JP7459405B1 - Power Conversion Equipment - Google Patents

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, sets a limit value such 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 (20) when no fault is detected in the power system (30), 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

The present disclosure relates to a power conversion device.

In recent years, many distributed power sources using renewable energy such as solar power generation facilities have been introduced into power systems. Along with this, an increase in the rate of change of frequency (RoCoF), which indicates the magnitude of frequency change per unit time, has become a problem in the event of an accident such as a generator falling off. A frequency stabilization device stabilizes a power system by controlling active power output from a power source such as a solar power generation panel and a storage battery using a power converter and applying a pseudo inertial force to the power system.

For example, Japanese Unexamined Patent Publication No. 2019-176584 (Patent Document 1) discloses a control device for a distributed power source. This control device sets virtual inertia for a power conversion device that connects distributed power sources to the power grid, and calculates the virtual inertia value based on the specifications and operating status of the distributed power sources. The virtual inertia is set in the power conversion device based on either the virtual inertia value given by the power converter or the requested inertia value requested by the system operator.

Japanese Patent Application Publication No. 2019-176584

The power conversion device as described above is operated so that it can output active power up to the upper limit during normal operation. However, in this case, the power converter does not have the capacity to increase the active power output to the power grid in the event of a grid failure (for example, when a generator falls off). Therefore, the power converter cannot apply inertial force to the power grid and cannot stabilize the grid frequency.

An object of an aspect of the present disclosure is to provide a power conversion device that can provide inertial force in the event of an accident in the power system while accommodating active power to the power system during normal times.

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 the synchronous generator based on AC voltage and AC current in the power system, and a generator simulation unit that generates a first voltage command value for the power converter. a current command generation unit that generates a first current command value for the power converter based on the first voltage command value that has been determined; a setting unit that sets a limit value such that a second current range according to the limit value is smaller than the range; a limiter that limits the first current command value to within a second current range to generate a second current command value; It includes a voltage command generation section that generates a second voltage command value based on the second current command value, and a signal generation section that generates a control signal for the power converter based on the second voltage command value.

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 the synchronous generator based on AC voltage and AC current in the power system, and a generator simulation unit that generates a first voltage command value for the power converter. a current command generation unit that generates a first current command value for the power converter based on the first voltage command value that has been determined; a limiter that generates a current command value; a voltage command generator that generates a second voltage command value based on the second current command value; and a voltage command generator that generates a control signal for the power converter based on the second voltage command value. and a signal generation section. If no fault is detected in the power system, the generator simulation unit calculates the first voltage command value based on the second active power that is smaller than the first active power calculated based on the current capacity of the power converter. Generate phase.

According to the power conversion device according to the present disclosure, it is possible to provide inertia force in the event of an accident in the power system while accommodating active power to the power system during normal times.

FIG. 1 is a diagram for explaining an example of the overall configuration of a power conversion system. FIG. 3 is a diagram showing an example of a temporal change in active power output from a power converter. FIG. 2 is a diagram illustrating an example of a hardware configuration of a control device. FIG. 3 is a block diagram showing an example of a functional configuration of a command generation section according to the first embodiment. FIG. 2 is a block diagram showing a configuration example of a voltage amplitude generation section. 5 is a flowchart illustrating an example of processing by an accident detection section and a setting section. FIG. 4 is a diagram showing an example of a time change in active power output from the power converter according to the first embodiment. 7 is a diagram for explaining an example of the configuration of a setting section according to a modification of the first embodiment. FIG. FIG. 13 is a diagram for illustrating another example of the configuration of the setting unit according to the modification of the first embodiment. 7 is a diagram showing an example of a temporal change in active power output from a power converter according to a modification of the first embodiment. FIG. FIG. 11 is a diagram showing another example of a time change in active power output from the power converter according to the modification of the first embodiment. 7 is a block diagram showing a configuration example of a command generation section according to a second embodiment. FIG. 7 is a block diagram showing a configuration example of a command generation section according to a modification of the second embodiment. FIG. FIG. 3 is a diagram for explaining the relationship between an active power command value and a power margin.

The present embodiment will be described below with reference to the drawings. In the following description, the same parts are given the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

Embodiment 1.
<Overall configuration>
FIG. 1 is a diagram for explaining an example of the overall configuration of a power conversion system. 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. Power conversion device 50 includes a control device 10 and a power converter 20.

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. .

Power converter 20 is, for example, a self-commutated converter such as a two-level converter, a three-level converter, or a modular multilevel converter. A self-excited converter is a converter using a self-extinguishing element, and the magnitude and phase of the output voltage can be freely controlled. Moreover, the self-commutated converter can exchange power between AC and DC even without a power source from the 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 power transmission system, a DC terminal of another power converter, or the like.

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

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

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 an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or a combination of these.

The command generation unit 100 mainly has a function of simulating the characteristics of a synchronous generator, and calculates the phase θ of the voltage output from the power converter 20 (that is, the phase of the voltage command value) and the voltage The amplitude (that is, the amplitude of the voltage command value) V is generated. The phase θ is a reference phase used to control the power converter 20. Details of the command generation unit 100 will be described later.

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.

The three-phase voltage generation unit 202 generates three-phase sinusoidal voltages Vu*, Vv*, and Vw* by two-phase/three-phase conversion based on the phase θ and the amplitude V.

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. PWM control section 204 outputs the control signal to power converter 20. Typically, the control signal is a gate control signal for controlling on and off of each switching element included in power converter 20.

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 hardware performance during normal times when no accidents occur in the power system 30, a problem as shown in FIG. 2 may occur. occurs.

FIG. 2 is a diagram showing an example of a temporal change in active power output from a power converter. The horizontal axis in FIG. 2 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 input (ie, absorbed) from the power system 30 to the power converter 20 is defined as a negative direction. Furthermore, in the example of FIG. 2, it is assumed that the DC circuit 40 is configured with a renewable energy power source that supplies power to the power converter 20.

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

Referring to FIG. 2, power converter 20 continues to output active power at the upper limit value during normal times. If a grid fault occurs (for example, a generator in power system 30 falls off) and the system frequency decreases, power converter 20 attempts to increase the active power output to power system 30 in order to increase the system frequency. However, the effective power cannot be increased due to limitations in hardware performance. That is, it is not possible to apply a pseudo inertial force to the power system 30, and the system frequency cannot be maintained at a specified value. Therefore, it is preferable that the power conversion device 50 is configured to be able to increase the active power output when the system frequency decreases.

Further, when a grid fault occurs (for example, a load in the power system 30 falls off) and the grid frequency increases, the power converter 20 reduces the active power output to the power grid 30 in order to lower the grid frequency. . However, in the example of FIG. 2, the renewable energy power source as the DC circuit 40 cannot absorb active power. Therefore, it is also necessary to appropriately set the lower limit value of the active power output by the power converter 50.

The power conversion device 50 according to this embodiment is configured to increase the effective power output to the power grid 30 and apply inertial force when the grid frequency drops. The specific configuration will be described later.

<Hardware configuration>
FIG. 3 is a diagram showing an example of the hardware configuration of the control device. FIG. 3 shows an example in which the control device 10 is configured by a computer.

Referring to FIG. 3, control device 10 includes one or more input converters 70, one or more sample and hold circuits 71, multiplexer 72, A/D converter 73, and one or more CPU ( A RAM (Random Access Memory) 75, a ROM (Read Only Memory) 76, one or more input/output interfaces 77, and an auxiliary storage device 78. Control device 10 includes a bus 79 that interconnects components.

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

A sample hold circuit 71 is provided for each input converter 70. The sample and hold circuit 71 samples and holds a signal representing the amount of electricity received from the corresponding input converter 70 at a specified sampling frequency.

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

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

The input/output interface 77 is an interface circuit for communication between the CPU 74 and external devices.

Note that, unlike the example of FIG. 3, it is also possible to configure at least a part of the control device 10 using circuits such as FPGA and ASIC.

<Command generation unit>
FIG. 4 is a block diagram showing an example of the functional configuration of the command generation section according to the first embodiment. Referring to FIG. 4, command generation section 100 includes generator simulation section 110, accident detection section 120, setting section 130, current command generation section 140, current limiter 142, voltage command generation section 144, It includes a coordinate conversion section 150, an AC power calculation section 152, and a voltage amplitude generation section 160. Note that in FIG. 4, it is assumed that the DC circuit 40 is constituted by a renewable energy power source.

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

The AC power calculation unit 152 calculates the 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.

The voltage amplitude generating unit 160 generates the 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.

Figure 5 is a block diagram showing an example of the configuration of the voltage amplitude generation unit. Referring to Figure 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.

Positive-sequence voltage calculating section 161 calculates positive-sequence voltage Vpos based on d-axis voltage Vd and q-axis voltage Vq. Subtractor 162 calculates deviation ΔQ (=Qref−Q) between reactive power command value Qref and reactive power Q. The subtracter 162 calculates a deviation ΔVpos (=Vacref−Vpos) between the system voltage command value Vacref and the positive-sequence voltage Vpos.

Voltage adjustment section 164 selects either automatic reactive power adjustment mode or automatic voltage adjustment mode, and generates 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 the voltage amplitude adjustment amount ΔVacref through feedback control to make 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 the voltage amplitude adjustment amount ΔVacref through feedback control to make the deviation ΔVpos less than or equal to a specified value (for example, 0). The voltage regulator 164 includes a PI controller, a first-order delay element, and the like.

The coordinate conversion unit 165 converts the d-axis component (i.e., the specified d-axis voltage command value Vdx) and the q-axis component (i.e., the specified q-axis voltage command value Vqx) of the specified voltage command value into an amplitude |Vx| and a phase φv. The specified d-axis voltage command value Vdx and the specified 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 sum 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).

Referring again to FIG. 4, generator simulating section 110 simulates the characteristics of the synchronous generator based on AC voltage Vsys and AC current Isys in power system 30, thereby determining voltage command value V1 for power converter 20. Generate *. Specifically, generator simulator 110 includes a subtracter 111 , an integrator 112 , an adder 113 , an integrator 114 , and a voltage command generator 115 .

The subtracter 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 the system operator.

The integrator 112 integrates the difference ΔP, which is the output value of the subtracter 111, over time and outputs the angular frequency deviation Δω. This simulates the braking force of the synchronous generator in controlling the power converter 20. "M" of 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 and the reference angular frequency ω0 in the virtual synchronous generator. The reference angular frequency ω0 is the angular frequency of the reference frequency (for example, 50 Hz or 60 Hz) of power in the power system 30.

The adder 113 adds the angular frequency deviation Δω and the reference angular frequency ω0 and outputs the angular frequency ω (=Δω+ω0). The integrator 114 calculates the phase θ by time-integrating the angular frequency ω. Voltage command generation section 115 generates voltage command value V1* based on amplitude Vref and phase θ.

The accident detection unit 120 detects an accident in the power system 30 based on the angular frequency deviation Δω. For example, the accident detection unit 120 determines that an accident has occurred in the power system 30 (that is, detects a system fault) when the angular frequency deviation Δω is greater than or equal to the set value, and the angular frequency deviation Δω is less than the set value. If so, it is determined that no accident has occurred in the power system 30. Accident detection section 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.

However, the above detection method is an example, and other known detection methods may be used. For example, the accident detection unit 120 may detect an accident in the power system 30 based on the difference between the active power command value Pref and the active power P or other signals within the generator simulator 110. Further, the accident detection unit 120 may detect an accident in the power system 30 based on the frequency fluctuation result of the AC voltage Vsys at the interconnection point 32.

The setting unit 130 sets the limit value of the current limiter 142. Specifically, the setting section 130 includes a selector 131, a current calculation section 132, and a subtracter 133.

The selector 131 outputs "Pmar" to the current calculation unit 132 when a system fault is not detected (that is, when the value of the signal Tr is "0"), and when a system fault is detected (that is, when the value of the signal Tr is "0"). , when the value of the signal Tr is “1”), “0” is output to the current calculation unit 132. Pmar indicates a 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 determined in advance by the system operator.

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 as the upper limit value Imax indicating the upper limit value of the limit value of the current limiter 142.

On the other hand, the current calculation unit 132 outputs "0" to the subtracter 133 when a system fault is detected. The subtracter 133 sets the current capacity Ica of the power converter 20 to the upper limit value Imax of the current limiter 142.

Note that since the renewable energy power source 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 current limiter 142 to zero.

As described above, when no fault is detected in the power system 30, the setting unit 130 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 lower limit value Imax. Set the 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.

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

FIG. 6 is a flowchart illustrating an example of processing by the accident detection section and the setting section. Referring to FIG. 6, accident detection unit 120 determines whether an accident has been detected in power system 30 (step S10). If an accident is detected (YES in step S10), setting unit 130 sets current capacity Ica of power converter 20 as upper limit value Imax (step S12). In this case, the power margin Pmar is not considered. On the other hand, if no accident has been detected (NO in step S10), the setting unit 130 sets a value that reflects the power margin Pmar on the current capacity Ica (i.e., Ica - Imar) as the upper limit value Imax (step S14). ).

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).

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

Current limiter 142 limits current command value I1* to within current range R2 to generate current command value I2*. Specifically, the current limiter 142 outputs a value obtained by limiting the current command value I1* to be greater than or equal to the lower limit value Imin and less than or equal to the upper limit value Imax as the current command value I2*. For example, when a system fault is not detected (that is, 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 0 or more and " Ica-Imar” or less.

Voltage command generation unit 144 generates voltage command value V2* of power converter 20 based on current command value I2*. Specifically, the voltage command generation unit 144 converts the current command value I2* using equation (1) to obtain the voltage command value V2* (specifically, V2*=Vsys−(X×I2 *)) is generated. Note that the voltage command value V2* corresponds to a voltage command value having a phase θ and an amplitude V output from the command generation unit 100 in FIG. Therefore, the signal generation 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 generation unit 100, and outputs the control signal to the power converter 20.

According to the above-mentioned configuration of the command generating unit 100, the change over time in the active power output from the power converter 20 is shown in Figure 7.

FIG. 7 is a diagram showing an example of a temporal change in active power output from the power converter according to the first embodiment. The horizontal axis in FIG. 7 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 from the power system 30 into the power converter 20 is defined as a negative direction.

Referring to FIG. 7, before the occurrence of an accident 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"). are doing.

When a system fault occurs (for example, a generator in the power system 30 falls off) and the system frequency decreases, the power converter 20 outputs active power to the power system 30 to increase the system frequency. It increases by Pmar and outputs the active power corresponding to the upper limit value at the time of the accident (that is, the active power corresponding to the current "Ica"). Thereby, pseudo-inertial force can be applied to the power system 30, and stabilization of the system frequency can be realized.

On the other hand, if a grid fault occurs (for example, a load in the power system 30 is dropped) and the grid frequency increases, the power converter 20 reduces the active power to the power grid 30 in order to lower the grid frequency. , outputs the active power of the lower limit value (that is, the active power corresponding to the current "0"). That is, the power converter 20 makes the active power output zero. Thereby, the lower limit value of the active power output of the power converter 20 is also appropriately controlled.

<Modified example>
In the first embodiment described above, an example in which the DC circuit 40 is configured with a renewable energy power source has been described. However, in a modification of the first embodiment, the DC circuit 40 exchanges power between the An example will be described in which the power source is configured of a power source (for example, a power storage element) that can exchange power. Energy storage elements differ from renewable energy sources in that they are capable of supplying and absorbing active power. For example, the power storage element is a power storage device including an electric double layer capacitor or a storage battery such as a lithium ion battery.

In addition, in the following description, a case will be explained in which the DC circuit 40 is a power storage element, but the DC circuit 40 may be, for example, a DC power system including a DC power grid or the like, or a DC terminal of another power conversion device. Good too. In the latter case, a BTB (Back To Back) system for connecting AC power systems with different rated frequencies etc. is configured by connecting two power converters.

FIG. 8 is a diagram for explaining an example of the configuration of a setting section according to a modification of the first embodiment. Referring to FIG. 8, a setting section 130A has a configuration in which a polarity reversing section 134 is added to the setting section 130 of FIG.

If a grid fault has not been detected, the subtracter 133 subtracts the current margin Imar from the current capacity Ica (Ica>0) of the power converter 20 and calculates the subtracted value (i.e., Ica - Imar) of the current limiter 142. Set the upper limit value Imax. Further, the subtracter 133 outputs the subtracted value to the polarity inverter 134. The polarity inverter 134 sets the value obtained by inverting the polarity of the subtraction value (ie, -Ica+Imar) to the lower limit value Imin of the current limiter 142.

When a system fault is detected, the subtracter 133 sets the current capacity Ica of the power converter 20 to the upper limit value Imax of the current limiter 142. Further, the subtracter 133 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 (ie, -Ica) as the lower limit value Imin of the current limiter 142.

From the 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.

On the other hand, when a system fault is detected, the setting unit 130A sets the upper limit value of the current capacity (i.e., Ica) as the upper limit value Imax, and sets the lower limit value of the current capacity (i.e., -Ica) as the lower limit value Imin. Set as .

Figure 9 is a diagram for explaining another example of the configuration of the setting unit according to the modified example of embodiment 1. Referring to Figure 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 of Figure 4.

The setting method of the upper limit value Imax of the current limiter 142 is the same as that described in FIG. 4 or FIG. 8.

The selector 135 outputs "Pmar2" to the current calculation unit 132 when a system fault is not detected (that is, when the value of the signal Tr is "0"), and when a system fault is detected (that is, when the value of the signal Tr is "0"). , when the value of the signal Tr is “1”), “0” is output to the current calculation unit 132. Pmar2 indicates a margin of active power output from the power converter 20 to the DC circuit 40 (for example, absorbed by the power storage element). The power margin Pmar2 is a value predetermined by the system operator. Typically, the power margin Pmar2 is a value different from the power margin Pmar of active power output from the power converter 20 to the power system 30.

The current calculation unit 136 calculates a current margin Imar2 necessary for outputting active power with a power margin Pmar2 when a system fault is not detected. The subtracter 137 subtracts the current margin Imar2 from the current capacity Ica of the power converter 20 and outputs the subtracted value (ie, Ica−Imar2) to the polarity inverter 138. The polarity inverter 138 sets the value obtained by inverting the polarity of the subtraction value (ie, -Ica+Imar2) as the lower limit value Imin of the current limiter 142.

On the other hand, when a system 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 value obtained by inverting the polarity of the current capacity Ica (i.e., -Ica) as the lower limit value Imin of the current limiter 142.

From the above, when a system fault is not 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 lower limit value of the current capacity ( That is, the value obtained by adding the current margin Imar2 to -Ica) is set as the lower limit value Imin.

On the other hand, when a system fault is detected, the setting unit 130B sets the upper limit value of the current capacity (i.e., Ica) as the upper limit value Imax, and sets the lower limit value of the current capacity (i.e., -Ica) as the lower limit value Imin. Set as .

As described above, when a system fault is not detected, according to the setting method of the setting units 130A and 130B, the upper limit value Imax is smaller than the upper limit value of current capacity (i.e., Ica), and the lower limit value Imin is smaller than the current capacity limit value Imax. Greater than the lower limit of capacity (ie, -Ica). Therefore, the current range R2 according to the limit value (that is, 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.

According to the configuration of the above-described modification, the time change in the active power output from the power converter 20 is shown as shown in FIG. 10 or 11.

FIG. 10 is a diagram illustrating an example of a temporal change in active power output from a power converter according to a modification of the first embodiment. The horizontal axis in 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 from the power system 30 into the power converter 20 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 grid 30 during normal operation.

Referring to Figure 10, before an accident occurs in the power system 30, the power converter 20 outputs active power corresponding to the upper limit value under normal conditions (i.e., active power corresponding to the current "Ica-Imar").

When a grid fault occurs and the grid frequency drops, the power converter 20 increases the active power output to the power grid 30 in order to increase the grid frequency, and increases the effective power corresponding to the upper limit value at the time of the fault. Output power (ie, active power corresponding to current “Ica”). On the other hand, when a grid fault occurs and the grid frequency increases, the power converter 20 reduces the active power to the power grid 30 in order to lower the grid frequency, and the active power corresponding to the lower limit value at the time of the fault (i.e. , active power corresponding to the current "-Ica") is absorbed by the power storage element.

FIG. 11 is a diagram illustrating another example of the temporal change in the active power output from the power converter according to the modification of the first embodiment. In the example of FIG. 11, the power converter 20 receives active power from the power grid 30 during normal operation.

Referring to FIG. 11, before an accident occurs in power system 30, power converter 20 absorbs active power corresponding to the lower limit value in normal times (that is, active power corresponding to current "-Ica+Imar"). ing.

When a grid fault occurs and the grid frequency drops, the power converter 20 increases the active power output to the power grid 30 in order to increase the grid frequency, and increases the effective power corresponding to the upper limit at the time of the fault. Output power (ie, active power corresponding to current “Ica”). On the other hand, when a grid fault occurs and the grid frequency increases, the power converter 20 converts the active power from the power grid 30 (that is, the active power corresponding to the current "-Ica") in order to lower the grid frequency. It is absorbed by the electricity storage element.

From the above, according to the modified example, the power converter 20 outputs active power to the power grid 30 when the grid frequency decreases, and outputs active power from the power grid 30 when the grid frequency increases. By absorbing it, it is possible to stabilize the system frequency.

<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 (for example, a renewable energy power source), the power that is effective for the power system 30 during normal operation of the power converter 50 is While accommodating power, when inertia is required due to an accident in the power system 30, pseudo-inertia can be provided by outputting appropriate active power.

In addition, when the DC circuit 40 is configured with a power source that can both output and absorb active power (for example, a power storage element, a DC transmission system, a DC terminal of another power converter, etc.), the active power cannot be used during normal operation. An active power margin for imparting inertial force can be ensured both when operating to transmit power to the power grid 30 and when operating to receive active power from the power grid 30. As a result, during normal operation of the power conversion device 50, active power is accommodated to the power system 30, and when inertia force is required in the event of an accident in the power system 30, appropriate active power can be output or absorbed. A pseudo inertial force can be applied.

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 simulation unit outputs a voltage command value V1* that reflects the active power margin.

FIG. 12 is a block diagram illustrating a configuration example of a command generation section according to the second embodiment. Referring to FIG. 12, the command generation section 100A includes a generator simulation section 110A, an accident detection section 120, a current command generation section 140, a current limiter 142, a voltage command generation section 144, and a coordinate conversion section 150. , an AC power calculation section 152, and a voltage amplitude generation section 160. Detailed description of the configuration similar to that in FIG. 4 will not be repeated. Note that in FIG. 12, it is assumed that the DC circuit 40 is constituted by a renewable energy power source.

The generator simulation section 110A includes a subtracter 111, an integrator 112, an adder 113, an integrator 114A, a voltage command generation section 115, a phase calculation section 116, and a limit setting section 117. The functional configurations of subtracter 111, integrator 112, and adder 113 are similar to those in FIG. 4.

The phase calculation unit 116 generates the phase θmarS based on the active power PmarS in consideration of the active power margin (for example, Pmar). For example, the active power PmarS is a value obtained by subtracting the power margin Pmar from the active power upper limit value (for example, Pref). Here, the relationship among 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).

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

When a system fault is detected (that is, 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 -∞. Set to . That is, limit setting section 117 does not limit the output value of integrator 114A.

On the other hand, when a system fault is not detected (that is, 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".

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 time-integrated value of the angular frequency ω 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.

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 the time-integrated value of the angular frequency ω as the phase θ of the voltage command value V1*.

The functional configurations of current command generation section 140, current limiter 142, and voltage command generation section 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.

FIG. 13 is a block diagram showing a configuration example of a command generation section according to a modification of the second embodiment. Referring to FIG. 13, command generating section 100B corresponds to a configuration in which generator simulating section 110A of command generating section 100A is replaced with generator simulating section 110B. Detailed description of the configuration similar to that in FIG. 12 will not be repeated. Note that in FIG. 13, it is assumed that the DC circuit 40 is constituted by a renewable energy power source.

Generator simulation section 110B includes subtracters 111A and 111B, an integrator 112, an adder 113, an integrator 114, a voltage command generation section 115, and a selector 118. The functional configurations of the integrator 112, the adder 113, the integrator 114, and the voltage command generation section 115 are similar to the functional configuration described in FIG. 4.

The selector 118 outputs "Pmar" to the subtractor 111A when a system fault is not detected (that is, when the value of the signal Tr is "0"), and when a fault is detected in the power system 30. (That is, when the value of the signal Tr is "1"), "0" is output to the subtracter 111A.

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

FIG. 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 from the upper limit value of the positive polarity of the current capacity determined by the hardware performance of the power converter 20.

The active power PmarS corresponds to the upper limit value of the active power during normal times. 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 is understood that the difference ΔP1 corresponds to the active power PmarS.

Referring again to FIG. 13, if no grid fault is detected, the subtracter 111B calculates the difference ΔP2 between the active power PmarS (that is, the difference ΔP1) and the active power P (that is, ΔP2=PmarS−P). Output to integrator 112. The integrator 112 outputs the angular frequency deviation Δω by time-integrating the difference ΔP2. The integrator 114 calculates the phase θ by time-integrating the angular frequency ω, which is the sum of the angular frequency deviation Δω and the reference angular frequency ω0. Voltage command generation section 115 generates voltage command value V1* based on amplitude Vref and 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*.

Note that the method for generating the phase θ when a system fault is detected is the same as that described with reference to FIG. 12.

As described above, when a system fault is not detected, the generator simulator 110A generates an active power that is smaller than the active power (for example, the active power command value Pref) calculated based on the current capacity of the power converter 20. (for example, PmarS), the phase of the voltage command value V1* is generated. Thereby, it is possible to output the voltage command value V1* in which the active power margin is taken into account.

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

Other embodiments.
The configuration exemplified as the embodiment described above is an example of the configuration of the present disclosure, and it is possible to combine it with another known technology, or omit some parts without departing from the gist of the present disclosure. , it is also possible to change the configuration. Further, in the embodiment described above, the processes and configurations described in other embodiments may be appropriately adopted and implemented.

The embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is indicated by the claims rather than the above description, and it is intended that all changes within the meaning and range equivalent to the claims are included.

10 control device, 20 power converter, 30 power system, 32 interconnection point, 34 transformer, 40 DC circuit, 50 power converter, 70 input converter, 71 sample 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 generation unit, 110, 110A, 110B generator simulation Section, 112, 114, 114A Integrator, 115, 144 Voltage command generation section, 116 Phase calculation section, 117 Limit setting section, 118, 131, 135 Selector, 120 Accident detection section, 130, 130A, 130B Setting section, 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 section, 200 signal generation section, 202 three-phase voltage generation section, 204 PWM control section, 1000 power conversion system.

Claims (10)

A power converter that converts power between a DC circuit and a power system;
and a control device that controls the power converter,
The control device includes:
a generator simulator that generates a first voltage command value for the power converter by simulating characteristics of a synchronous generator based on alternating current voltage and alternating 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 the limit value so that, when no fault is detected in the power system, 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;
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 generation unit that generates a second voltage command value based on the second current command value;
A power converter device comprising: a signal generation unit that generates a control signal for the power converter based on the second voltage command value. The DC circuit includes a power source that can transfer power to and from the power converter,
If no fault has been 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, and sets the margin to the lower limit value of the current capacity. The power conversion device according to claim 1, wherein the added value is set as the lower limit value of the limit value. the DC circuit includes a power source capable of transmitting 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 the 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 the lower limit value of the current capacity as the lower limit value of the limit value. The power conversion device according to claim 2 or 3, wherein, when an accident is detected in the power system, the setting unit sets 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 current capacity as the lower limit value of the limit value. The DC circuit includes a renewable energy power source that supplies power to the power converter,
If no accident has been 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, and sets the lower limit value to zero. The power conversion device according to claim 1. The generator simulator calculates a first angular frequency by time-integrating the difference between the active power calculated based on the AC voltage and the AC current and the target value of the active power,
The power conversion device according to any one of claims 1 to 3 , wherein the control device further includes an accident detection unit that detects an accident in the power system based on the first angular frequency. A power converter that converts power between a DC circuit and a power system;
and a control device that controls the power converter,
The control device includes:
a generator simulator that generates a first voltage command value for the power converter by simulating characteristics of a synchronous generator based on alternating current voltage and alternating 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;
a signal generation unit that generates a control signal for the power converter based on the second voltage command value,
When an accident is not detected in the power system, the generator simulator calculates the first active power based on a second active power that is smaller than the first active power calculated based on the current capacity of the power converter. A power conversion device that generates the phase of the voltage command value. According to claim 7, when no accident 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. power converter. When no accident is detected in the power system, the generator simulation unit
Calculating the difference between the first active power and the specified active power as the second active power,
calculating a first angular frequency by time-integrating the difference between the active power calculated based on the alternating voltage and the alternating current and the second active power;
calculating a first phase by time-integrating the first angular frequency;
The power conversion device according to claim 7, wherein the first phase is set as a phase of the first voltage command value. When an accident is detected in the power system, the generator simulation unit
calculating a second angular frequency by time-integrating the difference between the active power calculated based on the alternating voltage and the alternating current and the first active power;
calculating a second phase by time-integrating the second angular frequency;
The power conversion device according to claim 7, wherein the second phase is set as the phase of the first voltage command value.

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