Research On The Control Strategy Of The Single-phase Photovoltaic Grid-connected Inverter With LCL Filter

With the growing energy crisis and environmental issues, solar with its unique advantages gets more and more people’s favor. As the core technology of new energy power generation, grid inverter technology has been widespread concern. In order to truly solve the energy crisis, active research and development for photovoltaic grid inverters have to be made urgently. The DC power from the photovoltaic array can be inverted into high-quality power which can be fed into the national grid to millions of households. The main work of this paper is as follows:It studied the topology of PV grid-connected inverter, analyzed the control objectives of single-phase photovoltaic grid-connected inverter and compared the advantages and disadvantages of various single-phase and several common control technology of photovoltaic grid-connected inverter. Detailed study has been made on working principle and SPWM modulation technology of non-isolated single-phase photovoltaic grid-connected inverter. The boost circuit parameters have also been designed. The filtering performance of L, LC, LCL type filter in single-phase photovoltaic grid inverters have been compared and analyzed. The LCL filter is selected as a single phase photovoltaic grid inverters filter. Based on the constraints of LCL filter, the parameters of LCL filter have been designed.In the DC-AC section, to solve the problem of LCL-type single-phase grid-connected inverter prone to resonance, the control strategy of using grid current as the outer loop control volume and capacitor current as the inner loop control volume is adopted. In addition, tracking and adjusting output voltage of dual current loop control is also adopted. It designed the current double loop control parameters, and analyzed the characteristics of single-pase photovoltaic grid-connected system by using Sisotool to adjust the control parameters of internal hand external control loop. Genlock control strategies of single-phase coordinate transformation and grid inverter by using coordinate transformation have been analyzed. Control parameters of PLL based on synchronous rotating coordinate transformation have also been designed.Finally, according to the simulation model of LCL-type single-phase grid-connected inverter based on current double-loop control strategy on Matlab/Simulink software platform, it shows that LCL-type single-phase grid-connected inverter can effectively inhibit system oscillations, reduce the harmonic content of grid current and improve the system stability by adopting the dual current loop control strategy. It can also guarantee the sine wave of output current from grid-connected inverters and the same amplitude, frequency and phase of output voltage and grid voltage. It makes the single-phase grid-connected inverters work at a high power factor and achieve grid. The results verify the feasibility and rationality of the control strategy with dual current loop control.