JPS62152334A - Control of ac/dc converter - 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] [Technical Field of the Invention] The present invention provides a method for detecting an accident at one end of the AC power system when AC/DC conversion equipment is connected to the AC power system for the purpose of DC power transmission or frequency conversion. The present invention relates to a method of controlling an AC/DC converter when an AC/DC converter occurs.

[Technical background of the invention and its problems]

FIG. 3 shows a schematic block diagram of a control device in a conventional DC power transmission system converter.

In the converter of the DC transmission system, the DC sides of the converters LA and IB are connected by a DC transmission line 8 via DC reactors 2A and 2B, respectively, and the AC sides of each converter LA and IB are connected to a converter transformer 4A, 4B, breaker 5A,
It is configured to be connected to respective AC systems 6A and 6B via line 5B.

Conventional converters LA and IB have a constant margin angle control circuit 11A.

11B constant current control circuits 18A, 18B are provided, and the constant margin angle control circuits 11A, 11B control the minimum margin angle which is the output of the margin angle setter 18A, 18B which sets the minimum margin angle of the converter. The reference value and the output of the constant reactive power control circuit 48 necessary as a converter are added to the adder 17A.

Converter IA, IB
It operates to follow the margin angle of. Further, the current reference value that is the output of the constant power control circuit 44 and the DC current detection value that is detected by the DC current detectors 21A and 21B and converted into a value that is easy to handle as a control circuit are added to the addition circuit 23A.
, 23B and the difference is input to the constant current control circuit 13
A, 13B, the DC current flowing through the DC power transmission line 3 is controlled to follow the current reference value. Switch 24A.

24B is a current margin setting device 25A, with only the one corresponding to the converter operating as an inverse converter being closed.

The current margin which is the output of 25B is the current margin of the adder circuit 23A.
.

23B. This current margin function and control to select the output that advances the control advance angle of the converter among the outputs of the constant margin angle control circuits 11A, IIB, and the constant current control circuits 13A, 13B as the output. Due to the functions of the lead angle priority circuits 28A and 28B, if the switch 24B is closed and the switch 24A is open, the control lead angle priority circuit 28A receives the output of the constant current control circuit 13A. Furthermore, the output of the margin angle control circuit 11B is supplied to the control advance angle priority circuit 28B. (For convenience of explanation, the following description will be made assuming that the switch 24A is open and the switch 24B is closed.) The outputs of the control advance angle priority circuits 28A and 28B are respectively input to the phase control circuits 29A and 29B, where the converter The signal is converted into a pulse signal that determines the ignition timing of IA and IB, and is provided as a gate pulse signal to converters IA and IB via pulse amplification circuits 30A and 30B. It is a known technique to configure a control circuit for a converter as described above.

Next, FIG. 2 shows a detailed block diagram of a constant margin angle control circuit in a conventional control device for a DC power transmission system. Furthermore, the third
Elements that are the same as those in the figures are indicated by the same reference numerals, and explanations thereof will be omitted.

The constant margin angle control circuits 11A and IIB in the converter control device of the DC transmission system calculate the overlap angle using the DC winding voltage, DC current, and commutation reactance of the converter transformers 4A and 4B, and α= π-(u+r) [However, α...
Control advance angle, r: margin angle, U: overlapping angle], the control advance angle is determined so that the margin angle of the converter required at each time is maintained.

The minimum margin angle of the converter is set in the constant margin angle control circuits 11A and 11B. The margin angle setter 18A, 18B
The minimum margin angle setting reference value, which is the output of
The margin angle reference value added in 17B and the transformer 7A,
7B and signal converters 50A and 50B, the converter transformer 4 is converted into a value that is easy to handle as a control circuit.
DC winding voltage detection values of A and 4B and DC current detector 21
A, 21B, and a DC current detector that has been converted into a value that is easy to handle as a control circuit is inputted via signal transformers 51A and 51B, respectively. Constant margin angle control circuit 11A.

The DC current detection value inputted to 11B is multiplied by the commutation reactance via a multiplier 81. This signal and
The DC winding voltage detection values are each led to a divider 82 to obtain a signal as one overlap angle. This signal as the overlap angle is led to the adder 83, and the other input of the adder 83,
That is, after calculating the margin angle reference value which is the output signal of the adder 17, the output thereof is input to the function conversion circuit 84. The output of the function conversion circuit 84 is converted to a value that is easy to handle as a one-phase control circuit, and is then converted to a value that is easy to handle as a one-phase control circuit, and is then passed to the control advance angle priority circuits 28A, 28.
It is configured to lead to B. As explained above, it is also a known fact to configure a constant margin angle control circuit.

Now, the constant margin angle control circuit described above is an open loop control circuit. Open-loop control circuits have better resistance to disturbances than closed-loop control circuits, and like constant margin angle control circuits, they are required to always maintain a stable margin angle of the converter in the event of various disturbances. This is an extremely effective circuit configuration.

In other words, when there is a sudden change in AC system voltage or DC current, the change directly affects the signal that determines the control advance angle, which is the output signal of the constant margin angle control circuit, so that the appropriate margin angle can be quickly set. and can be reliably maintained, effectively preventing the converter from commutation failure.

However, the point that a change in the control advance angle changes the reactive power consumed by the converter, and the change in AC system voltage is as follows.
Considering the fact that it is approximately equal to the product of the change in reactive power and the reactance of the AC system, the conversion device equipped with a constant current control circuit is weak in the AC system, so-called the ratio of the short-circuit capacity of the AC system to the capacity of the conversion device. If the conversion device is connected to an AC system with a small value, the effect of the constant margin angle control circuit for stably operating the conversion device may have the opposite effect. In other words, for example, if the AC system voltage to which a converter functioning as an inverter is connected suddenly changes, the constant margin angle control circuit will quickly respond to the change in voltage and abruptly change the control advance angle. However, this series of operations causes a sudden change in the reactive power consumption of the converter, which induces an overvoltage of the AC system voltage and expansion of waveform distortion, resulting in a commutation failure. Not only is this unavoidable, but in weak AC systems, there is an inherent problem in that continuous commutation failures lead to system collapse.

[Purpose of the invention]

Therefore, an object of the present invention has been made to eliminate the above-mentioned drawbacks, and is a method for controlling an AC/DC converter, which minimizes the influence on the AC system and maintains stable operation of the AC/DC converter. It provides:

[Summary of the invention]

In order to achieve the above object, the present invention provides that the output signal of the constant margin angle control circuit which determines the control lead angle of the converter acting as an inverse converter is changed to a control lead angle. When the signal acts on the side that advances the control angle, it responds immediately, and when the same signal acts on the side that delays the control advance angle, it responds with an arbitrary time constant. In other words, when the control angle advances, open loop control is performed. By functioning as a circuit and delaying the control angle, by functioning as if it were a closed loop control circuit, the sudden change in the reactive power consumption of the converter that was caused by the conventional constant margin angle control circuit is slowed down, and the AC The aim is to minimize waveform distortion and overvoltage in the grid.

[Embodiments of the invention]

FIG. 1 is a block diagram showing one embodiment of the present invention.
The circuit 90 is an element added to achieve the object of the present invention, and has a discrimination function of responding to the output signal with a different time constant depending on the polarity of the rate of change of the input signal. Elements that are the same as those in FIGS. 2 and 3 are indicated by the same reference numerals, and explanations thereof will be omitted.

The operation of this circuit will be explained below. For convenience of explanation, it is assumed that an accident occurs in the AC system 6B and the AC system voltage drops while the converter IB is operating as an inverse converter.

In such a case, the constant margin angle control circuit 11B outputs a signal that rapidly advances the control advance angle, thereby acting to avoid commutation failure of the converter IB. Since the circuit 90 is configured in advance to respond immediately (time constant = O) when a signal that changes the control advance angle in the direction of advancing is input, a drop in the AC system voltage is detected via the signal conversion circuit 50B.
After that, it passes through a divider 82 and an adder 83, and then passes through a function conversion circuit 84 without delay even though it passes through a circuit 90.
Since it is led to the control advance angle priority circuit 28B and promptly changes the firing phase of the converter IB, it is possible to immediately respond to a voltage drop in the AC system 6B, and it operates in the same manner as the conventional control method.

Next, when the fault in the AC system 6B is removed and the AC voltage is restored, the output of the signal conversion circuit 50B returns to the value before the fault, and accordingly, the output of the divider 82. The output of adder 83 responds rapidly and acts to return the control advance angle to its pre-accident value.

In this case, the circuit 90 is configured to respond with an arbitrary time constant (τ>0) set in advance, so even if the output signal of the adder 83 changes rapidly in the direction of delaying the control advance angle, , since the input signal given to the function conversion circuit 84 changes slowly with the time constant of the circuit 90,
As a result, the firing phase of converter IB gradually returns to its pre-accident value.

Furthermore, if an accident occurs again in the AC system 6B during the series of operations after recovery from the accident described above, a circuit is installed so that the ignition phase of converter IB can be rapidly advanced as in the case of the first AC voltage drop. 90 works.

In other words, the single circuit 90 is not affected by the magnitude of the output signal of the adder 83 and responds only to the polarity of the rate of change of the signal, so it always functions in the same way even with repeated disturbances. The circuit system of the present invention does not fix the firing phase of the converter to a constant value for a certain period of time in response to a disturbance, and return it at an arbitrary time constant, unlike the conventional phase advance circuit. The ignition phase of the converter can be determined accordingly, without any loss of functionality of the conventional constant margin angle control circuit, and can be applied to AC systems caused by sudden changes in the reactive power consumption of converter IB. Since the expansion of waveform distortion of voltage 6B can be minimized, it is not only possible to prevent continuous infusion failure of converter IB, but also to effectively prevent overvoltage of AC system R6B due to recovery from an AC system fault. It has the advantage of being able to

The above explanation has been made only regarding the converter control circuit at one end of the AC/DC converter, but it goes without saying that similar control can be performed in the converter control circuit on either side.

Further, in the above example, the output signal of the adder 83 is configured to respond with different time constants depending on the direction of change (polarity of the rate of change), but the constant margin angle control circuit ILA (ILB)
The output signal, or the AC voltage detection signal or DC current detection signal input to the constant margin angle control circuit, or both have similar functions. A similar effect can be achieved by adding a responsive function.

〔Effect of the invention〕

As explained above, according to the present invention, when an accident occurs in the AC system, it is possible to stabilize the AC system without abruptly changing the reactive power consumed by the converter.
Moreover, stable operation of the AC/DC converter can be realized without causing continuous commutation failure or overvoltage in the inverter.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram of an AC/DC converter used in a DC power transmission system, and FIG. 3 is a block diagram of a conventional constant margin angle control circuit. IA, IB...Converter, 2A, 2B...DC reactor, 3...DC transmission line, 4A, 4B...Converter transformer, 5A, 5B... Breaker, 6A
, 6B...AC system, 7A, 7B...transformer,
11A, IIB... constant margin angle control circuit, 13A, 13
B... Constant current control circuit, 18A, 18B... Maximum margin angle setting device, 24A, 24B... Switch, 25A
, 25B...Current margin setter, 21A. 21B... DC current detector, 28A, 28B... Control advance angle priority circuit, 29A, 29B... Phase control circuit, 30A, 30B... Pulse amplifier circuit, 41...
- Power setting device, 43... Power detector, 45... Reactive power setting device, 47... Reactive power detector, 48... Constant reactive power control circuit, 84... Function conversion circuit, 90・・・
・Time constant discrimination circuit. Agent Patent Attorney Noriyuki Chika Yudo Hirofumi Mitsumata Figure 1

Claims (1)

[Claims] At least, in an AC/DC converter that has a constant current control system and a constant margin angle control system, if a sudden change occurs in the AC system on the inverter side, the constant margin angle control circuit that determines the control angle of the inverter A control method for an AC/DC converter, characterized in that a signal corresponding to an output signal is made to respond with different time constants depending on the polarity (direction of change) of the rate of change of the signal.