Research on Control Method of Double-Mode Inverter with Grid-Connection and Stand-Alone

Inverter system, as the interface device between the renewable energy system and grid, plays an important role in the distributed generation system. A double-mode single-phase inverter system, which can be operated in grid-connected mode or stand-alone mode with seamless transitions control, is proposed in this paper. The different control strategies applied on the system for the different modes are designed. In the grid-connected mode, the grid governs the load voltage, the inverter operates as a current source, and the grid current is directly controlled by a three-level hysteresis controller for faster dynamic responsibility and lower current ripple. In the stand-alone mode, the inverter is voltage-controlled, fuzzy controller with parameter self-adapting on-line is introduced to improve the system adaptability to the varieties of load and system parameters, so good quality of output sine-voltage can be obtained under various load conditions. In order to make the distributed generation utility-interactive, an algorithm, which controls the inverter to transfer seamlessly between grid-connected mode and stand-alone mode, is present. The DSP (TMS320LF2407A) based inverter prototype is developed to verify the analysis