Research On Robust Control Method Of Photovoltaic Grid-connected Inverter Based On Optimized LCL Filtering

Nowadays, energy shortage and environment pollution has increasingly become the focus of all countries. Vigorously developing renewable energy, which is one of the sustainable development roads, will be the future human to solve the energy crisis. Because the solar energy is infinite, clean and environmental-friendly, it becomes an important research focus of new energy fields. Among the exploiting of the solar energy, the research on robustness control for photovoltaic (PV) grid inverter system is a research hotspot. This paper mainly studies the robust control method of LCL filter in grid connected photovoltaic system. The main research contents are as follows:Firstly, the circuit topology of photovoltaic grid connected inverter is analyzed. The mathematical model of the flyback converter is established, and the principle of the active clamp flyback circuit and the maximum power point tracking algorithm based on the circuit are described in detail. The sinusoidal pulse width modulation technique is introduced, and the mathematical model of the double closed loop control of grid connected inverter is established.Secondly, the robust control method of LCL inverter is studied. Mathematical modeling and sensitivity of LCL filter are analyzed. In order to improve the control effect of the single-phase grid connected system with parameter change, a new approach to design the second order controller which is based on system dynamic response and phase margin is put forward. By this way, the parameter range of the second order controller can be acquired with the virtual requirement to improve the robust performance of the system.Based on Simulink simulation platform, the simulation model of single-phase photovoltaic grid connected inverter is built, PLL phase sequence detection test and grid connected test are finished respectively. Simulation results show that the maximum power point tracking strategy can achieve maximum power point tracking; phase locked loop (PLL) can detect the exact angle of the grid; the control performance of second order controller is clearly superior to the traditional PI controller, the adaptability and robustness of the system is improved.Finally, the software and hardware parts of the micro gird-connected photovoltaic inverter are designed. The active clamp flyback unit, full-bridge inverter, and related control circuit are designed with the implementation on DSP F28035. An experimental platform about micro gird-connected photovoltaic inverter is built to test the proposed method. The experimental results show that system has high efficiency, high power factor and low current harmonics, so that the system can achieve the grid connected requirements. And the correctness of the control strategy and circuit design is verified.