Research On Output-Filter Of Gird-Connecred Photovoltaic Power Generation

Humans have increased emphasis on environmental pollution and the shortage of petrochemical resources. Based on the advantages of clean and large reserves solar photovoltaic power generation has caused widespread concern. This paper studied on grid output filter to solve the problem of grid harmonic pollution caused by photovoltaic power generation. Then the LCL filter and the LLCL filter is applied to the output filter, through comparative analysis to reduce the harmonic content of the grid current and the grid contamination.This paper used a LLCL active power filter together with a DC voltage feedback and load fundamental current feedforward to got a complex control algorithms to solve non-linear loads pollution and to achieve the purpose of reactive current, harmonic current compensation. Then the paper designed a model for this control algorithm, simulation results showed that ultimately to achieve the maximum power point tracking and gird control.Firstly, in order to prepare for make the theoretical basis for control system, the paper establish mathematical model of L, LC, LCL inverter. Analyzed the limiting conditions of filter parameters, Mainly from the performance analysis, the inductor ripple inhibitory ability of inverter side, high frequency harmonics inhibitory ability of filter capacitor and grid inductor, the ratio relations of inverter inductor and grid inductor affect the performance of filtering, grid inductance effect on the filter. The standard of design parameters are presented, and finally determine the parameters.Secondly, this paper studied the effect of LCL filter’s performance indicator on filter and designed a control method for photovoltaic grid-connected inverter with LCL filter. This control method used a outer voltage loop and a inner current loop to got a dual-closed-loop control algorithm, compared to single inductor with the same inductance filter grid current harmonic content is greatly reduced. This paper then gave a full describe of the phase-locked loop. This chapter also gave a new topology filter that is LLCL filter and applied in the photovoltaic grid-connected inverter, to get that the inductance and the switching frequency harmonics are much smaller. Simulation results showed the correctness of the theory.Finally, in the case of insufficient light or temperature inappropriate the photovoltaic power generation system can’t output active power current to grid, in order to improve the utilization of PV systems require the function of compensation current to compensate for non-linear load harmonic current. First this paper studied the pq method and the ip-iq method of detecting the reactive current, harmonic current. This paper used a complex control algorithm based on the theoretical of DC voltage feedback and load fundamental current feedforward to got ip-iq method simulation results. Simulation results showed that compared with the traditional single-L active power filter photovoltaic grid-connected system, the LLCL Active Power Filter photovoltaic grid-connected system got better results.And when the grid voltage distortion, the LLCL Active Power Filter compensation current effect is good.