Power Control Of Paralleled Inverters With Different Power Ratings Based On The Current Droop Control

Micro-grid broken off the power grid into islanded mode when the power grid fault or the micro-grid needs to be run independently, it continues to supply load so as to ensure that the important load in micro-grid is not influenced. When the micro-grid operate in islanded mode, the control strategy that the distributed power sharing the load reasonably according to its own capacity and realize the distributed power "plug and play" in the micro-grid are the intention and purpose of this research.For the multi-paralleled inverters in low voltage micro-grid, The current droop control is proposed in this paper, Each inverter adjust independently to support the voltage amplitude and frequency of the micro-grid, In order to make the system impedance resistance, the voltage and current double closed-loop controller is designed and also the virtual resistor. The reasons why multi-paralleled inverters with different capacity can not share the load accurately is analyses in this paper, and the robust control strategy is proposed, eliminate the impact of system impedance on the active current output, and in result the multi-paralleled inverter with different capacity can share the load proportional precisely according to it’s capacity. In order to make sure the micro-grid stable and realize “plug and play”, the parallel pre-synchronous control strategy is proposed, avoiding the large current attack to the system when the inverter access to the micro-grid. In this paper the diode clamped three level inverter is adopt in order for using in the occasions of high voltage and large capacity, and it’s working principle is analysed. The software algorithm control strategy based on the SVPWM for the existence of the neutral point potential unbalance problem is proposed in this paper.Finally, the proposed control strategy is verified through the simulation. The experimental platform of diode clamped three level inverter parallel system is built, and the digital control of the proposed control strategy is realized based on DSP and FPGA. The experiment results show that multi-paralleled inverters with different capacity can share the load proportional precisely according to it’s capacity, the feasibility and effectiveness of the proposed control strategy are verified.