JP2002262574A - Separately excited power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separately excited power converter which secures an appropriate margin angle, and has no risk of a commutation failure. SOLUTION: The converter 1 which is fitted with a thyristor bridge 2 and converts an AC into a DC, and a margin angle controlling part 92 which computes and outputs the control angle of lag or control angle of lead of the thyristor bridge 2 from an input alternating voltage, flowing current, and commutation reactance of the converter 1, are provided. This control part 92 is provided with a commutation reactance correction signal outputting part 930, which corrects the commutation reactance Xc from the input alternating current or output direct current of the converter 1, and an open loop margin angle control part 920, which receives a signal from the outputting part 930, computes and outputs a margin angle control signal for the thyristor bridge 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separately-excited power converter for use in DC power transmission, frequency converters, and the like, and more particularly to a separately-excited power converter with improved margin angle control.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a conventional separately-excited power converter used for DC power transmission and frequency converters. FIG.
As shown in FIG. 1, the converter 1 is composed of a thyristor bridge 2 and an anode reactor 3, and the side to which the three anode reactors 3 are connected is connected to another terminal 5 via a smoothing reactor 4 to form a DC circuit. .

[0003] The AC side of the converter 1 is connected to an AC system 7 via a converter transformer 6. The control device 8 outputs a DC voltage Ed, a DC voltage from the DC voltage detector 9, a DC current detector 10, and a valve winding voltage detector 11 of the AC circuit.
The control angle α is output by inputting the DC current Id and the valve winding voltage Ei.

[0004] The valve winding voltage is detected by detecting the voltage on the system side of the converter transformer 6 and converting it to a valve winding voltage.
, There is also a detection method, but the values used as a result are the same. Therefore, FIG. 2 shows a configuration for directly detecting the valve winding voltage. The gate pulse generator 12 generates a gate pulse at the control angle α from the controller 8 and outputs the gate pulse to the thyristor bridge 2 of the converter 1.

FIG. 3 shows an example of the configuration of the control device 8. Although the configuration of the control device 8 is slightly different depending on the system, FIG. 3 shows an example basically used. The control device 8 receives the DC current Id, performs feedback control, and outputs a DC current control signal ACRα. The DC current control unit 80 receives the DC voltage Ed, performs feedback control, and outputs a DC voltage control signal AVRα. Voltage control unit 81, margin angle control unit 8 which receives DC current Id and valve winding voltage Ei, and outputs margin angle control signal AGRα.
And a control angle selector 83 for selecting the DC current signal ACRα, the DC voltage signal AVRα and the margin angle control signal AGRα and outputting the control angle α. The margin angle control unit 82 performs margin angle control of an open loop control system that calculates the margin angle control signal AGRα using the DC current Id and the valve winding voltage Ei.

FIG. 4 shows an example of the margin angle control unit 82. That is, the DC current Id,
The valve winding voltage Ei, the commutation reactance Xc and the margin angle reference γ are input as set values, and calculations are performed using the following relational expressions (1) and (2) to obtain the margin angle control signal A.
GRa is output. The following equation (1) holds between the control angle α and the margin angle γ.

[0007]

(Equation 1)

[0008] Ei: line voltage of the valve winding, Xc: commutation reactance, Id: DC current. When the margin angle control signal AGRα is obtained from the relational expression (1), assuming that the control angle α = the margin angle control signal AGRα, the following equation (2) is obtained.

[0009]

(Equation 2)

The open loop margin angle control unit 820 is given by the following equation (2).
And outputs the margin angle control signal AGRα.

[0011]

The margin angle control in the conventional separately-excited power converter described above has the following problems. Normally, the commutation reactance Xc input to the open-loop margin angle control unit 820 is used by setting the impedance of the transformer 6 for the converter in FIG. 2 to a fixed value for the set value of the commutation reactance Xc in FIG.

However, the actual commutation reactance is determined by the impedance of the transformer for converter 6 and the impedance of the anode reactor 3 shown in FIG. Further, since a saturable reactor is generally used for the anode reactor 3, the impedance is large when the current is small, and the impedance is small when the current is large. As a result, the commutation reactance X shown in FIG.
When a fixed value such as the set value of c is used, the margin angle control signal AGRα tends to be too small when the current is small, and tends to be too large when the current is large.

If the commutation failure occurs due to the improper output of the margin angle control signal AGRα, the converter may be stressed and possibly damaged. In addition, due to the commutation failure, the reactive power output from the converter 1 increases, and a serious accident may occur in the devices connected to the converter 1 and the AC system 7. Therefore, an object of the present invention is to provide a separately-excited power converter that secures an appropriate margin angle and does not cause a commutation failure.

[0014]

According to another aspect of the present invention, there is provided a separately-excited power converter having a thyristor bridge for converting AC into DC, an AC input voltage of the converter, and a power supply for the converter. A margin angle control unit for calculating and outputting a control delay angle or a control advance angle of the thyristor bridge from the current and the commutation reactance, wherein the margin angle control unit converts the input AC current or the output DC current of the converter into a A commutation reactance correction signal output unit for correcting commutation reactance, and an open-loop margin angle control unit that receives a signal from the commutation reactance correction signal output unit, calculates and outputs a margin angle control signal for the thyristor bridge. Configuration.

In the separately excited power converter of the present invention,
The impedance in the converter is appropriately reflected in the margin angle control signal calculated by the open loop margin angle control unit, and an appropriate margin angle can be secured to prevent commutation failure.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A separately-excited power converter according to an embodiment of the present invention will be described with reference to FIG. That is, the separately-excited power converter of the present embodiment has commutation reactance correction signal output section 930 in margin angle control section 92. Other configurations are the same as those of the conventional apparatus shown in FIGS.

Commutation reactance correction signal output section 930
Has a function of converting the impedance of the anode reactor 3 that changes according to the current into an approximate function by inputting the DC current Id, and outputting a total value of the commutation reactance Xc. The open loop margin angle control unit 920 controls the DC current I
d, the valve winding voltage Ei, and the commutation reactance Xc are input, and the margin angle control signal AGRα is output.

The impedance of the anode reactor 3 is determined by a current flowing through the anode reactor 3 and a flowing time. The maximum value of the current flowing through the anode reactor 3 is the same as the DC current. The flowing period is a period during which the converter is commutating, and a current flows during an electrical angle of 120 °. Since the period during which the current flows is almost constant, the impedance of the anode reactor 3 is determined by the DC current.

From this, it is possible to calculate the impedance value of the anode reactor 3 from the DC current Id. Therefore, the commutation reactance X is calculated from the DC current Id.
The value of c is determined and is directly input to the open loop margin angle control unit.

As described above, since the value of the commutation reactance Xc is determined by the current flowing through the converter 1, the commutation reactance Xc used for control does not become excessive or insufficient, and the output of the open-loop margin angle control unit 920 does not occur. The value AGRα can be made appropriate, and an accident of the converter 1 such as a commutation failure can be prevented.

As described above, in the separately-excited power converter of the present embodiment, an appropriate margin angle control signal AGRα can be obtained by correcting the commutation reactance Xc. Can be prevented.

[0022]

In the separately-excited power converter according to the present invention, an appropriate margin angle is secured for the thyristor bridge, and severe abnormalities such as commutation failure and system accidents are prevented from occurring. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of a separately-excited power converter according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional separately-excited power converter.

FIG. 3 is a block diagram showing a control device of a conventional separately-excited power converter.

FIG. 4 is a block diagram showing a margin angle control unit of a conventional separately-excited power converter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Converter, 2 ... Thyristor bridge, 3 ... Anode reactor, 4 ... Smoothing reactor, 5 ... Other terminals, 6 ... Transformer transformer, 7 ... AC system, 8 ... Control device, 9 ... DC voltage detector, 10 ... DC current detector, 11 ... Valve winding voltage detector, 12 ... Gate pulse generator, 80 ... DC current control unit, 81 ... DC voltage control unit, 82,92 ... Margin angle control unit, 83 ... Control angle selection 820, 920: open loop margin angle control unit, 930: commutation reactance correction signal output unit, Id: DC current, Ed: DC voltage, Ei: valve winding voltage, Xc: commutation reactance, γ: margin angle Criteria,
ACRα: DC current control signal, AVRα: DC voltage control signal, AGRα: margin angle control signal, α: control angle.

Claims (1)

[Claims] A converter having a thyristor bridge for converting alternating current to direct current, and calculating and outputting a control delay angle or a control advance angle of the thyristor bridge from an AC input voltage, a conduction current and a commutation reactance of the converter. A margin angle control unit that performs a commutation reactance correction signal output unit that corrects a commutation reactance from an input AC current or an output DC current of the converter, and outputs the commutation reactance correction signal. An open-loop margin angle control unit that receives a signal from the unit and calculates and outputs a margin angle control signal of the thyristor bridge.