A new PWM scheme to improve the input power quality of 18-Pulse rectifier Fed 3-level NPC inverter based induction motor drive

Distorted line current is always a common issue of induction motor drive (IMD) driven by an 18-pulse rectifier fed multilevel inverter (MLI). The basic 18-pulse diode bridge rectifier (DBR) used in IMD does not comply with the IEEE-519 standard. A 3-level neutral point clamped (NPC) MLI operating at low switching frequency is utilized on the motor side to provide compactness and good performance. Inverter switching uses pulse width modulation (PWM) technique which is largely affected by the total harmonic distortion (THD) produced by the DBR. A new PWM scheme is proposed which utilizes the injection of different odd harmonics into the multi-carrier based sixty-degree PWM (SDPWM) modulating signal to reduce harmonic contents of the line current. The proposed modulation technique reduces line current THD to 1.85%, which satisfies the requirement of IEEE-519 standard. The performance of the proposed PWM technique with 18-pulse 3-level NPC MLI fed IMD is analyzed by simulating it in MATLAB/Simulink environment under large load varying conditions. According to the simulation results, the system features a reduced line current THD and enhanced power quality performances