PWM Inverters Using Split-Wound Coupled Inductors

The number of voltage levels available in PWM voltage source inverters can be increased by using an inverter leg with a split-wound coupled inductor and interleaved PWM switching of the upper and lower switches. The magnetizing inductance of the split-wound inductor filters the PWM-cycle instantaneous voltage differences between the upper and lower switches. The windings of the same inductor present a high quality 3-level PWM voltage at the inverter output terminals, with the winding leakage inductance effectively in series with this voltage. Since dc-rail short circuits are not a serious issue, dead-time PWM signal delays can be minimized. The overall quality of the output PWM waveforms are improved with higher fundamental frequencies and fundamental voltages possible, and using higher PWM frequencies and lower common mode voltage stresses. The application of this technique in 3-phase inverters is emphasized. Simulation and experimental results are used to illustrate the operation of the proposed inverter structure.