Carrier Level-Shifted Based Control Method for the PWM 3L-T-Type qZS Inverter With Capacitor Imbalance Compensation

Abstract

This paper presents a modified carrier level-shifted based control method for a pulsewidth modulation controlled three-phase three-level T-type quasi-impedance-source inverter. The benefits of the proposed strategy are a uniform distribution of shoot-through states of constant width throughout the fundamental period and the mitigation of the inner capacitors' voltages imbalance. The latter is achieved by means of a proportional-integral controller, which adjusts the relative time application of redundant states. The improved performance is demonstrated in terms of reliability, as the capacitors do not suffer from neutral-point imbalance. The control method can also be implemented in a different multilevel inverter configuration with an impedance-source network. A comprehensive simulation study and several experiments were performed in order to validate the adopted method in situations of imbalanced capacitor voltages.