JP2017016556A - Self-excited power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self-excited power conversion device capable of operating stably while following up the frequency fluctuation of an AC power supply.SOLUTION: A voltage phase reference arithmetic unit 20 calculates the voltage phase reference θ of a self-excited converter from a voltage detected by a voltage detector. A converter control unit 30 controls a current flowing between an AC power supply and the self-excited converter on the basis of a current detected by a current detector and the voltage phase reference θ. The voltage phase reference arithmetic unit 20 includes a PLL circuit 25 for detecting the voltage phase θfb of the AC power supply from the voltage detected by the voltage detector, and an addition unit 60 for adding a phase difference Δθ between the phase of the voltage detected by the voltage detector that is inputted to the PLL circuit 25 and the voltage phase of the AC power supply that is outputted from the PLL circuit 25 to the voltage phase θfb of the AC power supply detected by the PLL circuit 25 and thereby calculating the voltage phase reference θ.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a self-excited power conversion device, and more particularly to a self-excited power conversion device including a PLL (Phase Locked Loop) circuit that detects a voltage phase of an AC power supply.

  For the control of the self-excited converter electrically connected to the AC power source, a PLL circuit is used to detect the voltage phase of the AC power source (for example, JP-A-11-356050 (Patent Document 1)). Table 2005-524378 gazette (patent document 2) and special table 2012-510252 gazette (patent document 3)).

Japanese Patent Laid-Open No. 11-356050 JP 2005-524378 A Special table 2012-510252 gazette

  The PLL circuit generally performs control for synchronizing the phase of the output signal with the phase of the input signal using a feedback loop. A PLL circuit used in a self-excited power converter uses an AC power supply voltage detected by a voltage detector as an input signal, and outputs a signal whose phase is synchronized with the input signal as a detected value of the voltage phase of the AC power supply. .

  However, when the frequency fluctuation of the AC power supply increases, the PLL circuit may have a state in which the phase tracking characteristic, that is, the phase matching accuracy and the response speed are insufficient. Therefore, there may be a phase detection error of the PLL circuit or a phase error due to operation delay. As a result, the self-excited converter is controlled in a state in which a phase error of the PLL circuit occurs, so that the control is broken, leading to a serious failure in which a current exceeding the current value allowed for the self-excited converter flows. There is a fear.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a self-excited power conversion device that can stably operate following the frequency fluctuation of an AC power supply. It is.

  A self-excited power conversion device according to an aspect of the present invention includes a self-excited converter that is electrically connected to an AC power source and includes a self-excited arc-extinguishing type switching element, and a voltage detector that detects a voltage of the AC power source. A current detector for detecting a current flowing between the AC power supply and the self-excited converter, a voltage phase reference calculating unit for calculating a voltage phase reference of the self-excited converter from the voltage detected by the voltage detector, and a current A converter controller configured to control the current flowing between the AC power source and the self-excited converter by switching the switching element based on the current and voltage phase reference detected by the detector; Prepare. The voltage phase reference calculation unit includes a PLL circuit that detects the voltage phase of the AC power supply from the voltage detected by the voltage detector, and a voltage detector that is input to the PLL circuit with the voltage phase of the AC power supply detected by the PLL circuit. And an adder for calculating a voltage phase reference by adding a phase difference between the phase of the voltage detected by the above and the voltage phase of the AC power supply output from the PLL circuit.

  According to the present invention, it is possible to provide a self-excited power converter that can operate stably following the frequency fluctuation of an AC power supply.

1 is an overall configuration diagram of a self-excited power conversion device according to an embodiment of the present invention. It is a circuit diagram which shows the structural example of the self-excited converter shown in FIG. It is a block diagram which shows the structure of the converter control part shown in FIG. FIG. 2 is a block diagram illustrating a configuration of a PLL circuit illustrated in FIG. 1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

(Configuration of self-excited power converter)
FIG. 1 is an overall configuration diagram of a self-excited power conversion device according to an embodiment of the present invention. In the present embodiment, a self-excited reactive power compensator used in a power system will be described as an example of a self-excited power conversion device according to the present invention. However, the self-excited power conversion device according to the present invention is not limited to the self-excited reactive power compensator as long as it is electrically connected to the AC power supply and operates in synchronization with the phase of the AC power supply.

  Referring to FIG. 1, a self-excited reactive power compensator 100 includes a self-excited converter 1, a converter transformer 2, a current detector 4, voltage detectors 5 and 6, a control device 10, and a direct current. And a capacitor C.

  Self-excited converter 1 is electrically connected to a power system 3 having u-phase, v-phase, and w-phase. The self-excited converter 1 includes a self-extinguishing type switching element. Self-excited converter 1 outputs reactive power to power system 3 based on the voltage smoothed by DC capacitor C. The converter transformer 2 transforms the voltage output from the self-excited converter 1 and outputs it to the power system 3. The electric power system 3 corresponds to an example of the “AC power supply” in the present invention.

FIG. 2 is a circuit diagram showing a configuration example of the self-excited converter 1 shown in FIG.
Referring to FIG. 2, self-excited converter 1 includes switching elements Q1-Q6 and diodes D1-D6. The switching elements Q1 to Q6 are, for example, GTO (Gate Turn Off thyristor), but are not limited to this as long as they are self-extinguishing type switching elements. Diodes D1-D6 are connected in antiparallel to switching elements Q1-Q6, respectively. A gate pulse signal is supplied from the control device 10 to the switching elements Q1 to Q6. Switching elements Q <b> 1 to Q <b> 6 perform a switching operation in accordance with the gate pulse signal, thereby converting a voltage smoothed by DC capacitor C, that is, a DC voltage, into an AC voltage and supplying it to power system 3.

  Referring to FIG. 1 again, the voltage detector 5 detects the voltage (system voltage) of the power system 3. The system voltage includes a u-phase voltage Vu, a v-phase voltage Vv, and a w-phase voltage Vw. The system voltage detected by the voltage detector 5 is given to the control device 10 as a feedback voltage.

  The current detector 4 detects the output current of the self-excited converter 1, that is, the current flowing between the power system 3 and the self-excited converter 1. The current detected by the current detector 4 is given to the control device 10 as a feedback current.

  The voltage detector 6 detects the voltage across the terminals of the DC capacitor C. The voltage of the DC capacitor C detected by the voltage detector 6 is given to the control device 10.

(Configuration of control device)
Next, the configuration of the control device 10 will be described. The control device 10 includes a voltage phase reference calculation unit 20 and a converter control unit 30.

  The voltage phase reference calculation unit 20 calculates the voltage phase reference θ of the self-excited converter 1 based on the system voltage detected by the voltage detector 5. The voltage phase reference calculation unit 20 includes a PLL circuit configured to detect the voltage phase of the power system 3 from the system voltage detected by the voltage detector 5. The detailed configuration of the voltage phase reference calculation unit 20 will be described later.

  The converter control unit 30 uses the voltage phase reference θ calculated by the voltage phase reference calculation unit 20 to control the switching operation of the switching elements Q1 to Q6 (FIG. 2) constituting the self-excited converter 1. Generate a gate pulse signal. The generated gate pulse signal is given to each switching element of the self-excited converter 1. The converter control unit 30 controls the switching operation of the switching elements Q <b> 1 to Q <b> 6 in the self-excited converter 1 based on the output current detected by the current detector 4, so that the self-excited converter 1 transfers to the power system 3. Controls the output current.

(Configuration of converter controller)
First, the configuration of the converter control unit 30 will be described. FIG. 3 is a block diagram showing a configuration of converter control unit 30 shown in FIG.

  Referring to FIG. 3, converter control unit 30 includes current detection unit 32, subtractors 34 and 36, PI calculation units 38 and 40, voltage reference value generation unit 42, and gate pulse generation unit 44. Including.

  In the converter control unit 30, the reactive current component and the active current component are controlled by a rotating coordinate system (dq coordinate system) having a d-axis and a q-axis, respectively. Control is based on the system voltage so that the d-axis is a component orthogonal to the system voltage and the q-axis is a component in phase with the system voltage.

  Based on the output current of the self-excited converter 1 detected by the current detector 4, the current detection unit 32 detects the effective current Iq and the reactive current Id output from the self-excited converter 1 to the power system 3. Specifically, the current detection unit 32 detects the u phase detected by the current detector 4 by coordinate conversion (three-phase / two-phase conversion) using the voltage phase reference θ output from the voltage phase reference calculation unit 20. The current Iu, the v-phase current Iv, and the w-phase current Iw are converted into an effective current Iq and a reactive current Id.

  The subtractor 34 calculates a current deviation ΔId (ΔId = Id * −Id) according to the difference between the reactive current command value Id * and the detected value of the reactive current Id. The PI calculation unit 38 is used for a proportional integral (PI) calculation. The PI calculation unit 38 calculates a reactive voltage Vd * (hereinafter also referred to as a reactive voltage reference value Vd *) required for the self-excited converter 1 based on the current deviation ΔId. That is, the subtractor 34 and the PI calculation unit 38 control the component related to the reactive current Id in the AC voltage output from the self-excited converter 1.

  The subtractor 36 calculates a current deviation ΔIq (ΔIq = Iq * −Iq) according to the difference between the effective current command value Iq * and the detected value of the active current Iq. The PI calculation unit 40 is used for proportional integration calculation. The PI calculation unit 40 calculates an effective voltage Vq * (hereinafter also referred to as an effective voltage reference value Vq *) required for the self-excited converter 1 based on the current deviation ΔIq. That is, the subtractor 36 and the PI calculation unit 40 control components related to the effective current Iq in the AC voltage output from the self-excited converter 1.

  The voltage reference value generation unit 42 is a reactive voltage reference value Vd calculated by the PI calculation unit 38 by coordinate conversion (two-phase / three-phase conversion) using the voltage phase reference θ output from the voltage phase reference calculation unit 20. * And the effective voltage reference value Vq * calculated by the PI calculation unit 40 are converted into output AC voltage reference values Vu *, Vv *, and Vw * that are voltages output from the self-excited converter 1.

  The gate pulse generator 44 generates a gate pulse signal for the self-excited converter 1 to output a voltage corresponding to the output AC voltage reference values Vu *, Vv *, Vw *, for example, by PWM (Pulse Width Modulation) control. To do. The gate pulse generator 44 supplies the generated gate pulse signal to the switching elements Q <b> 1 to Q <b> 6 that constitute the self-excited converter 1.

  As described above, the converter control unit 30 is a self-excited type according to the deviations (current deviations ΔId, ΔIq) between the currents Id, Iq detected by the current detection unit 32 and the current command values Id *, Iq *. The AC voltage reference (output AC voltage reference value) Vu *, Vv *, Vw * output from the converter 1 is calculated. The output AC voltage reference values Vu *, Vv *, and Vw * are obtained as outputs of a current feedback control system that uses the subtractors 34 and 36 and the PI calculation units 38 and 40 as controllers.

(Configuration of voltage phase reference calculation unit)
The voltage phase reference θ of the power system 3 used for the current feedback control system in the converter control unit 30 described above is based on the voltage phase of the power system 3 detected by the built-in PLL circuit in the voltage phase reference calculation unit 20. Calculated. The PLL circuit has a feedback loop. The voltage detected by the voltage detector 5 is used as a feedback loop input signal, and a signal whose phase is synchronized with this input signal is output from the feedback loop as a detected value of the voltage phase of the power grid 3.

  However, when there is an accident in the power system 3, the frequency of the system voltage may fluctuate. When the frequency fluctuation of the electric power system 3 becomes large, a state in which the phase tracking characteristic, that is, the accuracy of phase matching and the response speed are insufficient may occur in the PLL circuit. Therefore, there may be a phase detection error of the PLL circuit or a phase error due to operation delay. As a result, in the self-excited reactive power compensator, when the current feedback control system is executed in a state where the phase error of the PLL circuit has occurred, the control system breaks down, and the current value allowed for the self-excited converter 1 There is a possibility of leading to a serious failure such as the above current flowing.

  As a countermeasure against the frequency fluctuation of the power system 3, there is a method of increasing the response speed of the feedback loop in the PLL circuit. However, this method increases the responsiveness of the PLL circuit, but may impair stability. As a result, the power output from the self-excited converter 1 to the power system 3 is not stable, and the power system 3 may become unstable.

  Therefore, in the present embodiment, for the voltage phase reference θ used in the current feedback control system, the phase difference Δθ between the input signal and the output signal of the PLL circuit is set with respect to the voltage phase detected by the PLL circuit. Add as feed-forward control amount. This prevents the current feedback control system from failing due to frequency fluctuations of the power system 3.

Hereinafter, the configuration of the voltage phase reference calculation unit 20 will be described with reference to FIG.
FIG. 4 is a block diagram showing a configuration of the voltage phase reference calculation unit 20 shown in FIG.

  Referring to FIG. 4, voltage phase reference calculation unit 20 includes a PLL circuit 25 and an addition unit 60. The PLL circuit 25 includes a coordinate conversion unit 50, a phase difference detection unit 52, a PI calculation unit 54, an ω calculation unit (angular frequency calculation unit) 56, and an integration circuit 58. The coordinate conversion unit 50, the phase difference detection unit 52, the PI calculation unit 54, the ω calculation unit 56, and the integration circuit 58 form a feedback loop. Among these, the PI calculation unit 54, the ω calculation unit 56, and the integration circuit 58 constitute a “feedback calculation unit” in the present invention.

  In the following description, the voltage phase of the power system 3 detected by the feedback loop of the PLL circuit 25 is expressed as θfb. On the other hand, the voltage phase reference in the converter control unit 30 is expressed as θ. That is, the voltage phase θfb corresponds to the feedback control amount, and the phase difference Δθ between the input signal and the output signal of the feedback loop corresponds to the feedforward control amount. The voltage phase reference θ in the converter control unit 30 is obtained by adding the voltage phase θfb and the phase difference Δθ.

  The coordinate conversion unit 50 converts the system voltage (u-phase voltage Vu, v-phase) detected by the voltage detector 5 by coordinate conversion (three-phase / two-phase conversion) using the voltage phase θfb sent from the integration circuit 58. The voltage Vv and the w-phase voltage Vw) are converted into an effective voltage Vq and an ineffective voltage Vd.

The phase difference detection unit 52 calculates the phase difference Δθ based on the effective voltage Vq and the reactive voltage Vd. Specifically, when three-phase to two-phase conversion of the system voltage is performed, if the voltage phase θfb and the phase of the system voltage match, that is, if the phase difference Δθ is zero, the effective voltage Vq is The reactive voltage Vd becomes almost zero in proportion to the magnitude of the voltage. On the other hand, when the voltage phase θfb and the phase of the system voltage do not match, that is, when the phase difference Δθ is not zero, the invalid voltage Vd does not become zero. The phase difference detection unit 52 obtains tan Δθ based on the effective voltage Vq and the reactive voltage Vd (tan Δθ = Vd / Vq). Then, the phase difference detection unit 52 calculates the phase difference Δθ from tan Δθ (Δθ = tan ⁻¹ (tan Δθ) = tan ⁻¹ (Vd / Vq)).

  The PI calculation unit 54 calculates a control amount for making the phase difference Δθ zero by proportional integration calculation. The ω calculating unit 56 calculates the reference value ω of the angular frequency of the output voltage to be output from the self-excited converter 1 based on the control amount calculated by the PI calculating unit 54.

  The integration circuit 58 calculates the voltage phase θfb, which is a feedback control amount, by integrating the angular frequency reference value ω. The integration circuit 58 outputs the voltage phase θfb to the coordinate conversion unit 50.

  Here, as shown in FIG. 4, the voltage phase θfb calculated by the integration circuit 58 is also input to the adder 60. The adder 60 calculates the voltage phase reference θ by adding the voltage phase θfb and the phase difference Δθ. The voltage phase reference θ is given to the converter control unit 30.

  In the feedback loop shown in FIG. 4, a control amount for making the phase difference Δθ zero is calculated by the PI calculation unit 54. When the power system 3 is three-phase balanced, the phase difference Δθ is small, and therefore the phase difference Δθ reaches zero in a relatively short time. On the other hand, when the frequency fluctuation of the electric power system 3 occurs, the phase difference Δθ increases, so that it takes time until the phase difference Δθ reaches zero. Therefore, when the voltage phase θfb detected by the PLL circuit 25 is used as the voltage phase reference θ in the converter control unit 30, the voltage phase reference θ becomes the phase difference Δθ in the time until the phase difference Δθ reaches zero. In this state, the current output from the self-excited converter 1 to the power system 3 is controlled.

  On the other hand, according to the self-excited power conversion device according to the present embodiment, voltage phase reference calculation unit 20 uses voltage phase reference θ output to converter control unit 30 to detect the voltage phase detected by PLL circuit 25. It is generated by adding the phase difference Δθ detected in the feedback loop of the PLL circuit 25 to θfb. Thereby, the voltage phase reference θ can be made to follow the fluctuation of the phase of the system voltage. As a result, a current feedback control system based on the voltage phase reference θ following the frequency variation of the power system 3 is formed, so that it is possible to prevent a serious failure due to the failure of the current feedback control system.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Self-excited converter, 2 Transformer for transformers, 4, 6 Voltage detector, 5 Current detector, 10 Control part, 20 Voltage phase reference calculating part, 25 PLL circuit, 30 Converter control part, 32 Current detection part, 34, 36 Subtractor, 38, 40 PI calculation unit, 42 Voltage reference value generation unit, 44 Gate pulse generation unit, 50 Coordinate conversion unit, 52 Phase difference detection unit, 54 PI calculation unit, 56 ω calculation unit, 58 Integration circuit , 60 adder, 100 self-excited power converter, C DC capacitor, Q1-Q6 switching element, D1-D6 diode.

Claims (3)

A self-excited converter electrically connected to an AC power source and including a self-excited arc extinguishing type switching element;
A voltage detector for detecting the voltage of the AC power supply;
A current detector for detecting a current flowing between the AC power source and the self-excited converter;
A voltage phase reference calculator for calculating a voltage phase reference of the self-excited converter from the voltage detected by the voltage detector;
Based on the current detected by the current detector and the voltage phase reference, the current flowing between the AC power source and the self-excited converter is controlled by switching the switching element. A converter control unit,
The voltage phase reference calculation unit is
A PLL circuit for detecting a voltage phase of the AC power supply from a voltage detected by the voltage detector;
The voltage phase of the AC power source detected by the PLL circuit, the voltage phase detected by the voltage detector input to the PLL circuit, and the voltage phase of the AC power source output from the PLL circuit. A self-excited power converter including an adder that calculates the voltage phase reference by adding a phase difference between the two. The PLL circuit includes:
The voltage detected by the voltage detector is converted into an effective voltage and an ineffective voltage by coordinate conversion using the voltage phase of the AC power source output from the PLL circuit, and the effective voltage and the ineffective voltage are converted into the level. A phase difference detector configured to detect the phase difference;
A feedback calculation unit that calculates a voltage phase of the AC voltage by executing a feedback calculation based on the phase difference;
The self-excited power conversion device according to claim 1, wherein the adding unit adds the phase difference detected by the phase difference detecting unit to a voltage phase of the AC voltage calculated by the feedback calculating unit. The converter controller is
A current detection unit that converts the current detected by the current detector into an effective current component and a reactive current component output to the AC power supply by coordinate conversion using the voltage phase reference;
An active voltage reference value is calculated so that the active current component matches the active current command value, and a calculation unit that calculates the reactive voltage reference value so that the reactive current component matches the reactive current command value;
Based on the effective voltage reference value, the reactive voltage reference value, and the voltage phase reference, a voltage reference value generation unit that calculates an AC voltage reference value output to the AC power supply;
The self-excited power conversion device according to claim 1, further comprising: a gate pulse generation unit configured to generate a gate pulse signal for switching the switching element based on the AC voltage reference value.

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