Research On The Method Of Parallel Inverters Based On Single-phase PV Generation System

With the excessive consumption of traditional energy and the deterioration of ecological environment, the new energy power generation technology has an irreplaceable strategic position in the electricity market. As a meteoric rise in the new energy family, photovoltaic technology has its unique advantage so that it is becoming one of the dominant modes of the new energy generation in the future, and owns a very optimistic prospect. However, because of the rapid economic growth and the mature photovoltaic technology, the increasing demand for electricity, single photovoltaic device has been difficult to meet the requirements. Photovoltaic technology is moving toward the parallel operating direction of high-power and high security. So it is of great significance to conduct research on the photovoltaic parallel inverter system.Firstly, this paper takes the technology of parallel inverters in photovoltaic generation system as the research object and starts from the single-phase photovoltaic inverter. For the designed circuit, an integrated controller for the decoupled and latter circuits is also designed and analyzed in detail. Based on the mode of single-phase photovoltaic inverter system, this paper establishes an equivalent circuit of the inverter parallel system by taking a parallel inverter system which contains two single-phase PV inverters as the research object. Through the equivalent circuit, the multi-inverter parallel system is analyzed in detail and a control strategy based on virtual complex impedance is proposed.Secondly, focusing on the power quality of multi-parallel inverters with a nonlinear load, a method is put forward to improve the voltage waveform of microgrid in islanding mode. Introducing the feedback loop of specific time microgrid harmonic voltage, the method can adjust equivalent output impedance of inverters in real time to reduce the harmonic content of the point of common coupling and improve the voltage support of microgrid which effectively improves the output power quality of inverters. This paper designs an overall control strategy for multi-parallel inverters including a multi-loop voltage controller. The effects on this control system are analyzed under different compensation parameters, and the proper parameters are selected. A simulation analysis is carried out to demonstrate the effectiveness of the control method by using Matlab/Simulink simulation platform.Finally, the design and implementation of the hardware and software for experimental platform of parallel system which contains two single-phase PV inverters with a nonlinear load is introduced. The prototype experiments show that the proposed method doesn’t affect the power sharing effect. Meanwhile, it could effectively improve the output voltage waveform and significantly enhance the power quality, improve the multi-inverter parallel system’s performance with nonlinear load. The experimental results verify the correctness and effectiveness of the proposed method.