Modelling and field orientated current control of a two-star 6-phase IPMSM for gearless wheel drives

Today, in modern three-phase inverter based AC drive systems for electric and hybrid electric vehicles a trend to high voltage levels can be observed. An increase of voltage at constantly leaved power level inherently leads to lower currents in the inverter and in the motor compared with low voltage based drive systems. However, ensuring personal safety at high voltage levels is difficult, especially in accidental cases where possibly unpredictable fault conditions occur. Feeding the required electrical power at low-voltage trough two separate three-phase stars to the motor is a possible approach to keep the upcoming currents small. An ideal precondition for further reduction of currents is the distribution of required power to several or all of the vehicle's wheels with an in-wheel drive concept. Along with vehicle drive-train the proposed concept is generally applicable to low-voltage based drive systems with relatively high currents. The paper discusses mathematical modelling and two possible current control approaches for the two-star IPMSM.