| Solar energy,which is rich in reserves and cheap and clean,has become an indispensablepart of renewable energy.Photovoltaic grid-connected power generation is the mainstream way of using solar energy in the future.Grid-connected inverters serve as the link between the photovoltaic power generation unit and the power grid are crucial.This article takes three-level T-type inverter as the research object,and conducts in-depth research on leakage current suppression and high frequency resonance of LCL filter.Firstly,the structural characteristics and commutation process of the T-type three-level inverter are introduced.The working principle of the discontinuous space vector pulse width modulation(DSVPWM)strategy is analyzed.The relationship between the midpoint potential fluctuation and the space vector under the DSVPWM strategy is explained,and it is pointed out that this modulation has a problem that the leakage current cannot be sufficiently suppressed.Secondly,in order to analyze the generation process of leakage current,an equivalent model of the common mode circuit of the T-type three-level inverter is established.The effect of midpoint potential fluctuation and common mode voltage on leakage current is discussed,and an improved DSVPWM strategy is proposed.This strategy participates in the reference voltage synthesis by introducing the basic voltage vectors of adjacent small sectors,and a vector pair that can adjust the midpoint potential is formed.After improving the distribution factor method to achieve the balance of the midpoint potential,the purpose of fully suppressing the system leakage current is finally achieved.Establishing a dynamic mathematical model of the inverter system.To solve the problem of high-frequency resonance when the T-type three-level inverter is connected to the grid through LCL filtering,an active damped single closed-loop control method with current feedback on the inverter side is used.Aiming at the problems of complicated parameter design process of the active damping method and insufficient system stability,an efficient and fast parameter design method is proposed,which can make the system have better stability and dynamic and stable performance.Finally,the experimental circuit of T-type three-level grid-connected inverter was built.Through the analysis of the results of simulation and experiment,the feasibility of theimproved discontinuous space vector modulation strategy and the parameter design method of the grid-connected controller in the T-type three-level inverter are verified. |
