Two innovative unipolar current converters for low power electrical motor drives

Unipolar current inverters generally use extra switches, or special motor requirements, to control the voltage across the freewheeling capacitor. This paper proposes two different three switches - three phases inverter topologies able to control the voltage of the free-wheeling capacitor only exploiting the phase switches. A key feature of the proposed topologies is that the free wheeling energy of two motor phases is directly exploited to feed the third phase, thus reducing power losses and costs. Moreover, to ensure the correct voltage levels across the freewheeling capacitors a suitable voltage control system and a closed loop algorithm have been developed. In addition, a simple constant V/f speed regulation is introduced, thus avoiding expensive current and speed sensors