A Variable-Angle PSC-PWM With Interphase Angles for Three-Phase CHB Converters With Unbalanced Cell Operation

Cascaded H-bridge (CHB) multilevel converters are gaining increasing interest in both medium-voltage drive and grid-connected photovoltaic (PV) and energy storage applications due to their advantageous features in terms of modularity and power quality. However, the large leakage currents induced in the ground paths by the common-mode voltage (CMV) produced by the pulse width modulation (PWM) converter leads to reduced system performance and can cause reliability issues. These problems are further amplified when the converter operates in unbalanced conditions, with unbalanced power processed by each cell. In this article, a variable-angle phase-shifted carrier PWM technique is proposed to reduce the harmonic content of the phase voltage while also mitigating the generated CMV. The proposed scheme optimizes the phase-shift carrier angle together with the interphase angles avoiding both the introduction of additional filters or additional switches and the adoption of computationally intensive modulation schemes. An optimization routine is used in this article to identify the set of phase-shift and interphase angles depending on the operating conditions of the converter. Experimental tests are conducted on a three-phase seven-level setup to assess the validity of the proposed approach.