JPH05304723A - Device for controlling ac-to-dc converter - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a DC overvoltage after the inversion of a tidal current by suppressing the value of an output limiter to a low level for a fixed period during and immediately after the inversion of the tidal current. CONSTITUTION:When a tidal current inverting command is issued, a delay circuit 37 switches the value of a limiter from the upper limit to the lower limit by generating appropriate timing and, at the same time, inputs an output to a limiter control circuit 38. Upon receiving the output, the circuit 38 generates such a signal which lowers the value of the limiter for a fixed period and gradually increases the value to the original level thereafter. In addition, a minimum value selection circuit 39 selects the smaller value of the outputs of the circuit 38 and a switch 36 and controls the upper limiter of a constant-voltage control circuit 9. Therefore, the occurrence of a DC overvoltage can be prevented immediately after the tidal current is inverted, since the upper limit of the output of the circuit 9 is controlled by means of the output of the circuit 38 for a fixed period during and immediately after the inversion of the tidal current.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art FIG. 10 is a schematic block diagram showing an example of a conventional controller for a converter of a DC power transmission system. In the converter of the DC power transmission system, the DC sides of the converters 1A and 1B are connected by the DC power transmission line 3 via the DC reactors 2A and 2B, respectively.
The AC side of each converter 1A, 1B is configured to be connected to the respective AC system 6A, 6B via the converter transformers 4A, 4B and the circuit breakers 5A, 5B. Conventional converters 1A and 1B are provided with margin angle limiter control circuits 7A and 7B, constant current control circuits 8A and 8B, and constant voltage control circuits 9A and 9B, and margin angle limiter control circuits 7A and 7B are converters. This is a circuit that applies a limiter so that the margin angle does not fall below the output of the margin angle setters 10A and 10B that set the minimum margin angle. In addition, the current reference value that is the output of the DC current setter 11 and the DC current detected by the DC current detectors 12A and 12B are converted into values that are easy to handle as a control circuit by the current / voltage conversion circuits 13A and 13B. The detected value is input to the adding circuits 14A and 14B, and the difference is input to the constant current control circuits 8A and 8B, so that the direct current flowing through the direct current transmission line 3 is controlled so as to follow the current reference value. It

Further, the detected value of the DC voltage detected by the DC voltage detectors 17A and 17B is input to the adder circuits 19A and 19B together with the DC voltage set value which is the output of the DC voltage setter 18, and the difference between them is a constant voltage. By being input to the control circuits 9A and 9B, the DC voltage applied to the DC power transmission line 3 is controlled so as to follow the DC voltage set value. Switch 15A, 15
B is closed only on the side of the converter that operates the converter in reverse conversion,
The current margin output from the current margin setters 16A and 16B is input to the adder circuits 14A and 14B. By the minimum value selection circuits 20A and 20B that selectively output only the smallest output among the margin angle control circuits 7A and 7B, the constant current control circuits 8A and 8B, and the constant voltage control circuits 9A and 9B, If the switch 15B is closed and the switch 15A is opened, the output of the constant current control circuit 8A is selectively output to the minimum value selection circuit 20A, and the minimum value selection circuit 20B is selected.
The output of the margin angle control circuit 7B or the constant voltage control circuit 9B is selectively output to. For convenience of explanation, it is assumed that the switch 15A is open, the switch 15B is closed, and the output of the constant voltage control circuit 9B is selected as the output of the minimum value selection circuit 20B.

The outputs of the minimum value selection circuits 20A and 20B are
Input to the phase control circuits 21A and 21B, respectively,
It is converted into a pulse signal that determines the firing timing of 1A, 1B, and is given as a gate pulse signal to the converters 1A, 1B via the pulse amplifier circuits 22A, 22B. As described above, the control circuit of the converter is publicly known, and the operation curve of such a DC interconnection equipment is a DC current Id on the horizontal axis and a DC voltage Ed on the vertical axis.
It is also well known that the above is obtained as shown in FIG. Figure
In 11, a forward converter is a converter operating
In the operation curve of 1A, the part of, is the regulation part determined by the commutation impedance including the converter transformer 4A, and the part of, is the part of the constant current characteristic determined by the constant current control circuit 8A.

On the other hand, the ,, and are the operation curves of the converter 1B operating in the inverse converter, the part of, and is the constant current characteristic part determined by the constant current control circuit 8B, and the, are determined by the constant voltage control circuit 9B. This is a part of constant voltage characteristics. Here, the difference in the direct current from the point of the operation curve corresponds to the current margin. In this state, the converter of the DC transmission system is the converter
It is operated at point A, which is the intersection of the operating curves of 1A and converter 1B. By the way, in the DC transmission system of FIG. 10, in order to perform DC inversion, that is, in order to operate the converter 1A as an inverse converter and the converter 1B as a forward converter, the switch 15A is closed and the switch 15B is opened. As a result, the output of the constant voltage control circuit 9A is selected as the output of the minimum value selection circuit 20A, while the minimum value selection circuit 20A is selected.
The output of the constant current control circuit 8B is selected as the output of B. The operating curve of the converter in this case is as shown in FIG.
Converter 1A in which B, ′, ′ are in reverse converter operation
And the operating point of the DC transmission system is A '.

[0006]

Although the operating points A and A'shown in FIG. 11 are in the steady state, the transient state of DC inversion is shown in FIG. That is, in FIG. 10, when it is assumed that the converter 1A performs power flow inversion from the forward converter to the inverse converter and the converter 1B reverses from the inverse converter to the forward converter, the minimum value selection circuit 20A,
The output of 20B operates as shown in Fig. 12 (a). As a result, the DC voltage applied to the DC transmission line 3 is shown in FIG. 12 (b). In the figure, the part of, is the steady state before power reversal, the part of is the transient state of the power reversal by the current margin operation,
Is the steady state completed from the flow reversal. In the part of the transient state, in order to reverse the polarity of the DC voltage,
The absolute value is small, and if the constant voltage control circuit described above is left operating, the constant voltage control circuit operates in the direction of increasing the absolute value of the DC voltage, and delay elements are eliminated. Since it is generally included, an overvoltage may occur temporarily as shown by the part in the figure. Such overvoltage not only stresses the DC power transmission line, but also stresses devices such as DC filters and lightning arrestors, which are generally installed on the DC side, and also include long-distance cables in the DC power transmission line. In such a case, the overvoltage expands to cause a trouble such as hindering the operation of the converter. The present invention has been made in view of the above circumstances, and an object thereof is to provide a control device for an AC / DC converter that prevents a DC overvoltage at the time of power flow reversal.

[0007]

In order to achieve the above object, the present invention provides means for adjusting or switching the output limiter value of a constant voltage control system, and narrows down the output limiter during power flow reversal and for a certain period immediately after power flow reversal. I did it.

Therefore, even if the absolute value of the DC voltage decreases during the power flow reversal, the output of the constant voltage control circuit does not exceed the value of the output limiter, so that the overvoltage immediately after the power flow reversal can be prevented.

[0008]

Embodiments will be described below with reference to the drawings. Figure 1
FIG. 11 is a block diagram of an embodiment of a control device for an AC / DC converter according to the present invention. The same parts as those in FIG. In FIG. 1, the portion different from FIG. 10 is the portion indicated by the alternate long and short dash line. Although only the reference symbol B side is shown in the figure, the same constitution is also omitted on the A side, but is omitted. The symbol B is also omitted. Figure 1
The difference from 10 is that upper and lower limiters are provided in the constant voltage control circuit 9, and the upper limiter values thereof are the delay circuit 37, the limiter control circuit 38, the minimum value selection circuit 39 and the upper limiter setter 33, 34 and the switch 36, and the lower limit limiter value is set by the lower limit limiter setting devices 31, 32 and the switch 35.

Next, the operation will be described. In the output limiter of the constant voltage control circuit 9, the output of the upper limit limiter value 33 or 34 is selected by the switch 36 according to the flow direction, and the lower limit limiter value is set to the lower limit limiter setter 31 or 32. It is well known that the output of is selected by the switch 35, but in the present invention, when a power flow inversion command is issued, appropriate timing is generated by the delay circuit 37, and these upper and lower limit limiter values are switched, and at the same time, the delay circuit 37 The output is input to the limiter control circuit 38, which generates a signal that narrows the limiter value for a certain period and then gradually returns the limiter value. Further, the smaller value of the output of the limiter control circuit 38 and the output of the switch 36 is the minimum value selection circuit.
Selected at 39, the upper limiter of the constant voltage control circuit 9 is controlled. As a result, the upper limit of the output of the constant voltage control circuit 9 is limited by the output of the limiter control circuit 38 during the power flow reversal and for a certain period immediately after the power flow reversal, so that the output voltage of the converter does not become an overvoltage. According to this embodiment, the overvoltage immediately after the reversal of the power flow is suppressed, and as a result, the stress on the DC side device is reduced and the stable operation of the converter is continued.

FIG. 2 is a block diagram of another embodiment, showing only the one-dot chain line portion of FIG. In the previous embodiment (FIG. 1), the limiter control circuit and the minimum value selection circuit were used for the limiter control at the time of power flow reversal, but these are omitted in this embodiment.
Instead, it is composed of a timing control by the delay circuit 37 and a first-order delay circuit 40. In the case where the converter reverses the power flow from the forward converter operation to the inverse converter operation, the upper limit limiter of the constant voltage control circuit 9 is generally wide (the limiter value is large). The timing for expanding the limiter is delayed by the delay circuit 37, and the limiter value is gradually changed at the time of switching through the first-order delay circuit. According to this embodiment, since the upper limit limiter of the constant voltage control circuit is gradually widened after the voltage reversal operation by the power flow reversal is completed, the overvoltage as described above does not occur, and the embodiment of FIG. The same effect as can be obtained.

FIG. 3 is a block diagram of still another embodiment. In the present embodiment, the countermeasure against the commutation failure of the converter is taken into consideration. That is, when the voltage of the AC system 6 drops for some reason while the converter is operating as an inverse converter, the output of the margin angle control circuit 7 is selected.
Performs operation to prevent the commutation failure of the converter, but should a commutation failure occur, or if a commutation failure is expected to occur, that is, turn on a transformer or start a static converter at a nearby electrical station. If it is assumed that the voltage distortion will occur at, the β advance control circuit 41 is instructed by the instruction of the β advance command circuit 42 shown in FIG.
The β advance control is performed via. That is, the output of the β advance control circuit 41 is temporarily selected instead of the output of the constant voltage control circuit or the constant margin angle control circuit. However, in such a case, the absolute value of the DC output voltage becomes small, and as a result,
The error signal input to the constant voltage control circuit 9 becomes large.
Therefore, the output of the constant voltage control circuit 9 also becomes a large value and is normally held at the value of the upper limiter (not shown). When the β advance is released here, the output of the β advance control circuit 41 is promptly restored as shown in FIG. 6, whereas the output of the constant voltage control circuit 9 is delayed and returns to the original output. .. As a result, as shown in FIG. 6, the DC voltage temporarily becomes an overvoltage state. Such an overvoltage causes stress on the device on the DC side, which not only affects the service life, but also causes a problem that the overvoltage is amplified in a system having a long-distance cable system and causes an unexpected overvoltage. In FIG. 6, it is the output of the constant margin angle control circuit.

FIG. 3 shows a method for coping with these cases.
In the same manner as the previous embodiment, only a partial view is shown. Therefore, the constant voltage control circuit 9 has an upper limiter, and the limiter value is controlled by the output value of the β advance control circuit 41. Reference numeral 42 is a β advance command circuit. The operation in this case is as follows. β
When the β advance control circuit 41 operates according to the instruction of the advance instruction circuit 42, the DC output voltage decreases as described above, and as a result, the output of the constant voltage control circuit 9 increases and the output of the adder 19 increases. The signal operates, but the constant voltage control circuit 9
Since the output limiter of is narrowed, the output does not become a large value. In addition, since the output of the constant voltage control circuit 9 returns from a small value even when the β advance is released, the DC overvoltage unlike the conventional method is not generated. According to this embodiment, the overvoltage at the time of releasing the β advance is suppressed, and as a result, the stress of the DC side device is reduced and the cause of the abnormal overvoltage is removed.

FIG. 4 is a block diagram of still another embodiment. In the embodiment of FIG. 3, the output value of the β advance control circuit 41 is used as it is as the limiter value of the constant voltage control circuit 9. However, in the present embodiment, a limiter control circuit 43 is separately provided to release the limiter value. By adjusting the timing,
Fine adjustment can be performed more than the embodiment of FIG. 3, and the effect can be further enhanced.

FIG. 5 is a block diagram of still another embodiment. In FIG. 5, the constant voltage control circuit 9 has an output holding function, and is used together with the delay circuit 44 to hold the output of the constant voltage control circuit 9 at a pre-value during the β advance process.
By releasing the output holding and operating the normal constant voltage control after a certain time has elapsed after the advance cancellation, it is possible to suppress the overvoltage generated in the conventional method.

FIG. 7 is a block diagram of another embodiment. The present embodiment is for coping with an AC system fault in a state where the converter is connected to a transmission line having two AC lines. That is, for example, when a three-wire ground fault occurs in a single-line power transmission line, the circuit breakers at both ends of the power transmission line are opened, and after the fault is removed, a fixed time (usually several hundred ms) is passed before reclosing the circuit.
That is, an operation of returning both breakers to the original closed state is performed. At this time, the converter 1 connected to the AC system also performs the operation of stopping / restarting, but if restarting is to be performed in a short time, inconvenience occurs. That is, when the voltage is once reduced due to a ground fault and is removed by opening the breaker, the converter 1 is stopped and the phase advancing capacity of the filter and the phase-adjusting capacitor is left over, so that the voltage once becomes an overvoltage. When 1 is restarted, the transmission line is left open this time, and the short-circuit capacity is smaller than in the original state, so the voltage drops. Here, the transmission line is operated by the reclosing of both circuit breakers, and finally the original voltage is restored. In any case, since the short-circuit capacity is smaller than that in the case where two power transmission lines are operated, stable power transmission may not be possible at the rated power of the converter 1. Further, in the case of a failure across two lines of the transmission line, for example, an in-phase one-line ground fault, the short-circuit capacity at the time of removing the failure is remarkably reduced, and stable power transmission at the rated power cannot be performed, as described above.

FIG. 7 is applied to such a case, and the operation is stably continued without stopping the AC / DC converter even when a part of the AC power transmission line is open. It is a thing. In FIG. 7, a power detector 70 inputs the voltage and current after DC conversion. 71 is an adder which inputs the command value from the power command circuit 72, and the addition result is the power controller 73
To enter. 74 and 75 are pole control devices connected to the control poles of the converter (not shown). A voltage detector 76 is connected to the AC system. 77 is an accident detector, 78 is a sequence control circuit,
79 is a timer. 721 and 722 are switches, 723 and 72
4 is a power setting device.

Next, the operation of FIG. 7 will be described. First,
The accident detector 77 detects an AC system accident and causes the sequence control circuit 78 to perform stop / restart operations, while also sending an accident (or accident elimination) signal to the timer 79, which is preset by the timer 79. The output is in the state of 1 only during the period required for reclosing the existing transmission line, and then returns to the state of 0. In the power command circuit 72, the output of the timer 79 is 0.
In the case of, the switch 721 selects the normal power command value set by the power setter 723. On the other hand, when the output of the timer 79 is 1, the small power command value set by the power setter 724 is selected by the switch 722.
Therefore, during the period required for the reclosing of the transmission line, the power command value is narrowed down, and the converter 1 can continue stable operation even when the short-circuit capacity of the AC system is small. According to the present embodiment, even if a part of the two-line power transmission line is opened and the short-circuit capacity becomes small, it is possible to obtain the effect of stably continuing the operation without stopping the AC / DC converter.

FIG. 8 is a block diagram of still another embodiment, in which the same parts as those in FIG. In the embodiment of FIG. 7, the operation of narrowing the power set value itself is performed by the power command circuit 72, but in the present embodiment, the limiter 80 is provided at the output stage of the power controller, and further, the setting device is set.
A limiter control circuit 81 composed of 813 and 814 and switches 811 and 812 constitutes means for narrowing down the power command value.
Therefore, in normal times, the limiter value equivalent to the rated capacity is set by the setter 81.
3 is selected by switch 811 and the limiter value corresponding to the small power is set by the command of timer 79 when the accident is detected.
, And by the switch 812, the same effect as in FIG. 7 is obtained.

FIG. 9 shows still another embodiment. The same parts as those in FIG. 8 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, the receiving circuit 82 receives the open / closed states of the circuit breakers 84A and 84B. Breaker in this example
In a normal operation in which 84A and 84B are closed, the output of the receiving circuit 82 is 0, and the output of the power setting device 723 is selected by the switch 721. On the other hand, breakers 84A and 84B
When a part of is released, the output of the receiving circuit 82 becomes 1,
By selecting the output of the power setting device 724 with the switch 722, the power can be reduced until the transmission lines 85A and 85B are closed again, that is, the circuit breakers 84A and 84B are closed. Can be obtained. Further, in the present embodiment, when the number of power transmission lines is further increased,
, 85B accident situation (1-line 3-wire ground fault, 2-line in-phase 1-wire ground fault, etc.), the receiver circuit 82 has a multi-input, multi-output configuration, and the power consumption depends on the number of outputs of the receiver circuit 82. A plurality of command circuits and switches may be provided. In this case, the degree of reduction in short-circuit capacity can be estimated in advance due to the appearance of an accident in the transmission line. Therefore, finer control can be performed by setting the amount of power to be narrowed down according to the degree.

[0020]

As described above, according to the present invention, the output limiter of the constant voltage control circuit is adjusted during power flow reversal or during β advance processing, and at the same time, a part of the AC transmission line near the converter is removed. Since the power command value is narrowed down even during a failure, DC overvoltage can be prevented, and stable operation can be performed without stopping the AC / DC converter.

[Brief description of drawings]

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

FIG. 2 is a partial configuration diagram of another embodiment.

FIG. 3 is a partial configuration diagram of still another embodiment.

FIG. 4 is a partial configuration diagram of still another embodiment.

FIG. 5 is a partial configuration diagram of still another embodiment.

FIG. 6 is a diagram for explaining the effect of FIGS. 3, 4, and 5;

FIG. 7 is a configuration diagram of still another embodiment of the present invention.

FIG. 8 is a configuration diagram of still another embodiment of the present invention.

FIG. 9 is a configuration diagram of still another embodiment of the present invention.

FIG. 10 is a block diagram of a control device of a conventional conversion device.

FIG. 11 is a diagram illustrating an operation of a conventional conversion device.

FIG. 12 is a diagram illustrating a transient state of a conventional conversion device.

[Explanation of symbols]

 7 Margin angle control circuit 8 Constant current control circuit 9 Constant voltage control circuit 31, 32 Lower limit limiter setting device 33, 34 Upper limit limiter setting device 35, 36 Switch 37, 44 Delay circuit 38 Limiter control circuit 39 Minimum value selection circuit 40 Primary Delay circuit 41 β advance control circuit 42 β advance command circuit 43, 81 Limiter control circuit 70 Power detector 72 Power command circuit 74, 75 Pole controller 76 Voltage detector 77 Accident detector 78 Sequence control circuit 79 Timer 80 Limiter

Claims (3)

[Claims] 1. In an AC / DC converter having at least a constant current system and a constant voltage system, the constant voltage control system includes an output limiter and a circuit capable of appropriately adjusting the values of the output limiter,
A control device for an AC / DC converter, wherein an output limiter of a constant voltage control system at the time of power flow reversal is narrowed. 2. A controller for an AC / DC converter having a constant voltage control circuit and a β advance circuit, wherein the output limiter of the constant voltage control circuit is narrowed down during the β advance process. 3. A controller of an AC / DC converter having means for detecting an AC system accident and accident elimination, and means for executing a sequence of stop / restart by the output, a DC power is supplied by a timer and a command from the timer. A control device for an AC / DC converter, which is provided with means for narrowing a command value for a certain period.