The Research Of Three-Phase Photovoltaic Grid-Connected Inverter With LCL Filter

With the gradual depletion of traditional energy sources, as well as the deteriorating environment, the governments are committed to adjust the energy structure. The solar energy has received increasing attention in recent years, because it not only has huge potential of exploitation and utilization, but also has the advantages of being clean and renewable. The PV grid-connected inverter is a hot academic issue at home and abroad because it is one of the necessary equipment of the grid-connected photovoltaic system. This paper analyzes the maximum power point tracking (MPPT), damping resonance control strategy and DC component suppression strategy of the PV grid-connected inverter based on the three-phase PV grid-connected inverter with LCL filter. The study includes the following aspects:Firstly, the paper proposes a modified incremental conductance algorithm. The proposed algorithm not only can solve the oscillation problem of the incremental conductance algorithm, but also effectively improve the dynamic response speeds at sudden changing irradiance.Next, solve the problem of reactive power capacitor resonance that distorts the output voltage of PCC. Based on the dual-loop control strategy of the grid-connected inverter, the paper proposes a new damping resonance control strategy. This strategy can seamlessly embed the damping resonance control strategy into dual-current closed-loop control by detecting instantaneous voltage at the point of common connection directly, and applying multiple proportional resonance controllers in outer current loop, it can obtain zero steady-state error when tracking command current. Then, the design of damped resonance is also analyzed. Finally, simulation and experiment results prove the correctness of the proposed method.What is more, the paper analyses the causes and harm of the DC injection problem and proposes a new DC component suppression strategy of the non-isolated grid-connected inverter. On the basis of conventional fundamental current loop, a closed-loop control of the DC component is added to the current outer loop, which can suppress DC component into the grid. Through modeling analysis, the DC inhibition performance is confirmed. Finally, the simulation and experiment results further prove the effectiveness of the proposed strategyFinally, a 30KW three-phase PV grid-connected inverter with LCL filter is developed. In this paper, the main circuit parameters design and components selection are discussed in detail. Then, the control system hardware design is carried on thoroughly and particularly. The controller have designed base on DSP2812 and the peripheral circuit is also built on this. Last but not least, the paper describes the design idea of software program, and gives the main program, interrupt program, protection program flow chart, etc.