JPH02232000A - D/a output system of digital controller for generator exciter - Google Patents

Abstract

PURPOSE:To improve the accuracy of automatic voltage regulation by setting the digit width of a D/A converter at the final stage of a digital excitation controller of a generator to a nonlinear type so as to reduce it with respect to an analog output at the time of normal operation. CONSTITUTION:A predetermined field signal in a digital AVR is calculated in a predetermined field signal calculator 10 to be output, and a characteristic signal g1 having a smooth slope is applied to one input of an adder 18 through a proportional gain element (Kg1) 12. The output of the calculator 10 is applied to the other terminal as a characteristic signal g2 having an abrupt slope through an insensitive band element 14 and a proportional gain element 16. The phase of an igniting angle of a thyristor is controlled by using an analog signal D/A-converted from the output of the adder 18.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a D/A converter installed at the final stage of a digital control device for a generator excitation system, and particularly relates to a D/A converter installed in the final stage of a digital control device for a generator excitation system. D/ of digital control device for machine excitation system
Regarding the A output method.

[Conventional technology]

Automatic voltage regulators (AVRs) that operate to automatically compensate for generator terminal voltage fluctuations caused by changes in load, etc. and maintain a constant voltage, especially generators that control thyristor excitation type generators. Digital AV for excitation system
In the case of R, a D/A converter is provided between the final output section of the digital calculation section and the firing angle phase control section of the thyristor. Conventionally, in order to improve quick response, the excitation system has a field peak voltage V that can supply a maximum field current i, -8 that is 5 to 10 times the field current iro required to generate the no-load rated voltage. lm
ax is selected.

In other words, the excitation device has no-load field voltage ■. 5 based on
~10 times the field top voltage■,. ．． The width of the effective firing angle on the glass side of the thyristor of the thyristor pure bridge rectifier corresponding to this control width is about 0 to 1 pu/90 to 20''. Generally, the digit width and analog output of a D/A converter is a D/A output method that changes linearly in response to 0 to 2000 digits/0 to lpu. [Problem to be solved by the invention] However, According to the D/A output method of the digital control device for the generator excitation system described above, the digit width and the analog output change linearly.
Voltage on field term V (mae is 1 of no-load field voltage vro
If you select 0 times, the digit 1 value during no-load operation will be:
2000/10 times = 200, which results in automatic voltage control with coarse accuracy corresponding to 0.5% volt per digit.

Therefore, roughness becomes a problem in terms of AVH control accuracy.

Therefore, the purpose of the present invention is to reduce the %vol per digit, which is the minimum unit of digital calculation, during normal operation of the generator.
An object of the present invention is to provide a D/A output system for a digital control device for a generator excitation system, which can minimize the t value and perform automatic voltage adjustment with high control accuracy. [Means for solving the problem] D/
In the A output method, a D/A converter is installed at the final stage of the digital control device that controls the generator excitation system, and this D/A converter converts the digital output signal, which is the final output signal of the digital calculation section, into an analog signal. A digital control device for a generator excitation system configured to control the firing angle phase of a thyristor connected to a generator excitation coil using the analog signal; The input/output characteristic between the generator and the analog output is characterized by having a nonlinear characteristic such that the digit width becomes small during normal operation of the generator.

[For production]

D/ of digital control device for generator excitation system according to the present invention
According to the A output method, the digit width is small during normal operation of the generator compared to the input/output characteristics between the digit width of the D/A converter installed at the final stage of the digital control device and the analog output. Since it has non-linear characteristics such that the voltage can be adjusted automatically during normal operation with high accuracy.

〔Example〕

Next, an embodiment of a D/A output method of a digital control device for a generator excitation system according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is an input/output characteristic diagram of a D/A converter having nonlinear characteristics showing an embodiment of the present invention. In this example,
In the digital type AVH of the generator excitation system, the digital output signal, which is the final output signal of the digital calculation section in the AVR device, is converted to an analog signal via a D/A converter, and this analog signal is connected to the generator excitation coil. When controlling the firing angle and phase of the thyristor, the D/A conversion performs a nonlinear conversion as shown in Figure 1. In other words, as shown in Fig. 1, up to about 80% of the maximum digit value of the D/A converter, the D/A converter has a characteristic of slope g1.
A convert. As in the conventional example, the field top voltage V laa is selected to be the no-load field voltage V (6:10@), and the field current 5
If the analog output signal value of voltage equivalent to ro is lpu, the analog output signal value of voltage equivalent to field current 1fn during normal operation is approximately 2pu, so 1600 digits/
2 p u , which is approximately 0.1% volt per digit, allowing for much more precise control than in the past.

In addition, the maximum digit of the A/D converter corresponds to the analog signal value of the voltage equivalent to 1rn field current during normal operation to the analog signal value of the voltage equivalent to the maximum field current 1fmae corresponding to the peak voltage. Between about 80% and 100% of the value, D/A variation is performed using the characteristic of slope g2, resulting in rough control of 400 digits/8 pu, or 2% volt per digit.
However, since this only works infrequently, it has little practical effect. As described above, the D/A output method according to the present invention improves accuracy by setting the digital signal level equivalent to 1rn field current during normal operation of the generator to about 80% of the maximum digit value of the A/D converter. , %volt per digit of D/A conversion up to the top voltage, which only occurs in rare cases such as grid failures.
It makes it rough.

FIG. 2 is a block diagram showing an example for realizing the above-described D/A output method. In FIG. 2, reference numeral 10 is a required field signal calculation section in the digital type AVR, and the digital output of the required field signal calculation section 10 is sent to one side of the adder circuit 18 via a proportional gain element (Kg+) 12. The digital output of the required field signal calculation unit 10 is added to the input of the dead band element 14 to the other input of the addition time signal 18.
and is added via a proportional gain element (Kgz) 16. The digital output of this adder circuit 18 is converted into an analog signal by a D/A converter 20.

With this configuration, the digital signal of the required field signal calculation section 10 is converted into an analog signal with the D/A conversion characteristics shown in FIG. This analog signal may be used as the firing angle phase control signal of the thyristor.

〔Effect of the invention〕

As is clear from the embodiments described above, according to the D/A output method of the digital control device for generator excitation system of the present invention,
When converting a digital output signal, which is the final output signal of the digital calculation section in the device, into an analog signal, the D/A converter converts approximately 1.2 times the rated output of the generator into an analog signal.
By placing it within the % conversion digit, the digit width of the control signal during normal operation of the generator can be used effectively, and automatic voltage adjustment can be performed with high precision. Although preferred embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of the drawing]

Fig. 1 is an input/output characteristic diagram of a D/A converter with nonlinear characteristics to explain the D/A output method of the digital control device for a generator excitation system according to the present invention, and Fig. 2 is a diagram showing the input/output characteristics of a D/A converter with nonlinear characteristics. FIG. 2 is a block diagram showing an embodiment for realizing a D/A output method of such a digital control device for a generator excitation system. 10... Required field signal calculation unit 12... Proportional gain element 14... Dead band element 16... Proportional gain element 18... Addition circuit 20... D/A converter

Claims (1)

[Claims] (1) A D/A converter is installed at the final stage of the digital control device that controls the generator excitation system, and this D/A converter converts the digital output signal, which is the final output signal of the digital calculation section, into an analog signal. In a digital control device for a generator excitation system configured to control the firing angle phase of a thyristor connected to a generator excitation coil using the analog signal, the digit width of the D/A converter and the analog output are A D/A output system for a digital control device for a generator excitation system, characterized in that the input/output characteristics between them have nonlinear characteristics such that the digit width becomes small during normal operation of the generator.