I. Software implementation and algorithm research of digital excitation controller
It mainly discusses the software and control algorithm of digital excitation controller. Firstly, the main program of the digital excitation controller is designed, then the power parameter collection algorithm and the intelligent excitation control algorithm are researched and implemented on the CPU. In order to achieve accurate digital excitation control, real-time and accurate power data needs to be obtained, and to obtain real-time and accurate power data, it is necessary to use the AC sampling method, and derive the calculation formula of each power under AC sampling, and finally calculate and calculate Algorithm of power data. AC sampling is to measure the instantaneous value of the measured signal according to a certain rule, and then to determine the measurement method of the measured electric quantity parameter according to a certain mathematical algorithm. Discrete formulas in various algorithms of AC voltage, AC current, active power, reactive power, and power factor are given below.
Overall design scheme of digital excitation controller
Working power: Due to the working power requirements of the microprocessor, we need a stable 5V DC power supply. The operation of the signal conditioning circuit requires a set of ± 12V DC power. In addition, the switching output needs to drive a relay, so a + 24V DC power supply, so we need to design a power conversion module to get the three sets of DC power required for the system to work normally.
Design of main circuit of excitation output
The power output of the excitation controller is a DC output that can control current and voltage. The overall design determined that the rated voltage of this excitation rectifier output was 80V DC, the rated excitation current was 10A, and it reached 25A during strong excitation. Excitation power comes from AC power, which can be provided by the generator itself or externally. The externally provided power is usually relatively good and stable. The power provided by the generator is affected by the start-up, and it is possible during the operation. Unstable factors such as wave distortion will occur, which will affect the performance of the excitation output. So we research and design for the situation of getting electricity from the generator.
Fourth, the AC sampling phase-locked loop circuit
To perform AC sampling, synchronous sampling is usually required. Currently, AC sampling methods mainly include hardware synchronous sampling, software synchronous sampling, and asynchronous sampling. Hardware synchronization The hardware synchronization circuit raises an interrupt to the CPU to achieve synchronization. There are many forms of hardware synchronization circuits, such as phase-locked loop synchronization circuits. The hardware synchronous sampling method is a special hardware circuit that generates sampling pulses that are synchronized with the signal under test. It can overcome the shortcomings of the software synchronous sampling method such as truncation error and high measurement accuracy. The principle of phase-locked frequency tracking is used to realize synchronous equal interval sampling. The principle diagram is shown in Figure 2.3: adding n frequency divider to the phase-locked loop formed by the phase comparator PD, low-pass filter LP, and voltage-controlled oscillator VCO The input is the frequency of the measured signal, which is used as the reference frequency of the phase-locked loop, and the output is the sampling frequency. After n frequency division and comparison, according to the working principle of the phase locked loop, when locking / n =, that is: = n. Due to the time-tracking nature of the phase-locked loop, when the frequency of the measured signal changes, the circuit can automatically track and lock quickly, always satisfying the relationship of = n, that is, the sampling frequency is an integer n times the frequency of the measured signal, so that within one week, etc. Sample n points at intervals. In addition, the frequency division coefficient n can also be controlled by a program, and the value of n can be dynamically changed according to the measured signals of different frequencies and the speed of the CPU and A / D converter to achieve the best results.