A Discontinuous Modulation for Dual-parallel Three-level Inverters to Reduce Harmonic Distortion, Common-mode Voltage, and Circulating Current

Three-level t-type inverters (3LTI) are broadly used in high-performance applications. Conventional RCMV-DPWM mitigates common-mode voltage (CMV) and switching commutation in 3LTIs. Nevertheless, it distorts output current, has no neutral point voltage (NPV) control, and cannot provide side benefits except output power increase for parallel 3LTIs. This paper proposes a hybrid five-level discontinuous PWM (H5L-DPWM) for dual-parallel 3LTIs to reduce the CMV further while removing the drawbacks above. The proposed method constructs a five-level modulation considering the dual-parallel 3LTIs as a whole, significantly suppressing output current distortion. Besides, it distributes the switching signal of five-level modulation among 3LTIs using a specific state machine to make average circulating current (CC) zero, a critical operation factor in parallel 3LTIs. Meanwhile, if the dc-link capacitors' voltage goes unbalanced, the proposed method can accomplish NPV balancing control by employing balancer DPWM in a hybrid manner. Simulation results demonstrate the proposed method's effectiveness in reducing the CMV, CC, and current distortion in addition to adding NPV compensation ability.