Multi-Level Power Converters using Coupled Inductors and Parallel Connected 2-Level Inverters

Multi-level voltages can be produced for medium and low voltage motor drive applications using parallel-connected standard 2-level coupled inductors inverters with smaller voltage steps to reduce the machine winding stresses. Motor drives can be made small and compact with a significant reduction in the size of drive-related magnetics by generating pwm frequencies number of times higher than the inverter switching frequency, keeping the switching losses low. Coupled inductor modeling techniques have been described that account for the very low output impedance and high impedance between the parallel inverter legs. PWM control techniques and coupled inductor topologies are described that produce high-quality pwm voltages with high pwm frequency to reduce size of output filters. The resultant converter topology is described for a 3-phase system that is modular in design and has a very low output impedance. The latter feature produces very low fundamental voltage drops and is especially suited for generating high fundamental frequencies and lowering losses in high-speed machines. Simulated results have been experimentally validated.