JP2021141704A - Control system of power converter - Google Patents

Abstract

To provide a control system of a power converter in which the control system can perform voltage-control-type virtual synchronous generator control in normal operation, and can suppress overcurrent by current control in output overcurrent generation.SOLUTION: In the power converter which has a power converter 2 in which the virtual synchronous generator control is performed and is linked with an electric power system 5, a voltage control system and a current control system configured in an inner loop of the voltage control system are provided in a PCS output voltage control part 18, the PCS output voltage control part is allowed to operate as the voltage control system and the current control system according to a virtual synchronous generator model 16 which has an output angular frequency as ωr in the normal operation, the PCS output voltage control part is allowed to operate as the current control system to suppress overcurrent in such a manner that the angular frequency of the virtual synchronous generator model 16 is set as an output angular frequency ωpll of a PLL part in overcurrent generation, and the PCS output voltage control part is allowed to return to operation of the voltage control system and the current control system in such a manner that the output angular frequency is switched to ωr by an initialization function of the PLL part 17 when a phase difference between an output voltage Vac and the output of the PLL part 17 becomes less than a threshold during return of the output voltage Vac.SELECTED DRAWING: Figure 1

Description

The present invention relates to a control system of a power conversion device, and relates to an overcurrent suppression technique in a PCS (Power Conditioning Subsystem; power conversion device) having voltage control and current control to which virtual synchronous generator control is applied.

A power converter to which voltage-controlled virtual synchronous generator control is applied may stop due to converter overcurrent when the system is disturbed or overloaded, and a control method for suppressing this and continuing operation is required. ..

"Virtual Synchronverter Control that Can Suppress Converter Overcurrent", Toshiaki Kikuma (Central Research Institute of Electric Power), 2018 Institute of Electrical Engineers of Japan Electric Power and Energy Division Conference, 2018-09-12

Japanese Unexamined Patent Publication No. 7-336898

The virtual synchronous generator control is roughly classified into a voltage control type and a current control type, and in the case of the current control type, there is a method of limiting the current command value and controlling the current to an arbitrary value. On the other hand, in the voltage control type, the current value cannot be directly controlled. Therefore, for example, Non-Patent Document 1 proposes a method of correcting the voltage command value so that the voltage command value and the system voltage vector do not separate from each other.

However, since the current cannot be controlled to an arbitrary value by this method, an overcurrent may occur depending on conditions such as system impedance.

On the other hand, in the grid interconnection power converter, for example, as in Patent Document 1, there is a method of switching between voltage control and current control according to the state of the grid. According to Patent Document 1, a stable current can be output by performing current control during grid connection (normal time), and a stable voltage can be output by switching to voltage control during grid disconnection.

The present invention solves the above problems, and an object of the present invention is to perform voltage-controlled virtual synchronous generator control during normal operation, and to suppress overcurrent by current control when output overcurrent occurs. The purpose is to provide a control system for a converter.

The control system for the power conversion device according to claim 1 for solving the above problems is
Virtual synchronous generator control simulating a synchronous generator is performed, and it has a power converter that converts DC power of a DC power source into AC power, and the output of the power converter is interconnected with the power system via an LC filter. In the power converter
The output current detection value Iac, which detects the output current of the power converter, and the internal induced voltage Ef of the power converter are input, and the output voltage command value Vac ^{* is derived from the voltage drop due to the virtual synchronous impedance generated by the output current of the power converter.} Virtual synchronous impedance compensation unit that calculates
A virtual synchronous generator model having an angular frequency ωr calculation unit that calculates an angular frequency ωr simulating a synchronous generator for controlling the virtual synchronous generator, and a virtual synchronous generator model.
PLL (Phase) having a function of initializing the angular frequency of the virtual synchronous generator model when the output voltage of the power converter is restored by inputting the output voltage detection value Vac that detects the output voltage of the power converter. Locked Loop) section and
A PI-controlled voltage control system that has a feed-forward term for the output current detection value Iac and outputs a current command value, and an inner loop of the voltage control system, which is configured as an output voltage command value Vac ^* or an output voltage detection value. It has a P-control type current control system equipped with a Vac feedforward term, and outputs an output voltage control command Vcmd for controlling the ^{output voltage detection value Vac to match the output voltage command value Vac *.} Equipped with an output voltage control unit
The output voltage control unit
During normal operation in which the output current detection value Iac does not exceed the threshold value, the output voltage command value Vac ^* calculated by the virtual synchronous impedance compensation unit is selected as the feed forward term of the current control system. Operate as a voltage control system and a current control system according to the virtual synchronous generator model,
When the output voltage of the power converter drops and the output current detection value Iac becomes an overcurrent that exceeds the threshold value, the output angle frequency of the virtual synchronous generator model is switched to the output angle frequency ωpl of the PLL unit. The output voltage detection value Vac is selected as the feed forward term of the current control system, and the overcurrent is suppressed by operating as the current control system.
When the output voltage of the power converter is restored, the virtual synchronous generator model is used when the phase difference between the output voltage detection value Vac and the output of the PLL unit becomes less than the threshold value due to the initialization function of the PLL unit. The output angle frequency is switched to the output of the angle frequency ωr calculation unit, the output voltage command value Vac ^* is selected as the feed forward term of the current control system, and the voltage control system and current control according to the virtual synchronous generator model. It is characterized by operating as a system.

The control system for the power conversion device according to claim 2 is claimed in claim 1.
An overcurrent suppression operation determination unit that determines whether or not the output current detection value Iac exceeds the threshold value based on the output current detection value Iac and the output voltage detection value Vac.
A power calculation unit that calculates the electric output Pe of the virtual synchronous generator model based on the output current detection value Iac and the internal induced voltage Ef is provided.
The output voltage control unit controls the dq absolute value limiter unit that limits the dq absolute value with respect to the current command value of the voltage control system, and the excess control amount of the dq absolute value limiter unit of the voltage control system. It has an anti-windup unit that subtracts from the integration term, and selects the feedforward term of the current control system based on the determination result of the overcurrent suppression operation determination unit.
The virtual synchronous generator model has a selector for switching the output angular frequency based on the determination result of the current suppression operation determination unit.
The angular frequency ωr calculation unit of the virtual synchronous generator model divides the difference between the output command Pref and the electric output Pe calculated by the power calculation unit by the angular frequency ωr to obtain the input torque, and obtains the input torque from the input torque. It is characterized in that it is configured in a circuit in which integration is performed after subtracting and then dividing by the integration constant M.

(1) According to the inventions of claims 1 and 2, in a power converter in which virtual synchronous generator control is performed and is connected to a power system, voltage control type virtual synchronous generator control is performed during normal operation. When an output overcurrent occurs, the overcurrent can be suppressed by controlling the current. In addition, when the cause of overcurrent is released, it is possible to shift to voltage control after synchronizing with the system voltage by the PLL section, and system disturbance or output due to unnecessary phase difference with the power system side. Fluctuations can be suppressed.
(2) According to the invention of claim 2, since the dq absolute value limiter portion for limiting the current command value is provided, the operation is continued with the current limited to a certain magnitude. Can be done. Further, since the anti-windup unit is provided, it is possible to prevent saturation of the integral term of the voltage control system during current control.

The overall block diagram of the control system of the power conversion apparatus in the Example of Embodiment of this invention. The block diagram of the PCS output voltage control part in the Example of Embodiment of this invention. The block diagram of the virtual synchronous generator model according to the Example of Embodiment of this invention. The time chart of the overcurrent suppression operation in the Example of Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples of embodiments. In the present embodiment, in the voltage control type virtual synchronous generator control, the current control system is configured in the minor loop of the voltage control system, and the virtual synchronous generator is normally controlled by the voltage control, and the system is disturbed or short-circuited. In the event of a system accident that results in overcurrent, the power converter can be continued to operate by switching to the current control system and suppressing the overcurrent to an arbitrary current value.

FIG. 1 shows the overall configuration of the control system of the power conversion device (PCS) in the present embodiment. In FIG. 1, 1 is a DC power source having a storage battery, for example, and 2 is a power converter that is controlled by a virtual synchronous generator simulating a synchronous generator and converts the DC power of the DC power source 1 into AC power. be.

The power converter 2 is configured by, for example, bridging an IGBT, and is controlled on / off by a gate signal Gate generated by the PWM unit (19) described later.

The AC output side of the power converter 2 is connected (interconnected) to the power system 5 via an LC filter 3 composed of a reactor and a capacitor and a transformer 4.

Reference numeral 11 denotes an output current detection value Iac detected by the current transformer 12 for the output current of the PCS after the LC filter and the internally induced voltage Ef of the PCS as inputs, and a voltage due to the virtual synchronous impedance Zs generated by the output current of the power converter 2. This is a virtual synchronous impedance compensation (Zs compensation) unit ^{that simulates a drop Vz and calculates an output voltage command value Vac *} according to the simulated voltage drop Vz.

Reference numeral 13 denotes an output current detection value Iac that exceeds the threshold value based on the output voltage detection value Vac detected by the instrument transformer 14 and the output current detection value Iac of the PCS output voltage (output voltage of the power converter 2). This is an overcurrent suppression operation determination unit that determines whether or not an overcurrent has occurred.

Reference numeral 15 denotes a power calculation unit that calculates the electric output Pe of the virtual synchronous generator model (VSG (Virtual Synchronous Generator) model) 16 based on the output current detection value Iac and the internally induced voltage Ef.

Reference numeral 17 denotes a PLL (Phse Locked Loop) unit that receives the output voltage detection value Vac as an input and outputs an angular frequency ωpl, and is a virtual synchronous generator model 16 when returning from the overcurrent suppression operation to the normal voltage control. It has a function to initialize the angular frequency.

The virtual synchronous generator model 16 has an angular frequency ωr calculation unit that calculates an angular frequency ωr that simulates a synchronous generator for controlling a virtual synchronous generator, and determines that the power is output from the overcurrent suppression operation determination unit 13. The result signal flg_LCM, the set output power command value Pref, and the electric output Pe calculated by the power calculation unit 15 are input, and the angular frequency ωr or ωpl is output.

Reference numeral 18 denotes a PI control type voltage control system and a current control system configured in an inner loop of the voltage control system, and the output voltage detection value Vac is an output voltage calculated by the virtual synchronous impedance compensation unit 11. This is a PCS output voltage control unit (output voltage control unit of the present invention) that generates an output voltage control command Vcmd for controlling so as to match the command value Vac ^*.

Reference numeral 19 denotes a PWM unit that generates a gate signal Gate PWM-modulated by the output voltage control command Vcmd generated by the PCS output voltage control unit 18 and a PWM carrier, and PWM-controls the power converter 2. In the case of synchronous PWM, a PWM carrier having a frequency obtained by multiplying the angular frequency ωr determined by the virtual synchronous generator model 16 is used. In the case of asynchronous PWM, a fixed frequency PWM carrier is used.

Reference numeral 20 denotes a current transformer that detects the output current of the inverter 2. The PCS output voltage control unit 18 is configured as shown in FIG.

In FIG. 2, reference numeral 21 denotes a ^{subtractor that takes a deviation between the output voltage command value Vac *} calculated by the virtual synchronous impedance compensation unit 11 and the output voltage detection value Vac.

The deviation output of the subtractor 21 is multiplied by the proportional gain Kp in the proportional term 22 of PI control and multiplied by the integral gain Ki in the integral term 23.

Reference numeral 24 denotes a subtractor for subtracting the excess control amount of the dq absolute value limiter unit 25, which will be described later, from the integration term of the voltage control system (AVR). The deviation output of the subtractor 24 is temporarily stored in the buffer 26, and the output of the buffer 26 is added to the output of the integration term 23 in the adder 27.

The output of the adder 27 (integration term of the voltage control system), the output of the proportional term 22 (proportional term of the voltage control system), and the output current detection value Iac as the feedforward term of the voltage control system are determined in the adder 28. Will be added.

The current command value Iinv ^ ^* is output from the adder 28. The dq absolute value limiter unit 25 limits the dq absolute value with respect to the input current command value Iinv ^ ^* , and outputs the output current command value Iinv ^* .

Reference numeral 29 denotes a subtractor that takes a deviation (corresponding to the control amount of the dq absolute value limiter unit 25) between the input and the output (Iinv ^ ^* and Iinv ^{*) of the dq absolute value limiter unit 25.}

The deviation output of the subtractor 29 is multiplied by the feedback gain Kfb of the gain multiplier 30, and the output of the gain multiplier 30 is input to the subtractor 24 as a control amount of the excess of the dq absolute value limiter unit 25.

The subtractor 29, the gain multiplier 30, and the subtractor 24 constitute an anti-windup unit that prevents saturation of the integration term of the voltage control system.

^{Reference numeral 31 denotes a subtractor that takes a deviation between the output current command value Iinv *} output from the dq absolute value limiter unit 25 and the power converter current Iinv obtained by detecting the output current of the power converter 2 with the current transformer 20.

The deviation output of the subtractor 31 is multiplied by the gain of the proportional amplifier 32, and a voltage command (V) is obtained from the output.

^{33 selects either the normal output voltage command value Vac *} or the current suppression output voltage detection value Vac based on the determination result signal flg_LCM output from the overcurrent suppression operation determination unit 13 of FIG. It is a switch.

^{The Vac *} or Vac selected by the switch 33 is added to the voltage command (V) which is the output of the proportional amplifier 32 in the adder 34 as a feedforward term of the P control type current control system.

The output of the adder 34 is input to the PWM unit 19 of FIG. 1 as an output voltage control command Vcmd.

Further, the virtual synchronous generator model 16 is configured as shown in FIG. In FIG. 3, reference numeral 41 denotes a subtractor that takes a deviation between the power output command Pref and the electric output Pe calculated by the power calculation unit 15 in FIG.

Reference numeral 42 denotes a divider for obtaining the input torque by dividing the deviation output of the subtractor 41 by the angular frequency ωr temporarily stored in the buffer 48 described later.

Reference numeral 43 denotes a damping block for calculating the braking torque using the angular frequency ωr and the damping coefficient D stored in the buffer 48.

Reference numeral 44 denotes a subtractor that subtracts the braking torque, which is the output of the damping block 43, from the input torque, which is the output of the divider 42.

Reference numeral 45 denotes a divider that divides the output of the subtractor 44 by the constant of integration M. The output of the divider 45 is added to the angular frequency ωr stored in the buffer 48 in the adder 46 to obtain the angular frequency (ωr) of the VSG model.

The subtractors 41, 44, dividers 42, 45, damping block 43, adder 46, and buffer 48 constitute an angular frequency ωr calculation unit.

47 is the output angular frequency (output of the adder 46) of the angular frequency ωr calculation unit or the PLL unit 17 of FIG. 1 based on the determination result signal flg_LCM output from the overcurrent suppression operation determination unit 13 of FIG. This is a selector for selecting one of the output angular frequencies ωpl.

The output of the selector 47 is output to the PWM unit 19 as the output angular frequency of the virtual synchronous generator model 16 and is temporarily stored in the buffer 48.

Next, the operation of the apparatus configured as described above will be described together with the time chart of FIG. In FIG. 4, “AVR” indicates a period during which the PCS output voltage control unit 18 operates as a voltage control system, “ACR” indicates a period during which the PCS output voltage control unit 18 operates as a current control system, and flg_LCM indicates an overcurrent. Indicates the determination result signal output from the suppression operation determination unit 13, and is "0" when the output current detection value Iac is not an overcurrent exceeding the threshold value, and is "1" when the overcurrent exceeds the threshold value. It is a signal that becomes.

First, when the overcurrent suppression operation determination unit 13 does not detect the output overcurrent (when frg_LCM is "0"), the output voltage command value Vac is used as the feed forward term of the current control system of the PCS output voltage control unit 18. ^* Is selected by the switch 33, and the angular frequency ωr (output of the adder 46) calculated by the angular frequency ωr calculation unit is selected by the selector 47 as the output angular frequency of the virtual synchronous generator model 16.

As a result, the PCS output voltage control unit 18 operates as a voltage control system (AVR + ACR) having a current control system in the inner loop.

Next, at time t1, when the system voltage (output voltage detection value Vac) drops due to a system accident, the output current detection value Iac rapidly increases.

Next, at time t2, the maximum value of full-wave rectification of the output current detection value Iac exceeds the threshold value, so that the overcurrent suppression operation determination unit 13 determines that the overcurrent is overcurrent, and sets the determination result signal flg_LCM to "1". do.

As a result, the output voltage detection value Vac is selected by the switch 33 as the feedforward term of the current control system of the PCS output voltage control unit 18, operates as the current control system (ACR), and suppresses overcurrent.

At this time, the current command value Iinv ^* continues to operate in a state where the current is limited to a certain magnitude by the operation of the dq absolute value limiter unit 25. Further, during this current control, an anti-windup process is performed in which the control amount of the excess of the dq absolute value limiter unit 25 is subtracted from the integration term of the voltage control system by the subtractor 24, so that the voltage control system (AVR) can be used. Integral term saturation is prevented.

^{Further, since the voltage is not controlled by the output voltage command value Vac *} according to the virtual synchronous generator model 16 during the overcurrent suppression, the output of the inertial term of the virtual synchronous generator model is output by the selector 47 of the PLL unit 17. Switch to the output angle frequency ωpl. The phase difference φ between the output voltage detection value Vac and the output of the PLL unit 17 gradually increases. When the residual voltage is less than the threshold value, the control gain of the PLL section 17 is set to 0 and the operation is stopped to prevent the PLL section from diverging.

Next, when the system voltage is restored at time t3, the PLL unit 17 determines that the power frequency shift average value of the system voltage (Vac) has exceeded the threshold value, and the system voltage is determined by the angular frequency initialization function of the PLL unit. (The phase difference φ between the output voltage detection value Vac and the output of the PLL unit 17 becomes smaller).

Next, when the phase difference φ becomes less than the threshold value at time t4 (the output of the PLL unit 17 synchronizes with the system voltage (Vac)) and the output current detection value Iac decreases below the threshold value, the overcurrent suppression operation determination unit 13 The determination result signal flg_LCM of is "0". Therefore, for the output angular frequency of the virtual synchronous generator model 16, the angular frequency ωr (output of the adder 46) calculated by the angular frequency ωr calculation unit is selected by the selector 47, and the current control of the PCS output voltage control unit 18 is performed. ^{The output voltage command value Vac *} is selected by the switch 33 as the feed forward term of the system.

As a result, the operation returns to the operation of the voltage control system (AVR + ACR) having the current control system in the inner loop.

In this way, the function of the PLL unit 17 synchronizes with the system voltage (Vac) and then shifts to voltage control, thereby suppressing system disturbance and output fluctuation due to unnecessary expansion of the phase difference with the power system 5. be able to.

1 ... DC power supply 2 ... Power converter 3 ... LC filter 4 ... Transformer 5 ... Power system 11 ... Virtual synchronous impedance compensation unit 12, 20 ... Current transformer 13 ... Overcurrent suppression operation judgment unit 14 ... Instrument transformer 15 ... Power calculation unit 16 ... Virtual synchronous generator model 17 ... PLL unit 18 ... PCS output voltage control unit 19 ... PWM unit 21, 24, 29, 31, 41, 44 ... Subtractor 22 ... PI control proportional term 23 ... PI control Integration term 25 ... dq absolute value limiter part 26, 48 ... buffer 27, 28, 34, 46 ... adder 30 ... gain multiplier 32 ... proportional amplifier 33 ... switch 42, 45 ... divider 43 ... damping block 47 ... selector

Claims (2)

Virtual synchronous generator control simulating a synchronous generator is performed, and it has a power converter that converts DC power of a DC power source into AC power, and the output of the power converter is interconnected with the power system via an LC filter. In the power converter
The output current detection value Iac, which detects the output current of the power converter, and the internal induced voltage Ef of the power converter are input, and the output voltage command value Vac ^{* is derived from the voltage drop due to the virtual synchronous impedance generated by the output current of the power converter.} Virtual synchronous impedance compensation unit that calculates
A virtual synchronous generator model having an angular frequency ωr calculation unit that calculates an angular frequency ωr simulating a synchronous generator for controlling the virtual synchronous generator, and a virtual synchronous generator model.
PLL (Phase) having a function of initializing the angular frequency of the virtual synchronous generator model when the output voltage of the power converter is restored by inputting the output voltage detection value Vac that detects the output voltage of the power converter. Locked Loop) section and
A PI-controlled voltage control system that has a feed-forward term for the output current detection value Iac and outputs a current command value, and an inner loop of the voltage control system, which is configured as an output voltage command value Vac ^* or an output voltage detection value. It has a P-control type current control system equipped with a Vac feedforward term, and outputs an output voltage control command Vcmd for controlling the ^{output voltage detection value Vac to match the output voltage command value Vac *.} Equipped with an output voltage control unit
The output voltage control unit
During normal operation in which the output current detection value Iac does not exceed the threshold value, the output voltage command value Vac ^* calculated by the virtual synchronous impedance compensation unit is selected as the feed forward term of the current control system. Operate as a voltage control system and a current control system according to the virtual synchronous generator model,
When the output voltage of the power converter drops and the output current detection value Iac becomes an overcurrent that exceeds the threshold value, the output angle frequency of the virtual synchronous generator model is switched to the output angle frequency ωpl of the PLL unit. The output voltage detection value Vac is selected as the feed forward term of the current control system, and the overcurrent is suppressed by operating as the current control system.
When the output voltage of the power converter is restored, the virtual synchronous generator model is used when the phase difference between the output voltage detection value Vac and the output of the PLL unit becomes less than the threshold value due to the initialization function of the PLL unit. The output angle frequency is switched to the output of the angle frequency ωr calculation unit, the output voltage command value Vac ^* is selected as the feed forward term of the current control system, and the voltage control system and current control according to the virtual synchronous generator model. A control system for a power converter characterized by operating as a system. An overcurrent suppression operation determination unit that determines whether or not the output current detection value Iac exceeds the threshold value based on the output current detection value Iac and the output voltage detection value Vac.
A power calculation unit that calculates the electric output Pe of the virtual synchronous generator model based on the output current detection value Iac and the internal induced voltage Ef is provided.
The output voltage control unit controls the dq absolute value limiter unit that limits the dq absolute value with respect to the current command value of the voltage control system, and the excess control amount of the dq absolute value limiter unit of the voltage control system. It has an anti-windup unit that subtracts from the integration term, and selects the feedforward term of the current control system based on the determination result of the overcurrent suppression operation determination unit.
The virtual synchronous generator model has a selector for switching the output angular frequency based on the determination result of the current suppression operation determination unit.
The angular frequency ωr calculation unit of the virtual synchronous generator model divides the difference between the output command Pref and the electric output Pe calculated by the power calculation unit by the angular frequency ωr to obtain the input torque, and obtains the input torque from the input torque. The control system for a power conversion device according to claim 1, further comprising a circuit that performs integration after subtracting and then dividing by an integration constant M.

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