JPS61210826A - Controller for dc multi-terminal power transmission - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a control device for DC multi-terminal power transmission, and more particularly to a control device effective for speeding up power recovery when a conversion device fails in commutation.

[Background of the invention]

Practical use of DC multi-terminal power transmission is desired to expand the scope of application of DC power transmission. FIG. 2 is a diagram showing one form thereof. In the figure, 1, 71, 72 are AC systems, 2, 61, .
62 is a transformer, 3,51°52 is an AC to DC or DC to DC converter, 40 is a DC transmission line, 41.42 is a DC reactor, 300, 510, 520 are converters 3,
It is a control device of 51°52. In order to clarify the problems of multi-terminal power transmission, the converter 3 will be explained as a forward converter that converts alternating current to direct current, and the converters 51 and 52 will be explained as inverse converters that convert direct current to alternating current. .

As is known from Japanese Patent Publication No. 43-8641, in order to operate a multi-terminal system stably, it is necessary to
An effective control method is to determine the (DC) voltage and the (DC) current for the remaining terminals.

In this case, it is assumed that the control method is followed, and the forward converter 3 determines the DC voltage, and the inverse converters 51 and 52 determine the DC current. Note that this assumption is not essential to the invention, and there is nothing wrong with determining the voltage with one of the inverters. A diagram showing the operation of each converter in such a case is shown in FIG. In the figure, the horizontal axis shows the DC current and the vertical axis shows the DC voltage, and the forward converter 3 has constant voltage characteristics of the DC voltage Vp and the maximum allowable current of the converter 1. It has a constant current control characteristic that limits the current. On the other hand, the inverse converter has a constant current control characteristic of a current value of 1 pl corresponding to the required power, Ipz, and a constant margin angle control characteristic in which the converter keeps the margin angle constant during commutation. Therefore, the operating point is 01+02 points. Note that the operating point O indicates the case where two inverse converters are combined. In this operating state, for example, if a ground fault occurs in the AC transmission line of the AC system 71 and the inverter 51 fails to commutate due to a drop in AC voltage, the current flowing in the inverter 52 will also flow to the inverter 51. As a result, electricity transmission will have to be stopped. Commutation failures occur frequently in inverters, and if power transmission is stopped every time commutation failures occur, power transmission reliability will drop. As a countermeasure to this problem, it has been considered to increase the value of the DC reactor 41, 42, etc. in order to slow down the rise of the current flowing through the inverter and prevent the spread of the accident, but this is not a complete countermeasure and is uneconomical. Dechiru. Another method has been considered to use a DC breaker to disconnect a converter that has failed commutation from a multi-terminal system, but this method is more expensive than the former and also makes maintenance and inspection of the DC breaker difficult. Tomo.

[Purpose of the invention]

An object of the present invention is to solve the problems of the prior art described above and to provide a multi-terminal power transmission control device that can operate stably without stopping power transmission even when converter commutation fails.

[Summary of the invention]

In order to prevent a commutation failure from occurring at one terminal of a multi-terminal power transmission system, which would lead to a power transmission stoppage, the control angle of the forward converter is adjusted by the detection signal from the converter's commutation failure detection device. was shifted to the inverter side for a certain period of time to cut off the DC current in the system and return to the original operating state after eliminating the commutation failure.

[Embodiments of the invention]

An embodiment of the present invention will be explained below with reference to FIG. The same numbers as the previous one indicate the same thing, so to explain the new ones, 301 to 304 indicate detailed blocks of the control device 300 of the forward converter 3, and 301 sets the converter current to the maximum allowable value ■, 302 is a constant voltage control circuit for limiting the voltage of the multi-terminal system to Vp; 303 is a constant current control circuit for limiting the voltage of the multi-terminal system to Vp;
a selection circuit for selecting the output of 1 or 302;
4 is the output (control) of the control circuit selected by 303
This is a phase control circuit that outputs a pulse whose phase is controlled according to voltage Ec. An example of the input/output characteristics of this phase control circuit is shown in FIG. In Figure 4, the control angle α with respect to the control voltage
1. It shows a linear phase characteristic in the range of ~α1.8,
The characteristic is that if the control voltage is increased, the phase (control angle) of the output pulse of the phase control circuit is also increased. On the other hand, 511~
514 and 521 to 524 are control devices 510 and 52, respectively.
0, 511 and 521 are constant margin angle control circuits, and 512 and 522 are current command values Ipl and I, respectively.
A constant current control circuit having F5 operates so that the currents flowing through each converter become Ipl and Ipz. 513,5
23 is a selection circuit which selects the output (control) voltage of the circuit in the operating state from among the outputs of the constant margin angle control circuit and the constant current control circuit described above. 514 and 524 are the same fourth
This is a phase control circuit with the phase characteristics shown in the figure. The above are the details of the conventional control device, and the present invention uses a commutation failure detection device, for example, increasing the control voltage of the J@ converter for a certain period of time based on the detection signal of Japanese Patent Application No. 118992/1982 to shift the control angle. Lower the voltage of the forward converter by
A device has been added to cut off the direct current in the grid. 3
05,306 is the Sonata circuit. Reference numeral 305 is a signal generation circuit for shifting the control angle to the inverter side for a certain period of time based on a commutation failure detection signal from the commutation failure detection device described below.
A control voltage Ec' necessary for shifting to 20 degrees is output. 306 is a maximum value detection circuit, which is similar to the selection circuit 3 described above.
This circuit outputs the larger voltage between the control voltage selected by No. 03 and the output of the signal generation circuit. Naturally, the signal generated by the signal generating circuit also varies depending on the phase characteristics of the phase control circuit, and the case of the phase characteristics shown in FIG. 4 will be described here. The operation of this circuit will be explained using FIG. FIG. 5 shows the DC voltage Va of the forward converter 3, the current of the inverse converter 51, and the inverse converter 52.
FIG. 4 is a diagram showing a case where an accident occurs in the AC system of the inverse converter 71 and the inverse converter 51 causes a commutation failure at a current of , and a control voltage Ec of the forward converter 3. When commutation failure occurs at time t1, the current in inverter 51 increases and the current in 52 decreases.

If no control is performed, the current in the inverse converter 51 will constantly flow at the maximum allowable current of the forward converter, as shown by the dashed line. However, when the signal generation circuit is activated by the detection signal of the commutation failure detection device described below and the control angle is sufficiently shifted by increasing the control voltage E of the forward converter 3, the current of the inverse converter 51 is attenuated. However, it becomes zero at time t2.

13)1. When the control voltage Ec of the forward converter 3 is returned to its original value at the point in time, the inverse converters 51 and 52 perform normal commutation operation, and operation can be resumed without stopping power transmission as previously thought. Can continue.

Note that it is preferable for system operation that the signal generation circuit is not activated when a single commutation failure occurs, but activated when commutation failure occurs continuously over a specified period of time. This is because commutation failures in the converter rarely occur consecutively, and in many cases, it is possible to recover by one commutation failure.

Furthermore, when interrupting the DC current and restoring the original operating state, it is clear that it is preferable to use a method that allows the DC voltage and current to rise smoothly in order to prevent overvoltage from occurring when the DC transmission line is long. Since this can be easily inferred from the present invention, the details will not be described.

〔Effect of the invention〕

According to the present invention, without having to do things such as enlarging the DC reactor or installing a DC circuit breaker in the DC circuit, by adding a simple device, it is possible to stabilize power transmission without stopping even in the event of successive commutation failures. This has the effect of realizing multi-terminal power transmission that can be operated.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a control device for multi-terminal power transmission according to the present invention, and FIG.
The figure is a diagram of one form of a multi-terminal system, Figure 3 is a diagram for explaining the operating state of each terminal in Figure 2, Figure 4 is a diagram of one phase characteristic of the phase control device, and Figure 5 is a diagram for explaining the operating state of each terminal in Figure 2. It is an operation waveform at the time of commutation failure by the control device of the present invention. 1.71.72...AC system, 2,61.62...
Transformer, 3,51.52...Converter, 40...DC transmission line, 41.42...DC reactor, 300,5
10°520...control device, 301,512,522
... constant current control circuit, 302 ... constant voltage control circuit,
511゜521... Constant voltage control circuit, 303,513
゜523...Selection circuit, 304,514,524...
・Phase control circuit, 305...Signal generation circuit, 306・
...Maximum value selection circuit.

Claims (1)

[Claims] 1. In DC multi-terminal power transmission where at least two or more converters are connected in parallel to a DC transmission line, the control angle of the forward converter that converts AC to DC is determined by the commutation failure detection signal. A control device for DC multi-terminal power transmission, which is characterized by shifting to the inverter side for a certain period of time.