Research And Implementation On Switching Transient Current Characteristics Based On FPGA

The load of large capacity, nonlinear, impulsive being connected to the grid or the instantaneous connection of new energy to the grid can pollute the power quality. The pollution can disturb appliances’normal work, which even may cause the normal working appliance interrupted suddenly, or powered-on or off suddenly, which will affect the performance of household electrical appliances, and accelerate the aging of household appliances. In addition, high-power appliances will also have impact on the power quality in the switching moment. The switching transient current signals have the characteristics of non-stationary, mutation and short duration, it needs high-speed and synchronicity on data acquisition and storage. To analysis the transient signal, it needs global analysis combined time domain characteristics with frequency domain characteristics. Now, few people studies on switching transient characteristics of household appliances at home and abroad.This dissertation put forward the research on the transient current characteristics of appliances switch based on FPGA technology. The main work and achievements are as follows:(1) The research status of data collection and relevant theories including synchronous acquisition and cache technology were introduced. Besides, the six national standards of power quality and low voltage electrical standards for our country were introduced especially(2) The key technology of steady-state current characteristics of the appliances were studied deeply, which contains signal synchronous acquisition technology and FFT. Realize synchronous sampling of steady state current by the digital frequency multiplier programmed with VHDL language on FPGA. The digital frequency multiplier was simulated, measured, and the results were analyzed in detail. The experiments show that:the digital frequency multiplier based on the FPGA can track the power signal as128times frequency, improving the accuracy for harmonic analysis. This paper adopts the MATLAB software to conduct FFT spectral analysis of the actual collected appliance steady-state current waveforms.(3) The key technology of the transient current characteristics of appliances were studied, mainly on the high-speed acquisition and cache technology. Realize high-speed data collection and save based on FPGA, DSP receives the saved data. The FPGA chip is ACEX1K EP1K30QC208-3of Altera company, the A/D chip is ADS830E of TI company, the DSP chip is TMS320F2812of TI company. Two kinds of cache, the synchronous and asynchronous cache were discussed.The asynchronous cache is implemented by FIFO, synchronous cache adopt Ping-Pang cache mode using the FIFO or dual-port RAM to store the data. The two methods are described in detail. The system can realize high speed data acquisition of50MHz, asynchronous FIFO cache of50MHz input1MHz output, and1MHz synchronous cache as well.(4) In addition, the basic research is carried out on the transient spectrum analysis technology, analysis the short-time Fourier spectrum of transient data of appliances with MATLAB tools. According to the nonlinear model of load and power quality standards, the influence was preliminary analyzed on power quality and the performance of the household appliances caused by switching transient, through the comparison of the working steady-state and switching transient current of household appliances.The thorough and careful research on data acquisition and spectrum analysis technology of steady-state and switching transient current of appliance was done based on FPGA and DSP. Although the study aimed at the appliance field, the key techniques can also be applied to the general high speed data acquisition and processing field, such as power systems, photovoltaic grid-connected system and so on.