Research On H6-Type Non-Isolated Single Phase Photovoltaic Grid-Connected Inverter

With the world's energy shortage and environmental pollution becoming more and more serious,the grid-connected power generation using clean energy represented by solar is getting more and more attention.As the interface of renewable energy power generation system and power grid,the grid-connected inverter determines the reliability and efficiency of the whole system.At pr esent,non-isolated inverter is frequently used in the single phase photovoltaic system in order to reduce the volume,and improve the efficiency.A problem for the non-isolated inverter is to restrain the common-mode leakage current after the isolation transformer is moved.Otherwise,it may cause serious EMI,and even endanger the safety of people.Under this background,this thesis studies the working principle and control strategy of H6 topology.Firstly,the working principle of H6 topology in active and reactive power control mode is analyzed.For the problem that the H6 topology will cause current distortion of the grid when exchanging reactive power with power grid,a control strategy of H6 topology is proposed,so that the inverter has the ability o f reactive power control,that is,if the H6-type inverter doesn't work under unit power factor conditions,it will not lead to current distortion of power gird.A dual stage PV grid-connected inverter structure with BOOST circuit as the first stage and H6 topology as the second stage is designed.The small signal model of H6 topology using state-space averaging method is established,and the main circuit,the inductor and capacitor of the filter and the control circuit are designed.The block diagram of the transfer function of the control system of the H6 topology is established,the current loop of PI controller is designed,and the bode diagram is drawn by MathCad software.The QPR control algorithm is used to design the control system,which solves the problem that the PI control algorithm can not track the AC reference without static error,realizes smaller steady-state error and improves the anti-disturbance performance of the system.In order to use DSP to realize digital control,the transfer functio n of the regulator is discretized,the time sequence and logic of control scheme are analyzed,and the PLL control algorithm is studied and designed.Finally,the simulation model is built in MATLAB,and the improved control strategy is simulated,and the fact that the improved control strategy can control the reactive power without current distortion of the grid is verified.A single phase grid-connected inverter system based on H6 topology is designed and constructed.The experimental results verify the rationality of the design of H6-type single phase grid-connected inverter.