Research Of Global MPPT And Inverter Control Strategy For Grid-connected PV System

Photovoltaic cell is a kind of typical nonlinear power supply and its output is direct current. In order to use the output of photovoltaic cells efficiently, the appropriate control strategy need to be adopt for power transformation. MPPT and the inverter control strategy are keys to their high efficiency and high quality in photovoltaic grid-connected power generation. For this reason, the global MPPT and inverter control strategy of photovoltaic grid-connected system have been studied.The mathematical model of dual-diode model is introduced and the output characteristics under different circumstances are simulated and analyzed in this paper. According to the structure of photovoltaic array, the power output will present multiple peak properties when it appears mismatch. A method of the global MPPT based on Ant Colony algorithm with small-step perturbation and observation method is proposed. The results show that, the global maximum power point of photovoltaic array with multiple peak properties can be tracked rapidly and accurately and the output power of photovoltaic array is improved in complex environments.According to the characteristics of three-phase bridge inverter, proportional resonant algorithm is selected as the current-loop control and it is disposed in discrete and anti-windup strategies. PI controller is used to stabilize DC bus voltage in the outer voltage loop. The simulation results show that the control strategy can get stable grid current and DC bus voltage. The output current have low harmonic rate and high tracking precision.The experimental prototype based on TMS320F28335 for photovoltaic grid-connected has been built, and the design of software and hardware modules were described in detail. A number of experiments were conducted on the prototype. The experimental results show that the proposed MPPT algorithm can accurately track the global maximum power point of photovoltaic array, and the inverter control strategy can also make the system output stable and standard sine current.