Three single-phase control of NPC three-level photovoltaic grid-connected inverter based on Quasi-PR control

In this paper, a novel control strategy, based on three single-phase quasi-proportion resonant (Quasi-PR) control, is proposed for neutral point clamped (NPC) three-level grid-connected inverter in photovoltaic system. Compared with voltage oriented vector control (VOC), the proposed strategy avoids coordinate transformation and decoupling control. Meanwhile, it inherits the advantages of the proportion resonant (PR) controller. Furthermore, the Quasi-PR controller enhances the ability to resist the grid frequency offset due to its wider bandwidth. The bode plots of the Quasi-PR controller are designed to analyze the different parameter influence on the control performance. And the respective harmonic compensation controller is introduced to reduce the low order harmonics. In addition, the neutral point balance is achieved through the feedback of the voltage difference between the upper and lower capacitors. Simulations are carried out in MATLAB/SIMULINK. And the results show that the strategy presented in this paper is superior.