Duty Ratio Modulation Strategy to Minimize Torque and Flux Linkage Ripples in IPMSM DTC Systems

The active vector effects on torque and flux linkage are different in interior permanent magnet synchronous motor (IPMSM) systems at different times under direct torque control (DTC). These different effects may cause overcompensation or undercompensation to torque and flux linkage leading to large torque and flux linkage ripples in the IPMSM DTC systems. A novel duty ratio modulation strategy for the IPMSM DTC systems is presented, which considers these differences that are ignored in conventional duty ratio modulation strategies. The proposed duty ratio modulation strategy aims at minimizing torque ripple and flux linkage ripple, which makes sure that the control system can work in an optimum state. The active angle, the impact angle, the active factor, and the impact factor are first introduced. The active angel and the impact angle are used to get the active factor and the impact factor, respectively. Every sector is divided into five small sectors based on the impact angels, and then, a switching table is redesigned according to the small sectors division. Also, the vector selection rules for the redesigned switching table are described in details. Subsequently, an optimal duty ratio can be derived through the simplified duty ratio determination method. Finally, the effectiveness of the proposed novel modulation strategy is verified through the experimental results on a 100-W IPMSM drive system.