2Sakarya University, Dept. of Electrical and Electronics Eng., SAKARYA
Multi-level rectifiers have low harmonic content and electromagnetic interference (EMI). In recent years, especially in medium and high-power applications are increasing use. As the voltage level per switch and switching frequency are low, the multi-level rectifiers have low losses and high efficiency. In this study, three-level neutral point clamped (NPC) rectifier topology with pulse width modulation (PWM) is investigated and the decoupled equations in the d-q synchronous rotating axis of the rectifier are given and a space vector PWM (SVPWM) control algorithm based on the d-q synchronous rotating axis of three-level rectifier is proposed. The control of the whole system is provided by voltage oriented control (VOC) strategy, which enables the realization of control in cascade system with outer voltage and inner current control blocks. This paper is focused on explaining in detail modulus optimum and symmetrical optimum methods used in the design of the inner current and outer voltage PI controllers of the three-level rectifiers, respectively. PI voltage controller is used to keep the rectifier output voltage constant, and PI current controller is used to reduce the harmonic content of the grid current. In addition, a simplified method compared to conventional SVPWM is used to calculate switching times and switching sequences. In this study, three-level rectifier is simulated in Matlab / Simulink with the help of SVPWM. The performance of the circuit has been tested by changing both the load value and the load voltage suddenly and successful results have been achieved.