Due to the advantages of high power level, small torque ripple, and strong reliability, dual three-phase permanent magnet synchronous motors (DTP-PMSM) have been widely used in electric vehicles, ship propulsion, and aerospace power systems. The high fault-tolerant capability for open-phase faults is an important application feature of DTP-PMSM. Developing fault-tolerant control strategies is crucial for improving fault-tolerant performance. While both the minimum loss (ML) and maximum torque (MT) control strategies offer their advantages, stator copper loss and torque output capacity cannot be simultaneously considered. The full range minimum loss (FRML) control strategy comprehensively considers both ML and MT optimization objectives. The stator copper loss is effectively reduced without sacrificing the output torque range. Currently, the FRML control strategies usually add the restriction of sinusoidal current mode. However, the restriction of the sinusoidal current mode narrows the solution space of the current reference and prevents further improvement of the fault-tolerant performance. Therefore, a FRML control strategy based on harmonic current injection is proposed.

Firstly, considering the control complexity and optimization effect, third harmonics are injected into the fault-tolerant phase current to expand the solution space. By optimizing the current references, the fault-tolerant performance of ML and MT control strategies is further improved. Secondly, considering the stator copper loss and torque output capacity holistically, an allocation coefficient is introduced to combine the ML and MT strategies nonlinearly. The fault-tolerant trajectory can be smoothly switched online by adjusting the allocation coefficient under various load conditions. The proposed FRML control strategy simplifies the implementation complexity and produces a unified expression of current reference, which effectively reduces stator copper loss over the torque range. Finally, the proposed control strategy is verified on a surface-mounted DTP-PMSM platform. The quasi-proportional resonance controllers ensure accuracy in tracking the AC current reference. Both ML and MT control strategies achieve smaller stator copper loss and larger torque output capacity after the third harmonic injection than the sinusoidal current mode. When the FRML control strategy based on harmonic current injection is applied, the allocation coefficient is modified in real-time with the change of load condition. Under the rated load of 65.5%, 67.7%, and 69.7%, the stator copper loss is lowered by 6.2%, 4.91%, and 3.1%, respectively, compared to the MT control strategy. The fault-tolerant control strategy is verified.

The following conclusions can be drawn. (1) The strategies with the injection of third harmonic exhibit the superior performance of copper losses and torque output capability than that with sinusoidal current mode thanks to the more thorough current optimization. Therefore, the fault-tolerant control strategy based on third harmonic injection is more favorable for the stator copper loss optimization in the full torque range. (2) The proposed FRML control strategy based on harmonic current injection can further expand the range of torque optimization and enhance adaptability to various load conditions. (3) The proposed fault-tolerant control strategy is scalable. Future work will be focused on extending the applicability of the proposed control strategy to other polyphase motors, such as nine-phase motors.