The soft-switching-inverter is a very promising candidate as the next motor driving inverter, because the soft-switching inverter has a low switching-loss and a low EMI (the electromagnetic-interference) properties. On the other hand, the soft-switching inverter has difficulties to be solved at the present time. In this report, after describing the types of soft-switching circuits, research results of the delta-configured circuit are presented. The delta configured circuit applies no excess voltage stress on the switching devices and produces no continuous loss, because of no inserted circuit parts in the power line. Drawbacks of the low output voltage properties of this type have been overcome by a newly developed control algorithm. Improvement of the output property has been confirmed with the computer simulation and the experimental inverter apparatus. A torque fluctuation problem newly emerged and was solved with program compensation. In the report, the operating algorithm is also described.
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