JPS6112457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating a self-excited converter applied to DC power transmission equipment.

Figure 1 shows the operating method of conventional DC power transmission equipment. Arm 1 is connected to AC system 1 via transformer 11.
A separately excited converter 9 composed of U to 1Z is connected, and AC power is converted to DC power. The converter 9 operating as a rectifier is generally controlled under constant current control. The feedback signal 17 from the DC current transformer 18 is calculated with the current reference signal Iref 16 and applied to the current control amplifier 15, the output of which is sent to the automatic phase shifter 14. Automatic phase shifter 14
The output voltage of the converter 9 is adjusted by changing the control angle of the converter 9 from 0 degrees to 180 degrees depending on the magnitude of the input voltage. A pulse is generated from the automatic phase shifter at a position corresponding to the control angle, and a gate signal is sent to each arm in the gate circuit 13, and the conversion device 9
is operated so that the DC output power is constant. The DC power from the converter 9 is transferred to the DC power line 1
0, the power is sent through DC reactors 12 and 22 to a separately excited converter 8 consisting of arms 2U to 2Z operated by an inverter, where it is converted into AC power and transmitted to an AC system 22 via a transformer 21. .
Generally, closed-loop margin angle control is used in inverter operation to prevent commutation failure. The margin angle applied to the arm is detected by the margin angle detector 27, used as a feedback signal, calculated with the reference margin angle δref24, inputted to the margin angle control amplifier, and fixed via the automatic phase shifter 14 gate circuit 13. Margin angle control is performed. In order to ensure a sufficient margin angle in the separately excited inverter, the control advance angle becomes large, and the converter 8 consumes reactive power with a large delay. Reactive power equipment 28 is required for this purpose.
Its capacity is said to be 50 to 60% of the converted power.
Reactive power equipment increases converter site or construction costs and power losses.

The present invention aims to eliminate the above-mentioned drawbacks of the conventional converter by applying a self-excited converter with a reactive power control function as a DC power transmission converter.

FIG. 2 shows an embodiment of the present invention. The converter 9 on the power transmitting side of the DC power transmission equipment, which is in operation as a rectifier, is a separately excited converter that performs constant current control according to the current reference signal Iref16. DC power is applied to the self-excited converter 4 through the DC power transmission line 10 and the DC reactor 42 .
An AC output terminal of the self-commutated converter 4 is connected to the AC system 3 via a transformer 31. Conversion device 4
The inverter is composed of arms 4U to 4Z and is a so-called voltage type self-excited inverter, a detailed diagram of which is shown in FIG. To explain the configuration of one phase of the U phase in the arm, the main thyristor 2UM connected to the positive DC pole P, the auxiliary thyristor 2UA, the diode 2UD, and the main thyristor 2XM connected to the negative pole N, and the auxiliary thyristor 2XA. , diode 2XD
It consists of a commutation circuit consisting of a reactor L and a capacitor C. The main thyristors 2UM and 2XM are alternately conductive for each cycle of 180°. Due to the conduction of the auxiliary thyristor 2UM, the discharge current of the capacitor C flows through the main thyristor 2UM, and a reverse voltage is applied to the main thyristor 2UM to extinguish the arc. After that, the main thyristor 2XM becomes conductive. 2XM, 2
XA works similarly. VW phase is 120 each
By operating with a delay within one cycle, a rectangular three-phase AC voltage is generated at the output terminals U, V, and W. Returning to FIG. 2, a capacitor 43 and a DC voltage detector 44 are connected between DC terminals P and Q of the converter 4. The self-excited inverter 4 operates as a three-phase inverter by sequentially sending the gate signal from the gate circuit 41 to the P-side auxiliary thyristor, the N-side main thyristor, the N-side auxiliary thyristor, the P-side main thyristor, and the P-side auxiliary thyristor. are doing. The current flowing to the AC system 3 is detected by a current transformer 32, the system voltage is detected by a transformer 33, the generated reactive power is fed back as a signal 35 by a reactive power detector 34, and a reference reactive power Qref signal 36 and a calculator 37 are detected. The reactive power control amplifier 38
has been entered. The output serves as a reference signal for DC voltage control of the capacitor 43, is calculated by the signal 15 from the DC voltage detector 44 and the calculator 39, and is input to the DC voltage control amplifier 40.
The output of the DC voltage control amplifier 40 serves as an input signal to a phase adjustment circuit 50 that adjusts the phase difference between the output voltage of the converter 4 and the output voltage of the AC system 3. In this example, the phase adjustment circuit 50 includes a phase comparator 46 and a filter for comparing the voltage phase difference between the rectangular wave voltage signal for one arm of the hexadecimal ring counter 45 for the three-phase self-excited inverter and the AC system 3. 4
7, a voltage controlled amplifier 48, and a voltage controlled oscillator 49, forming a so-called phase lock loop. Depending on the magnitude of the input signal from the DC voltage control amplifier 40 to the voltage control amplifier 48, the voltage phase difference between the self-excited converter 4 and the AC system 3 advances or lags.

The DC power converted from the converter 4 to the AC system 3 and the reactive power generated will be determined. As shown in FIG. 5, the output voltage of the converter 4 is E ₄ =
E ₄ e ^j 〓Let the voltage on the grid side be E ₃ = E ₃ , and consider the case where E ₄ is ahead by phase θ. Considering only the leakage reactance X _T of the transformer 31 as the reactance as the interconnection impedance, Converted power P=
E ₄・E ₃ /X _T sinθ, generated reactive power Q=E ₃ /X _T
(E ₄ cosθ− E ₃ ). As shown in Figure 4a, the phase difference θ=0
In this case, no power conversion will be performed.
Further, as shown in b, the power is converted by taking the phase difference θ. The reactance X _T of a transformer is usually around 10% in percent impedance, and sin θ is a small value. Therefore, cos θ
is close to 1, and the generated reactive power Q≒E ₃ /X _T (E ₄ −E ₃ )
You can think about it. From the formula for the generated reactive power Q, it can be understood that if the system voltage E ₃ is constant, E ₄ will be constant by controlling the reactive power to be constant. As can be seen from the waveform of E ₄ in Figure 4, the fact that E ₄ is constant means that the DC input power of converter 4
It also follows that Ed is constant. Also, the conversion device 4
By keeping the DC input current constant, the independent state quantities of voltage and current can be determined.
Enables stable driving. Generated reactive power Q=0
When the converter 4 is controlled so that the transformer 3
1, it will always operate with a power factor of 1, and if the installed capacity is AMVA, AMW power transmission will be possible. Furthermore, if the system requires BMVAR reactive power, it is possible to transmit up to √ ² − ² MW if the installed capacity is AMVA. In Fig. 2, suppose now that the reactive power Q=
In a state where constant control of 0 is being performed, assuming a state where the voltage of the AC system 3 suddenly drops, the conversion device 4 supplies leading reactive power to the grid due to the voltage drop on the grid 3 side. Since the output of the reactive power detector 34 increases from zero, a deviation occurs from the reference signal which is zero, and the input signal to the DC voltage control amplifier 40 is lowered so as to lower the DC voltage Ed. Therefore, the deviation from the DC voltage signal 5, which is a feedback signal from the capacitor voltage, increases, the input signal to the phase difference adjustment circuit 50 increases, and the oscillation frequency of the voltage controlled oscillator 49 apparently increases, resulting in a phase difference. θ becomes larger.
As the phase difference θ increases, the converted power P increases and the DC charge of the capacitor 43 is also discharged.
The capacitor voltage will drop. It can be seen that as a result, the voltage of the AC system 3 and the output voltage of the converter 4 become equal, and the generated reactive power returns to zero. In this state, the voltage phase difference θ between one output signal of the ring counter 45 and the system 3 is
has almost returned to its original state. Even if the system voltage rises, the system similarly returns to the state where the reactive power Q=0. As explained above, it can be seen that stable operation can be obtained by applying a self-excited converter having a constant reactive power control function as a converter in which the DC input current of the DC power transmission equipment is constant.

In general, it is thought that DC power transmission equipment is mostly used for the purpose of power transmission, and it is thought that it is desirable to have a secondary function as a reactive power generator. Therefore, active power priority control is required in self-excited converters. This is to use the converter equipment for the purpose of converting active power as much as possible, and if the required conversion power P is less than the equipment capacity A, reactive power can be generated up to a maximum of √ ² − ² . If the reactive power Q required by the grid is smaller than √ ² − ² , use Q as the reference value for reactive power control, and if Q is larger than √ ² − ² , use √ ² − ² as the reference value for reactive power control. It will be adopted as The configuration is shown in FIG. The active power detector 60 calculates active power by combining the output of the current transformer 61 and the output of the grid voltage transformer 62, calculates the allowable reactive power from the equipment capacity A by the allowable reactive power calculator 63, and calculates the allowable reactive power from the installed capacity A. In comparison with the required reactive power Q, a reactive power reference value Qref used for reactive power control is determined.

Further, there are cases where it is desired to employ constant power control as well as constant reactive power control on the power receiving side, and in this case, the current reference value calculator 70 shown in FIG. 2 can be used. The power/voltage calculation is performed by the divider 7 using the power reference value Pref signal 6 that is desired as constant power and the DC input voltage signal 5 of the self-excited converter 4 as input, and the obtained value is used to set the DC current on the power transmission side to be constant. It can be seen that it can be used as a reference signal for control.

The self-excited converter used in the above explanation was a three-phase voltage-type self-excited inverter, but because the harmonics flowing out to the AC side become large, the DC input terminal of the inverter with a phase difference is generally used. In this method, the three-phase AC output terminals are connected in parallel to transformer windings with a phase difference, and the inverter output waveform is made closer to a sine wave by multiplexing, thereby suppressing the generation of harmonics.

As detailed above, according to the present invention, a self-commutated converter having a constant reactive power control function is used as a converter in a DC power transmission system, and as a converter in which the DC input current of the DC power transmission system is constant. By applying this, it is possible to operate a stable DC power transmission system.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional DC power transmission facility, Fig. 2 is a block diagram showing an embodiment of the operating method of the present invention, and Fig. 3 is an example of a voltage-type self-excited inverter used to explain the present invention. 4 is an operation waveform diagram, FIG. 5 is a system configuration diagram for explaining the operation of the present invention, and FIG. 6 is an operation explanatory diagram for implementing the present invention more effectively. be. In the figure, 4 is a self-excited converter, 3 is an AC system, 3
1 is a transformer, 42 is a DC reactor, 43 is a capacitor, 44 is a DC voltage detector, 34 is a reactive power detector, 38 is a reactive power control amplifier, 40 is a DC voltage control amplifier, 41 is a gate circuit, and 50 is a voltage converter. The phase difference regulator 70 is a current reference value calculator. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A self-excited converter connected to an AC power system, configured to convert DC power input to the self-excited converter into AC power and transmit the power to the AC power system. In the self-commutated converter, the DC input power of the self-excited converter is controlled to be constant, and the phase difference between the output voltage of the self-excited converter and the voltage on the AC power system side is adjusted. An operating method for a converter, characterized in that reactive power generated from the exciter converter is controlled to a constant level. 2 If the AC power P converted to the AC power system is smaller than the installed capacity A of the self-excited converter,
2. The method of operating a converter according to claim 1, wherein the converter is configured to generate reactive power equal to or less than the value of ^A2 - ^P2 . 3 A value obtained by dividing the power command value converted into AC power by the self-excited converter by the DC input voltage to the self-excited converter is used as a reference value for the constant DC input current to the self-excited converter. An operating method for a converter according to claim 1.