JP3232885B2 - Power conversion device and control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for controlling the phase of a power converter applied to a power system such as a DC transmission converter or a static var compensator.

[0002]

2. Description of the Related Art The key technologies of power electronics, such as DC power transmission realized by making full use of power electronics technology and thyristor controlled series capacitors currently being promoted in the United States, are large-capacity power semiconductor devices. Power converter technology is important. In order to operate a power semiconductor device, that is, a large-capacity power converter composed of thyristors stably even in the event of an AC system accident, an appropriate phase matching the movement of the AC system in response to a phase command from the control device. There is a need for a phase control device that can issue control pulses.

Conventionally, in order to obtain a pulse controlled based on a phase command from a control device, an AC voltage zero of an AC system is always detected for each phase, and a control pulse is generated from a reference synchronization point based on the voltage zero. The way has been taken. However, when the zero point of the voltage is detected for each phase, if the single-line ground fault that occurs most frequently occurs in the power system, the zero point of the fault phase cannot be detected, so that the phase difference cannot be determined well. Therefore, the reference synchronization point from which the control pulse is created deviates from the voltage zero point of the AC system, causing not only an error in the phase of the control pulse during the fault period but also a shift of the reference synchronization point at the time of the fault elimination. The recovery time for the operation of the device to reach a steady state also increases.

For this reason, as disclosed in Japanese Patent Application Laid-Open No. 52-42216, a storage circuit for storing the phase of the system voltage immediately before the accident and a switching circuit are newly provided. The control pulse is obtained by switching the phase from the switch to the phase of the storage circuit by the switching circuit.

[0005]

However, since a countermeasure circuit must be provided for each of the three phases, the control circuit is composed of a large number of components. Therefore, a simpler control circuit has been desired.

It is an object of the present invention to provide a high-precision and simple-structure control device capable of generating a reference synchronization pulse even when an unbalance accident occurs in an electric power system and an AC voltage is lost.

[0007]

SUMMARY OF THE INVENTION A power converter composed of a power semiconductor element is input to and output from the power converter.
A control device of the power conversion device for controlling based on a control pulse synchronized with a reference synchronization point of the phase AC voltage includes a synchronization signal detection unit, a synchronization signal detection unit, a control circuit, and a phase shift unit.

The synchronizing signal detecting means inputs a three-phase AC voltage, and creates a reference synchronizing point using a new three-phase voltage vector obtained by vector-converting the phase voltage vector of the three-phase AC voltage. The control circuit outputs a control signal according to the phase command, and the phase shifter has a function of outputting a control pulse shifted from the reference synchronization point based on the control signal.

[0009]

In order to obtain a reference synchronization point, three-phase AC voltage vectors Vu, Vv, and Vw vectors (hereinafter, abbreviated as Vu, Vv, and Vw, which represent vectors) input and output to and from the power converter are represented by several numbers. 1, new three-phase AC voltage vectors A, B, and C are created.

A = {Vu− (Vv + Vw)} / 2 B = {Vv− (Vw + Vu)} / 2 (Equation 1) C = {Vw− (Vu + Vv)} / 2 This new vector AC voltage vector A, By using B and C, a reference synchronization point that does not change before and after the accident can be obtained. By outputting the control pulse shifted from the reference synchronization point by the phase shift means based on the reference synchronization point and the control signal corresponding to the phase command, the synchronization point can be maintained even if an AC system unbalance accident occurs. The power converter can be operated stably without disappearing.

[0011]

FIG. 1 shows an embodiment in which the present invention is applied to a phase control device of a DC power transmission control device. By passing the AC / DC converter between the AC system 11 and the AC system 12, power can be exchanged only by simple frequency and phase adjustment. On the side of the AC system 11, the conversion transformers 21 and 22 convert AC into DC by the power converters 31 and 32 for the respective conversion transformers, and the DC transmission line 5 passes through the DC reactor 41.
Power is transmitted to 1,52. On the other hand, the DC power transmitted from the DC transmission lines 51 and 52 is taken into the power converters 33 and 34 from the DC reactor 42 and converted into AC, and is transmitted to the AC system 12 via the transformers 23 and 24 for conversion. Is done.

The synchronizing signal detecting circuit 61 includes an AC voltage transformer 6
This is a circuit which is a source when generating ignition pulses for the power converters 31 and 32 based on the AC voltage at the AC / DC interconnection point detected at 01. The control voltage Vs output from the control circuit 62 based on the operation command and the output of the synchronization signal detection circuit 61 are input to the phase shift circuit 63, and the firing pulses of the power conversion devices 31 and 32 are output.

An AC voltage transformer 601 for the power converters 31 and 32, a synchronizing signal detecting circuit 61, and a control circuit 6
2, and the power converters 33 and 34 as in the phase shift circuit 63.
, An AC voltage transformer 701, a synchronization signal detection circuit 71, a control circuit 72, and a phase shift circuit 73 are required.

The details of the synchronization signal detection circuit 61 will be described below with reference to FIG. 2, including the control of the control circuit 62 and the phase shift circuit 63. A fundamental signal is extracted from the system voltage detected by the AC voltage transformer 601 by the band-pass filter 602,
The arithmetic circuit 603 performs the operation of Expression 1 to detect a zero point of the voltage signal of each phase.

The phase difference detection circuit 604 outputs the output of the arithmetic circuit 603 shown in FIG.
After calculating the phase difference of each phase from the output of the decoder 608, the respective phases are summed and output to the smoothing circuit 605. The smoothing circuit 605 smoothes the output waveform from the phase difference detection circuit 604 and outputs a smoothed voltage Vc (FIG. 2 (iii)). The data processing method of the arithmetic circuit 603 and the phase difference detection circuit 604 will be described later in further detail.

The voltage pulse oscillating circuit 6 shown in FIG.
06 outputs a pulse having a frequency proportional to the output Vc of the smoothing circuit 605, and is also called a phase-locked oscillator (vco). The pulse oscillated by the voltage pulse oscillation circuit 606 is frequency-divided by the counter 607, distributed as a pulse having a phase difference from the system voltage zero point by the decoder 608, and output to the phase difference detection circuit 604 and the sawtooth wave generation circuit 609. The phase difference detection circuit 604 to the decoder 608 are so-called PLL (Phase Locked Loop) circuits.

The sawtooth wave generating circuit 609 is shown in FIG.
As shown in the figure, a sawtooth wave is formed from the counted pulses, and the phase shift circuit 63 converts the output of the sawtooth wave generation circuit 609 and the control voltage Vs output from the control circuit 62 into a power conversion device 31, A firing pulse having a firing angle α ₁ of 32 is output (FIG. 2 (vi)).

Next, Equation 1 obtained by the arithmetic circuit 603 will be described with reference to the vector diagram of FIG. The arithmetic circuit 603 calculates Equation 1 to obtain new three-phase AC voltage vectors A, B, and C.
Ask for. When the vectors of each phase are represented based on the AC voltage vector Vu, A in Equation 1 is a u-phase vector as is apparent from FIG. 3 (i), B is a v-phase, C
Represents the w phase.

Now, let u, v, and w be the synchronization points, which are the voltage zeros when the three-phase AC voltage shifts from negative to positive, respectively. Assuming that the synchronization points are x, y, and z, respectively, x, y, and z are u,
180 degrees behind v and w. Therefore, the synchronization point is u →
It circulates in the order of z → v → x → w → y → u. on the other hand,
The pulses u ′, z ′, v ′, divided by the counter 607,
x ', w', y 'are system voltage zeros u, z, v, x,
decoder 608 so as to have a certain phase difference from w and y.
Sort by. Note that the fixed phase difference is desirably 60 degrees or more, and the basis thereof will be described later.

The phase difference detecting circuit 604 is constituted by an integrating circuit or a flip-flop, and the zero points u, z,
A constant value is added to the integration circuit or a flip-flop is set by v, x, w, y, and output pulses u ′, z ′, v ′, x ′, w ′, and w ′ of the sawtooth wave generation circuit 608 are output.
The signal of each phase is always integrated by subtracting or resetting a constant value from the integrating circuit at y '.

FIG. 4 shows the operation of the arithmetic circuit 603 and the phase difference detection circuit 604 in a normal state in comparison with the output of the decoder 608, and shows the synchronous point (zero voltage) detection signals u,
For z, v, x, w, and y, a normal synchronization point is calculated every 60 degrees according to Equation 1. Therefore, in the phase difference detection circuit 604, the phase difference is set by the output of the arithmetic circuit 603 and reset by the output u ', z', v ', x', w ', y' of the decoder 608. It will be repeated every degree.
The figure shows the outputs u ', z', v ', x',
In this example, w 'and y' are delayed by 70 degrees from the synchronization point detection signals u, z, v, x, w, and y.

The output of the phase difference detection circuit 604 is averaged by the smoothing circuit 605 to become Vc, and a pulse having an oscillation frequency corresponding to the magnitude is output from the voltage pulse oscillation circuit 606, and the function described above is obtained. Therefore, the power converters 31 and 32 are controlled.

FIG. 3 shows a case where the u-phase voltage is lost due to a one-line ground fault (1LG) among the unbalanced faults in the AC system.
The operation will be described with reference to the voltage vector of (ii) and the operation of the arithmetic circuit 603 and the phase difference detection circuit 604 of FIG.

A in equation (1) becomes a u-phase vector and the magnitude of the signal changes, but the phase is the same as the u-phase vector, and the zero point of the voltage does not change. B is a voltage vector advanced by 30 degrees from the original phase of the v phase, and C is a voltage vector delayed by 30 degrees from the phase of the original w phase. Therefore, from the phase difference detection circuit 604, the reference synchronization point does not change at the time of the accident and before the accident, so that there is no change in the total phase difference from the viewpoint of all three phases.

In fact, as shown in FIG. 5 (iii), the smoothed output of the arithmetic circuit 603 is 90% for the v phase and the w phase for the u phase.
Although there is a phase difference of one degree, the phase difference detection circuit 6 per one cycle
04 output is the same Vc as the normal (i) average.
It is.

Therefore, since the oscillation frequency of the voltage pulse oscillation circuit 606 is not different from that in the normal state, the sawtooth wave generation circuit 60
U ', z', v ', x', w ', shown in FIG.
The pulse signal of y 'does not change.

FIG. 6 shows the case where the u-phase and v-phase voltages disappear due to a two-line ground fault (2LG) among the AC system imbalance faults. In equation (1), A = -Vw / 2, so the voltage vector is delayed by 60 degrees from the zero-point phase of the original u-phase voltage, and B = -Vw / 2, the voltage vector leads by 60 degrees from the zero-phase of the original v-phase voltage. Although the magnitude of the voltage vector, C, is 1/2, a voltage vector having the same phase as the original w-phase voltage phase is obtained. There is no change in the phase difference.

That is, in the arithmetic circuit 603, the u phase, v
The synchronization points of the phase and the w phase are created at the same position. Therefore, the output of the phase difference detection circuit 604 in this case is as shown in FIG. 6 (iii), and also in this case, the phase difference detection circuit 6
The average value of the 04 output is the same as the normal average value Vc
Becomes Accordingly, since the oscillation frequency of the voltage pulse oscillation circuit 606 is not different from that in the normal state, u ', z', v ', x', w ', y' shown in FIG.
Is unchanged.

In order to prevent the total phase difference of the three phases from changing, a zero point shift of ± 60 degrees occurs when the two phases are lost.
It may be adjusted so that the phase difference between the 608 outputs (for example, u and u ') is 60 degrees or more.

By determining the zero point of each phase using the three-phase instantaneous voltage signal in this manner, even when the one-phase or two-phase synchronization signal is lost due to an AC system accident, the same reference as in the normal state is obtained. A synchronization point is obtained. When the reference synchronization point is obtained, a pulse whose phase is shifted by a magnitude corresponding to the output voltage of the control circuit 62 from this point is created by the phase shift circuit 63, so that appropriate control pulses for the power conversion devices 31 and 32 can be generated. Obtainable.

If the voltage is lost in all three phases due to the AC system three-phase equilibrium fault, the operation cannot be performed by the calculation means as is apparent from the vector diagram of FIG.
Phase storage is required, as described in Japanese Patent Publication No. 6 (1994).

FIG. 7 shows another embodiment in which the phase control circuit of the present invention is applied to a thyristor phase control circuit of a thyristor controlled series capacitor. For long-distance transmission lines,
Three-phase AC transmission line 7
Series capacitors 81, 82, 83 are inserted into 1, 72, 73. The reactor 81 is connected in parallel with this series capacitor.
1, 812, 813, and thyristor circuits 821 to 826 connected in series and anti-parallel to the reactor in order to allow a current for canceling the series capacitor current to flow through the reactor.
Is connected and controlled. At this time, the AC voltage transformers 901 to 903 detect the voltage across the series capacitors 81, 82, 83.

A synchronizing signal detecting circuit 61 and a phase shift circuit 63
1 is the same as FIG. 1, and the thyristor 8 phase-shifted according to the control signal from the control circuit 91 of the thyristor control series capacitor
21 to 826 are controlled. In this configuration as well, a reference synchronization point is created from the voltage across the series capacitor by the synchronization signal detection circuit 61, and the phase shift circuit 63 controls the thyristors 821 to 826 phase-shifted according to the control signal from the control circuit 91. A control pulse is created. Therefore, the operation of the phase control circuit when an accident occurs in the AC system and the synchronization signal is lost is the same as the control of the power converters 31 and 32 described above.

[0034]

Conventionally, the voltage zero point is detected for each phase of the AC voltage, and the phase difference is detected from this detection signal, so that the apparatus becomes large and is not economical. However, in the present invention, the instantaneous three-phase AC voltage is converted into a vector, and a reference synchronization point that does not change before and after the accident can be obtained based on the new voltage vector.

Since the system synchronization point can be obtained at high speed even when the accident is eliminated, a phase control pulse with an appropriate phase according to the synchronization point of the AC system can be issued. Furthermore, when the AC voltage is recovered by the removal of the accident, an appropriate phase pulse synchronized with the AC system can be output at high speed, so that the operation recovery of the power converter can be performed quickly. Thereby, the power converter can be operated stably at the time of AC system imbalance accident and at the time of accident elimination.

[Brief description of the drawings]

FIG. 1 shows an embodiment in which the control device of the present invention is applied to a DC power transmission control device.

FIG. 2 is an operation explanatory diagram of a synchronization signal detection circuit 61.

FIG. 3 is a vector diagram showing calculation contents of a calculation circuit 603;

FIG. 4 is an explanatory diagram of an operation of the synchronization signal detection circuit 61 in a normal state.

FIG. 5 is an operation explanatory diagram of the synchronization signal detection circuit 61 at the time of one-line ground fault.

FIG. 6 is a diagram illustrating the operation of the synchronization signal detection circuit 61 when a two-wire ground fault occurs.

FIG. 7 shows an embodiment in which the control device of the present invention is applied to a control device for a thyristor controlled series capacitor.

[Explanation of symbols]

11, 12 ... AC system, 31 to 34 ... power conversion device, 5
1, 52: DC transmission line, 61: synchronous signal detection circuit, 62
... Control circuit, 63 ... Phase shift circuit, 81, 82, 83 ... Series capacitor, 91 ... Thyristor controlled series capacitor control circuit, 601 ... AC voltage transformer, 602 ... Band pass filter, 603 ... Calculation circuit, 604 ... Phase difference detection circuit,
605: smoothing circuit, 606: voltage pulse oscillation circuit, 6
07 ... Counter, 608 ... Decoder, 609 ... Sawtooth wave generation circuit, 821-826 ... Thyristor, 901-90
3: AC voltage transformer.

Continuation of front page (56) References JP-A-56-46660 (JP, A) JP-A-52-42216 (JP, A) JP-A-60-109760 (JP, A) JP-A-59-162767 (JP) JP-A-60-9369 (JP, A) JP-A-5-122940 (JP, A) JP-A-6-165501 (JP, A) JP-A-6-90597 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/19 H02M 7/155

Claims (4)

(57) [Claims] 1. A control device for controlling a power converter constituted by a power semiconductor element based on a control pulse synchronized with a reference synchronization point of a three-phase AC voltage input / output to / from the power converter.
In the power converter provided with a three-phase AC voltage , the control device inputs the three-phase AC voltage and converts the phase voltage vector of the three-phase AC voltage into a vector by using a new three-phase voltage vector. a synchronization signal detection means for producing a point, and a control circuit for outputting a control signal corresponding to the phase instruction, and a phase shifting means for outputting the control pulse is shifted from the reference synchronization point based on the control signal
The synchronization signal detecting means detects the magnitude of the three-phase AC voltage.
An AC voltage detecting means for detecting the three-phase AC voltage,
Transform the voltage vector into a new three-phase voltage vector
From the three-phase AC voltage and calculate the voltage zero point of each of the three phases.
A calculating means for calculating, and a dividing means separately formed from the calculated voltage zero point.
To detect the difference from the reference phase and sum and output the three phases
Phase difference detection means, and a mean for averaging the output of the phase difference detection means.
Voltage pulse having a smoothing means, a frequency corresponding to an output of said smoothing means
A voltage pulse oscillating means for outputting the reference pulse; a counter means for counting the voltage pulse; and dividing the voltage pulse into three phases to output the reference phase.
It said dividing unit that, the power conversion device characterized by comprising the. 2. A power converter according to claim 1 , further comprising a control device provided with said calculating means for obtaining new three-phase vectors A, B and C based on the following equation. A = {Vu- (Vv + Vw)} / 2 B = {Vv- (Vw + Vu)} / 2 C = {Vw- (Vu + Vv)} / 2 Vu, Vv, Vw: Three-phase AC voltage input / output to the power converter Vector . 3. The apparatus according to claim 1 , wherein a difference between a phase outputted from said frequency dividing means and a phase outputted from said calculating means when a three-phase voltage is sound is set to 60 degrees or more. Power converter. 4. A control method for a power conversion device, comprising: controlling a power conversion device including a power semiconductor element based on a control pulse synchronized with a reference synchronization point of a three-phase AC voltage input to and output from the power conversion device. In the above, the three-phase AC voltage is input and the three-phase AC voltage
Convert the voltage vector into a new three-phase AC voltage
The voltage zero point of each layer of the three phases is obtained from the three-phase AC voltage.
From the voltage zero and the frequency dividing means formed separately.
The difference from the reference phase is detected, and the three phases are summed up.
Averaging the calculated values, a voltage pulse having a frequency corresponding to the average value
And divides the voltage pulse into three phases to produce the reference phase
A method for controlling a power conversion device, comprising: