Lcl Type Photovoltaic (pv) Grid Inverter Control Strategy Research

With the increasingly serious energy shortages and environmental problems in the world, photovoltaic technology has been paid more and more attention. Grid-connected inverter as a core component of photovoltaic power generation system has become a hot topic of current research. In this paper, three-phase LCL-type grid-connected inverter as the main object of study, in-depth analysis of the mathematical model of the LCL-type grid-connected inverter and resonant mechanism, discussed the optimal design method of LCL output filter, proposed three LCL inverter performance and network control strategy, the control performance of the three methods are compared and analyzed by simulation.First, the paper analysis L-type, LC-type and LCL-type grid inverter topology and mathematical models, then analysis of them characteristics by Bode plots. By comparison, this paper has superior high-frequency harmonic suppression capabilities and cost advantages of LCL-type grid-connected inverter for the study. And in-depth analysis of the LCL-type grid-connected inverter resonant generation mechanism and hazards, LCL type of grid-connected inverter control method.Secondly, for the characteristics of the LCL-type photovoltaic grid connected inverter, a control strategy based on the current double closed loop of repeated PR grid has proposed. The inner current loop to achieve effective suppression of the high-frequency resonance of the LCL output filter by capacitor current feedback; current outer loop use repeat the PR composite control strategy to achieve high-performance control of the grid current.Finally, the paper propose a direct power control method of LCL type of grid connected inverter based on instantaneous power theory, and designed a optimized switching table, to achieve good control of the instantaneous active and reactive power. And join in an active power damping control link in the control system in order to suppress the resonance of the LCL filter. On this basis, a quasi-direct power control method of inner loop using the current control and outer loop power control has proposed, the method has advantages of both the direct power control and current control.