JPS5943913B2 - AC/DC converter operation control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an operation control method for an AC/DC converter, and more particularly to an operation control method suitable for keeping loss in a damping circuit of a converter within an allowable range.

The AC/DC converter can generally handle 51 reactive power loads, and can make the DC system cooperate with the voltage reactive and power control of the connected AC system. FIG. 1 is a diagram showing an example of applying a DC system to reactive power control of a generator. In the figure, GI and G2 are generators, Li is load,
DCL is DC reactor, DL is DC line, CONI,
C0N2 is an AC/DC converter that converts alternating current to direct current and direct current to alternating current, TR is a converter transformer, ACPT is an alternating current voltage converter, ACCT is an alternating current transformer, and PD is the detected alternating current voltage of the alternating current system and alternating current. Current to said converter CO
A power detector that detects the power flowing into the NI, Pp is a signal from an operation command center (not shown), and a power command value for setting the power transmitted in the DC system, SUM, is the power command value Pp and the above-mentioned power. An adder PA adds the output of the detector PD with the polarity shown, and PA is a power differential amplifier that amplifies the output of the adder SUMI, and the power command value Pp, detected power value Pf, adder SUMI, and power deviation The amplifier PA constitutes a constant power control circuit PR.

DCCT is a direct current transformer, SUM2 is an adder that adds the output of this direct current transformer DCCT and the output of the power deviation amplifier PA with the polarity shown, and CA is this adder SUM.
A current deviation amplifier that amplifies the output of the power deviation amplifier PA, a detection value 11 of the DC current, and an adder SUM.
2 and the current deviation amplifier CA constitute a constant current control circuit ACR. API is an automatic pulse phase shifter that outputs a gate pulse of the thyristor of the converter C0N according to the magnitude of the output of this constant current control circuit, and PFD is an AC voltage and an AC current of a different AC system. A power factor detector that detects the power factor of the system from the detection signal and outputs a voltage corresponding to the power factor, PFp is a signal from an operation command center (not shown) and is a power factor setting value, and SUM3 is this power factor setting. an adder that adds the value PFp and the output of the power factor detector PFD with the polarity shown; PF;
A is a power factor deviation amplifier that amplifies the output of this adder SUM3, and AP2 is an automatic pulse phase shifter similar to the above API. Generally, when a generator is connected to a large-capacity cable or an ultra-high voltage power transmission system, phase-advanced operation of the generator during light loads becomes a problem.

However, by interconnecting the DC system as shown in Figure 1, the converter (inverse converter) is a load that takes delayed reactive power from the generator's perspective, so the required reactive power of this inverse converter is By controlling the electric power, it is possible to prevent the generator from operating in phase advance mode. now,
If the active and reactive powers of the generator are P,, Q8, those of the converter are Pl, Ql, and those of the load are Pt, Qt-Qc, then in the AC system, Pg-Pt-Pi, Qg2Qi+Qt
-QO relationship is established. Here, if the active power Pt is constant and the lagging reactive power load Qt is reduced, the generator has no choice but to perform phase-advancing operation. At this time, phase advance operation of the generator can be prevented by detecting the power factor of the lightning generator, increasing the control angle β of the inverter, and increasing the required reactive power Q1. This reactive power control of an AC system using DC interconnection has the advantage of quick response and a high degree of freedom.
However, if large phase-lag reactive power is required to prevent phase-advancing operation of the generator, the control angle of the converter becomes large, which increases the loss of the damping circuit DAC shown in FIG. 2. FIG. 3 is a diagram depicting the loss of the damping circuit with the control angle as the horizontal axis, using the commutation reactance X of the converter as a parameter, and represents this. An increase in the loss of this damping circuit does not necessarily mean that the efficiency of the converter deteriorates, but also that a resistor Rd and capacitor C4 of a size that matches the loss of this damping circuit are required9.
This is undesirable because the damping circuit occupies more space within the valve, making the device larger. An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide an AC/DC converter that can operate stably while suppressing the loss of the damping circuit to an allowable value.
It is to provide a driving method.

The main points of the present invention will be explained using FIGS. 4 and 5.

Figure 4 shows the loss of the damping circuit at an AC voltage of 1p. u. ，
DC current 1p. U. , is a diagram illustrating an example of the maximum allowable control angle when the control angle is 40 pressure (the design value of the damping circuit) and when the AC voltage changes. FIG. 5 is a diagram when the direct current is similarly changed. As shown in the figure, the control angle to keep the loss of the damping circuit within the allowable range varies linearly with changes in AC voltage and DC current (), and the converter is operated at a control angle below this value. Then, the loss of the damping circuit can be kept within the allowable value. For this reason, a limiter having the characteristics shown in FIGS. 4 and 5 is provided in the control circuit in response to changes in alternating current voltage and direct current to prevent the loss of the damping circuit from exceeding an allowable value at all times.

Since the FhI leg angle (voltage value) of this limiter differs when the converter is operating as a forward converter and when operating as a reverse converter, two limiters are used when the converter is operating as a forward converter and when operating as a reverse converter. It can now be changed using a setup switch.

In addition, since it is necessary to operate beyond this allowable range when starting or stopping, etc., a switch is set to remove the limit when starting or stopping. In addition, in order to ensure stable operation even in the event of an accident such as commutation failure, we have made it possible to operate beyond this allowable range for a short period of time depending on the magnitude of the DC voltage. An embodiment of the present invention is shown in FIG.

Items with the same symbols as in the previous figure indicate items that operate in the same way, so only those with new symbols will be explained. 0R is a constant margin angle control circuit for specifying a control angle that allows stable commutation operation when the converter is in reverse operation. The set value Q,
A reactive power control circuit for controlling so that PR is a constant power control circuit, and a signal ΔI from an operation command center (not shown)
d is a current margin command which functions to saturate the amplifier of the constant current control circuit by using the switch SW to add to the adder SUM2 with the polarity shown in the figure only when the converter CONl is in reverse converter operation. VS is a voltage selection circuit that selects the most suitable output voltage for the converter CON, Q operation from among the constant current swing leg circuit, constant margin angle control circuit GR, and reactive power control circuit QR, and FGl and FG2 are the voltage selection circuits for selecting the output voltage most suitable for the operation of the converters CON and Q; It is a function generator that outputs an output pressure corresponding to the maximum 11jI leg angle at which the loss of the damping circuit is an allowable value from the voltage detection value and the DC voltage detection value (FGl is the converter CO
Nl is used during sequential converter operation, and FG2 is used during reverse converter operation). This specific circuit is shown in FIG. 7, and the operation of this circuit is not shown in FIG. In FIG. 7, R1 to Rl3
is a fixed resistance, VRl to VR3 are variable resistances, 0P1 to 0P
3 is an operational amplifier. To explain the operation of this circuit with reference to Fig. 8, the operational amplifier 0P1 outputs a voltage proportional to the deviation of the DC current from a certain reference value (proportionality coefficient Ki). The operational amplifier 0P2 outputs a voltage proportional to the deviation of the AC voltage from a certain reference value (proportionality coefficient K8) (the operational amplifier 0P2 may have a delay to remove ripples in the input signal), 0P3 is used to add the outputs of these operational amplifiers 0P1 and 0P2 and the bias voltage (voltage Vα that provides the arm angle α at which the loss of the damping circuit determined by the standard value of AC voltage and standard value of DC current is an allowable value). It is something. This circuit determines the allowable control angle at any AC voltage value and DC current value.

In addition, switches SWl and SW2 in FIG. 6 close SWl when the converter CONl is performing a forward converter operation and close SW2 when the converter CONl is performing an inverse converter operation according to a command from the switch drive circuit DS. , it closes when the converter starts and stops. D, to D4 are diodes, IN is a sign inverter 9, Dl and D2 output the higher one of both input voltages, and D3 and D4 output the lower one of both input voltages. Due to the action of this diode, the control angle can be suppressed within an allowable range. Therefore, operation can be performed while the loss of the damping circuit is suppressed within the permissible value. Although the figure shows a block diagram of the control circuit for only one converter station, a similar control circuit is provided at the other end, so that when one end of V1 operates as a forward converter, the other end operates as an inverse converter. Perform the operation as usual. As described above, according to the present invention, since operation can be performed within the allowable loss of the damping circuit of the converter, efficient operation can be achieved and an economical valve structure can be achieved.

Another embodiment of the invention is shown in FIG.

In this embodiment, the converter Q reactive power is controlled in a closed loop, whereas the previous figure controlled it in an open loop. Components with the same symbols as in the previous figure operate in the same way, so we will only explain the new ones. A detection circuit, SUM4, is an adder that adds the output of this reactive power detection circuit QD and a reactive power set value Qp (signal from an operation command center, not shown) with the polarity shown, and QA amplifies the output of this adder. This is a reactive power deviation amplifier.

With this circuit, as in the previous figure, the reactive power output by the converter can be controlled to a set value within the allowable loss of the damping circuit.

However, as shown in Figures 6 and 9, since the upper limit of the control angle is limited in these embodiments, if a DC system accident such as commutation failure occurs, the accident can be suppressed. The disadvantage is that sufficient control is not possible.

An example in which this measure is taken is shown in FIG. The difference from the previous figure is that the detected value Vdf of the DC voltage is additionally used as the human input signal of the function generators FGl and FG2.
To explain only the parts that are different from the previous figure, DCPT is a DC voltage converter for detecting DC voltage. ．． FG,, FG2 use the extra DC voltage detection value Df as an input signal of the function generator shown in FIG. This allows operation beyond the permissible range. The specific configuration of this circuit can be easily realized by adding a correction circuit based on a DC voltage detection value in parallel to the operational amplifier 0P3 shown in FIG. An example of this is shown in FIG. FIG. 12 shows another embodiment of the present invention including a correction circuit based on a detected DC voltage value.

In this figure, the control angle limiters are collectively provided in the voltage selection circuit VS. This circuit also allows stable operation while keeping the loss of the damping circuit within the allowable range, as in the previous figure.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a DC system that performs conventional reactive power control operation, Figure 2 is a diagram showing a damping circuit, and Figure 3 is a block diagram of a DC system that performs conventional reactive power control operation.
The figure does not show the loss of the damping circuit with respect to the control angle. Figures 4 and 5 show the control angle for suppressing the loss of the damping circuit to an allowable value when changing the AC voltage and DC current. 6 is a diagram showing an embodiment of the present invention, FIG. 7 is a specific example of a circuit for realizing the characteristics shown in FIGS. 4 and 5, and FIG. 8 is an explanatory diagram of the operation of the circuit shown in FIG. 7. , FIGS. 9 to 12 are diagrams showing other embodiments of the present invention. GR: Constant margin angle control circuit, QR:
Reactive power control circuit, PR...--Power control circuit, V
S...Voltage selection circuit, N...Sign inverter, SWl, SW2...Switch, DS...
...Switch drive circuit, D, to D4...Diode, FG,, FG2...Function generator, Δ
Id...Current margin command, Qp,...
- Reactive power setting value, E2t...AC voltage detection value, Idf...DC current detection value.

Claims (1)

[Claims] 1. In a method for controlling the operation of an AC/DC converter configured with a thyristor or the like, a control angle limiter is provided, and the limit value of the control angle limiter is set to a permissible range of loss in a damping circuit of the AC/DC converter, A method for controlling the operation of an AC/DC converter, characterized in that the AC voltage and the DC current are changed based on the magnitude of the AC voltage and the DC current. 2. In the operation control method according to claim 1, the control angle limiter is configured to release the restriction on the control angle when the AC/DC converter is started or stopped. Control method.