JPS6360617B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency control method for an AC system using a power converter used for DC power transmission or the like.

As a power conversion device used for DC power transmission and frequency conversion, a three-phase thyristor bridge 1 is used as shown in FIG. The three-phase thyristor bridge 1 is composed of thyristors U, Z, V, X, W, and Y.
R, S, and T are AC side terminals, and P and N are DC terminals. By controlling the phase of the thyristors U, Z, V, X, W, and Y, AC voltage can be converted to DC voltage, and power can be sent from the AC side to the DC side and from the DC side to the AC side.

Phase control of each thyristor of this three-phase thyristor bridge 1 is performed in synchronization with the frequency of the alternating current voltage. According to this phase control, the power flow can be changed quickly, so it is sometimes used to improve the frequency of an AC system.

FIG. 2 shows an example of a configuration for improving the frequency of an AC system, in which 201 and 202 are AC generators, and 203 is an AC bus bar. The AC voltage from the AC bus 203 is converted to DC voltage by the three-phase thyristor bridge 205 via the transformer 204, and the current on the AC side is sent out to the DC side. The current converted to DC, that is, the DC current, is transferred to DC reactor 2.
Three-phase thyristor bridge 2 through 06,207
08, and after being converted into alternating current, transformer 2
09 to the load 210. The three-phase thyristor bridges 205 and 208 are controlled so that the DC voltage Vd is approximately constant, and the power flow can be changed by changing the DC current Id. 211 is a voltage transformer for detecting alternating current voltage Vac. The frequency detector 214 detects the frequency F of the AC bus using the AC voltage -Vac. Further, the DC current detector 215 detects the DC power Pd based on the DC voltage signal from the DC voltage detector 212 and the DC current signal from the DC current detector 213. 220 is an analog control device that calculates a DC current reference Id used when controlling the phase of a three-phase thyristor bridge. 216 and 218 are adders, and 217 and 219 are arithmetic units that perform PID calculations and the like.

FIG. 3 is a power-frequency characteristic diagram illustrating how the frequency fluctuation of the AC bus 203 in FIG. 2 is suppressed by controlling the phase of the three-phase thyristor bridge 205. In FIG. 3, the power and frequency characteristics from the generators 201 and 202 on the AC bus 203 are represented by G1 and G2, and the load 20
The characteristics of the power and frequency supplied to 1 are represented by L1 and L2. Now in Figure 3, generators 201 and 20
2 is operated with the characteristics of G1, and when the power supplied to the load 210 is on the characteristics of L1, the three-phase thyristor bridge 205 is phase controlled so that the specified frequency Fref and the supplied power Pdp, Driving is carried out at points. If the generator 202 suddenly stops at this time, power will be supplied only from the generator 201, so the power-frequency characteristic from the generator supplied to the AC bus will be G2. If the three-phase thyristor bridge 205 continues to operate with the characteristic of L1 without stopping the generator 202, it will operate at point B, the frequency will drop to _F2 , and the generator 201
may become unable to continue driving. In this case, if the power characteristics supplied by the load are set to L2, operation will be performed at point C, the frequency will be Fref, and the generator 2
01 can continue to operate stably. That is, if the power supplied to the load by the three-phase thyristor bridge 205 is set to _P2 , the generator 201 can continue to operate stably.

A control method for maintaining the frequency of the AC bus 203 constant will be described with reference to FIG. 2. The frequency F of the three-phase AC voltage obtained from the AC bus 203 via the instrument transformer 211 is detected by the frequency detector 21.
Detected by 4. The difference between the frequency F and the reference frequency Fref of the AC bus is calculated by the adder 216 in the analog control device 220, corrected by the arithmetic device 217, and then sent to the adder 21 as the power reference correction signal ΔPdp.
Added to 8. Further, the DC voltage and DC current detected by the DC voltage detector 212 and the DC current detector 213 are added to the adder 218 by the DC power detector 215 as a DC power signal Pd. The adder 218 converts the DC power signal Pd from the power reference Pdp.
A value obtained by subtracting the DC power reference correction signal ΔPbp is obtained, and this is passed through the arithmetic unit 219 to obtain the DC current reference Idp. The DC current reference Idp obtained in this way increases when the frequency of the AC bus 203 decreases and decreases when it increases, so by controlling the phase of the three-phase thyristor bridge 205 using this DC current reference Idp, the AC Bus line 20
3 can be kept constant.

Conventionally, control devices used for DC power transmission and the like are often implemented using analog circuits, and the frequency signal from the frequency detector 214 is often output as an analog voltage value. However, in recent years, with the development of microcomputers and the like, control devices used for DC power transmission and the like have been configured with digital circuits.

FIG. 4 shows an example of the configuration of a digital phase control device using a computer. In the figure, 401 is a phase detector, 402 is a computer, and 403 is a gate logic. The phase detector 401 is a circuit that takes in AC voltage signals ^eR , ^eS , and eT from the AC side terminals R, S, ^and T of the power converter 1 shown in FIG. 1, and extracts a phase signal θ synchronized with the AC side voltage. Yes, special request 1977
A phase lock loop circuit (hereinafter referred to as a PLL circuit) as shown in No.-107368 (Phase Detector) (Japanese Unexamined Patent Publication No. 55-34851) is used. computer 4
02 is the frequency signal f of the AC system, the DC power Pd,
The DC current Id, DC voltage Vd, etc. are taken in as feedback amounts, and a phase control signal Ec to be sent to the DC side of the power converter 1 is calculated. The gate logic 403 converts the digital phase signal θ and the digital phase control signal Ec into the thyristor U of the power converter 1,
The output time of the ignition pulse Tp given to Z, V, X, W, and Y is determined, and the ignition pulse Tp is output. The computer 402 reads the feedback amount at every fixed sampling period and performs calculations. Here, attention is paid to the frequency F as the amount of feedback. F/V converters are often used to convert frequency to voltage. FIG. 5 shows a conventional example in which a frequency signal f is input into a computer 402 using an F/V converter as a frequency detector. In the figure, 501 is an F/V converter, and 502 is a computer 4.
Analog-to-digital converter (hereinafter referred to as A/D) in 02
503 is a central processing unit (hereinafter referred to as CPU) in the computer 402. The frequency f from the AC bus is converted into an analog voltage frequency signal f by the F/V converter 501, and further converted into a digital signal by the A/D converter, and then sent to the CPU 503.
The frequency is taken in as the frequency F _CNT and used for calculations.

However, the conventional method described above has the following drawbacks.

It generally takes time for an A/D converter to convert an analog quantity into a digital quantity, which causes the sampling period of the computer to become longer, thereby impairing the accuracy of calculations performed by the computer.

Since the computer can only obtain frequency information at each sampling period, large frequency fluctuations occur only when the computer inputs the frequency, and after that, the computer causes the calculated value to vary widely even at the reference frequency. , frequency control may instead result in disturbance to the AC system.

The present invention was made in order to improve the drawbacks that occur when frequency control is performed using a digital phase control device using a computer as described above, and is a PLL circuit that generates pulses synchronized with the frequency of an AC power source. By counting the pulses from the phase detector configured with a constant cycle and detecting the frequency, the frequency control by the power conversion device can be performed with high precision.
The aim is to provide a method that achieves high response.

An embodiment of the present invention will be described below with reference to FIGS. 6 and 7. Components in the figure that are the same as those in FIG. 4 are given the same numbers.

In FIG. 6, 401 is a phase detector which takes in AC side voltage signals ^eR , ^eS , ^eT of the converter 1 and generates a phase synchronization pulse SPLS synchronized with the frequency. The phase detector 401 is the same as the phase detector shown in FIG. 4, and the phase synchronization pulse SPLS is extracted as one signal of the digital phase signal θ from the phase detector. A counter 602 counts the phase synchronization pulse SPLS, and repeats counting in response to a reset signal RST that sets the count to 0. 402 is a computer that controls the power conversion device 1;
This is the same computer as shown in FIG.

The phase detector 401 receives AC voltage signals ^eR , ^eS ,
^e Phase synchronization pulse in response to fluctuations in the frequency of T.
Phase synchronization pulse SPLS is output by varying the output time interval of SPLS. After the reset signal RST is output from the computer 402, the counter 602 starts counting the phase synchronization pulses SPLS. The computer 402 performs control calculations at every sampling time of a fixed period and outputs a phase control signal Ec that controls the power converter 1.
After reading the contents of the counter 602 at every sampling time, a reset signal RST is output to the counter 602.

FIG. 7 is a flowchart outlining the contents of the program that the computer 402 executes at each sampling time. The computer 402 checks at each sampling time whether the number of sampling times has reached 100 from the previous 100th time,
When the count reaches 100 times, read the content F _CNT of the counter 602 and output a reset signal to the counter 602, then check the difference between the content F _CNT of the counter 602 and the value F _NRM corresponding to the standard frequency of the AC system. Accordingly, frequency control is performed by correcting the DC current reference value Idp of the power converter 1. The number of sampling times is
If it does not reach 100 times, the previous DC current standard
The phase control signal Ec is calculated and outputted using Idp, and the program for the current sampling time ends.

By performing frequency detection as described above,
Frequency detection can be performed in a shorter time than the conventional method using an F/V converter and an A/D converter, and frequency fluctuations can be taken as an average value over a certain period of time, so frequency control as shown in Figure 3 is used. It can be done quickly and with high precision.

In addition, in FIG. 6, the digital phase control device 4
Although it is configured to perform frequency control using the phase synchronization signal from the phase detector 401 in 00,
It is also possible to separately provide a PLL circuit with the same function as the phase detector 401 in the digital phase control device to generate the phase synchronization pulse SPLS.

As described above, the present invention reads, at predetermined intervals, the output of a phase-synchronized signal synchronized with the frequency of the AC voltage of an AC system connected to a DC transmission system, and reads the output at a predetermined period. Since the phase control signal for controlling the AC side power converter is formed, there is an effect that highly accurate frequency control with quick response can be performed.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a three-phase thyristor bridge, Figure 2 is a block diagram showing an example of a configuration for improving the frequency of an AC system, Figure 3 is a power-frequency characteristic diagram, and Figure 4 is a digital phase control diagram. FIG. 5 is a block diagram showing a conventional example of frequency detection by a computer, FIG. 6 is an explanatory diagram of the frequency control method according to the present invention, and FIG. 7 is a flowchart. 400... Phase control device, 401... Phase detector, 402... Computer, 403... Gate logic, 600... Counter.

Claims (1)

[Scope of Claims] 1. A phase detection system that is configured with a phase lock loop circuit and generates a phase synchronization signal that is synchronized with the frequency of the AC voltage given an AC voltage signal of an AC system connected to a DC transmission system. a measuring circuit that measures the phase synchronization signal from the phase detector at predetermined intervals; and a measuring circuit for reading the output of the measuring circuit at predetermined intervals to control the power converter of the DC power transmission system. A control device for a power converter, comprising: a computer that forms a phase control signal, and provides the phase control signal to the power converter to perform frequency control. 2. In the device according to claim 1, the phase detector generates pulses synchronized with the alternating current voltage, the measuring circuit counts the pulses at predetermined intervals, and the computer performs predetermined sampling. reading the counting output of the measuring circuit at each time and giving a reset signal to the measuring circuit;
and a control device for a power converter, which forms a phase control signal to be given to the power converter.