JP3114351B2 - SVC control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an SVC control circuit used in a power system in which a series capacitor is connected for reactance compensation on a power supply side, for example, in an AC electric railway.

[0002]

2. Description of the Related Art As is well known, in an electric railway, load fluctuations are irregular and severe voltage fluctuations occur. Feeder transformers often bear a load about three times their capacity due to inrush currents, etc., for a relatively short time,
As a result, the voltage drop due to the reactance of the feeder transformer is about three times that at the time of the rated load, and a large voltage drop occurs on the secondary side. Therefore, feeding circuit transformer as shown in FIG. 6 (inductive reactance jX _s to) of the secondary to the primary side by inserting a series capacitor (and -jX _c capacitive reactance) transformer reactance jX _s 100 By compensating for the%, the power supply capacity is apparently increased to solve the above problem.

Since the above-mentioned series capacitor is connected in series to the system, it is necessary to provide overload protection in the event of a heavy load or system short circuit, and to provide a no-load transformer when the electric vehicle passes through a section where the feeding section is divided. At power up, protection against low frequency vibrations caused by LC resonance between the series capacitor and the vehicle transformer is required. On the other hand, as a countermeasure that can be implemented on the load side, it is common practice to connect an SVC as shown in FIG. Where SVC
In this technology, for example, a reactor and a capacitor are connected in parallel to a feeder circuit, and the current flowing therethrough is continuously controlled by a thyristor.

[0004]

In the case where the series capacitor is provided in the system and the SVC is installed, when the electric vehicle passes through the section, it takes several hundred milliseconds.
When a power failure of a certain level occurs and the power is restored, an inrush current having a waveform as shown in FIG. 8 is generated, and the magnetic flux of the vehicle transformer is temporarily saturated. As a result, the low-frequency voltage is applied to the series capacitor to be charged, and the low-frequency vibration is repeatedly generated on the feeding side (primary side of the vehicle transformer) due to the difference between the power supply voltage and the voltage of the series capacitor. . In the waveforms of the feeding voltage and the magnetic flux of the transformer core shown in FIG.
The levels are indicated by broken lines. On the other hand, when the SVC is combined, the low-frequency vibration is further promoted due to the shift of the firing angle phase of the thyristor in the SVC because the feeding voltage causes the low-frequency vibration as shown in the figure. As a result, there is a problem that overvoltage is continuously generated at both ends of the series capacitor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to extract low-frequency vibration caused by an inrush current by various means and cancel it without promoting it. To provide an SVC control circuit that operates the SVC to protect the series capacitor.

[0006]

In order to achieve the above object, the present invention provides a static var compensator (hereinafter referred to as SVC) connected to a secondary side of a feeder transformer together with a series capacitor for compensating its reactance. A filter for extracting a low-frequency vibration component of the load current,
The low-frequency vibration component extracted by this filter reverses the polarity.
Input and turned on in synchronization with the SVC firing pulse.
To cancel the low frequency vibration component.
A current command increase / decrease switch that outputs a command such as
Means for applying a command output from this switch to the current control system of the SVC.

[0007]

According to the present invention, the low-frequency oscillation component of the load current is reduced by, for example, the load current itself or the secondary current of the feeder transformer or the secondary voltage of the feeder transformer (feeder voltage).
By injecting this vibration component into the thyristor current command of the SVC in the opposite phase, the SVC operates to make the low-frequency vibration component zero and acts to suppress the overvoltage continuation phenomenon of the series capacitor. I do.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing a first embodiment of the present invention.
In the figure, the main circuit of the feeder circuit includes a feeder transformer 1, a series capacitor 2, an overvoltage relay 3 for detecting an overvoltage of the series capacitor 2, a short circuit breaker 4 for short-circuiting the series capacitor 2, an SVC 5, , Synchronous power transformer 9, feeder transformer secondary current detection CT 10, load current detection CT 1
SVC5 is a high impedance transformer 6,
A thyristor device 7, a phase-advancing filter capacitor 8, and a reactor 12 are provided.

On the other hand, the synchronous power transformer 9 and each CT 10,
An SVC control circuit 13 which takes in the output of the SVC 11 and outputs a firing pulse to the thyristor device 7 of the SVC 5 generates a synchronization signal synchronizing with the feeding voltage and generating a synchronization signal serving as a reference of the reactive power calculation and the firing pulse. A detection circuit 14, a prediction control circuit 15 for predicting and calculating the reactive power of the load, a correction control circuit 16 for correcting the reactive power remaining on the secondary side of the feeder transformer 1 due to a calculation error, and the like, Q adjuster 17 for adjustment, pulse generation circuit 18 for generating a firing pulse for thyristor device 7, low frequency vibration suppression circuit 19 which is a main part of the present invention, predicted value Q of reactive power, correction amount And an adder 20 for adding ΔQ and the output of the low-frequency vibration suppression circuit 19. In the above configuration, the correction control circuit 16 and the Q adjuster 17 are not essential to the present invention.

Next, the configuration of the low frequency vibration suppression circuit 19 will be described in detail with reference to FIG. This suppression circuit 19
Detecting the low-frequency vibrations from the load current I _L taken by T11, it serves to output a command that cancels it to the input side of the pulse generation circuit 18. In other words, suppression circuit 19 includes a bandpass filter 191 to detect only the low-frequency component of the load current I _L, a predetermined amount the output phase, a phase shifter 192 for correcting the output of the band-pass filter 191 is added Comparator 193
And the off-delay timer 194 to which the output is added
And an analog switch 195 that is on / off controlled by its output, inverters 196 and 197, and an analog switch 198 having switches 198b and 198a connected to the outputs of the inverters 196 and 197, respectively. . The output of the analog switch 198 is output to the adder 2 together with the predicted value Q of the reactive power and the correction amount ΔQ.
It has been added to zero.

Here, the band-pass filter 191 has, for example, characteristics as shown in FIG. 3, and the phase shifter 192 is used for performing phase adjustment when the band-pass filter 191 is configured by an active filter. The analog switch 195 and the comparator 193 operate when the detected value of the low frequency component exceeds a certain value.
The off-delay timer 194 is for setting the on-time of the analog switch 195. Analog switch 1
Reference numeral 98 denotes a U-phase switch 198a and an X-phase switch 198b that operate in synchronization with the U-phase and X-phase positive and negative firing pulses of the thyristor device 7 .

Next, the operation of this embodiment will be described with reference to FIG. Magnetizing inrush current flows when the electric vehicle sections pass, when the load current I _L becomes negative unbalanced waveform as shown in FIG. 4, from the band-pass filter 191, a delay due to the characteristics shown in FIG. 3 Is output. This low frequency component is output to the phase shifter 192.
, And after being appropriately amplified, the analog switch 19
8 for the X-phase switch 198b. The output of the inverter 196 is again inverted by the inverter 197 and is applied to the U-phase switch 198a in the analog switch 198.

As described above, each switch 198a, 19
8b operates in synchronism with the U-phase and X-phase positive and negative firing pulses, so that its on / off operation and each switch 198a, 1
The output waveform of 98b is as shown in the figure. Therefore, each switch 198a, which is input to one input terminal of the adder 20,
The combined output of 198b becomes as shown in the figure, and becomes an analog command to increase or decrease the current command of the thyristor device 7 in the direction of decreasing when the load current is large, and in the direction of increasing when the load current is small. This command is added to the predicted value Q and the correction amount ΔQ of the reactive power in the adder 20, and the pulse generator 18 that receives the addition result outputs a firing pulse of the thyristor device 7.

[0014] With the above operation, the thyristor device current (SVC current) I _SVC as shown at the bottom of Figure 4, began to change in a direction that promotes the unbalance of the load current I _L if conventional However, according to the present invention, the imbalance is changed in a direction to eliminate the imbalance, the low-frequency vibration component is canceled, and the overvoltage continuation phenomenon of the series capacitor 2 is suppressed.

FIG. 5 shows a main part of another embodiment of the present invention. These embodiments are different from the first embodiment in that the low-frequency component of the load current is extracted. In the second embodiment, the low-frequency component is detected from the secondary current of the current transformer 1 detected by CT10. In the case of the third embodiment, a low-frequency component is extracted from the secondary voltage (feeding voltage) of the feeder transformer 1 detected by the synchronous power transformer 9. In any of these embodiments, the extracted low-frequency component is input to the low-frequency vibration suppression circuit 19 in FIG. 2, and the low-frequency vibration is suppressed by the same operation as in the first embodiment.

In each of the above embodiments, the current of the thyristor device 7 is detected by CT, and the detected value is output to the output of the inverter 196 via a secondary delay filter, an integrator (neither is shown), or the like. By adding, it is also possible to add a function of preventing high-impedance transformer 6 from being demagnetized.

[0017]

As described above, according to the present invention, a low-frequency vibration component of a load current is extracted by a filter, and the low-frequency vibration component is injected into the SVC current control system in an opposite phase, thereby obtaining a low-frequency vibration component. Since the SVC is operated so as to cancel the component, there is no possibility that the overvoltage phenomenon of the series capacitor caused by the low-frequency vibration component is sustained, and the series capacitor can be protected.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a main part of FIG. 1;

FIG. 3 is a characteristic diagram of the bandpass filter in FIG. 2;

FIG. 4 is a waveform chart showing the operation of the first embodiment.

FIG. 5 is a configuration diagram showing a main part of the second and third embodiments of the present invention.

FIG. 6 is a system configuration diagram for explaining a problem of the related art.

FIG. 7 is a system configuration diagram for explaining a problem of the related art.

FIG. 8 is a waveform chart for explaining low-frequency oscillation of the feeding circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Feeding transformer 2 Series capacitor 3 Overvoltage relay 4 Short circuit breaker 5 SVC 6 High impedance transformer 7 Thyristor device 8 Leading phase filter capacitor 9 Synchronous power transformer 10 Feeding transformer secondary current detection CT 11 Load current detection For CT 12 Reactor 13 SVC control circuit 14 Synchronous signal detection circuit 15 Predictive control circuit 16 Correction control circuit 17 Q regulator 18 Pulse generation circuit 19 Low frequency vibration suppression circuit 20 Adder 191 Bandpass filter 192 Phase shifter 193 Comparator 194 Off Delay timer 195 Analog switch 196 Inverter 197 Inverter 198 Analog switch

Continued on the front page (72) Inventor Masahiro Sawasato 1-1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Kiyoshi Kato 1-1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Fuji (56) References JP-A-5-189067 (JP, A) JP-A-5-257549 (JP, A) JP-A-5-2546 (JP, U) (58) Fields surveyed (Int .Cl. ⁷ , DB name) G05F 1/70 H02J 3/18

Claims (3)

(57) [Claims] In a control circuit of a static var compensator (hereinafter referred to as SVC) connected to a secondary side of a feeder transformer together with a series capacitor for reactance thereof, a low frequency oscillation component of a load current is reduced. The filter to be extracted and the low-frequency vibration component extracted by this filter have the opposite polarity.
Input and turned on in synchronization with the SVC firing pulse.
To cancel the low frequency vibration component.
An SVC control circuit comprising: a current command increasing / decreasing switch for outputting such a command; and means for applying a command output from the switch to a current control system of the SVC. 2. The SVC control circuit according to claim 1, wherein a low-frequency oscillation component of the load current is extracted from a secondary current of the feeder transformer. 3. The SVC control circuit according to claim 1, wherein a low-frequency oscillation component of the load current is extracted from a secondary voltage of the feeder transformer.