Research On Control Technology Of Single - Phase Grid - Connected Inverter System

With the increasingly severe energy and environmental problems, the new renewable energy such as wind power, photovoltaic power generation is getting the world wide attention for the reasons of non-consumption of chemical energy, resource reserves, almost unlimited, non-polluting and other advantages. At present, the grid connected inverter in grid connected power generation system, which is the important role, has gradually become the focus of scholars at home and abroad. In this paper, the control strategy of single phase grid connected inverter system, phase locked loop algorithm and other key technologies are studied in order to improve its comprehensive performance.Firstly, the working principle of the grid connected inverter system are analyzed, and on the basis of studying the existing control scheme, a current hysteresis control algorithm is proposed based on digital fixed switching cycle. The working mechanism of them is described in detail. And this paper derives in the switching period and the current ripple with the distribution of power angle. A current hysteresis control strategy based on the fixed switching frequency is proposed to improve the control performance of the proposed current hysteresis control strategy.Secondly, the working principle of the traditional enhanced phase locked loop and its working characteristics under the condition of non-ideal grid is analyzed in detail. In view of the problem that the traditional phase locked loop can’t be accurately locked in the condition of non-ideal power network, an enhanced phase locked loop technique based on the delay sampling filter and Goertzel filter is proposed. It can achieve phase angle, frequency and amplitude of accurate online estimation in non-ideal grid fundamental, which improves the system of power grid disturbance and distortion robustness.Thirdly, the overall scheme of the single phase grid connected inverter system is obtained based on the proposed digital current hysteresis control strategy and the enhanced phase locked loop. The simulation model is built in the Matlab/Simulink simulation environment. The enhanced phase locked loop and the whole system are simulated and verified by the hybrid filter based on the proposed digital current hysteresis control strategy.Finally, the experimental platform, who gives the detailed design scheme and software program flow, of the full digital single phase grid connected inverter system with TMS320F28335 chip DSP as control core is presented. In this paper, the proposed digital current hysteresis control strategy, based on the hybrid filtering of the enhanced phase locked loop and the whole system is verified in detail. The experimental results are given. The correctness and feasibility of the proposed control strategy and the phase locked loop algorithm are verified.