JPS61227672A - Overvoltage suppressing control circuit of ac/dc converter - Google Patents

Abstract

PURPOSE:To prevent the operation of an AC overvoltage relay by advancing the control advancing angle of an inverter when an AC overvoltage exceeds the prescribed value, thereby suppressing the AC overvoltage. CONSTITUTION:The voltage of an AC bus detected by an instrument transformer is fed to the maximum value selector 14B, and a larger voltage value is selected and added in negative polarity to an adder 15B. When the voltage value of the bus exceeds the prescribed value, the output voltage of the adder 15B becomes negative, and is fed to a controller 17B. The output of the controller 17B is selected by the minimum value selector 10B, fed through a control voltage limiter to a phase controller, and the control advancing angle of the inverter is advanced by the output. The control system is constructed so that the advancing operation of the control advancing angle is fast and the reverse operating is slow.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an AC/DC converter for suppressing AC overvoltage when it occurs in an AC system to which an AC/DC converter is connected, particularly in a weak AC system. The present invention relates to an overvoltage suppression control circuit for a converter.

[Technical background of the invention and its problems]

FIG. 3 shows a schematic configuration diagram of a DC power transmission facility, in which one AC bus is connected, and IB is a converter JA consisting of a series-parallel connection of a plurality of thyristors, for example, via a conversion transformer JA e JB, It is connected to JR and converts alternating current to direct current or direct current to alternating current by controlling the firing phase of each thyristor. 4A.

4B is a smoothing reactor, 5 is a DC power transmission path, and 6 is a 6B
is a potential transformer (P, D) for two people, rB is a potential current transformer (
C, T).

The control device in such a main circuit configuration is composed of constant current control circuits (ACR) 8A, 1B, constant margin angle control circuit (CJCR) II, 913, and the like.

In addition to the constant current control circuit 8B and the constant margin angle control circuits 9h and 9B, a constant voltage control circuit (VR) for controlling the DC voltage to a constant level may be added.

Constant current control circuit 8, 8B, constant margin angle control circuit Ik, 9
The value calculated by B is used as the control voltage (go) by the minimum value selection circuit (LVG) zoA.

10B and this minimum value selection circuit ZoA.

10B is for automatically selecting the control system that advances the control angle the most among various controls, and the control voltage selected here is the control voltage limiter circuit Z Z A e Z J B
(ECL) is applied and input to the 1-phase control circuits 12A and 12B. This phase control circuit 1
2, 12B determines the nine firing phases corresponding to the control voltage and outputs the firing phase to the thyristor. In the AC/DC converter configured in this way, as is well known, the current margin (Δ By switching, one is operated as a forward conversion device by constant current control, and the other is operated by constant margin angle control.

Now, in the following description, for convenience of explanation, in FIG. 3, the converter 3A is assumed to be a forward converter, and the converter 3A is assumed to be an inverse converter.

In Figure 3, 1. Assume that an overvoltage occurs on the AC bus line IB for some reason. For example, if the load is interrupted in the AC system connected to the AC bus line IB, or if an AC system accident occurs due to lightning or the like, and the circuit is disconnected. At this time, if the above-mentioned overvoltage value becomes large and continues, of course,
The AC/DC converter equipment must be protected by an AC overvoltage relay, that is, the AC/DC converter equipment must be stopped immediately.
Although not shown in FIG. 3, it is necessary to separate the AC filter and the 7-Yant/Y/4 filter. The generated overvoltage value is relatively large, especially when the AC system is a weak AC system, and the overvoltage occurs frequently. This means that the change in AC voltage is generally approximately equal to the product of the change in reactive power and the actance of the AC system, and a weak AC system means that the actance of the AC system is large. Because there is.

Therefore, when an AC/DC converter is connected to a weak AC system, using only the conventional control method, there is a problem in that the AC/DC converter equipment must be frequently stopped due to AC overvoltage.

[Purpose of the invention]

Therefore, the present invention has been made to eliminate the above-mentioned problems, and when an AC overvoltage occurs, the AC overvoltage is suppressed by controlling the AC/DC converter, thereby preventing the operation of the AC overvoltage relay. Therefore, it is an object of the present invention to provide an overvoltage suppression control circuit for an AC/DC converter to improve the operating rate of the AC/DC converter.

[Summary of the invention]

In order to achieve the above object, the present invention adjusts the control advance angle (hereinafter abbreviated as β) of the inverter (hereinafter abbreviated as INV) when the AC overvoltage exceeds a predetermined value. A new control circuit that operates in the advancing direction is provided, and this control circuit operates quickly in the direction in which β is advanced and slowly in the opposite direction.

[Embodiments of the invention]

FIG. 1 is a block diagram showing an embodiment of only the main parts of the present invention. In FIG. 1, the same functions as those in FIG. 3 are denoted by the same reference numerals, and explanations thereof will be omitted. Furthermore, although the explanation has been made using the control advance angle (β), from now on, for convenience of explanation, the control delay angle will be abbreviated as α, and the explanation will be made using α. Furthermore, if the control delay angle is α and the control lead angle is β, then α and β
Since it is a well-known fact that the following relational expression holds true between the two, the explanation of this expression will also be omitted.

α+/=180° In FIG. 1, the detection signal detected at 6B is transmitted to the potential transformer (P, T) 6 of FIG. 3 by the maximum value selection circuit 14B.
The larger AC voltage value of the two is selected and added to the adder 15B with negative polarity. The other input signal of the adder 15B is set by the set value of the setter 16B.
For example, this setting device 16B is set to a voltage equivalent to an AC overvoltage value of 1.2 pu. Therefore, when the voltage value of AC bus line IA or IB in FIG. 3 exceeds -11.2 pu, the output voltage of adder 15B becomes negative polarity.
Sent to B. This control circuit J7B constitutes a feedback control system and can be said to be a kind of AC voltage constant control circuit. The output voltage of the control circuit 77B is output from the adder 18B,
Further, the set value of the setter 19B is added to this adder 18B, and this set value is set to a voltage corresponding to α=180°, for example.

Therefore, if the AC voltage value of AC buses ZA and IB is 1.2
If it is less than pu, the output voltage of the control circuit 17B has positive polarity, so the output voltage of the adder 111B is the voltage corresponding to α;180° and the output voltage of the control circuit 77B are added with the same polarity, so that α>180 In this case, the control circuit 77B is essentially not operating.

However, if the AC voltage value of AC buses IA and IB is 1.
When it becomes 2pu or more, the output voltage of the control circuit 27B becomes negative polarity, so the output voltage of the adder 18B is finally α - 180°, and this value is finally the minimum value selection circuit 10.
B, and the converter will be operated by this control circuit 77B.

Further, FIG. 2 shows an embodiment showing a specific circuit of the control circuit 11B), 20B and 21B are inverting amplifiers, and 22B to J
OB is a resistor, 29B.

30B indicates Kya/#Sita.

Hereinafter, for convenience of explanation, the resistor will be abbreviated as R and the capacitor as C. In FIG. 2, as is well known, the dyne of the inverting amplifier 20B is star 422, and the second lag time constant is R24.
It is XC29. The inverting amplifier JMB is used in this embodiment only to invert the polarity of the signal. Therefore, the dyne of this circuit is assumed to be 1.

Next, the present invention having the above configuration will be explained in detail.

First, in a steady state, that is, when no AC overvoltage occurs,
Or, even if it is generated, it is less than 1 or 2 pu. In this case, as mentioned above, the adder 111B
The voltage corresponds to the output voltage line α = 180', and the output voltage of the constant margin angle control circuit 9B is 1, for example α =
The voltage is equivalent to 150'((180'), and now!
As we are thinking about the formula, as is well known, the output voltage of the constant current control circuit 8B is a voltage corresponding to α>180°, so the minimum value selection circuit 10BK finally selects the constant margin angle control circuit 9B. The output voltage of INV is selected
is operated at α; 150°. In this state, for example, if an AC overvoltage is observed at the AC bus IB and its value exceeds 1.2 pu, the output voltage of the adder 15B will be Therefore, the output voltage of the adder 18B becomes a voltage corresponding to α;180° or less, and this value is finally selected by the minimum value selection circuit 10B.

The conversion device is a type of device that consumes delay ineffectiveness,
Since the power factor is expressed by , when α=90°, the operation that consumes the most reactive power is when the rotation φ is 0. Therefore.

By changing α from 150° to a small value, a large amount of reactive power is forcibly taken from the single AC system. That is, AC bus I
This will suppress the AC overvoltage of B.

At this time, in order to rapidly suppress the generated AC overvoltage, it is desirable that the control circuit 17B is a function with a high speed and high r-in constant. However, if the control circuit is made to have a high speed and a high gain,
The weak AC system causes other problems such as power fluctuations. In particular, when the AC overvoltage is 1.2 pu or more, the control circuit 77B operates at high speed to suppress the AC overvoltage to 1.2 pu or less, and when the AC overvoltage is large, the control circuit 77B quickly becomes inactive, causing AC overvoltage to occur again. There is a risk that a kind of hunting phenomenon may occur. However, in the present invention, since the control circuit J7B is configured as shown in FIG. 2, there is no such fear. In other words, even if the 1-inverting amplifier ROB is set to high speed and high gain, if R25 and C30 have a large delay time constant, the input voltage of the 1-inverting amplifier 20B will be negative polarity (the generated AC overvoltage will be 1 .2 pu), the output voltage of the inverting amplifier 21B does not immediately become negative, but gradually decreases.

According to this embodiment, a control circuit is provided that operates in a direction to advance β of INV when an AC overvoltage occurs and exceeds a predetermined level, and the control circuit operates in a direction to advance β. By configuring it so that it operates at high speed when moving in the opposite direction, and at low speed when moving in the opposite direction, AC overvoltage can be suppressed and other new problems can be avoided. [Effects of the Invention] As explained above, the present invention is particularly effective in the case of a system in which an AC/DC converter is connected to a weak AC system.
Effectively suppressing AC overvoltage has the remarkable effect of improving the operating rate of the AC/DC converter and enabling economical design regarding the overvoltage withstand capacity of attached equipment.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the main parts of the present invention. FIG. 2 shows a partial detailed configuration diagram of the η1 diagram, and FIG. 3 shows a configuration diagram of the DC power transmission equipment. 8B... Constant current control circuit, 9B... Constant current control circuit, 1073... Minimum value selection circuit, 14B... Maximum value selection circuit, 16B, 19B river setting device, 77B... Control circuit, 15 B, 1 # B--Adder, 20B
. 21B... Inverting amplifier, 22B-28f3... Resistor, 29 B j 30 B-'37f"7. Applicant's agent Patent attorney Takeshi Suzue Child's picture 1 figure I! 2 figure *3 m!ri ρ

Claims (1)

[Claims] At least in an AC/DC conversion system equipped with a constant current control system and a constant margin angle control system, when the AC system voltage to which the AC/DC converter is connected is detected and the detected value exceeds a predetermined value,
An overvoltage suppression control circuit is provided that operates in a direction to advance the control advance angle of the inverter, and the overvoltage suppression control circuit operates at high speed in the direction of advancing the control advance angle and at low speed in the opposite direction. An overvoltage suppression control circuit for an AC/DC converter device.