A multi-stage converter for electric traction applications has been implemented and tested. This technology allows modulating the output voltage by amplitude instead of pulse-width. The amplitude modulation is based on a digital cascade of 'H' converters scaled in power of three, and with each converter able to generate three levels of voltage. The multi-stage converter developed in this work, has a chain of four converters per phase (4-Stage Converter), with a 'Main converter' that manages more than 80% of the total power, and three 'Slave converters' that take the rest of the power (less than 20%). With this technology, the pulsating torque generated by harmonics is eliminated, and the power losses into the machine due to harmonic currents are also eliminated. Another advantage of this drive is that the switching frequency of the Main converter is at the fundamental frequency, reducing their power losses at minimum values. Besides, the power ratings of the semiconductors of the Slaves become very small. The paper also shows how the problem of isolated power supplies required for each converter can be overcome, by using isolated motor windings for each phase of the traction motor, and by using bidirectional regulated power supplies for the Slaves. Simulations using PSIM (Power Electronics Simulator) have demonstrated the feasibility to build multi-stage converters for real electric vehicles or electric buses. These simulations have been compared with voltage and current waveforms obtained with conventional PWM inverters. The experimental multi-stage prototype has a rating power of 3 kW, and some experimental results are displayed and compared with the simulations.
Multi-stage converters: A new technology for traction drive systems
Mehrebenen-Konverterschaltung: eine neue Technologie für Antriebssysteme
2003
11 Seiten, 12 Bilder, 16 Quellen
Conference paper
Storage medium
English
Traction drive system for electric vehicles, using multilevel converters
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