Optimized Pulse Patterns for Five-Level Medium-Voltage Drives with DC-Link Voltage Ripple Minimization

This paper presents a control strategy for medium-voltage (MV) drives based on a five-level neutral-point-clamped (NPC) H-bridge inverter and a 36-pulse diode rectifier. The proposed method leverages optimized pulse patterns (OPPs) to achieve superior steady-state performance compared to conventional approaches. Specifically, tailored OPPs are employed that effectively suppress the significant dc-link voltage ripple, including the dominant second harmonic, which is inherent to the five-level NPC H-bridge topology. This is accomplished by performing harmonic analysis of the dc-link voltage and formulating an OPP optimization problem that minimizes its harmonic content, while bounding the stator current harmonic distortion to ensure load-friendly operation. To enable high-bandwidth control, a model predictive control (MPC) strategy adjusts the OPP switching time instants in real time. As a result, fast transient responses and excellent disturbance rejection are achieved. The effectiveness of the proposed approach is demonstrated through system-level simulations, with performance comparisons highlighting its advantages over conventional methods.