JPH05173654A - Controller for reactive power of self commutated converter - Google Patents

Abstract

PURPOSE:To suppress the generation of an overvoltage after accident removal if an accident occurs to an AC system to which the self commutated converter is connected. CONSTITUTION:An AC deficient voltage relay 17 monitors the voltage of the AC system 1. If the system accident occurs to the AC system 1 and is the AC deficient voltage relay 17, a control system reads the output signal of the AC deficient voltage relay 17 and limits the plus-side limit value Qmax of a reactive power limiter 14 to a proper value which is less than that in normal operation, e.g. zero, thereby setting the range of the reactive power limiter from-Qmax to 0.

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 a self-excited converter used in a power system.

[0002]

2. Description of the Related Art A self-excited converter is used in an AC / DC converter such as a DC power transmission system, a frequency converter, a grid interconnection device or a reactive power compensator in a power system, and the reactive power control method is basically the same. It is common to each device. Therefore, here, the operation principle of the inverse converter for converting DC power into AC power will be described. FIG. 6 shows a configuration diagram of an inverse conversion device using a self-excited converter. A self-excited converter 3 is connected to an AC system 1 via a transformer 2, and the converter is a so-called voltage type self-excited converter composed of 6-phase or 12-phase arms. A capacitor 4 and a DC reactor 5 are installed on the DC terminal side. The self-excited converter 3 performs an inverse converter operation to convert the DC power generated by the DC power supply 6 into AC power. As the DC power supply 6, a DC power supply such as a fuel cell power generator, a DC output on the forward conversion operation side in the frequency converter, or a DC voltage stored in a capacitor can be considered.

Next, the control system will be described. The active power detector 7 detects active power P _det between the AC system 1 and the converter 3, and the reactive power detector 8 detects reactive power Q _det between the AC system 1 and the converter 3. Further, the voltage detector 9 detects the voltage V _det of the AC system 1. The active power detection value P _det is added to the active power controller (APR) 10 in association with the active power setting value P _ref, and the active power controller (APR)
The active power control value P _con that is the output of PR) 10 is obtained. On the other hand, the reactive power detection value Q _det is the reactive power set value Q
_ref and AC voltage detection value V _det and AC voltage set value V _ref
And added to the constant voltage controller (AVR) 11
It is added to the reactive power controller (AQR) 12 together with the obtained correction signal ΔQ _ref, and the reactive power control value Q _con which is the output of the reactive power controller (AQR) 12 is obtained. The active power limiter 13 and the reactive power limiter 14 limit the control values of the active power and the reactive power thus obtained.

The output P of the active power limiter 13 and the output Q of the reactive power limiter 14 obtained in this way are given to the arithmetic unit 15, and in the arithmetic unit 15, the active power output and reactive power output of the converter are converted into those values. Phase angle θ and control rate M
Is calculated. P, Q and θ, M have the following relationship. Here, V _s is the system side AC voltage value of the transformer, X is the impedance value of the transformer, E _d is the DC voltage value, and K is a constant = π.
/ 6. The pulse generator 16 generates a gate-on pulse and a gate-off pulse according to the phase angle θ and the control rate M obtained by the calculator 15, and supplies the gate-on pulse and the gate-off pulse to each arm of the self-exciting converter 3 to generate the self-exciting converter 3 Is its output power P
And Q set active power P _ref and reactive power Q _ref
Drive while keeping If the output active power becomes larger than the set value, the output signal of the active power controller (APR) 10 changes in the negative direction and operates to lower the active power output of the converter. If it becomes smaller, the output signal of the active power controller (APR) 10 changes in the negative direction and operates so as to increase the active power output of the converter, so that the active output of the converter is maintained as set. It The same applies to reactive power.

However, since the voltage of the AC system can be controlled by the reactive power, a constant voltage control system output signal of the AC voltage is often added to the reactive power control system as an auxiliary signal.
That is, in FIG. 6, it is assumed that the reactive power is maintained at the set value Q _ref . That is, it is assumed that the vehicle is operating with Q _det = Q _ref . At this time, when the voltage of the AC system 1 drops, the detection value V _det detected by the AC voltage detector 9 becomes the set value V _det.
It becomes lower than _ref , and the output of the constant voltage controller 11 changes in the positive direction. Since the output signal is applied to the reactive power controller 12, the reactive power output operates so as to increase, and as the reactive power output from the converter 3 increases, the voltage of the AC system 1 increases and the set value V It has the same value as _ref . When the voltage of the AC system 1 rises, the reverse operation is performed. However, here, as the sign of the reactive power, the direction in which the converter consumes the reactive power and lowers the AC voltage is the negative (negative) direction, and the direction in which the converter supplies the reactive power to the grid and increases the AC voltage is positive. The explanation is for the (correct) direction. By performing this operation, the converter 3 operates so as to maintain the active power and the reactive power as set values when the voltage of the connected AC system does not fluctuate, and when the voltage of the AC system fluctuates. The active power operates so as to suppress the AC voltage fluctuation while holding the set value.

[0006]

In the conventional control device described above, the limit value P _max of the active power limiter 13 is increased.
The limit value Q _max of the reactive power limiter 14 is a constant value determined by the rated capacity of the device and the rated DC power during operation. Here, when an accident such as a ground fault occurs in the AC system 1 to which the converter 3 is connected to cause a voltage drop, the converter 3 controls to suppress the fluctuation of the AC voltage as described above. That is, the control for increasing the AC voltage works and operates so as to supply a large reactive power to the system side.
Even if the accident is eliminated in that state and the AC voltage recovers rapidly, there is a delay in control, and since the conversion device continues to supply a large amount of reactive power, an AC overvoltage is likely to occur. That is, the control for maintaining the voltage of the converter works in the direction of generating an overvoltage in the event of a system fault. Further, conventionally, in order to solve this problem, when an AC accident occurs, there is a method in which the reactive power is forcibly fixed to the most negative value, that is, -Q _max and the operation is continued. If the method is used, the AC voltage during an accident may be further decreased, and even after the accident is removed, unnecessary reactive power may be consumed, resulting in a decrease in the AC voltage.
The present invention has been made in view of the above circumstances, and when a system fault such as a ground fault or a short circuit occurs in an AC system to which a self-exciting converter is connected, an overvoltage suppressing function of the converter against an overvoltage after the accident is removed. It is an object of the present invention to provide a reactive power control device of a self-excited converter that improves and effectively suppresses overvoltage generated in an AC system.

[0007]

In order to achieve the above object, the present invention is a reactive power control device using a self-excited converter used in a power system, in which an accident occurs on the side of the AC system connected to the converter. Is generated by detecting the occurrence of AC voltage drop, and the detection signal is used to narrow down the upper limit value of the limiter of the reactive power control device.

[Operation] The voltage of the AC system is monitored by the AC undervoltage relay. When a system fault occurs in the AC system and it is detected by the AC undervoltage relay, the control system reads the output signal of the AC undervoltage relay and sets the positive limit value Q _max of the reactive power limiter. Limit to an appropriate value in the negative direction, such as zero, during normal operation,
Set the range of the reactive power limiter to -Q _max ~ 0. In a control system configured in this way, when an accident occurs on the AC system side, the reactive power supplied to the AC system side is limited to zero, so overvoltage that occurs immediately after the accident is eliminated can be suppressed. it can. In addition, the limiter on the negative side is -Q even for overvoltage that may occur during subsequent voltage recovery.
Since it is open up to _max , reactive power can be consumed on the converter side, and overvoltage can be suppressed.

[0008]

Embodiments will be described below with reference to the drawings. Figure 1
2 is a configuration diagram of an embodiment of a reactive power control device for a self-excited converter according to the present invention. In FIG. 1, the same parts as those in FIG. The characteristic part of the present invention is that an undervoltage relay 17 and a timer 18 are provided.The limit value of the reactive power limiter 14 is switched by the output signal of the undervoltage relay 17, and the switched value is held for a certain time by the timer 18. , Is to work to restore the original value. FIG. 2 shows the internal structure of the reactive power limiter 14. The reactive power limiter 14 is provided with two types of limit values, Q _max (1) and Q _max (2), for the device rated capacity (MVA) _max , Q _max (2): An arbitrary value (for example, zero) within the range of Q _max (2) ≤ Q _max (1) is set. In normal operation, the switch 19 selects the terminal A, that is, Q _max (1). At this time, the undervoltage relay 17 operates and “O
When the "N" signal is issued, the switch 19 is switched to the terminal B.
After the state is maintained for a certain time by the timer 18, the switch 19 returns to the terminal A again. The output Q _max of the switch 19 thus given is compared with the output signal Q _con of the reactive power controller 12 in the minimum value selection circuit 20, and the smaller value is selected. Also, the sign inversion circuit 21 causes Q _max (1)
Is converted into a negative value −Q _max (1), and the value and the output signal of the minimum value selection circuit 20 are compared in the maximum value selection circuit 22, and the larger value is selected. Its output is a reactive power limiter
The output value Q of 14 is given to the arithmetic circuit 15 of FIG. In the arithmetic circuit 15, the Q thus obtained and the active power controller 10
The phase angle θ and the control rate M are calculated using P obtained from

Next, the operation will be described. FIG. 3 shows the operations of the undervoltage relay 17, the timer 18, and the reactive power limiter 14 when this embodiment is applied. During normal operation, the outputs of the undervoltage relay 17 and the timer 18 are in the “OFF” state, the switch 19 is connected to the terminal A, and Q _max (1) is selected as the reactive power limit value. Therefore, the reactive power is controlled within the range of -Q _max (1) to Q _max (1). Here, when an accident occurs in the AC system and the voltage drops, the output of the undervoltage relay 17 becomes "ON" as shown in FIG. 3, and thereby the output of the timer 18 also becomes "ON". The timer 18 holds this "ON" signal for a fixed time t _con . t _con is set to a time obtained by adding the time from the accident detection to the accident removal and the time from the accident removal to the convergence of the transient disturbance. This timer
The output “ON” signal of 18 is applied to the switch 19, so that the switch is switched to the terminal B. As a result, Q _max (2) is selected as the upper limit value (plus side limit value) of the reactive power limiter. Therefore, the supply of reactive power to the AC system can be suppressed.

While this state continues, the protection works in the AC system to eliminate the accident and restore the voltage. Immediately after this accident is removed, overvoltage may occur due to the supply of reactive power, but when the present invention is applied, the reactive power supplied from the converter to the grid is limited to Q _max (2) (= 0). Therefore, overvoltage immediately after the accident is removed can be suppressed. In addition, the reactive power is -Q _max (1) to Q _max (2) for overvoltage that may occur during the subsequent voltage recovery.
Since it is controlled within the range of (= 0), overvoltage can be suppressed by the reactive power consumed by the converter. However, here, as the sign of the reactive power, the direction in which the converter consumes the reactive power and lowers the AC voltage is the negative (negative) direction, and the direction in which the converter supplies the reactive power to the grid and increases the AC voltage is positive. It is in the (correct) direction. The shaded area is the reactive power control range. According to the above-mentioned embodiment, by using the control circuit of the self-excited converter, the control which prevents the supply of extra reactive power to the grid in the event of an AC grid fault and enables consumption of the reactive power in the converter. You can Therefore, it is possible to suppress the overvoltage generated in the AC system and reduce the system fluctuation.

FIG. 4 is a block diagram of a reactive power limiter according to another embodiment. In FIG. 4, when an accident occurs on the AC system side and the output of the AC undervoltage relay turns on,
The output from the reactive power controller 12 is input to two minimum value selection circuits. The minimum value selection circuit 20 is given Q _max (1) as the maximum limit value, and the minimum value selection circuit 23 is given Q _max (2) as the maximum limit value. During normal operation, the switch 19 is on the terminal A side, and Q _max (1) is given as the maximum limit value. Here, when the output of the AC undervoltage relay is turned “ON” due to a system side accident, the switch 19 is switched to the terminal B, and the maximum limit value is Q.
_max (2). Therefore, the operation is the same as the embodiment of FIG.

FIG. 5 is a block diagram of a reactive power limiter according to another embodiment. This example is a reactive power limiter
In addition to 14, another reactive power limiter 24 is installed, and when an accident occurs on the AC system side and the output of the AC undervoltage relay turns "ON", the switch 19 switches from terminal A during normal operation. Switching to the terminal B, the reactive power control by the reactive power limiter 14 during normal operation is switched to the reactive power control by the reactive power limiter 24. Here, set the range of the reactive power limiter 24 to -Q.
By setting _max (1) to Q _max (2),
The same effect as that of the embodiment can be obtained. From these examples, it is understood that the present invention achieves the object by limiting the limiter in the positive direction of the reactive power, that is, in the direction of increasing the AC voltage when an AC system fault occurs. Further, in the operation explanatory view of FIG. 3, when the signal of the timer 18 changes from “ON” to “OFF” and the normal operation state is returned, the limiter is returned to the original state step by step, but it is a transient state. When it is necessary to reduce the fluctuation, a circuit having a time constant and gradually returning to the original state may be provided.

[0013]

As described above, according to the present invention, in the control device of the AC / DC converter using the self-excited converter used in the power system, a system fault occurs in the AC system to which the converter is connected. In this case, the operation was performed while limiting the supply of reactive power to the grid by the detection signal of the accident, so that the overvoltage that occurs immediately after the AC grid accident is eliminated is suppressed, and also when the voltage is restored. As for the overvoltage, the converter can consume the reactive power to suppress the overvoltage and reduce the system fluctuation.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a reactive power control device for a self-excited converter according to the present invention.

2 is a diagram showing an internal configuration of a reactive power limiter according to an embodiment of the present invention in the control system shown in FIG.

FIG. 3 is a diagram for explaining the operation of the embodiment shown in FIG.

FIG. 4 is a diagram showing an internal configuration of a reactive power limiter according to another embodiment.

FIG. 5 is a block diagram of a reactive power limiter according to another embodiment.

FIG. 6 is a diagram showing a configuration of a conventional self-excited AC / DC converter system and its control system.

[Explanation of symbols]

 1 AC bus 2 Transformer 3 Self-excited converter 4 Capacitor 5 DC reactor 6 DC power supply 7 Active power detector 8 Reactive power detector 9 Voltage detector 10 Active power controller 11 Constant voltage controller 12 Reactive power controller 13 Active Power limiter 14 Reactive power limiter 15 Arithmetic unit 16 Pulse generator 17 AC undervoltage relay 18 Timer 19 Switch circuit 20, 23 Minimum value selection circuit 21 Sign inversion circuit 22 Maximum value selection circuit

Claims (1)

[Claims] 1. In a reactive power control device using a self-excited converter used in a power system, the occurrence of an accident on the AC system side connected to the converter is detected by an AC voltage drop,
A reactive power control device for a self-excited converter, characterized in that an upper limit value of a limiter of the reactive power control device is narrowed down using the detection signal.