Micro-grid And Grid-connected Inverter Software Control And Realization

Currently the great mass of the electricity systems in the world have become large-scale network systems with centralized generation and long-distance transmission. But in recent years, the increasing capacities of the power loads and the improving dependency rate of the external power supply result in the lower and lower operation stability and security in the power grids. To solve the problems, Microgrid, which is integrated distributed generation technology and storage technology, has been proposed since 1990s.The inverter technology for power grid is a key technology to achieve the electric power contact between Microgrid and main power grid. The main function of an inverter is to invert the electric power of the DC bus composed of intermittent energy generations into AC power, and obtain the equi-amplitude, equi-frequency and equi-phase to achieve ideal grid-connection by introducing certain control strategies.This paper introduces various micro power supplies and carries out detailed analysis and comparison of different topology structures and related control strategies of the existing grid inverters by referring to the corresponding national standards. The results lead to the selected full-bridge type grid inverter with SPWM control strategy in the practical project. The main research contents of this paper include:1) The single-polarity and dual-polarity SPWM modulation modes and the corresponding control principles of the single-phase and three-phase grid inverters are described to determine the modulation methods of the single-phase and three-phase grid inverters;2) A practical control system for the single-phase grid inverter was developed based on the TMS320F2812DSP chip and CCS2000 software platform;3) A practical open-loop control system for the three-phase grid inverter was also developed in the work. The experimental results show that the developed system can achieve good control for the three-phase inverter, e.g., the actual AC frequency offset <0.5Hz and the phase offset <1o comparing to the ideal inverter.4) To improve the performance of the open-loop control system, a closed-loop control scheme was further proposed in the work, with overall design and Matlab/Simulink-based simulation system completed. The results show that the performance of the closed-loop control system is better than that of the open-loop control system. Based on the above analysis, the studies on the practical systems including data acquisition, data processing and serial interface communication module were also carried out, which provide good bases for the development of the closed-loop control system of the practical three-phase grid inverter.