Control Of Grid-Connected Inverter For Three-Phase Photovoltaic Power System

As a renewable energy sources, solar energy can ease the contradiction between energy and the environment. Photovoltaic grid-connected power system can not only solve self-power, but also reduce power loss of the power gird transmission. And it plays a load shifting role with great social and economic benefits. In this paper, a single-stage three-phase photovoltaic grid-connected system is mentioned. The principle characteristics of photovoltaic cells, maximum power point tracking(MPPT) control, the inverter control strategy, the phase-locked loop(PLL), harmonic detection, basic islanding protection and other key technologies are theoretically analyzed, and off-line simulation and experimental studies are implemented.The mathematical model of the PV grid-connected system in the natural coordinates is established. And the control model based on voltage oriented vector control, PLL and dual-closed-loop proportional-integral controller are designed.To overcome the defects of poor performance caused by operating parameters and external conditions change, load disturbance in PV grid-connected systems of PI controllers with fixed parameters, a particle swarm optimization (PSO) method with dual constraints to track changes of the PV grid-connected system in a real-time way is proposed. Parameters for a new excellent outer loop PI controller can be found when the system changes.The key hardware circuits of lOkW single-stage three-phase PV grid-connected device is designed. Then, the software codes for the various control modules are tested by using DSP+Q8+xPC as the controller, and implant all control modules into DSP, including PI control and the dual-constraint PSO optimization method for outer-loop PI parameter control, maximum power point tracking, phase-locked loop, coordinate transformation, harmonic detection, software protection. Experiment results show that the control algorithm takes the DC side stability control and AC side current high quality into account, ensuring that the photovoltaic grid-connected system can be in stable operation.