Vector space decomposition (VSD) model has been widely utilized for dual three-phase permanent magnet synchronous machine (dual-PMSM) control, in which two DQ frames, DQ1 and DQ2, are introduced to facilitate controller design. Existing studies show that harmonic current injection in DQ2 frame can increase the output torque for a given peak phase current, which is referred as maximum torque per peak current (MTPPC) control. However, the injected harmonic current will induce a small dc torque and the harmonic torque. This paper firstly proposes a comprehensive torque model considering the harmonics in PM flux linkages, inductances and stator currents to investigate the induced torque components, which are neglected in existing approaches. These torque components are then considered in the harmonic current design to improve MTPPC control performance. The harmonic current design results in a multi-objective optimization problem, and genetic algorithm is employed to optimize the harmonic current to maximize the output torque with minimal torque harmonic. Compared with existing approaches, the proposed approach is applicable to both surfaced-mounted and interior dual-PMSMs. Experimental investigations on a laboratory interior dual-PMSM demonstrate that the output torque of test motor can be increased by more than ten percent with a negligible increase in torque ripple.

This paper investigates open-phase fault modeling and fault tolerant control (FTC) of dual three-phase permanent magnet synchronous machines. A comprehensive fault model that considers both the permanent magnet torque and reluctance torque under the open-phase fault is proposed at first. This model shows that under open-phase fault the average torque of dual three-phase PMSM will decrease, while torque ripple will increase significantly. Then, a novel optimized FTC approach is developed based on the proposed fault model, in which genetic algorithm (GA) is applied to optimize the stator currents to maximize the average torque and minimize the torque ripple under open-phase fault condition. The proposed fault model and GA-based FTC are applicable to both surface-mounted and interior dual three-phase PMSMs. However, existing approaches are only applicable to the surfaced-mounted dual three-phase PMSMs because the reluctance torque has been neglected. Moreover, the proposed approach is simple in implementation as it employs the original control structure, and it is capable of smooth switching between the healthy operation and FTC without inducing noticeable torque pulses. The proposed GA-based FTC is demonstrated with design examples, compared with existing approach and validated with experimental tests on a laboratory interior dual three-phase PMSM.

This paper proposes a novel gradient descent based maximum torque per ampere (MTPA) control algorithm for interior permanent magnet synchronous machines (IPMSMs) by using the measured speed harmonics. The proposed approach does not require machine parameters and thus is not influenced by the machine and drive nonlinearities. Hence, the proposed approach can ensure a robustness MTPA control under different loading conditions. Specifically, in the proposed approach, a small q-axis harmonic voltage is injected into the machine to induce a small harmonic component in the machine speed. Based on the PMSM torque equation, the mathematical relation between the induced speed harmonic and the output torque is derived, which shows that the magnitude of the induced speed harmonic is proportional to the output torque of an IPMSM. Therefore, the speed harmonic is explored to seek the MTPA angle, in which the MTPA angle is found when the speed harmonic magnitude is maximized. In particular, the gradient descent algorithm is employed to detect the MTPA angle, which is computationally efficient and converges quickly. The proposed approach is evaluated through both simulations and experimental tests based on a laboratory IPMSM drive system.

Permanent magnet (PM) temperature is crucial to high-performance control and condition monitoring of the permanent magnet synchronous machines (PMSMs). Thus, this paper proposes a non-invasive PM temperature estimation approach based on the PMSM steady-state equation. Firstly, a linear temperature model, dependent solely on the PM temperature, is derived from the PMSM steady-state equation and the PM thermal model. Thus, the PM temperature can be directly estimated from the measurements using the derived model. In order to improve the estimation performance, a linear state-space model is developed based on the derived temperature model, and Kalman filter is employed for PM temperature estimation. The inverter nonlinearity is considered and compensated in the proposed model to improve the estimation performance. Compared with existing methods, the proposed approach is non-invasive and computationally-efficient. More importantly, the derived model does not involve machine parameters such as winding resistance and machine self and mutual inductances, and thus the proposed estimation approach is independent from the winding temperature rise, magnetic saturation and cross-coupling effect. The proposed approach is evaluated with extensive experimentations under various speed and load conditions.

This paper proposes a novel method of efficiency improvement in a vector controlled permanent magnet synchronous motors (PMSM) through system level maximum efficiency point determination using current angle as a control variable. Loss models for the inverter and the motor fundamental and harmonic losses, which are capable of being solved online using available terminal measurements in the system are initially developed. The loss models and DC link power measurement are then used to seek the maximum efficiency angle for different operating conditions using a gradient descent optimization algorithm. The developed method is robust against changes in inductances due to saturation and cross-saturation with loading conditions as well as temperature effects. The effectiveness of the developed method in improving the system efficiency is verified and compared with conventional maximum torque per ampere method. The proposed strategy has been validated on a laboratory interior PMSM, and the efficiency has been calculated for different speed and torque conditions. The experimental validations confirm the effectiveness of the proposed solution in improving the motor drive system energy efficiency.

Torque ripple has been a critical issue for high-performance applications using permanent magnet synchronous machines (PMSMs). An efficient approach to minimize torque ripple is to control the stator current to follow an optimized current reference, which will produce an extra torque ripple to cancel the existing one. This paper proposes a multiple reference frame (MRF)-based controller for torque ripple minimization, in which the measured speed ripple is explored as the feedback control signal. The proposed MRF-based controller consists of a torque ripple minimization (TRM) controller whose task is to find the optimal current reference and a current controller whose task is to control the actual current to follow the optimized current reference. In the TRM controller, the control of reference current magnitude and phase angle is decoupled, and PI controller is able to achieve TRM control. In the current controller, MRF is adopted to convert harmonic current control into DC current control, thus PI controller is able to achieve harmonic current control with the use of MRF. Compared with existing approaches, the proposed controller is capable of torque ripple minimization under both steady-state and transient conditions. The proposed controller is experimentally evaluated on a laboratory PMSM drive system.