JP2000245066A - Control equipment of dc power transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve control precision of a DC power transmission system to which a capacitor commutation converter is applied, and realize cost reduction of equipment. SOLUTION: In the control equipment of a DC power transmission system in which converters 2a, 2b on the power inverter side are constituted of at least two capacitor commutation converters, a control means 10 which controls a converter current to be a previously designated constant value is installed on the power rectifiers 1a, 1b side, and a control means 20 is installed on the power inverter side. The control means 20 consists of a load side synchronous signal forming means 206 for setting the frequency of a load side AC system, a control angle commanding means 203 for controlling at least one power inverter 2a to be in a fixed control angle, a constant voltage control means 202 for controlling the voltage of a load side AC system to be a designated value, and a control angle command value control means 205 for controlling the control angle of the residual power inverter 2b on the basis of deviation between the control angle commanding means and the constant voltage control means, and controls the control angle of the residual power inverter in such a manner that the voltage of the load side AC system becomes the designated value.

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 DC power transmission system which converts AC into DC in a power supply system and converts the AC into DC again on the load side to supply power.
The present invention relates to a control device for a DC power transmission system to which a capacitor commutation type converter that stably transmits power to a system without a power source is applied.

[0002]

2. Description of the Related Art Conventionally, a separately-excited converter using a thyristor, which has been used in a DC power transmission system (including an asynchronous interconnection system and a frequency conversion system), uses the power of an AC system to supply power to the converter. Performs commutation operation. Therefore, when used in an AC system with a small short-circuit capacity or a system with a large waveform distortion, especially when operating an inverter that converts DC to AC, there was a problem that the converter failed to commutate and stable operation was not possible. . Recently, a capacitor commutation type converter (CCC) constructed by inserting a power capacitor between a separately-excited converter and a conversion transformer has been reviewed, and its application as a converter in a DC power transmission system has been studied. I have. Since this converter does not take reactive power during commutation, there is no need for a reactive power compensator and the cost of the converter station can be reduced.In addition, the occurrence of overvoltage during an emergency stop of the converter in a system with a short-circuit capacity is small. It is considered that there is an advantage that the problem can be avoided and the commutation operation is easily performed, so that stable power transmission can be performed even to a system having a small short-circuit capacity. Furthermore, it is said that since no reactive power compensation is required, the system can be operated in the same manner as a self-excited converter even in a system without a power supply. If power can be transmitted stably even in a non-powered system, it can be applied to remote island power transmission as an alternative to the self-commutated converter currently under development, and the applicable range of CCC can be expanded.

[0003]

However, the DC power transmission system to which the capacitor commutation type converter is applied has the above-mentioned advantages, but the capacitor commutation type converter is used as a control device of the DC power transmission system with high accuracy. No consideration has been given to controlling and reducing the cost of the apparatus. An object of the present invention is to improve the control of a DC power transmission system using a capacitor commutation type converter capable of transmitting power in a system without a power supply similarly to a self-excited converter and capable of stable operation even in the event of a system failure, An object is to reduce the cost of the apparatus.

[0004]

In order to solve the above-mentioned problems, in a control device of a DC power transmission system in which a converter on the inverter side is composed of at least two capacitor commutation type converters, AC is converted to DC. On the side of the forward converter for conversion, there is provided control means for controlling the converter current to a predetermined value specified in advance, and on the side of the inverse converter, load-side synchronization signal generating means for setting the frequency of the load-side AC system, Control angle command means for controlling at least one of the inverters to a fixed control angle, constant voltage control means for controlling the voltage of the load side AC system to a specified value, and control angle command means and constant voltage control means. Control means comprising control angle command value control means for controlling the control angle of the remaining inverter based on the output deviation is provided, and the control angle of the remaining inverter is adjusted so that the voltage of the load side AC system becomes a specified value. To control. The control means on the side of the forward converter is provided with constant voltage control means for controlling the AC voltage on the load side to a command value, and controls the forward converter in accordance with the AC voltage on the load side. The control means on the side of the forward converter is provided with constant power control means for controlling the power on the load side to a command value, and controls the forward converter in accordance with the power on the load side. Further, the converter on the side of the forward converter includes at least two capacitor commutation type converters. Here, before starting the inverter, the control angle command values of the remaining inverters are controlled to a fixed control angle, and after the start, a time constant is given from the fixed control angle to another fixed control angle. Control. Here, before the start of the inverter, the control angle command values of the remaining inverters are controlled to a fixed control angle, and after the start, the voltage of the load-side AC system is given a time constant from the fixed control angle. Control is performed by switching to the control angle for controlling to the specified value.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a control device of a DC power transmission system according to an embodiment of the present invention. The DC power transmission system of the present embodiment is a system in which a capacitor commutation type converter (CCC) configured by inserting a power capacitor between a separately-excited converter and a conversion transformer is applied to an inverter. is there. The reverse converter for converting DC into AC in the DC power transmission system includes two capacitor commutation converters. In FIG. 1, 1a and 1b are two forward converters constituted by separately-excited converters, 2a and 2b are two inverse converters constituted by separately-excited converters, and the two inverse converters are , Power capacitors 3a, 3b between the inverters 2a, 2b and the conversion transformers 24a, 24b, respectively.
Are operated by a so-called capacitor commutation type converter (CCC) configured by inserting the inverter. 11 is an AC system on the power transmission side, 21 is an AC system on the power receiving side, and here, the AC system 21 on the power receiving side is a simple load system that does not include a generator or the like. 12, 22 are AC buses to which the converters are connected, 13, 2
Reference numeral 3 denotes a circuit breaker, 14a, 14b, 24a, and 24b are conversion transformers, 15 is a DC reactor for smoothing a DC current, 30a is a main DC transmission line, and 30b is a return line.
In the case of an asynchronous interconnection system or a frequency conversion system, there may be no transmission line. 10 is a separately-excited converter 1
a, a control device 101 for controlling a DC current Id to a predetermined current command value Idref (a DC current corresponding to active power required by a load);
6 is an AC voltage transformer for detecting the AC voltage of the AC system 11, 102 is a synchronous signal detecting circuit for detecting a synchronous signal of the AC system from the detected AC voltage, and 103a and 103b are synchronized with the AC voltage phase of the AC system 11. And the forward converter 1 phase-shifted according to the control command value from the constant current control circuit 101.
a pulse phase control circuit for generating control pulses a and 1b;
Reference numeral 18 denotes a DC current detector that detects the DC current Id.
20 is a control device for the capacitor commutation type converters 2a and 2b,
25 is an AC voltage transformer for detecting the system voltage of the load side AC system 21, 201 is a rectifier circuit for detecting the magnitude of the AC voltage, 202 is controlling the voltage of the load side AC system 21 to a predetermined voltage value Vref. Constant voltage control circuit, 203 is a control angle command circuit, 204 is a subtraction circuit that calculates the difference between the output of the constant voltage control circuit 202 and the output of the control angle command circuit 203,
205 is a control angle command value control circuit, 206 is a load side synchronizing signal generation circuit that outputs a synchronizing signal synchronized with the frequency of the load side AC system, and 207a and 207b are control pulses of the capacitor commutation type converters 2a and 2b. 3 shows a pulse phase control circuit that outputs a pulse signal.

Next, the operation of this embodiment will be described. In the control device 10 of the forward converters 1a and 1b, when the current command value Idref specified in advance and the DC current Id detected by the DC current detector 18 are input to the constant current control circuit 101, the pulse phase control circuit 103a 103b, the DC output voltage is changed and the DC current Id is changed to the current command value Idre.
A control pulse for the forward converters 1a and 1b is generated so as to be f. In the control device 20 of the inverter, the control angle command circuit 2
03, the pulse phase control circuit 207a creates a control pulse for one capacitor commutation type converter 2a, and generates a voltage value Vref and a rectification circuit 2
When the voltage V2 of the load-side AC system 21 detected via the signal line 01 is input to the constant voltage control circuit 202, the output of the subtraction circuit 204 for obtaining the difference between the output of the constant voltage control circuit 202 and the output of the control angle command circuit 203 Control angle command value control circuit 205
The pulse phase control circuit 207b generates a control pulse for another capacitor commutation type converter 2b based on the output command of the control angle command value control circuit 205.

Here, the control angle command value control circuit 205
2 is shown in FIG. 210 is a control angle command value Ecp of the time function according to a preset sequence command value SIG.
Is a command pattern generating circuit for outputting the output Ecp of the command pattern generating circuit 210 and the constant voltage control circuit 20.
2 is a minimum value selection circuit that selects the smaller value of the output Ec of the subtraction circuit 204 for obtaining the difference between the output of the control angle instruction circuit 203 and the output of the control angle command circuit 203.

FIG. 3 shows an operation waveform when the time of this circuit is plotted on the horizontal axis. The output Ecp of the command pattern creation circuit 210 is initially at the command value of the minimum control angle αmin, and is a time constant set by the converter start command to (FIG. 3 shows a case where the output changes in a ramp shape). That is, a command value in which the control angle command value Ecp increases toward the maximum control angle αmax is output. On the other hand, the difference between the output of the constant voltage control circuit 202 and the output of the control angle command circuit 203, that is, the subtraction circuit 20
4 is the maximum control angle αma before the start command to.
x, the voltage of the load-side AC system increases with the start command to, and the control angle command value Ec advances forward. The minimum value selection circuit 211 selects the smaller one of Ecp and Ec, and becomes the control angle command value of αb at time tr. This control angle command value αb becomes the control angle command value of the capacitor commutation type converter 2b. The control angle command value of the other capacitor commutation type converter 2a is indicated by αa.

Now, let αa be 180 degrees (αmax), αb
Is 10 degrees (αmin), the capacitor commutation type converter 2a operates as an inverse converter and the other capacitor commutation type converter 2b operates as a forward converter so that the DC voltage Vd is expressed by the following equation. Therefore, the electric power is recirculated between 2a and 2b and does not flow to the AC system on the load side. (Note that the control angle is 0 to 90.
When the angle is in degrees, the forward converter is operated, and when the control angle is 90 to 180 degrees, the inverse converter is operated)

[Formula 1] Vd = kE2 [cos α−0.5X] where E2: DC side AC voltage for conversion α: control delay angle X: commutation reactance k: coefficient Next, the time to when the start command is issued to Is the control angle command value Ec
When p changes in a ramp shape by the control angle command value control circuit 205 as shown in FIG. 3, that is, when the capacitor commutation type converter 2b is delayed toward the inverter, pulse phase control is performed based on this Ecp. The circuit 207b outputs a pulse signal and controls the capacitor commutation type converter 2b. As a result, current flows into the load-side AC system, and the AC voltage V2 gradually rises. The period between times to and tr in FIG. 3 is an operation for establishing the AC voltage V2 on the load side. When the AC voltage V2 on the load side rises, it approaches the specified voltage value Vref, and the constant voltage control circuit 20
Command value output by operation 2 and control angle command circuit 20
3, the output of the subtraction circuit 204 for calculating the difference between the command values, ie, the control angle command value Ec, gradually decreases. At time tr, the control angle command value Ec becomes smaller than Ecp.
Automatically switches from Ecp to Ec. Or later,
The control angle command value αb of the capacitor commutation type converter 2b is controlled so that the AC voltage V2 on the load side becomes the specified value Vref. In this way, power transmission to an AC system without a power source is established.

The control angle is preferably shifted in the direction in which the control angle is delayed in consideration of the stable operation of the inverter operation. The power adjustment of the load can be performed by changing the current command value Idref of the forward converters 1a and 1b. When the circuit breaker is turned on, for example, the circuit breaker 13 is activated before the forward converters 1a and 1b are activated, and the circuit breaker 23 is switched to the capacitor commutation type converters 2a and 2b.
It may be applied after tr at which the AC voltage after the start instruction “to” becomes a specified value. Although the frequency of the load-side AC system was created based on a command from the load-side synchronization signal creation circuit 206, the signal from the synchronization signal detection circuit 102 on the forward converter side, that is, the power transmission side, was easily obtained. It may be obtained as a synchronization signal on the load side. If the load has a power supply, the operation can be synchronized with the load AC system by detecting a synchronization signal from the AC voltage in the same manner as the forward converter.

As described above, in the present embodiment, the control pulse of one capacitor commutation type converter 2a is created based on the command of the control angle command circuit 203, and the other capacitor commutation type converter 2b Is generated based on the output command of the control angle command value control circuit 205, the DC power transmission system to which the capacitor commutation type converter is applied can be controlled with high accuracy.
Since the control angle command value control circuit 205 which forms the main element of the above is composed of the command pattern creation circuit 210 and the minimum value selection circuit 211, the cost can be reduced.

FIG. 4 shows another embodiment of the present invention. The difference from FIG. 1 is that instead of controlling the AC voltage on the load side by the inverters 2a and 2b, the constant voltage control circuit 202 is moved to the control device 10 of the forward converters 1a and 1b, and the constant current control circuit 1
01 and the constant voltage control circuit 202, and the inverter 2
a, the input to the adder 204 of 2b of the control device 20 to a fixed value AL _P, sequentially converts the AC voltage of the load side unit 1a, 1b
To control by controlling the current. In this case, the two inverters 2a, 2b are constantly controlled by a fixed control angle α. In FIG. 4, the forward converter 1
In the control device 10 of a and 1b, the voltage command value Vref specified in advance and the voltage V2 detected by the rectifier circuit 201 are used.
Is input to the constant voltage control circuit 202, the DC output voltage is changed by the pulse phase control circuits 103a and 103b to control the DC current Id, and the forward conversion is performed such that the AC voltage V2 on the load side becomes the voltage command value Vref. A control pulse for the devices 1a and 1b is created. In the control unit 20 of the inverter, the pulse phase control circuit 207a creates a control pulse for one capacitor commutated converter 2a in accordance with an instruction of the control angle command circuit 203, also, the control angle a fixed value AL _P Command circuit 2
03 is input to the control angle command value control circuit 205, and the pulse phase control circuit 2 is output based on the output command of the control angle command value control circuit 205.
07b creates a control pulse for another capacitor commutation type converter 2b. At this time, two inverters 2a, 2
b is constantly controlled by a fixed control angle α. Also,
The activation (stop) of this embodiment is the same as that described with reference to FIG. As described above, in the present embodiment, similarly to the embodiment of FIG. 1, a DC power transmission system to which a capacitor commutation type converter is applied can be controlled with high accuracy, and power can be stably transmitted to a system without a power supply. can do.

FIG. 5 shows another embodiment of the present invention. The difference from FIG. 1 is that the forward converters 1a and 1b are controlled according to the power on the load side. In FIG. 5, reference numeral 104 denotes a constant power control circuit that controls the load-side power P2 to a command value Pref, and outputs a DC current command value Idp that controls the load-side power P2 to a specified value. Reference numeral 26 denotes an AC current transformer for detecting an AC current on the load side, reference numeral 210 denotes a power detection circuit for detecting power from a detected value of the AC voltage and the AC current on the load side. Use for signals. As described in the embodiment of FIG.
The AC voltage V2 on the load side causes a current to flow to the load side in accordance with the difference between the control angles of the inverters 2a and 2b. Then, the control angle αb of the inverter 2b is controlled to an appropriate value by the operation of the constant voltage control circuit 202 so that the AC voltage Vref is instructed. In the present embodiment, when the AC voltage V2 appears, the current flowing to the load side is detected by the AC current transformer 26, the power detection circuit 210 detects the load side power P2, and the constant power control circuit 104 detects the load side power P2. The DC current command value Idp is generated so that the power P2 of the DC current coincides with the command value Pref, and the constant current control circuit 101 controls the DC current Id to match the command value Idp. By such an operation, the power required by the load is automatically adjusted by the DC power transmission system, and stable operation is possible.

In this case, the direct current command value Idp generated by the constant power control circuit 104 is
a, 1b with an upper limiter that suppresses the command value to the maximum current according to the current withstand capability.
Minimum current value for preventing current interruption, for example, 10
Set the lower limiter to a value such as%. The load-side AC voltage command value Vref and the control angle command value control circuit 2
05 also sets upper and lower limits. For example, as the upper limit value of the control angle command value, an upper limiter is added to the maximum value of 180 degrees of the control angle, and as the lower limit value, a limiter is provided to the control angle such as 10 degrees of the minimum control angle. By providing the limiter in this manner, the occurrence of overcurrent and unstable operation of the converter can be prevented, and the reliability of the device can be increased.

FIG. 6 shows another embodiment of the present invention. In the present embodiment, a capacitor commutation type converter is used on the forward converter side as well as on the inverse converter side. The configuration of the control device 10 may be the same as the embodiment of FIG. 5, and the operation is also the same. In the present embodiment, the phase converter on the side of the forward converter becomes unnecessary, the cost of the forward converter is reduced, and the occurrence of overvoltage at the time of emergency stop of the system can be suppressed.

FIG. 7 shows another embodiment of the present invention in which the transmission power is large and the inverter is composed of a plurality of inverters. FIG.
As shown in the figure, if the signal consists of four inverters,
A pair of two inverters is formed, and one of the inverters is operated as a forward converter and the other is operated as an inverter as described above. By shifting to the operation, the DC power transmission system can be stably operated even when the inverter includes a plurality of inverters.
In FIG. 7, “′” is added to one of the numbers of the two pairs. In this case, the synchronization signal may be set at one point as a reference, and the others may be adjusted to this. For this reason, the control devices are connected by signal lines in order to exchange signals.

Although the DC power transmission system has been described as a control object of the present invention, it is needless to say that the present invention can be applied to an asynchronous interconnection system or a frequency conversion system.

[0018]

As described above, according to the present invention,
Creates a control pulse for one capacitor commutation type converter based on the control angle command, and creates a control pulse for another capacitor commutation type converter based on the control angle command value obtained by controlling the control angle command. Therefore, the DC power transmission system using the capacitor commutation type converter can be controlled with high accuracy, and the control angle command value control circuit that forms the main element of the control device is selected from the command pattern creation circuit and the minimum value selection circuit. Since it is constituted by a circuit, the cost can be reduced. In addition, since the AC voltage on the load side is controlled by controlling the current on the forward converter side, it is possible to control the DC power transmission system using the capacitor commutation type converter with high accuracy, and to control the system without power supply. Power can be transmitted stably. Also, since the power on the load side is detected and controlled so that the power on the load side matches the command value, the power required by the load is automatically adjusted by the DC power transmission system, and stable operation is possible. In addition, upper and lower limiters are provided to limit the DC current command value created by the constant power control circuit, and the upper and lower limit values are also set for the AC voltage command value on the load side and the control angle command value of the control angle command value control circuit. With the provision, the occurrence of overcurrent and unstable operation of the converter can be prevented, and the reliability of the device can be increased. Also, by using a capacitor commutation type converter on the forward converter side as well as on the reverse converter side, phase adjustment equipment on the forward converter side becomes unnecessary, and the cost of the forward conversion station is reduced. In addition, the occurrence of overvoltage at the time of an emergency stop of the system can be suppressed. Further, even when the transmission power is large and the inverters are composed of a plurality of inverters, the DC transmission system can be operated stably.

[Brief description of the drawings]

FIG. 1 is a control device of a DC power transmission system according to an embodiment of the present invention.

FIG. 2 is a detailed block diagram of a control angle command value control circuit of the control device of the present invention.

FIG. 3 is a diagram for explaining an operation at the time of starting the DC power transmission system of the present invention.

FIG. 4 shows another embodiment of the present invention.

FIG. 5 shows another embodiment of the present invention.

FIG. 6 shows another embodiment of the present invention.

FIG. 7 shows another embodiment of the present invention in which the inverter is composed of a plurality of capacitor commutation type converters.

[Explanation of symbols]

1a, 1b: separately excited converter (forward converter), 2a, 2b:
Capacitor commutation type converter (inverter), 3a, 3b: power capacitor, 11, 21: AC system, 12, 22:
AC buses 13, 23: circuit breakers, 14a, 14b, 24
a, 24b: Transformer for conversion, 15: DC reactor, 3
0a: Main line of DC transmission line, 30b: Return line 10: Control device of separately-excited converter 1, 101: Constant current control circuit, 16: AC voltage transformer, 102: Synchronous signal detection circuit, 103a, 103b: Pulse phase control Circuit, 18:
DC current detector, 20: capacitor commutation type converter 2a,
2b, 25: AC voltage transformer, 201: rectifier circuit, 202: constant voltage control circuit, 203: control angle command circuit, 204: subtraction circuit, 205: control angle command value control circuit, 206: load side synchronization Signal creation circuit, 207a, 20
7b: pulse phase control circuit 104: constant power control circuit, 26: AC current transformer, 21
0: Power detection circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hironari Kawazoe 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Takayoshi Sano 6-19, Tsukiji, Chuo-ku, Tokyo No. 20 F-term (reference) in Technology Research Institute of Japan 5G066 CA04 5H007 AA06 BB02 CA03 CB05 CC06 CC12 CC32 CD09 DA03 DA04 DA05 DA06 DB01 DC02 DC05 FA01 FA03

Claims (9)

[Claims] In a control device of a DC power transmission system in which a converter on an inverter side is composed of at least two capacitor commutation type converters, a forward converter for converting AC into DC is provided in advance with a designated converter. Control means for controlling the converter current to a constant value, a load-side synchronization signal generating means for setting the frequency of the load-side AC system, and at least one of the inverters fixed on the inverter side. Control angle command means for controlling the control angle, constant voltage control means for controlling the voltage of the load side AC system to a specified value, and the remaining inverse conversion based on the output deviation between the control angle command means and the constant voltage control means. Control means comprising control angle command value control means for controlling the control angle of the converter, wherein the control angle of the remaining inverter is controlled so that the voltage of the load side AC system becomes a specified value. Control unit for DC power transmission system. 2. The method according to claim 1, wherein the control means on the side of the forward converter includes constant voltage control means for controlling the AC voltage on the load side to a command value, and controls the forward converter in accordance with the AC voltage on the load side. A control device for a DC power transmission system. 3. The method according to claim 1, wherein the control means on the side of the forward converter includes constant power control means for controlling power on the load side to a command value, and controls the forward converter in accordance with the power on the load side. A control device for a DC power transmission system, comprising: 4. The control device for a DC power transmission system according to claim 1, wherein the converter on the side of the forward converter comprises at least two capacitor commutation type converters. . 5. The method according to claim 1, wherein a control angle command value of the remaining inverters is controlled to a fixed control angle before starting the inverters, and the control angle command value is controlled after starting the inverters. A control device for a DC power transmission system that provides a time constant from a fixed control angle to another fixed control angle. 6. The method according to claim 1, wherein a control angle command value of the remaining inverters is controlled to a fixed control angle before starting the inverter, and after starting the inverter, A control device for a DC power transmission system that switches a control angle to control a voltage of a load-side AC system to a specified value with a time constant from a fixed control angle and controls the voltage. 7. The control according to claim 5, wherein the control angle is switched from a fixed control angle before starting to a control angle for giving a time constant after starting and controlling the voltage of the load side AC system to a specified value. A control device for a DC power transmission system, wherein the movement of an angle is switched by moving in a direction of delay of a control angle. 8. The control device for a DC power transmission system according to claim 1, wherein a frequency on a power transmission side is used as a reference frequency of said load-side synchronization signal generating means. 9. The method according to claim 1, wherein the control means for controlling the converter current on the forward converter side includes an upper limiter and a lower limiter for the current, or the load side on the inverter side. The upper limiter and the lower limiter of the voltage are controlled by the constant voltage control means for controlling the voltage of the AC system to the specified value, or the control angle command value control means is controlled by the control angle of the remaining inverter on the inverter side. A control device for a DC power transmission system, comprising an upper limiter and a lower limiter for an angle command value.