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A new six-phase 2.4-MVA soft-switched medium-voltage drive system utilizing series-stacked modules with low-voltage devices has been developed. The drive system combines a new soft-switched DC-DC converter with resonant DC-link inverter technology to deliver extremely low total harmoic distortion sinusoidal output, high power density, and high efficiency. The series-stacked configuration with the associated single-phase loading lead to unique power and control design challenges. Device selection, control of parasitic elements, sensing methods for converter control, custom magnetic component design, and clamping techniques have lead to a substantial improvement in device voltage utilization. The DC-DC converter controls must regulate the intermediate DC-bus voltage under single-phase loading while balancing transformer excitation and maintaining zero-voltage switching, among other tasks. Proper control of the resonant DC-link inverter requires the selection and tuning of the appropriate modulator and understanding its effect on the power circuit ratings.
Bendre et al. (Sun,) studied this question.