Torque Density Improvement of Doubly Salient Electromagnetic Machine With Asymmetric Current Control

Due to the introduction of field winding, the doubly salient electromagnetic (DSEM) machine is featured with good torque production capability. However, this capability is limited by the problems of the phase current reversal and excessive back- electromotive force with traditional control methods. In this paper, a new control method, namely asymmetric current control (ASCC), is proposed to further improve the output torque. Two control angles α and γ are introduced to implement the current-angle control. Simultaneously, the pulse width modulation control is utilized to shape the waveform of phase current. Consequently, the torque is increased drastically because of more effective phase current waveforms, which presents the asymmetry of positive and negative half period. Furthermore, the reluctance torque resulting from the interaction between self-inductance and asymmetric phase current exerts favorable effects on the torque output. By field-circuit-coupled analysis, the ASCC method for a 1.3 kW prototype is analyzed and compared with other traditional control methods. Laboratory testing of the 1.3 kW DSEM machine driven by the new control method confirms the validity of theoretical analysis and simulation improvement of torque. The simulation and experimental results show that the torque and power density can be improved to 1.5 times by the proposed control method.