A Discontinuous PWM Method for Balancing the Neutral Point Voltage in Three-Level Inverter-Fed Variable Frequency Drives

The paper describes a new discontinuous carrier-based pulsewidth modulation (PWM) method for use in variable frequency drives (VFD) driven by three-level inverters. The method introduces three different switching patterns for the full range of operating speeds. Depending on the actual operating speed, the proposed algorithm is developed to select the most suitable PWM switching pattern that improves the VFD performance. This results in low imbalance in the DC-link capacitor voltage, and low current distortions without increasing switching losses. Theory, simulation, and experimental results are presented.