5-Level PWM Scheme for a Dual Inverter Drive Using an Open Winding Machine

This paper presents a carrier based PWM scheme for a dual inverter drive using an open ended winding induction machine, where the modulating signals are derived using the differential and average components of the two inverter references of each phase. The scheme is able to produce a high quality 5-level line voltage for any arbitrary fundamental phase difference between the two inverters of the drive. Hence, the scheme can be used with both a dual inverter drive with a floating capacitor bridge which requires a phase difference of 90°, or a drive with two isolated DC supplies which usually requires a phase difference of 180°. Since the scheme is carrier based, sector identification and lookup tables are not necessary, and can be easily implemented on a DSP. The proposed scheme is compared with conventional sinusoidal PWM in simulation, and is shown to reduce the current THD and harmonic volt seconds, resulting in a reduction of high frequency conduction and iron losses in the machine. The effects of deadtime on THD are also simulated. These results are validated experimentally.