JPS63114534A - Control of ac/dc converter - Google Patents

Abstract

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

Description

[Detailed Description of the Invention] [Objective of the Invention] (Technical Field of the Invention) The present invention provides a method for converting power to one end of an AC power system when AC/DC converter equipment is connected to an AC/DC power system for the purpose of DC power transmission or frequency conversion. This invention relates to a method of controlling an AC/DC converter when an accident occurs.

(Prior Art) FIG. 3 shows a schematic block diagram of a control device in a conventional conversion device for a DC power transmission system. In the converter for a DC power transmission system, the DC sides of converters 1A and 1B are connected by a DC power transmission line 3 via DC reactors 2A and 2B, respectively, and each converter 1A.

The AC side of 1B is converter transformer 4A, 4B, and circuit breaker 5A.
, 5B to the respective AC lines 6A.

6B.

Conventionally, the constant margin angle control circuit 11A was installed in the converters 'IA and 1B.
,, 11B, constant current control circuits 13A, 13B are provided, and the constant margin angle control circuits 11A, 11B are a margin angle setting device 18A that sets the minimum margin angle of the converter.

The minimum margin angle setting base Q (((value) and the output of the constant reactive power control circuit 48 necessary as a converter are added by the adders 17A and 17B)
It operates to follow the margin angles of converters 1A and 1B.

Further, the current reference value which is the output of the constant power control circuit 44,
DC current detector 21A.

The DC current detection value detected by 21B and converted into a value that is easy to handle as a control circuit is input to adders 23△ and 23B, and the difference is input to constant current control circuits 13A and 13B to control the DC transmission line. The direct current flowing through No. 3 is controlled so as to follow the current reference value.

Of the switches 24A and 24B, only the one corresponding to the converter acting as an inverse converter is closed, and the current margins that are the outputs of the current margin setters 25A and 25B are input to the adders 23A and 23B. This current margin function and the constant margin angle control circuit 11A.

113, a control advance angle priority circuit 28A that selects, as its output, an output that advances the control advance angle of the converter more among the output signals of the constant current control circuits 13A and 13B;
28B, if the switch 24B is closed and the switch 24A is open, the output of the control advance angle priority circuit 28A is the constant current control circuit 13.
The output of the constant margin angle control circuit 11B is selected as the output of the control advance angle priority circuit 28B. (For convenience, the following description will be made assuming that the switch 24A is open and the switch 24B is closed.) The output signals of the respective control advance angle priority circuits 28A and 283 are input to the phase control circuits 29A and 293,
Here, it is converted into a pulse signal that determines the firing timing of the converters 1A and 1B, and is sent to the PUMES amplifier circuit 30A.

The signal is configured to be applied as a gate pulse signal to the converters 1A and 1B via 303.

Configuring a control circuit for a converter as described above is a known technique.

Next, FIG. 2 shows a detailed block diagram of a phase detector used in a phase control circuit in a conventional control device for a DC power transmission system. Incidentally, the same elements as in FIG. 3 are indicated by the same reference numerals, and the explanation thereof will be omitted.

Phase control circuit 29A in converter of DC power transmission system
, 29B uses a phase detector using a phase-locked loop (hereinafter abbreviated as PLL). The input signal of the phase detector is the transformer 7A.
, 7B, the three-phase signal eiu detected from the AC system to which the converter is connected.

eiv and eiw are used. Said transformer 7A.

The AC system voltage detected at 7B is guided to the phase detector 50, where it is converted from three phases to two phases to produce two-phase sine wave signals eid, e.
It becomes iq. eid and eiq can be respectively expressed as e i d=Eo − cosθO e iq=EO−s i nθO, and the two-phase sine wave signal e with unit amplitude of
Since od and eoq can be similarly expressed as eod=cosθ1 eoq=s inθ1, the phase difference Δθ (=00-01) between these two sets of two-phase sine wave signals is expressed by the trigonometric function relational expression % θ0)2 By controlling the phase θ1 of the unit amplitude two-phase sine wave signals eod and eoq so that this phase signal Δθ becomes smaller, the unit amplitude two-phase signal that follows the input signals eid and eiq is obtained. By obtaining a sine wave signal, phase detection is performed without performing zero voltage detection or the like.

Detecting the phase using such a method is also a well-known technique, and can quickly follow changes in the frequency and phase of the input signal.

(Problem to be Solved by the Invention) However, even in converter equipment equipped with a phase detector having such excellent characteristics, the converter has a weak AC system, that is, the short circuit capacity of the AC system with respect to the @ amount of the converter. When connected to an AC system in which the ratio of

For example, if a sudden and large voltage fluctuation occurs due to an accident in the AC system to which the converter is connected,
The above-mentioned defective phenomenon is observed.

The output signal of the divider 59 inside the phase detector 50 is the phase difference Δ
This is a signal that increases or decreases depending on θ, and the control amplifier 61 functions to minimize the phase difference Δθ according to this signal.

Therefore, if a disturbance other than the phase difference signal, which is induced by a disturbance caused by an accident in the AC system from which the three-phase sine wave signal is obtained as an input signal, is superimposed on the output signal of the divider 59, the control amplifier 61 loses its ability to follow the original phase difference signal, making it impossible for the phase detector 50 to detect a normal phase. As a result, converter 1A,
This causes a disturbance in the phase of the gate pulse applied to 1B, and the forward converter in FIG. 3 becomes unable to function in response to the output signal of the constant current control circuit 13A (13B). 11B) becomes impossible. This is because the phase control circuit 29A (29B>
and constant current control circuit 13A (13B) and constant margin angle control circuit 11A (11B).In particular, since the constant margin angle control circuit is an open loop control circuit, fluctuations in AC system voltage As a result, the reactive power consumed by the converter changes suddenly, which further fluctuates the AC system voltage.These series of fluctuations are caused by the phase control circuit 5.
0, but also affects the active power that the constant current control circuit is trying to control, and the disturbance occurring in the AC system does not converge, and the divider 59 of the phase detector 50 This results in a continuous disturbance to the output signal. If such a phenomenon occurs in a converter connected to a weak AC system, there is a problem that not only the converter cannot be operated stably, but also a system collapse of the AC system.

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

(Structure of the Invention) (Means and Effects for Solving the Problems) In order to achieve the above object, the present invention adds a notch filter (band-elimination filter) to the phase detector for the phase control circuit of the converter. By doing so, in the event of an AC system fault, the disturbance signal superimposed on the phase difference signal (Δθ) of the phase detector is eliminated, stable operation of the converter is obtained, and fluctuations in the active power and reactive power applied to the AC system are minimized. This is what we are trying to do.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention, in which a band-elimination filter (notch filter) 80 is an element added to achieve the object of the present invention.

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. AC system 6A
(6B> is superimposed on the input signals eiu, eiv, eiw through the transformer 7A (7B) and taken into the phase detector 50, and as a result of the calculation, the output signal s of the divider 59 is
This appears as a disturbance of inΔθ, but since there is a band elimination filter 80 with a cutoff frequency according to the period of the disturbance before reaching the arc sine function conversion circuit 60, the disturbance signal in the desired frequency band is divided. Output signal sinΔθ of the device 59
Since only the original phase difference signal is applied to the arc sine function circuit 60 and the control amplifier 61, the phase detector 50 can faithfully follow the fundamental frequency of the AC system voltage, and the converter 1A (1B ) without causing any disturbance in the phase of the gate pulse given to the gate pulse, and also to eliminate continuous fluctuations in the AC system voltage caused by sudden changes in reactive power due to the behavior of the inverse converter starting from the disturbance in the pulse phase. It has the advantage of being able to

The above explanation is based on the case where a band-elimination filter with a single cut-off frequency is used, but when the disturbance appearing in the phase difference signal Δθ cannot be uniquely determined due to the AC system conditions and the transfer function of the control circuit. It goes without saying that similar effects can be obtained by using a combination of band-stop filters having corresponding cut-off frequencies.

Further, in the above example, a band-elimination filter is placed at the output of the divider 59, but a filter having the same function may be inserted at each input of the sum-of-squares square root circuit 58 and the divider 59, or vice versa. The same effect can be achieved even if a similar filter is inserted into the output circuit of the sine function circuit 60, or even if a similar function is added to both.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to effectively remove disturbances that heavily cloud the phase control circuit due to the relationship between the AC system conditions and the transfer function of the control circuit when an accident occurs in the AC system. , it is possible to realize stable operation of the AC/DC converter.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram of a conventional phase detection circuit, and FIG. 3 is a block diagram of an AC/DC converter used in a DC power transmission system. 1A, 1'B... Converter, 2A, 2B... DC reactor 3... DC transmission line 4A, 4B... Converter transformer 5A, 5B... Circuit breaker 6A, 6B... AC system 7A, 7B... Transformer 11A, 11B... Constant current control circuit 13A, 13
B... Constant current control circuit 18A, 18B... Minimum margin angle setter 24A, 24B... Switch 25A, 25B... Current margin setter 21A, 2
1B...DC current detector 28A, 28B...Control advance angle priority circuit 29A,
29B... Phase control circuit 3OA, 30B... Pulse amplifier 41... Power setting device 43... Power detector 45... Reactive power setting device 47... Reactive power detector 48... Constant Reactive power control circuit 50... Phase detector 80... Band-stop filter representative Patent attorney Nori Chika Ken Yudo Wang Hou Hongbun Figure 1 Figure 2

Claims (1)

[Claims] An AC/DC converter equipped with a phase detector that obtains an appropriate phase signal necessary for control by knowing the phase difference between three-phase AC signals, characterized in that a band elimination filter is inserted in the phase detector. A method of controlling an AC/DC converter using a detector.