Research on Double Closed-Loop Control System of NPC Cascaded H-Bridge Photovoltaic Inverter

Aiming at the problems of unstable output voltage and large current harmonic distortion rate of photovoltaic grid-connected, based on three-level H-bridge cascaded inverter, this paper focuses on the topology and control strategy of two-cell cascaded structure. In the system, each photovoltaic module is independently controlled by maximum power point tracking (MPPT), which can improve the power generation efficiency of the photovoltaic system. According to the topological structure and working principle of the three-level cascaded H-bridge inverter (CHI), based on the carrier phase shift control method (PS-PWM), a double closed-loop control method is proposed of voltage outer loop PI control and current inner loop proportional-resonant (PR) control, and its mathematical model and circuit model of photovoltaic inverter is established. The system simulation is carried out in MATLAB/ Simulink. The simulation results show that the system control method can accelerate the current dynamic adjustment speed, reduce the current harmonic distortion rate, and thus verify the feasibility and practicability of the strategy proposed in this paper.