A Preprocessed PWM Scheme for Three-Limb Core Coupled Inductor Inverters

A discontinuous pulse-width modulation (PWM) scheme is presented for a six-switch three-limb coupled inductor inverter. Three-level PWM phase output voltages are produced with a reduced switch count and reduced dv/dt stresses on loads and output filters. The PWM scheme described lowers the coupled inductor and semiconductor losses by lowering the inductor winding high-frequency current ripple using two techniques: 1) winding excitation flipping within each carrier cycle; and 2) the inductor magnetic flux is kept within the three-limb core, neglecting natural leakage, by avoiding switching states that produce common-mode voltage excitation of the three-limb inductor. To make best use of the nonstandard switching patterns produced, reference signals are preprocessed before being delivered to the PWM modules using only one carrier signal: representing an approach well suited for implementation in a low-cost digital signal processor. The digital output signals of each PWM module represent the desired switching states of each switch in the inverter. This approach contrasts with previous published work, where postprocessing of the PWM module output signals is necessary using digital logic circuitry, such as a field-programmable gate array. Experimental results, with inductor loss and inverter efficiency comparisons for different operating conditions, confirm that the three-phase six-switch inverter PWM patterns lower the high-frequency current ripple in the inductor windings and, hence, significantly lower the inverter losses and increase the power conversion efficiency.