Third-Harmonic Current Injection Control of Five-Phase Permanent-Magnet Synchronous Motor Based on Third-Harmonic Current Reference Online Identification

The ratio of torque to copper loss can be increased by injecting third-harmonic current into five-phase permanent-magnetic synchronous motor (PMSM). Accurate flux linkage information is indispensable in the process of calculating third-harmonic current reference corresponding to the maximum torque/copper loss ratio. In harsh working environments, the flux linkage will deviate from the initial measured value, resulting in the deviation between the third-harmonic current and the maximum torque/copper working point. Therefore, a third-harmonic current injection control strategy of five-phase PMSM based on third-harmonic current reference online identification is proposed in this paper. The key of this strategy is to transform the steady-state voltage equations into an equation containing only voltages and currents. The transformed equation has a characteristic that it is equal to 0 when the motor operates at the maximum torque/copper loss ratio working point. Meanwhile, an observer is designed to estimate the third-harmonic current reference by using the characteristic. Finally, the observer is applied in third-harmonic current injection control of five-phase PMSM. Compared with previous methods, the proposed strategy is simple, no need of flux linkage information and not affected by the change of flux linkage. The experimental results demonstrate the robustness of the proposed strategy.