JP2736211B2 - Control and protection device for AC / DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control and protection device for an AC / DC converter used for a DC power transmission or a frequency converter.

[0002]

2. Description of the Related Art A conventional AC / DC converter and its control and protection device are shown in FIG. 3 (edited by the Technical Committee of the Institute of Electrical Engineers of Japan, DC Commentary on DC Transmission Technology, Corona, 1978). In FIG.
1 is a converter bus, 2 is a converter transformer, 3 is an AC / DC converter, 4 is a DC reactor, DCPT is a DC voltage transformer,
DCCT is a DC current transformer, 5 is a voltage transformer, and constitutes a main circuit of the AC / DC converter by the above. Reference numeral 10 denotes an example of a control device of the AC / DC converter, which includes adders 11 and 14, a constant voltage control circuit 12, a constant margin angle control circuit 13, and a constant current control circuit.
15, a minimum value selection circuit 16, a phase control circuit 17, and a pulse generation circuit 18. Reference numeral 20 denotes an example of a protection device for the AC / DC converter. When the AC / DC converter is applied to a DC power transmission or a frequency converter, although not shown, there is another set of AC / DC converters having the same configuration, one of which is used as a forward converter and the other as an inverse converter. .

In FIG. 3, a converter transformer 2 converts the AC voltage of the converter bus 1 to a voltage level convenient for the AC / DC converter 3, and the AC / DC converter 3 converts AC and DC by phase control. Do. The DC reactor 4 reduces high frequency components in the DC current and ensures stable operation of the AC / DC converter. DC voltage transformer DCPT, DC current transformer DCC
The T and voltage transformer 5 converts various quantities such as the voltage and current of the main circuit to a level that can be easily handled by the control device 10 and the protection device 20. Constant voltage control circuit in controller 10
12 is intended to keep the DC output voltage of the AC-DC converter to a constant, the detected DC voltage detected value through a direct voltage transformer DCPT are combined per a DC voltage set value E _dp and the adder 11, It is calculated to be equal. The constant margin angle control circuit 13 operates such that the converter secures a minimum margin angle based on the DC current detection value detected by the DC current transformer DCCT and the AC voltage detection value detected by the voltage transformer 5.

In the constant current control circuit 15, a DC current transformer DC
The DC current detection value detected by CT is the DC current set value I
_Operates to follow _dp . The lowest value selection circuit 16 selects the output of the control circuit. Normally, the output of the constant current control circuit 15 is selected on the forward converter side because the output is the smallest. On the other hand, in the inverter-side output of the constant current control circuit 15 by setting the current margin [Delta] I _d increases, the output of the constant voltage control circuit 12 is selected instead.
Further, when the AC voltage of the converter bus 1 on the inverter side decreases, the output of the constant margin angle control circuit 13 decreases and the output is selected. The control voltage E whose output is selected in this manner is
_c is converted into a firing pulse at a required timing by a phase control circuit 17, further shaped and amplified by a pulse generation circuit 18, and supplied to the AC / DC converter 3 as a gate signal.

Now, consider the case where the AC / DC converter operates as an inverse converter. Normally, the output of the constant voltage control circuit 12 is selected as described above. However, the case where the AC voltage of the converter bus 1 decreases due to a ground fault or the like in an AC system not shown in the figure. Think. Here, when the degree of the decrease in the AC voltage is small, the output of the constant margin angle control circuit 13 is selected as described above, and the AC / DC converter operates so that the operation can be stably continued. However, when the degree of the voltage drop is large, stable operation of the AC / DC converter becomes difficult, so that the protection device 20 generally detects the voltage drop and issues a command to stop the operation of the converter. is there. By the way, the protection device 20 generally makes a determination based on the level of the AC voltage.However, even if the voltage drops the same, the difficulty with which the AC / DC converter can continue to operate stably depends on the aspect of the failure. Obviously, the greater the degree of voltage drop, the greater the difficulty.

[0006]

In the control and protection device of the conventional AC / DC converter described above, when the AC voltage drops, the constant margin angle control circuit 13 keeps operating stably in a range where the protection device 20 does not operate. Although it operates so as to be able to operate, when the unbalance failure occurs, the operation is insufficient, and there is a case where the operation cannot be stably continued due to a commutation failure or the like.
Further, when the protection circuit 20 operates, the AC / DC converter stops, and there is a problem that power transmission stops. The present invention has been made in order to solve the above-described drawbacks, and has as its object to provide a control and protection device for an AC / DC converter that can continue operation as much as possible and continue stable operation even when the AC voltage decreases. And

[0007]

According to the present invention, in order to achieve the above object, in an AC / DC converter for performing phase control, an AC voltage of each phase is inputted from an AC bus of a converter, and an AC voltage of each phase is inputted. A voltage detector that determines the degree of decrease and a failure type of an unbalanced failure or a balanced failure, a β advance amount calculation circuit that calculates an appropriate β advance amount according to the determination result of the voltage detector, a β processing circuit including a β advance circuit for performing a β advance process for inputting a β advance amount and having a time constant after a predetermined β advance time,
The output of the processing circuit is introduced to a lowest value selection circuit for selecting a control voltage for the phase control.

The voltage detector determines the amount of AC voltage drop and the appearance of the failure, and based on the output, the β advance amount calculation circuit calculates the β advance amount required for stable operation of the AC / DC converter, and further outputs the output. Perform β advance processing in the β advance circuit based on the
By sending the output to the lowest value selection circuit, stable operation is ensured.

[0008]

An embodiment will be described below with reference to the drawings. FIG.
1 is a block diagram of an embodiment of a control protection device of an AC / DC converter according to the present invention. In FIG. 1, the same elements as those in FIG. In FIG. 1, 31 is a voltage detector, 32 is a β advance amount calculation circuit, 33 is a β advance circuit,
The output of the β advance circuit is introduced to the lowest value selection circuit 16. Next, the operation will be described. When a voltage drop of the converter bus 1 occurs, the voltage detector 31 determines the type of failure and the amount of voltage drop. The reason is usually
This is because, since the input AC is a three-phase AC, it is possible to determine whether an imbalance fault such as a one-line ground fault or a balance fault due to a three-phase short circuit is obtained by looking at each phase voltage. Based on the result, the β advance amount calculation circuit 32 calculates the β advance amount necessary for stable operation of the AC / DC converter. The β advance amount is, for example, an equation that gives the advance angle β of the constant margin angle control, , The margin angle γ is a value obtained by adding a margin to the minimum margin angle γ _min , X is the commutation reactance (PU) of the transformer for converter 2, I _d is a DC current, but 1.0 PU is assumed, and E is an AC The calculation may be performed as the maximum value of the voltage drop amount. or,
Equation (1) may be replaced with a slightly simpler approximation,
It is also possible to classify into several regions in advance according to the voltage drop amount and the failure type, and to select a corresponding β advance amount in a pattern.

The β advance amount thus obtained is input to the next β advance circuit 33, and the β advance processing as shown in FIG. 2, for example, is performed. In FIG. 2, a and β advance amounts are the values determined as described above in the β advance amount calculation circuit 32 of FIG. 1, and b and β advance times are failure removal times of the AC system (generally tens of milliseconds). ), A value obtained by adding a slight margin, C, and a return time constant may be values that cooperate with the response time of the control device of the AC / DC converter at the other end (not shown). According to the above embodiment, even when the AC voltage decreases, the AC / DC conversion device can be stably operated. In addition, since the detection level of the protection device 20 of FIG. 1 can be reduced as compared with the related art, there is an effect that the possibility that the operation can be continued is increased. In the above embodiment, the β advance amount calculation circuit
The input of 32 was only the output of the voltage detector 31, but (1)
By inputting the DC current detection value as shown in the formula,
More detailed control can be performed, and an effect exceeding that of the present embodiment can be obtained.

[0010]

As described above, according to the present invention, the amount of .beta. Advance required for stable operation is calculated and the .beta. Advance process is performed according to the amount of AC voltage decrease and the failure mode. It is possible to provide a control and protection device for an AC / DC converter that can continue operation and operate stably.

[Brief description of the drawings]

FIG. 1 is a block diagram of an AC / DC converter and a control protection device thereof according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining β advance processing.

FIG. 3 is a block diagram of a conventional AC / DC converter and its control and protection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Converter bus 2 Converter transformer 3 AC / DC converter 4 DC reactor 5 Voltage transformer DCPT DC voltage transformer DCCT DC current transformer 10 Control device of AC / DC converter 11, 14 Adder 12 Constant voltage control circuit (AVR) 13 Constant margin angle control circuit (AγR) 15 Constant current control circuit (ACR) 16 Minimum value selection circuit (LVG) 17 Phase control circuit (PHS) 18 Pulse generation circuit (PG) 20 Protection device 31 Voltage detector 32 β advance amount Arithmetic circuit 33 β advance circuit

Claims (1)

(57) [Claims] In an AC / DC converter for performing phase control, an AC voltage of each phase is input from an AC bus of a converter.
Of the input AC voltage of each phase and the unbalance fault or balance
A voltage detector for determining the type of failure
And β advancing amount calculation circuit for calculating an appropriate β advanced amount depending on out device determination result, enter the β advancing amount perform have allowed Ru β advances the process time constant after a predetermined β advancing time β advanced circuit And at least a β processing circuit comprising
A control protection device for an AC / DC converter, wherein an output of a processing circuit is introduced to a lowest value selection circuit for selecting a control voltage for the phase control.