Capacitance Reduction of Switched Reluctance Motor Drives
Switched reluctance motors (SRM) have several advantages when compared to other competing machines, which make SRMs a serious contender for propulsion systems in electric vehicles (EVs), including hybrid EVs (HEVs), plug-in hybrid EVs (PHEVs), and battery EVs (BEVs). However, during the period of current commutation between various phases, there exists significant energy transfer between the DC source and the machine, which would lead to large current ripple in the DC source. In EVs, the DC source would often consist of Lithium-ion (Li-ion) battery packs because of its high power and energy density. Such large ripple current required by SRM would cause excessive temperature rises in the battery pack causing capacity fading and performance degradation, which leads to bigger cooling systems and higher thermal management requirements. As a result, the cost and size of the battery pack and thermal management usually forms a major part of the overall system. Conventionally, large electrolytic capacitors are used to restrain this undesirable ripple power, however, the theoretical lifetime of electrolytic capacitances is much shorter than the lifetime of semiconductors and other passive components.
The researchers in REVT lab have proposed two new topologies for SRM drive applications in order to solve the problem without using large electrolytic capacitors. The new topologies are based on multi-port and Z-source converters. In addition, they are capable of four-quadrant operations, making them suitable for various electric propulsion applications.