The Control Research Of Two-stage Photovoltaic Grid-connected System Based On Dual Buck Inverter

Solar power generation in the total power generation proportion is prominent increasingly.As a key equipment in photovoltaic system,inverter has important research significance.This paper takes the two-stage photovoltaic grid-connected system based on dual buck inverter as the research object and analyzes the control strategy.Firstly,the composition and basic control strategy of the two-stage grid-connected photovoltaic system are presented.The working principle of photovoltaic panel,DC/DC active clamp flyback circuit,single-phase dual buck inverter and grid-connected LCL filter are analyzed in detail.The mathematical model of photovoltaic cell and inverter circuit are established,and the basic control strategy including MPPT,double-loop control and PLL technology are given.Secondly,when using deadbeat control,disturbance factors such as model parameter perturbation,grid voltage harmonic and bus voltage secondary pulsation leads to the increase of odd harmonic content in grid-connected current.Traditional repetitive control has good harmonic suppression ability,but it still has the disadvantage of slow dynamic response and dc bias which affect the control performance.Hence the deadbeat fast repetitive control is proposed which structure and embed mode are improved.It has simple structure,fast dynamic response,and reduce the grid current total harmonic distortion rate effectively.Meanwhile,the control delay is offset by using two step prediction method.To ensure the operation safety of photovoltaic system,the mechanism of transient overvoltage at the inverter terminal caused by sudden change of photovoltaic output power is analysed.Mathematical model of inverter output is established which contains deadbeat controller.The phenomenon of overvoltage is caused by underdamped oscillation of capacitive voltage which is the result of the interaction of LCL filter and fast response of controller.And oscillation amplitude and frequency are affected by parameters of controller,power circuit impedance parameters,the state variable initial value and feedforward power coefficient.In order to avoid overvoltage phenomenon at the end of the inverter,the actual system can be predicted according to the established model and appropriate relevant parameter values can be selected.Finally,the proposed algorithm and model were simulated by Matlab/Simulink platform,and the simulation results are consistent with theoretical analysis.On this basis,the two-stage photovoltaic grid-connected system experiment platform based on TMS320F28035 controller is presented and the effectiveness of the proposed algorithm is further verified.