A Snubberless Solid-State Tap Changer for Permanent Magnet Synchronous Motors

A stator winding tap changer has been studied for a permanent magnet synchronous motor (PMSM) drive for speeds exceeding the base speed range. At low speeds, all stator windings are configured to fulfill the high output torque; at high speeds, a portion of the stator windings are configured to relieve the burden of the stator winding turns, i.e., large inductive impedance, back electromotive force (BEMF), and field-weakening current. The conventional solid-state tap changers for the PMSMs require snubber capacitors and bleeder resistors. The snubber capacitor is necessary for providing an inductor current path during the stator winding tap-change period. However, it induces long transition times and energy losses. In this article, a snubberless solid-state tap changer is proposed for PMSMs. The proposed mechanism is composed of only three-switches for each tap and controls the leakage inductance current by employing an appropriate switching sequence. With the proposed tap changer, the transition period is reduced and energy loss by bleeder resistance is eliminated. The results of a simulation and an experiment are used to validate the proposed scheme.