Research On The Controlling Of The Inverter With Stand-alone And Grid-connected Operation Modes

Recently, as the environmental pollution getting worse and the appearance of energy crisis, renewable resources and new energy development are becoming more and more important. And the distributed generation is needed for the large-scale application of the new energy. As a result, it is necessary to develop high performance grid-connected inverters.This paper focuses on the grid-connected inverter which operates in stand-alone mode and grid-connected mode. As the pivotal techniques of the grid-connected inverter, the topology, control strategy and the parameters design are analyzed in detail. The voltage-sharing strategy in the half-bridge is explained. A novel control strategy is chosen, which realizes the seamless transfer between grid-tied mode and off-grid mode.Basing on the analysis of math model, the load current feed-forward is added to improve the characteristic of the output voltage. The comparison between the two kinds of load current feed-forward is made in stand-alone mode and grid-connected mode respectively. From theory, simulation and the experiment, it concludes that adding of the load current feeding-forward to the current regulator will improve the characteristic of the output voltage while not affecting the grid current.The electricity quality supplied by grid-tied inverter is an important parameter to measure the performance of inverter. This paper discusses this parameter from three parts: grid current total harmonic distortion, the dc component of the grid current and the power factor.Finally, factors affecting the electricity quality are analyzed. The simulation analysis is done basing on the theory analysis. A 1kVA dual buck half-bridge inverter has been implemented to verify the analysis. As the parameters are optimized, the prototype achieves low THD of grid current and high power factor. The topology also ensures high reliability and high efficiency.