Research On Grid-Connected Control Strategy With High Performance Of Double Boost Single-Phase Inverter

Renewable energy sources,such as photovoltaic modules,and battery energy storage systems usually generate low DC terminal voltages,which are subsequently interfaced to AC load or the AC grid using DC-AC boost inverters.Moreover,the low voltage DC bus in the AC/DC hybrid system also are subsequently interfaced to the AC bus using DC-AC boost inverter.Therefore,so many authors have done a lot of research work in the boost inverter and its control strategy.The single-stage double Boost single-phase inverter,which has great advantages in improving the power quality of both the AC side and DC side of single-phase system,is adopted as the grid-connected interface in this thesis.This thesis mainly studies from the following aspects.The working principle of double Boost single-phase inverter is studied in this thesis firstly.The basic working principle of inverter is introduced in this thesis,including the basic working mode and the dual mode working principle(differential mode and common mode).The small signal model of grid-connected double Boost single-phase inverter is built based on the dual mode working principle,which provided a theoretical basis for parameter tuning of proposed strategy.Furthermore,the effect of modulation mode on switching subripple is analyzed and an interleaved Pulse-Width Modulation(PWM)is introduced to further reduce the switching frequency ripple in the DC current and grid current.The shortcomings of existing grid-connected current control strategy of double Boost single-phase inverter are analyzed.An improved single loop current control strategy is designed for the double Boost single-phase inverter to reduce the harmonic of grid current and to improve the dynamic response of the system.In addition,the effectiveness of the proposed control strategy is verified by simulation and experiment.The principles of power coupling and power decoupling of double Boost single-phase inverter are analyzed deeply,and the power decoupling control strategy is designed to obtain high quality input current.The harmonics introduced in the DC current of double Boost single-phase inverter due to the power coupling are analyzed based on mathematical derivation,which provides a theoretical basis for the design of power decoupling control.The suppression mechanism of power decoupling control on the second order harmonic of DC side is analyzed in detail.Then the influence of power decoupling control on the performance of double Boost single-phase inverter is analyzed,especially the effect of capacitance mismatch.Moreover,the concrete realization method of power decoupling control is proposed and the measures to improve the influence of power decoupling control are proposed,which can significantly suppress the harmonic introduced due to capacitance mismatch.Finally,the effectiveness of power decoupling control is verified by simulation and experiment.To solve the complicated resonance problem of grid-connected double Boost single-phase inverter,the resonance mechanism of double Boost single-phase inverter is studied careful in this thesis.By establishing the reflected equivalent circuit in the AC frame,it is found that the double Boost single-phase inverter contains two resonances with different frequencies,which are related to all the passive elements on the AC and DC sides.In order to suppress the resonant frequency component,an active damping control is proposed based on the resonance mechanism,which effectively restrains the resonance phenomenon.Finally,the effectiveness of the theory and control is verified by simulation and experiment.