JPH0634639B2 - Excitation control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an excitation control device for controlling a terminal voltage of a synchronous generator, and more particularly to a system in which an input voltage of a thyristor converter for supplying an excitation current is a system ground fault or the like. An excitation control device for a synchronous generator capable of reliably igniting a thyristor with a narrow pulse even when the overlap angle at commutation of the thyristor converter becomes 60 ° or more due to a decrease due to an accident. .

[Background of the Invention]

FIG. 8 shows the configuration of a conventional generator excitation control device. In the figure, the field winding 2 of the generator 1 is excited by a three-phase full-wave type thyristor converter 4, and the power supplies U, V, W of the thyristor converter 4 are supplied by an exciting power supply transformer 3, and The primary winding of the transformer 3 is connected to the armature of the generator.
The output of the generator is generally connected to the main transformer 6, and this transformer is used for parallel insertion after step-up or through the breaker 7 for transmission lines 10, 11
It is connected to the. The power transmission lines 10 and 11 are connected to power transmission line breakers 8 and 9, respectively. Then, for example, when a ground fault or the like occurs at point F of the power transmission line 11, a protective relay (not shown) opens the breaker 9 and the circuit breaker to disconnect the fault circuit, and the generator transmits the power via the power transmission line 10. Continue driving.

In this way, a three-phase ground fault (short circuit) occurs on the high voltage side of the main transformer.
Even if an accident occurs, it is necessary to continue operation without stopping the generator, but the problems at this time are described below. Now, at the closest end of the main transformer 6, as at point F of the transmission line 11, 3
Generator terminal voltage V when a phase ground fault (short circuit) occurs
Changes in _G and field current I _F are as shown in FIG. That is, if a three-phase ground fault occurs at the point F of the transmission line at time t ₁ , the generator terminal voltage V _G is instantaneously increased to a voltage determined by the impedance of the main transformer 6 and the internal impedance of the generator. Fall to. Since the impedance of the main transformer 6 is generally about 10% to 15% and the transient impedance of the generator is about 20% to 30%, the generator terminal voltage V _G is about 30% of the rated voltage. At this time, the armature current of the generator becomes several times the rated current due to a ground fault, and as is well known, a direct current containing an AC component is transiently induced in the field winding 2 by the armature reaction of the generator. The field current I _F, that is, the peak value of the output current of the thyristor converter 4 is about 3 to 4 times the rated field current. When at time t ₁₀ teeth and disconnection device 9 is opened fault point F is disconnected, the generator terminal voltage V _G and the field current I _F is restored to approximately accident previous value.

When the field current I _F increases in this manner, the commutation mode of the thyristor converter changes when the ignition pulse has a narrow width. FIG. 10 equivalently shows the portion of the thyristor converter 4, and the field winding 2 becomes a large inductive load of the thyristor converter. Now, assuming that the AC reactances of all the phases in FIG. 10 are all equal X and the voltages of each phase are all equal E, the direct current IF ₀ when the output terminal of the thyristor converter is short-circuited is Is. Range and control delay angle δ of the field current I _F to give each commutation mode this value as a reference is expressed as follows.

Commutation mode I; Commutation mode II; Commutation mode _{III; 3/4 ≦ I F} / IF 0 1, δ = π / 6 ...... (4) This is illustrated in Figure 11, increasing the field current I _F is, mode II or When it becomes III, the occurrence of the control delay angle cannot be avoided.

On the other hand, the gate control of the thyristor converter 4 is performed as follows. In FIG. 8, the generator terminal voltage is PT1.
Detected by 2 and converted to direct current by the rectifier 13, and the deviation from the voltage setting value 15 is detected by the adder 14 and increased by the amplifier 16 to control the pulse phase shifter 17A. Pulse phase shifter 17
A applies a phase-controlled gate pulse to the thyristor converter 4 according to the output of the amplifier 16 via the wide pulse amplifier 18. The synchronous power supply of the pulse phase shifter 17A is obtained from PT12 because it is affected by the waveform distortion due to the commutation of the thyristor when taken from the secondary side of the excitation power supply transformer 3. By the way, as described above, when the generator voltage V _G is remarkably reduced due to the ground fault of the transmission line, the output of the amplifier 16 gives the maximum raising signal and accordingly the ignition pulse phase angle of the pulse phase shifter 17 is outputted. It operates so that α is minimized and the output voltage of the thyristor converter 4 is maximized. (The firing angle α of the thyristor during normal operation is about 60 °.) The firing pulse of the thyristor conversion circuit is generally used 1
In the case of a narrow pulse of 50 μsec to 200 μsec, the commutation mode is II or III when the field current I _F increases as described above.
become. For this reason, two pulses having the original phase of the ignition pulse and a phase delayed by 60 ° are set, and the ignition is performed by the second delayed pulse. Therefore, even if the original gate phase control angle α is controlled to be zero, the result is equivalent to the actual phase shift of 60 °. FIG. 12 shows the waveforms of the thyristor waveform, the gate pulse, and the thyristor current when the firing angle α = 0 of the thyristor is set. Even if the failure of the generator circuit is eliminated once this state is entered. ,
Normal commutation does not occur. As a method for solving these problems, as disclosed in Japanese Patent Laid-Open Nos. 49-39016 and 49-39017, a signal corresponding to the field current and a signal corresponding to the terminal voltage of the synchronous machine, or the field When the thyristor is commutated by the signal corresponding to the voltage, the signal corresponding to the terminal voltage of the synchronous machine, and the signal indicating that the firing angle of the thyristor is the minimum (the state where the thyristor is fired by the second pulse) There is known a method of detecting the existence of the thyristor and temporarily delaying the firing angle α of the thyristor or turning off or turning off the firing signal. This method can recover from an abnormal state to a normal control state with a simple logic. However, in order to improve the stability of the system, it is important to increase the output of the thyristor converter as much as possible, including when the system side accident continues. If the firing angle α is uniformly delayed by 30 ° or more or the gate pulse is cut off in the state of forced phase shift as described above, the maximum output as a thyristor converter is obtained at the interface between modes I and II. About 80% or 0% of the available voltage
Only the output is output, and the operation is almost equivalent to lowering the top voltage of the excitation system. For this reason, in the case of an exciter whose commutation mode is II or III in the event of a system fault, a wide pulse of 120 ° width which gives a pulse during the normal commutation period of the thyristor has been used as the gate signal instead of the narrow pulse. . However, in the wide pulse driving system, the output capacity of the pulse amplifier 18 is several tens of times larger than that of the narrow pulse driving system, so that the capacity of the pulse amplifier is several tens of times and the capacity of the power supply device is also several tens. It doubles. When the single-unit capacity of the generator is in the 1000 MW class, the ratio of the pulse amplifier to the entire control device becomes about 60%, so that there is a problem that the cost is greatly increased when the wide pulse drive system is used.

[Object of the Invention]

An object of the present invention is to eliminate the drawback of increasing the capacity of a conventional pulse amplifier for driving a wide pulse and to narrow the width of the thyristor so that the thyristor can be surely controlled even when the weight angle of commutation is large. An object is to provide an excitation control device for a pulse drive type generator.

[Outline of Invention]

The present invention detects the ignition delay angle at the thyristor firing angle α = 0 from the signal corresponding to the input voltage of the thyristor converter and the signal corresponding to the output current of the thyristor converter, and controls the input signal of the pulse phase shifter. Alternatively, by controlling the pulse phase shifter itself so that the firing angle is always larger than the detected firing delay angle, even a narrow pulse can be reliably fired. It is characterized by having done.

Example of Invention

Hereinafter, the present invention will be described with reference to examples. FIG. 1 shows an embodiment of the present invention. A limiter circuit 19 is provided in the input circuit of the pulse phase shifter 17A, and the limiter circuit 19 is provided.
The input signal δ of the resistor 21 and the signal V _G corresponding to the input voltage to the thyristor converter 4 from the output of PT12 (which may of course be equivalently detected by CT from the AC side of the thyristor converter 4) Output current I detected by
_F and _F are input to the arithmetic circuit 20 to calculate. The pulse amplifier 18B is for a narrow pulse. The configuration other than these is the same as the conventional device in FIG.

FIG. 2 shows the details of the arithmetic circuit for the control delay angle .delta., And FIG. 3 shows an example of the operation waveform of each part thereof. The signal corresponding to the input voltage E of the thyristor converter is the taken-in generator terminal voltage V _G, which is first rectified by the rectifier circuit 201 to remove unnecessary ripples and IF expressed by the equation (1). _A coefficient circuit 202 calculates a signal corresponding to ₀ . On the other hand, the output current of the thyristor converter 4, that is, the detected value of I _F is normally a DC current with almost no ripple, but when the armature current of the synchronous generator rapidly increases due to a short circuit or the like, it is shown in FIG. As described above, it becomes a direct current in which an alternating current having the same frequency component as the power supply frequency is superimposed. For this reason, the commutation mode cyclically changes from mode I to mode III within one cycle. Therefore, due to the time delay of the arithmetic circuit 20, it cannot be used as it is as a signal of I _F for calculating the control delay angle δ with which the thyristor converter 4 is reliably fired. Therefore, the peak value of I _F captured by the peak value detection circuit 205 is detected, and the peak value is set as I _F again to calculate the control delay angle δ at which the thyristor is reliably fired. However, in general, the peak value detection circuit uses a non-linear filter having a short charging time constant and a long discharging time constant.
Therefore, when the system fault is recovered and I _F is instantaneously decreased as shown at time t ₁₀ in FIG. 3, the generator voltage is recovered so that the output of the peak value detection circuit 205 instantaneously becomes the actual value. The circuit 205 is reset by the signal R indicating that this has occurred. The dividing circuit 203 calculates I _F / IF ₀ using the thus obtained I _F, and the number generator circuit 204 determines the commutation mode and calculates the control delay angle δ from the formulas (2) to (2). Follow step 4). Note that δ in the commutation mode II is given by the inverse triangular number, but as shown in FIG. 12, this can be regarded as a substantially straight line and can be approximated without any problem.

Next, the output signal δ of the arithmetic circuit 20 and the operation of the limiter circuit 19 will be described. The limiter circuit 19 includes a pulse phase shifter 17
In order to prevent the firing angle of the thyristor converter 4 output from A from becoming less than the firing delay angle δ, the pulse phase shifter 17
It is a variable signal limiter capable of variably setting the input signal level of A (the output signal V _CL of the limiter circuit 19) according to the ignition delay angle δ. That is, the limiter 19 originally has a limiter characteristic of being saturated at V _CL = V ₁ with respect to the input V _C , but as shown in FIG. 4, change the saturation value V ₁ to V ₂ by the ignition delay angle δ. You can The relationship between the input V _CL and the output phase α of the pulse phase shifter 17A is shown by the broken line C in FIG. Also in this case, if V _C increases linearly with time t after the occurrence of the system failure as shown in FIG. 5, the output V _CL of the limiter circuit 19 also increases linearly, and eventually saturates at V _CL = V ₁ . . The minimum value of the firing angle at this time is indicated by α ₁ . However, when the ignition delay angle δ obtained by the arithmetic circuit 20 is not 0, the saturation value of V _CL becomes the fifth value.
Since the value is changed to V ₂ as in the case after t = t _{b in the} figure, the minimum value of α is also switched to α ₂ correspondingly. Therefore α ₂ ＞
If V ₂ is changed in accordance with δ so as to be δ, the firing angle is always larger than δ, and even a narrow pulse can be reliably fired. The circuitization means for such a limiter circuit 19 is not particularly difficult and can be realized by known circuit technology.

FIG. 6 shows another embodiment of the present invention, in which the pulse phase shifter 17B is provided with the same function instead of providing the limiter circuit. That is, the pulse phase shifter 17B outputs the firing angle α to the input V _{C according} to the characteristic as shown in FIG. 7, but when the minimum value of α becomes δ> 0, α ₁ to α ₂ It has the property of changing to various values. Therefore, it is obvious that the same effect as that of the first embodiment can be obtained by setting α ₂ > δ, and from another viewpoint, the limiter circuit 19 of FIG. It can be considered that it is built in.

〔The invention's effect〕

As is clear from the above embodiments, according to the present invention, depending on the commutation mode of the thyristor, the minimum point of the pulse phase shifter is not less than the minimum ignition delay angle that can be fired as a thyristor converter. Since the arc angle can be limited, the thyristor can be ignited with a narrow pulse as in a normal thyristor conversion circuit.
Therefore, there is an effect that the capacity of the pulse amplifier and its power supply device can be greatly reduced. In addition, the minimum ignition delay angle can be calculated according to the generator terminal voltage and the field current to maximize the ability of the thyristor converter. The same effect can be obtained by increasing the top voltage by about 20% as compared with the conventional narrow pulse method.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the details of the arithmetic circuit in the embodiment of FIG. 1, and FIG. 3 is an operation waveform of each part of the arithmetic circuit of FIG. FIG. 4, FIG. 4 and FIG. 5 are explanatory views of the operation of the limiter circuit in the embodiment of FIG. 1, FIG. 6 is a view of another embodiment of the present invention, and FIG. 7 is of FIG. The figure which shows the characteristic of the pulse phase shifter in an Example, FIG. 8 is a figure which shows the conventional excitation control apparatus, FIG. 9 is a figure which shows the change of the generator voltage and the field current at the time of a grid fault, FIG. 10 is a circuit diagram of the thyristor converter, FIG. 11 is an explanatory diagram of the ignition delay angle,
FIG. 12 is a waveform chart of each part showing the operation of the thyristor converter. 1 ... Synchronous generator, 2 ... Field winding, 4 ... Thyristor converter, 12 ... PT, 17A, 17B ... Pulse phase shifter, 18B ... Narrow pulse amplifier, 19 ... Limiter circuit, 20 ... Arithmetic circuit.

Claims (2)

[Claims] 1. A thyristor converter for converting an alternating current output of a synchronous generator into a direct current to obtain a field current of the synchronous generator, and a deviation between a value obtained by rectifying the alternating current output of the synchronous generator and a voltage setting value. In the excitation control device, which comprises a control means for outputting an ignition pulse having a phase angle α corresponding to the above to the gate of the thyristor converter, a signal corresponding to an input voltage of the thyristor converter is rectified to output the thyristor converter. A means for obtaining a direct current IF ₀ when the ends are short-circuited, a means for detecting the peak value I _F of the field current, a value for I _F / IF ₀ , and a commutation mode is determined from this value to determine the commutation mode. An excitation control device comprising means for obtaining a control delay angle δ according to a flow mode and means for limiting a phase angle α of the ignition pulse so as not to be equal to or less than the control delay angle δ. 2. The commutation mode I according to claim 1, wherein: Commutation mode II: Commutation mode _{III: 3/4 ≦ I F} / IF 0 ≦ 1 δ = π / 6 excitation control apparatus characterized by determining the control delay angle [delta] with determining commutation mode by.