Compound Control Strategy For Photovoltaic Grid-Connected Inverter With LCL Filter

With the rapid development of human society, the energy problem has become an important problem restricting the development of a country. More and more countries pay attention to photovoltaic(PV) generation, wind power generation and other new clean energys. In recent years, photovoltaic develops rapidly and holds the pivotal status in the national economy. As an important part of grid-connected PV system, photovoltaic grid-connected inverter directly determines the stability of grid-connected PV system and the effect of interconnection. Especially in the case of grid voltage containing harmonic, power harmonic will affect the output current waveform quality of photovoltaic grid-connected inverter. The harmonic from photovoltaic grid-connected inverter will make further pollution, which will ultimately affect the stability of the inverter. Therefore, it has the vital significance to study the photovoltaic inverter control technology, which will guarantee the inverter system running effectively and stably.This paper first analyzes the principle of the photovoltaic cells, and through the simulation show the influence on the output voltage under different conditions. Then compares several kinds of filter characteristics, analyses the LCL filter and gives the calculation method of LCL filter parameters. Inverter-side current control and grid-side current control system working principle were both introduced in this paper, then photovoltaic grid-connected inverter with LCL filter system is modeling. Analysis the stability of two kinds of control system by Routh Criterion, the results shows that the inverter-side curent feedback control system has high stability.In view of the LCL filter will bring in the resonance problem, this paper has compared the principle of active damping control and passive damping control and their advantages and disadvantages. Finally this paper choose the active damping control to suppress the resonance of LCL filter. Thus, put forward a kind of the inverter-side current feedback and capacitive current feedback of dual-current closed-loop control strategy, this strategy not only ensuring the stability of the system, but also can suppress the resonance of LCL filter, and effectively damp the resonance of LCL filter. The simulation results show that dual-current closed-loop control system is stable, and can output good grid-connected current.Besides, in view of grid has low-order harmonics, Using a grid voltage feed-forward control to eliminate these harmonics, and finally form the compound control strategy of dual-loop control and grid voltage feed-forward control in this paper. Then set up the simulation model base on compound control strategy, and verify the effectiveness of the proposed control strategy by simulation under the condition of ideal grid conditions and background harmonic. Finally verify the compound control strategy’s dynamic response ability and robustness by sinulation under the grid voltage saltation.