Research On Control And Modulation Of Three-phase And Three-level Inverter

With the reduction of conventional energy sources and the crisis of power supply,the industry of photovoltaic has been greatly promoted by development of power electronics technology.Power electronic devices have become increasingly high-efficient thanks to the update of control strategy and modulation methods.The traditional two-level topology is now difficult to meet the application requirements in high-power and other occasions.The researches of multi-level inverter,especially three-level inverter,gradually become important issues.Three-level inverter has significant advantages for its simple structure,convenient operation and reliability.And it will be adopted widely.This paper focuses on the research of three-phase three-level inverter system.The working principle of the three-level inverter is introduced and the model of system is built to analyze the controller of system.Due to the low-efficiency of single-inductance filter at high frequencies,LCL filter is introduced to improve system filtering capability and the quality of the grid current.Volume and costs of system is reduced as well.The double current loop control strategy is used to suppress resonance of LCL filter.The three-level space vector modulation method(SVPWM)is specifically analyzed and neutral-point potential unbalance in the neutral point clamped three-level system is discussed.A control method is proposed to suppress neutral-point voltage fluctuation.By comparing sinusoidal pulse width modulation(SPWM)with space vector modulation(SVPWM),the equivalent relationship between the two scheme is studied and an equivalent three-level SPWM modulation method is proposed,which can suppress the neutral-point potential unbalance.A detailed design produce of the circuit is investigated.The parameters of Boost inductors,DC-side capacitors,and high-frequency switch tubes are calculated.The other circuit module such as drivers and snubbers are analyzed.The inductance and capacity of the LCL filter are calculated.Then system control process and the controller are discussed.The effectiveness of the three-phase three-level inverter system is analyzed in the paper.The SPWM modulation method and LCL filter are verified.A simulation model and a three-phase three-level experimental platform are built.The results of simulationand experimental has verified the effectiveness and practicality of the proposed modulation and control strategy.