Research On Power Sharing Control For Parallel Inverters In Microgrid

With the increasing depletion of fossil energy and the increasing crisis of climate change,the contradiction between distributed generation and large power grid is increasingly prominent when the installed capacity of distributed generation device with clean energy and renewable energy is increasing.With the advantages of integrating the distributed generations,improving the efficiency of resource utilization,reducing the contradiction between distributed power supply and large grid,reducing the power loss on the transmission lines and improving the power supply quality at the end of the power grid,microgrid is being favored by the researchers.Inverter as the interface between distributed generation and Microgrid,multiple distributed power sources are connected to AC bus,which forms the objective environment of multiple inverters in paralleling.Droop control has been widely used because of the advantages of simple controller,no communication,high redundancy,plug and play,and the ability to control the inverters sharing the load power according to its own capacity.Meanwhile,the diversity of loads in microgrid also challenges the traditional droop control technology of parallel inverters.In this paper,two single-phase parallel inverters with resistive droop control are researched.According to the equivalent model of single-phase inverter,the equivalent output impedance is designed to be resistive at the fundamental frequency by designing the voltage and current double loop controller and output current feedforward controller.The power decoupling is realized,the gain is greatly attenuated in the low frequency range,and the output voltage fall is decreased.Under the nonlinear load condition,the line impedance mismatch is the main reason for the uneven distribution of fundamental active power and harmonic current according to the fundamental frequency and harmonic frequency equivalent model of the parallel system.An improved droop control method based on variable droop coefficient and variable no-load voltage amplitude is implied at fundamental frequency and an adaptive virtual harmonic impedance method is used in harmonic domain.The active power is equally shared and the harmonic current circulation is restrained finally.In order to verify the effectiveness of the proposed method,a simulation model of parallel single-phase full bridge inverters by PSIM software has been built.The experimental platform of two parallel inverters with the core of STM32F407ZG CPU has also been built up.Simulation and experimental results verify the effectiveness of the proposed control strategy.