JP2000217399A - Exciter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the generator voltage to a target level by setting a reference frequency in correspondence with the frequency of a synchronous machine, sampling the output voltage of the synchronous machine depending on the reference frequency and determining an output voltage value thereby detecting an accurate output voltage value even if the frequency is low when an exciter is started. SOLUTION: In an automatic voltage regulator AVR for a synchronous machine, a high speed operating section of a digital converter performs frequency calculation 12, amplitude operation (average value processing) 13, and three-phase average voltage operation 14. A frequency mode decision processing 15 is provided additionally in order to decide a frequency mode based on a flag value from the main CPU of the AVR thus setting a reference frequency. Subsequently, sampling is made at a sampling period corresponding to the reference frequency and an output voltage is determined based on the sampled voltage value. More specifically, the reference frequency is set differently for normal mode and low frequency mode and the output voltage value is detected accurately even in the low frequency mode thus controlling excitation of a synchronous machine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exciting device for a synchronous machine, and more particularly to a constant control of a generator voltage.

[0002]

2. Description of the Related Art FIG.
73 is a configuration diagram of a conventional excitation system shown in No. 73103,
In the figure, 1 is a synchronous machine, 2 is its field winding, 3 is an exciter that supplies a field current to the field winding 2, and 4 is an instrument transformer for detecting the voltage of the synchronous machine 1. A transformer (hereinafter referred to as PT) 5 is an instrument transformer (hereinafter referred to as CT) for detecting the current of the synchronous machine 1.

[0003] Reference numeral 6 denotes an automatic voltage regulator (hereinafter referred to as AVR) for controlling the voltage of the synchronous machine 1 to be constant.
4. Generator voltage (V), active power (P), voltage / frequency ratio (V / F), reactive power (Q) from CT5 signal
, A reference unit 62 for producing a control target value of the voltage of the synchronous machine 1, a control target value of the reference unit 62 and a generator voltage (V) which is a signal from the digital converter 61. A6 to amplify the difference
3. a phase compensator 64 for improving the stability of voltage control;
Adder 6 for adding signals from other additional function devices (described later)
5. The output of the adder 65 is further amplified and the exciter 3
And an amplifying unit B66 for outputting a signal to

[0004] Reference numeral 7 denotes a system stabilizing device for increasing the stability of the system by giving an output signal P from the digital converter 61 as an input signal and supplying an auxiliary signal to the AVR 6, and 8 denotes a digital converter. This is a V / F limiting device for performing a limiting control so that the V / F value, which is an output signal from 61, is an input signal and an AVR 6 is supplied with an auxiliary signal so that the V / F value does not exceed a certain value.

Reference numeral 9 designates low excitation which controls the operation state of the synchronous machine 1 so that the operation state of the synchronous machine 1 does not become lower than a predetermined value by inputting P and Q which are output signals from the digital converter 61 as input signals and supplying an auxiliary signal to the AVR 6. The limiting device 10 is a shunt for detecting a current flowing through the field winding 2, and 11 is for detecting an over-excitation state based on an output signal of the shunt 10. Is an overexcitation limiting device for limiting control of

FIG. 7 is a hardware configuration diagram of the digital converter 61. The digital converter 61 is composed of one print card, and has three PT4 and CT5 inside.
High-speed operation unit that calculates each signal (V, P, V / F, Q) from each of the three-phase signals of the isolator 611, PT4, and CT5 that insulates the phase input signals (va, vb, vc, ia, ib, ic). 612, 2-port register 61 for arithmetic processing
3. It is composed of a PIO bus interface 614 that outputs signals (V, P, V / F, Q) for control.

Next, the operation will be described. The output voltage of synchronous machine 1 is stepped down by PT4, and the signal is input to AVR6. In the AVR 6, first, the signal of the PT 4 is converted into a digital signal V by the digital converter 61 by a software operation method described later. The value of the reference unit 62 is a control target value for the AVR 6 that is trying to control the voltage of the synchronous machine 1. The reference unit 62 and the digital converter 61
The difference between the output signal V and the output signal V is obtained, and the amplified signal is amplified to an appropriate value by the amplifier A63.

If the difference signal is a positive value, the output voltage of the synchronous machine 1 is lower than the control target voltage value set by the reference unit 62, and therefore, the AVR 6 increases the output of the exciter 3 by a control signal. , The current flowing through the field winding 2 is increased, and the operation of increasing the output voltage of the synchronous machine 1 is performed.

The phase compensating section 64 compensates the output of the amplifying section A63 in order to enhance the stability of the voltage control.
In 5, the output of the phase compensator 64 is added to the output of various attached devices (system stabilizing device 7, V / F limiting device 8, etc.).
Outputs a signal proportional to the field current output from the exciter 3 (that is, the exciter 3 also has one amplifying function). Through a series of these operations, the output voltage of the synchronous machine 1 is controlled so as to become the control target value set by the reference unit 62 in the AVR 6.

Next, a software operation method in the high-speed operation unit 612 will be described. (A) As shown in FIG. 8, for example, one cycle of a va AC signal, which is one of the three-phase signals of PT4, is sampled by dividing it into 12 periods. The AC signal in this case is sampled based on the reference frequency. As the reference frequency, a rated frequency such as 50 Hz is used. (B) The following operation is performed from the above sampling value. FIG.
Shows the details of the arithmetic expression of each input signal. In the arithmetic operation, the va value is obtained from the two sampling data (vam and vam-3) by the expression (1) using the product of the amplitude value arithmetic expressions, and the three phases (va, v
The voltage (V) is obtained from the average value of (b, vc).

[0011]

(Equation 1)

(C) The frequency Fa (Fb, Fc) can also be calculated by equation (2) in the same manner as for va.

[0013]

(Equation 2)

The above calculation method does not cause an error at the reference frequency, but causes an error when there is a frequency fluctuation. The error due to the frequency fluctuation can be theoretically obtained as described below. Va which is an AC signal from PT4 is set as follows. Vam = Vsinωt Vam−3 = Vsinω (t−3Ts) (3) where Ts is a sampling period. At this time, the amplitude Va can be calculated by the equation (4) as shown in FIG.

[0015]

(Equation 3)

For example, if the reference frequency is 50 Hz, the sampling frequency is 600 Hz (Ts = 1/600 [s
ec]), Va = V at the reference frequency, and the error is zero. However, at the frequency of 49 Hz, Va = 1.0158 V to 0.9841 V, that is, the error is 1.58% to -1.59%.

In order to reduce this error, in step 13 shown in FIG. 10, the following average processing is performed.
For example, if a binary average processing is performed, the amplitude Va 'can be calculated as in the equation (5).

[0018]

(Equation 4)

In this case, at a frequency of 49 Hz, V
a ′ = 1.00049 V to 0.99951 V, that is, the error is 0.049% to −0.049%. The amplitudes Vb and Vc can be calculated in the same manner as Va.

The frequency calculation in step 12 in FIG. 10 is the calculation in equation (2). The frequency (Fa, Fb, Fc) of the output voltage of the synchronous machine obtained in equation (2) is calculated in step 13 It is calculated by substituting into the frequency f of ω (2πf) in the equation (5). In addition, the three-phase average voltage calculation in step 14 in FIG. 10 is based on the following equation shown in FIG.

[0021]

As described above, the conventional exciter reduces the error between the amplitude of the voltage and the current at the reference frequency when the voltage and the current are detected by the digital converter. Therefore, the accuracy described above is sufficient for a general power plant. On the other hand, in the case of a thyristor starting system in which a generator is used as a motor at the time of starting, it is necessary to perform excitation control by accurately detecting a voltage in a frequency range of 10 Hz to 40 Hz with respect to a rated frequency of 50 Hz. However, the current voltage detection method described above has a problem that the voltage is detected to be larger than the actual voltage value / current value, and the generator voltage cannot be controlled to be constant.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and uses the output of a digital converter capable of accurately detecting voltage and current even at a low frequency at the time of starting in a thyristor starting system. An object of the present invention is to provide an excitation control device capable of controlling a generator voltage to a control target value.

[0023]

(1) An exciting device according to the present invention samples an output voltage of a synchronous machine according to a set reference frequency, and calculates an amplitude value including an average value process based on the sampled value. Voltage detecting means for calculating an output voltage value by performing excitation control according to a comparison between the obtained output voltage value and a control target value, and control means for controlling the output voltage of the synchronous machine to the control target value. , Wherein the reference frequency is calculated as a frequency corresponding to the frequency of the synchronous machine.

(2) voltage detecting means for sampling the output voltage of the synchronous machine in accordance with the set reference frequency and performing an amplitude value calculation including an average value process based on the sampled value to obtain an output voltage value; An excitation device that performs excitation control according to a comparison between the obtained output voltage value and the control target value, and controls the output voltage of the synchronous machine to the control target value. A second voltage detecting means for rectifying and smoothing the voltage to obtain a DC output voltage, wherein the synchronous machine is compared with the control target value using the DC output voltage while the synchronous machine is operating in a low frequency range. When the synchronous machine is operating near the rated frequency, the calculation is performed using the reference frequency as the rated frequency, and the obtained output voltage value is compared with the control target.

(3) voltage detecting means for sampling the output voltage of the synchronous machine in accordance with the set reference frequency and performing an amplitude value calculation including an average value process based on the sampled value to obtain an output voltage value; An excitation device that performs excitation control according to a comparison between the obtained output voltage value and the control target value, and controls the output voltage of the synchronous machine to the control target value. A third voltage detecting means for obtaining an output voltage value according to a peak value of the voltage waveform is provided. While the synchronous machine is operating in a low frequency region, the output voltage value obtained by the third voltage detecting means is used. In comparison with the control target value, while the synchronous machine is operating near the rated frequency, the calculation is performed with the reference frequency as the rated frequency, and the obtained output voltage value is compared with the control target. .

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. Note that the overall configuration of the excitation device is the same as that of FIG.
FIG. 1 shows the processing in the high-speed operation unit 612 of the digital converter 61. In FIG. 1, the frequency calculation in step 12, the amplitude value calculation (average value processing) in step 13, and the three-phase average voltage calculation in step 14 are the same as the conventional processing shown in FIG.

The frequency mode determination processing in step 15 is as follows.
This is a step of determining a frequency mode based on a flag value from the main CPU of the AVR 6 and setting a reference frequency. During operation of the exciting device, the CPU determines the flag value based on an external signal indicating whether the synchronous machine is in a low speed state (low frequency) depending on the operation state of the synchronous machine or in a state near the normal rated speed (near the rated frequency). decide. Therefore, a reference frequency corresponding to the frequency of the output voltage of the synchronous machine is selected, sampling is performed at a sampling cycle corresponding to the reference frequency, and an output voltage value is obtained from the sampling voltage value.

Next, the operation will be described. FIG. 2 shows an algorithm for setting a reference frequency for calculating the frequency correction coefficient of the voltage value and the current value of the digital converter 61. (1) In step S1, the presence or absence of a mode change is determined based on information (flag value) on whether the mode is the low frequency mode or the normal mode determined by the main CPU of the AVR 6, and if there is a mode change, step S2. If no, go to step S6.

(2) In step S2, it is determined whether the frequency mode after the change is the low frequency mode or the normal mode. If the frequency mode is the low frequency mode, the process proceeds to step S3, and if it is the normal mode, the process proceeds to step S4. (3) In step S4, the reference frequency is set to the value of the normal mode, that is, the conventional reference frequency, and the sampling frequency is set to 12 times the reference frequency, that is, the sampling cycle is set to 1/12 times the cycle of the reference wave.

(4) In step S3, the reference frequency is set to 1/2 the reference frequency in the normal mode, and the sampling frequency is set to 12 times the reference frequency in the low frequency mode. For example, the reference frequency in the normal mode is 50 Hz
In this case, the sampling frequency in the normal mode is 600 Hz, and the reference frequency and the sampling frequency in the low frequency mode are 25 Hz and 300 Hz, respectively.
Hz. (5) In step S5, the values of the variables in the memory are initialized. (6) In step S6, the arithmetic processing shown in FIG. 1 is performed.

A specific example of a voltage value at a frequency of 27 Hz is as follows.
When calculated at (Ts = 1/600), the error is 19.9% to −25.0% according to the equation (5), whereas the reference frequency of the low frequency mode is 25 Hz (Ts = 1/3).
The error in 00) is considerably small, from 0.78% to -0.79%.

As described above, according to the first embodiment,
High-speed operation unit 612 of AVR6 digital converter 61
In the standard mode and the low frequency mode, the frequency of the reference frequency is changed and set, so that accurate voltage and current can be detected even at a low frequency, and the excitation control is performed so that the generator voltage becomes the control target value. There is an effect to do.

Embodiment 2 FIG. In the first embodiment, the frequency mode is determined according to the flag value. However, the frequency of the voltage output from the synchronous machine may be detected, and the reference frequency may be changed according to the detected frequency. Good.

Although the reference frequency is switched in two stages of the "low frequency mode" and the "normal mode" in the frequency mode,
Switching may be performed in three steps such as “low frequency”, “medium frequency”, “normal rated frequency”, or a multi-step switching of more steps. For example, the reference frequency may be set to three levels of 20 Hz, 30 Hz, and 50 Hz according to the frequency of the synchronous machine. Further, the number of stages may be more than that, or the reference frequency may be continuously changed in accordance with the frequency of the synchronous machine without any stages.

Embodiment 3 FIG. FIG. 3 is a diagram showing a configuration of the excitation device according to the third embodiment. FIG. 3 is a block diagram of the conventional exciter shown in FIG. 6, which includes a voltage detector 67 and a digital converter 6 connected in parallel with the digital converter 61.
1 and a switch 68 for selecting the voltage detector 67 is added. FIG. 4 shows the voltage detector 6 of FIG.
FIG. 7 is a diagram showing an internal configuration of a seventh embodiment.

Next, the operation will be described. (1) The voltage detector 67 outputs the three-phase signal (va, v
b, vc) is converted into a small-level analog signal by a full-wave rectifier circuit including a three-phase transformer 671, a semiconductor 672, a resistor 673, and a capacitor 674, and an adjustment resistor 675 is provided.
Output the voltage (V) by correcting the characteristics.

(2) At the reference frequency, the switch 6
By connecting the contact a of No. 8 to the contact c, the voltage (V) is detected by the digital converter 61 and the excitation control is performed as in the conventional method. (3) At low frequencies, the contact a of the switch 68
Is connected to the contact b, the voltage (V) is detected by the above-described voltage detection unit 67, and the excitation control is performed.

As described above, by switching between the voltage detector 67 capable of accurately detecting the voltage regardless of the frequency of the AC signal from the PT 4 for each frequency mode and the conventional digital converter, the low frequency In the mode, voltage detection with a small error becomes possible.

As described above, according to the third embodiment,
In the AVR 6, the digital converter 61 and the voltage detector 67 are switched between the normal mode and the low frequency mode for use, so that an accurate voltage can be detected even at a low frequency, and the generator voltage becomes the control target value. Thus, there is an effect that the excitation control is performed.

Embodiment 4 FIG. In the first embodiment, the high-speed operation unit 6 of the digital type converter 61 of the AVR 6 is used.
12, the case where the reference frequency is changed and set between the normal mode and the low frequency mode has been described. In the fourth embodiment, the amplitude shown in FIG. Average value processing 1 of value calculation
3 is replaced with FIG.

In the normal frequency mode, the prescribed frequency of the synchronous machine is used as a reference frequency, and the voltage V is calculated by the operation formula shown in Expression (5) using the value sampled at the reference frequency. Then, in the low frequency mode, the amplitude of the voltage is calculated using the equation (6).

[0042]

(Equation 5)

Here, vn is the peak value of the amplitude in the AC voltage waveform (maximum positive / negative value of the waveform in every 1/2 cycle), and equation (6) represents the peak value of the amplitude at 12 points (6 cycles) in the voltage waveform. (Peak value of minutes) is defined as the voltage V. In this calculation method, at low frequencies, the error is smaller than the error generated by the conventional calculation method, and the voltage detection accuracy is improved.

As described above, according to the fourth embodiment,
In the high-speed operation unit 612 of the digital converter 61,
By switching the amplitude value calculation method between the normal mode and the low frequency mode, the calculation error at low frequencies is reduced, the accuracy of voltage detection is improved, and the excitation control is performed so that the generator voltage becomes the control target value. Has the effect of doing

[0045]

As described above, according to the present invention, even if the frequency of the synchronous machine is low, an accurate output voltage value is detected, so that the generator voltage becomes equal to the control target value. Excitation control can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing arithmetic processing in a high-speed arithmetic unit of a digital converter according to Embodiment 1 of the present invention.

FIG. 2 is a flowchart showing an operation of the digital converter according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of an excitation device according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of a voltage detector according to Embodiment 3 of the present invention.

FIG. 5 is a block diagram showing arithmetic processing in a high-speed arithmetic unit of a digital converter according to Embodiment 4 of the present invention.

FIG. 6 is a circuit diagram showing a configuration of a conventional excitation device.

FIG. 7 is a circuit diagram showing a configuration of a conventional digital converter.

FIG. 8 is a waveform chart showing an example of conventional sampling.

FIG. 9 is a block diagram showing a calculation process in a high-speed calculation unit of a conventional digital converter.

FIG. 10 is a block diagram showing a calculation process in a high-speed calculation unit of a conventional digital converter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Synchronous machine 2 Field winding 3 Exciter 4 Instrument transformer 5 Instrument transformer 6 Automatic voltage regulator 61 Digital converter 62 Reference section 63 Amplification section A 64 Phase compensation section 65 Addition section 66 Amplification section B 67 Voltage Detector 68 Switch 612 High-speed operation unit 613 Two-port register 614 PIO bus interface 671 Three-phase transformer 672 Semiconductor 673 Resistance 674 Capacitor 675 Adjustment resistance

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H590 AA22 CC01 CC18 CD01 DD64 DD70 EA07 EB02 EB21 FA06 GA02 GB05 HA02 HA05 HA06 HA07 HA09 HB02 JA02 JA19 JB02 JB04 JB15 JB16

Claims (3)

[Claims] A voltage detecting means for sampling an output voltage of a synchronous machine in accordance with a set reference frequency, performing an amplitude value calculation including an average value process based on the sampled value, and obtaining an output voltage value, Control means for performing excitation control in accordance with the comparison between the output voltage value and the control target value and controlling the output voltage of the synchronous machine to the control target value. An exciter for a synchronous machine, wherein the computation is performed as a frequency corresponding to the frequency of the synchronous machine. 2. A voltage detecting means for sampling an output voltage of a synchronous machine in accordance with a set reference frequency, performing an amplitude value calculation including an average value process based on the sampled value, and obtaining an output voltage value, An excitation device that performs excitation control according to a comparison between the output voltage value and the control target value, and that controls the output voltage of the synchronous machine to the control target value. A second voltage detecting means for obtaining a DC output voltage by performing a smoothing process, and when the synchronous machine is operating in a low frequency region, the voltage is compared with the control target value using the voltage value of the DC output voltage. An exciting device characterized in that when the synchronous machine is operating near the rated frequency, the above calculation is performed using the reference frequency as the rated frequency, and the obtained output voltage value is compared with the control target. 3. A voltage detecting means for sampling an output voltage of a synchronous machine in accordance with a set reference frequency, performing an amplitude value calculation including an average value process on the basis of the sampled value, and obtaining an output voltage value; An excitation device that performs excitation control in accordance with the comparison between the output voltage value and the control target value, and control means for controlling the output voltage of the synchronous machine to the control target value. A third voltage detecting means for obtaining an output voltage value according to the peak value;
While the synchronous machine is operating in the low frequency range, the output voltage value obtained by the third voltage detecting means is used to compare with the control target value. An exciting device characterized in that the above calculation is performed with the frequency as the rated frequency, and the obtained output voltage value is compared with the control target.