The power conversion device according to claim 1, wherein the control device further includes a fault detection unit that detects a fault in the power grid based on the first angular frequency.

7. a power converter that performs power conversion between the DC circuit and the power grid; a control device for controlling the power converter, The control device a generator simulation unit that generates a first voltage command value for the power converter by simulating characteristics of a synchronous generator based on an AC voltage and an AC current in the power system; a current command generating unit that generates a first current command value for the power converter based on the first voltage command value generated by the generator simulation unit; a limiter that limits the first current command value to a current range according to a current capacity of the power converter and generates a second current command value; a voltage command generating unit that generates a second voltage command value based on the second current command value; a signal generating unit that generates a control signal for the power converter based on the second voltage command value, When no fault is detected in the power system, the generator simulation unit generates the phase of the first voltage command value based on a second active power that is smaller than a first active power calculated based on a current capacity of the power converter.

8. 8. The power conversion device according to claim 7, wherein, when no fault is detected in the power system, the generator simulator sets a phase calculated based on the second active power as a phase of the first voltage command value.

9. When no fault is detected in the power grid, the generator simulator calculating a difference between the first active power and a specified active power as the second active power; calculating a first angular frequency by time-integrating a difference between an active power calculated based on the AC voltage and the AC current and the second active power; calculating a first phase by integrating the first angular frequency over time; The power conversion device according to claim 7 , wherein the first phase is set as a phase of the first voltage command value.

10. When a fault is detected in the power system, the generator simulator calculating a second angular frequency by time-integrating a difference between an active power calculated based on the AC voltage and the AC current and the first active power; calculating a second phase by integrating the second angular frequency with respect to time; The power conversion device according to any one of claims 7 to 9, wherein the second phase is set as a phase of the first voltage command value.

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