Performance Evaluation and Experimental Validation of a Three-Level Neutral-Point-Clamped Inverter With 240CPWM

Neutral Point Clamped Three-Level Inverters (NPC 3LI) are widely used in dc to ac power conversion due to their superior waveform quality and reduced voltage stress compared to two-level inverters. The performance of NPC-3LI can be further improved by employing a low-loss 240◦-Clamped Pulse Width Modulation (240CPWM) technique. 240CPWM is currently the lowest switching loss PWM method in cascaded configurations comprising a dc-dc stage followed by a dc-ac stage, reducing the dc-ac stage switching losses by at least 80% compared to the conventional Space Vector PWM (SVPWM) at unity power factor. In this work, the performance enhancement of NPC-3LI using 240CPWM in terms of total harmonic distortion (THD) and switching loss is presented and compared with benchmark PWM methods. The THD analysisis carried out using the concept of virtual stator flux ripple, and power losses (switching and conduction) are derived by analyzing the switching device char acteristics and the phase relationship between the modulation voltage and output current. A three-closed-loop control method is also developed for the front-end boost converter to achieve an effective neutral-point voltage balance. The analytical results are validated using a 3 kW experimental prototype. A peak efficiency of 97.71% is achieved for NPC-3LI with 240CPWM at 3 kW, compared to 97.22% with SVPWM, while maintaining comparable THD performance.