This paper focuses on a multi-stage optimization scheme for variable-leakage-flux machines (VLFMs), where the leakage flux is passively controlled by armature-reaction-induced magnetic saturation. In VLFMs, the magnetic flux is regulated by the flux weakening (FW) method and controllable leakage flux. This intrinsic coupling complicates the consideration in the flux-adjustable range during the optimization procedure, thereby limiting the full utilization of the inherent advantages of the VLF property to optimize the overall performance. Therefore, a novel design optimization scheme is developed for the VLFM in this paper, which can well decouple the armature reaction and VLF property by employing a three-stage field-circuit coupled model. The proposed model accounts for three representative operating conditions. In the first stage, key performance requirements like peak torque at low speed are considered. In the second and third stages, the minimum and maximum q-axis currents are applied, respectively, allowing direct acquisition of the PM flux linkage while eliminating the influence of the d-axis armature reaction. Consequently, the flux-adjustable range can be directly calculated and optimized in the optimization procedure. Afterwards, the proposed design optimization scheme is implemented on a recently developed partitioned magnet pole VLFM (PMP-VLFM) to obtain an optimal design. Finally, finite element (FE) simulations and experimental tests are carried out to verify the feasibility of the proposed design optimization scheme.

Existing variable flux memory machines (VFMMs) typically suffer from the unavailability of operation envelope expansion and insufficient torque at the high magnetization state (MS), which severely hinders their potential for overall highly efficient operation through MS regulation. In this article, a novel efficiency-oriented stepwise (EOS) optimization strategy for VFMM is proposed. This strategy can innovatively take the coil flux linkage directly as an optimization objective, which can flexibly regulate the operation envelopes and permanent magnet (PM) torques at different MSs. A 27-slot/4-pole VFMM with the magnetic circuit complementary (MCC) concept is taken as a design example. First, the operation principle, multiple operation conditions, and key requirements of the VFMM are theoretically investigated. Then, the MCC-VFMM and the EOS optimization strategy are introduced and implemented, respectively. Furthermore, the key electromagnetic characteristics of the initial and optimized VFMMs are comprehensively compared. Finally, an optimized prototype is fabricated and experimented with to confirm the feasibility of the proposed optimization approach.

Due to high dc-link voltage utilization and less required power devices, series-end winding machine drives have potential applications in permanent magnet synchronous machines (PMSMs). However, the zero-sequence current distortion increases the torque ripple and the overall power loss of the machine drive system. Besides, the common-mode voltage caused by the modulation strategy also impairs the lifespan and performance of both the converter and machine sides. Nonetheless, the combined suppression of zero-sequence current and common-mode voltage for series-end winding machine drives has not been reported until now. Thus, a spatial active zero-state-based space vector modulation (SVM) strategy is proposed in this article, where two spatial voltage vectors are selected to replace the zero-voltage vector. Moreover, a virtual voltage vector is established to cope with the high switching frequency in the proposed method, which makes the switching actions exactly the same as traditional 3-D SVM strategies and lower than the existing active zero-state-based SVM. The experimental results are carried out to verify the effectiveness of the proposed strategy, and it shows that comparable converter and machine common-mode voltages, better current distortion suppression effects, lower power loss of the converter, and higher machine efficiency can be realized compared with the existing active zero-state-based SVM strategy.

This study addressed the overload capability of shaftless propulsion system by proposing a system-level thermal modeling approach based on LPTN. A high-order thermal network for the permanent magnet motor was established and reduced in order, integrated with inverter and battery models. Thermal parameters were identified using the PSO algorithm (prediction error ≤7.9°C). Analysis revealed speed-dependent segmented constraints: battery thermal stability limited low-speed operation (<2800 rpm), insulation temperature endurance dominated medium-speed (2800-2900 rpm), and battery discharge characteristics governed high-speed regions (>2900 rpm). A significant negative correlation was observed between ambient temperature and overload capacity. These findings provided theoretical support for thermal management under extreme conditions, extensible to aircraft electric propulsion systems.

Variable flux memory machines (VFMMs) can perform flexible online magnetization state (MS) regulation via d-axis magnetizing current injection. However, the ultra-short duration and large amplitude of the magnetizing current, combined with significant parameter perturbation disturbances during MS manipulations, impose stringent demands on current tracking accuracy and system robustness. Conventional linear active disturbance rejection control (LADRC) suffers from inherent phase lag that impairs current tracking accuracy, whereas the error-based LADRC (ELADRC) improves dynamic response but leaves the critical need for enhanced disturbance rejection. The above demerits make the conventional LADRC unsuitable for VFMMs. To address these limitations, the compensation function ELADRC (CF-ELADRC) is proposed for VFMM drive systems, which is an inherently straightforward and robust current control strategy that offers faster dynamic response and exceptional anti-disturbance performance. Experimental results demonstrate that the proposed CF-ELADRC substantially outperforms both LADRC and ELADRC in terms of magnetizing current tracking accuracy and steady-state recovery rate during flux regulation operations, thereby confirming both the effectiveness and theoretical correctness of the proposed CF-ELADRC.

Variable leakage flux machine (VLFM) is considered a competitive candidate for electric vehicle (EV) applications due to its distinct advantages of a wide speed range and high overall efficiency. Meanwhile, the active-short-circuit (ASC) technique is widely implemented for EV traction drive systems to prevent hardware damage from overvoltage during high-speed operation. However, it may induce large ASC currents and unexpected PM demagnetization in turn. Therefore, this article first investigates the potential of ASC fault tolerance in VLFMs, introducing a segmented, arc-shaped PM VLFM design aimed at simultaneously achieving a wide speed range, high efficiency, and improved ASC fault-tolerant capability. Initially, the topologies of the benchmark PM machine (PMM) and VLFMs are introduced and clarified. Then, an ASC fault analysis is conducted to elucidate its underlying principles, and both the steady and transient short-circuit currents are analyzed and compared under ideal scenarios, demonstrating the inherent ASC fault tolerance of the VLFMs. Furthermore, the electromagnetic characteristics, for example, loss distributions and efficiency maps, are compared and investigated, verifying the advantages of the proposed design in terms of speed range and high-speed efficiency. Finally, a prototype is built and experimentally tested to verify the feasibility and effectiveness of the proposed VLFM design. The results provide valuable insights for traction machine design considering practical ASC operation in EV applications.

Transverse flux PM linear generator (TF-PMLG) enables a higher power density under low-speed wave characteristics. However, thrust pulsation and magnetic leakage are major issues in these generators. To address the foregoing problems, a hybrid excitation TF-PMLG is proposed. However, it presents significant control challenges due to large phase inductance and non-negligible internal resistance, particularly under conditions of insufficient bus voltage. Additionally, the necessity for electromagnetic thrust to adapt in real time to wave variations further intensifies the demands on the dynamic performance of the control system. To this end, this article proposes a model predictive thrust control (MPTC) strategy based on optimal flux linkage vector selection. It can effectively mitigate thrust fluctuations of the generator in response to wave action. Furthermore, a dynamic flux-enhancing strategy is developed, which can reduce the dependence on bus voltage magnitude, thus increasing the peak thrust of the generator. Finally, simulations and experimental results are provided to validate the effectiveness of the proposed MPTC methods in direct-drive wave energy converter system.

In this article, the robust variable-axis high-frequency (HF) injection-based sensorless method with online polarity identification for magnet-axis-shifted interior permanent magnet synchronous motor (MAS-IPMSM) is realized by retransforming and multiplexing the HF current, where the effect of HF vibration on polarity identification is first revealed, which is decoupled via the proposed conjugate auxiliary current reference frame (CAC-RF). First, the variable-axis HF injection-based MAS-IPMSM vibration model is established. It is revealed that, for MAS-IPMSM, vibration is mainly produced from HF torque ripple and induced tangential injected-frequency vibration can produce HF second-order current, invalidating conventional polarity identification method. Besides, a novel vibration coupled HF reluctance model is proposed, which also proves that the vibration effect is naturally decoupled for conventional IPMSM. Subsequently, the robust CAC-RF based MAS-IPMSM sensorless method is proposed, which concurrently obtains intact inductance saliency and vibration effect decoupled polarity information. The proposed vibration coupled reluctance model and CAC-RF based robust sensorless method are verified with experiments.

In this article, the extended back-electromotive force (EMF) is generalized to variable-axis, by orienting toward which, a universal auxiliary reference frame sliding-mode observer (ARF-SMO) based sensorless method is proposed for magnet-axis-shifted interior permanent magnet synchronous motor (MAS-IPMSM). First, the variable-axis extended (VAE) back-EMF is proposed, which characterizes the information of the asymmetrical back-EMF due to magnet-axis-shifting (MAS) effect and unifies the back-EMF model of different rotor saliencies and symmetries. Subsequently, a universal ARF-SMO based sensorless method coping with MAS effect is proposed, in which the proposed auxiliary reference frame can obtain the unbiased position information by orienting toward the VAE back-EMF. The proposed ARF-SMO is a generalization of conventional SMO and keeps the universality for both MAS-IPMSM and typical PMSM. Additionally, the stability of the proposed ARF-SMO is proved based on the lyapunov theory. Finally, the effectiveness of the proposed method is verified with the experiments.

Model predictive control (MPC) for three-phase for surface-mounted permanent magnet synchronous motors (SPMSMs) has been broadly researched due to its superior dynamic response and high efficacy in controlling nonlinear systems. However, MPC has high computational complexity, constraining its applications in scenarios with limited computational resources. Conventional MPC strategy evaluates eight cost functions to optimize voltage vectors (VVs) in one control period, where heavy computational burden is inevitable. This paper proposes a sliding-mode based model predictive control with constrained optimization strategy (SM-MPC) for PMSM. In the proposed strategy, VVs are pre-selected according to sliding-mode strategy. Initially, a pair of error quantification functions are derived to characterize the discrepancy observed between the reference current and the actual one. Subsequently, the proposed control strategy rigorously applies Lyapunov stability criterion to enforce asymptotic error convergence in current tracking, ensuring the output current precisely follows its reference, and then the qualified VVs can be selected. The proposed method demonstrates a 5us computational load reduction compared to conventional MPC. Moreover, SM-MPC achieves steady-state and dynamic performance metrics comparable to conventional MPC. Its efficacy is demonstrated through experimental results on a 0.5 kW PMSM drive setup.

Hybrid-variable-flux machines (HVFMs) can achieve more pronounced efficiency improvement compared to the single-variable-flux machine by integrating both variable magnetization state (MS) and variable leakage flux (VLF) properties. However, the optimal magnetic-circuit configuration for arranging these two variable-flux units remains unclear, yet is critical for practical HVFM design. To fill this gap, this paper presents a comparative study of HVFMs with integrated- and separated-magnetic-circuit designs, highlighting the advantages, limitations, and trade-offs of each configuration. Firstly, the machine topologies and operating principles are introduced, with magnetic equivalent circuits (MEC) developed to identify the differences in magnetic-circuit coupling between two variable-flux units, and provide physical insights into how the leakage bridges influence flux regulation behaviors. Then, to ensure a fair comparison, a design optimization is performed to obtain the optimal topologies for each machine design. Afterwards, a comparative study of the electromagnetic performance of the two HVFMs is conducted, including torque capability, efficiency maps, and other metrics. Moreover, mechanical stress are also performed. Finally, a prototype with a separated-magnetic-circuit configuration is manufactured and experimentally tested, which validates the theoretical analyses.

In high-frequency injection-based saliency tracking, harmonic errors arise from nonidealities in interior permanent magnet synchronous motor and inverter. Conventionally, achieving both high-bandwidth observation and reduced low-order harmonics presents an inherent tradeoff. Adaptive notch filter (ANF), featuring harmonic suppression characteristic without affecting the target signal, is gaining increasing attention. In this article, the saliency tracking bandwidth-constrained divergence phenomenon in conventional ANF-based harmonic suppression is first revealed. Due to the inherent closed-loop nature in saliency tracking, there is inevitable phase misalignment between detection and compensation, which could lead to high risk of divergence in harmonic suppression, especially in low-speed and high bandwidth observation. Subsequently, a novel dynamic phase-synchronized adaptive notch observer is proposed, which has the ability to counteract the closed-loop effect. The convergence boundary is expanded and full-order harmonics can be suppressed under high-bandwidth observation at low-speed. The convergence boundary is analytically proven and the enhancements of the proposed harmonic suppression method are verified with experiments.

This article proposes a novel deadbeat sliding mode predictive control (DB-SMPC) strategy for T-type three-phase four-leg three-level voltage source inverters. Developed in the alpha beta gamma frame, the control strategy integrates the advantages of traditional sliding mode control (SMC) and deadbeat predictive control (DBPC), offering enhanced robustness, stability, and superior dynamic and steady-state performance. It outperforms traditional SMC and DBPC in terms of voltage regulation and dynamic response under varying load conditions. This strategy also reduces system chattering, ensures a fixed switching frequency, thereby simplifying the design of LC-filters. The four-leg inverter topology effectively addresses unbalanced and nonlinear loads. When integrated with the proposed DB-SMPC strategy, it enables robust system performance under such conditions. In addition, it significantly reduces total harmonic distortion for nonlinear loads and improves the dynamic and steady-state performance of balancing neutral-point voltage under unbalanced load conditions. Experimental results verify the effectiveness of the proposed strategy.

Hybrid-variable-flux PM machine (HVF-PMM) can achieve higher flux regulation (FR) flexibility and wider high-efficiency operation regions, as it integrates both variable magnetization state (MS) and variable leakage flux (VLF) properties. However, introducing the VLF property via leakage bridge designs inevitably increases the difficulty of remagnetizing low-coercive-force (LCF) magnets, thereby leading to an oversized inverter rating. To address this issue, this article proposes an inverter-rating-reduction (IRR) design methodology that intentionally avoids difficult-to-remagnetize regions of the LCF magnets while maintaining the required performance. To achieve this, multioperating-mode field-circuit coupled models are established, in which the re- and demagnetizing currents are constrained to have equal amplitudes. Consequently, the inverter rating can be reduced by balancing the re- and demagnetizing currents. First, the machine configuration, FR principles, and the underlying mechanism by which the leakage bridges influence the magnetizing currents are introduced and analyzed. Then, the IRR methodology is clarified and detailed, followed by sensitivity-based optimization to obtain the optimal design. Furthermore, a comparative study of the electromagnetic characteristics of the HVF-PMM before and after the optimization is conducted, showing a 28.8% reduction in inverter current rating owing to the balanced magnetizing currents. Finally, a prototype of the HVF-PMM is manufactured and tested, and the results validate the effectiveness and practicality of the developed design methodology.

Model-free predictive control (MFPC) based on ultra-local model (ULM) is characterized by enhanced robustness to parameter mismatches. However, the selection of control gains, actually, still relies on the parameters, and the gain deviation degrades the control performance. To solve this issue, this article proposes an improved MFPC with a novel input-output-variation-driven gain observer. With a conceptual ULM-based MFPC, the impacts of gain deviation on the control performance and system stability are analyzed in detail. Then, the proposed method is expatiated, and in particular the stability of the proposed gain observer is proven based on the Lyapunov stability theorem. Meanwhile, the design guideline of feedback coefficients of the proposed observer is also presented. Based on the theoretical analyses, a finite-control-set model-free predictive current control (FCS-MFPCC) method with the suppression of gain deviation is designed and applied to a permanent magnet synchronous machine (PMSM) drive system. The digital delay compensation and the discriminator of zero-voltage vectors are considered for performance improvement and inverter switching frequency reduction, respectively. Finally, some critical experiments are conducted based on a PMSM test rig to verify the proposed gain observer and FCS-MFPCC method. In particular, different initial values of control gains are set, indicating that the proposed FCS-MFPCC method does not require any prior knowledge of electrical parameters of the PMSM under test.

In this paper, two novel asymmetric variable flux memory machines with U-type permanent magnet (PM) configurations are proposed. These designs feature variable PMs (VPMs) placed on one side and constant PMs (CPMs) on the opposite side of the U-shaped cavity, with or without additional VPMs in the middle cavity. Both machines are firstly designed and optimized using finite element method with the same 21-slot/4-pole stator and rotor inner/outer diameters. The electromagnetic performance of the optimized designs are analyzed and compared. Results show that the middle VPMs can enhance the flux regulation (FR) capacity but contribute less to the torque. As a result, the machine with the middle VPMs can achieve a wide FR range and improved overall efficiency, whereas the machine without the middle VPMs can deliver higher torque density. Finally, two prototypes are fabricated and tested for validation.

The concept of multiplexing power legs makes series-end winding permanent magnet synchronous machines (SEW-PMSMs) have the merits of high DC-link voltage utilization, low volume, and high efficiency. However, the increased leg current of multiplexing power legs inevitably leads to high power loss of converter. Besides, the multiplexing power legs also have a large weight in the common-mode voltage from machine sides, which leads to large amplitude and dv/dt stress of common-mode voltage, compared with nonmultiplexing ones. Therefore, although multiplexing power legs brings apparent superiorities to SEW-PMSM, they lead to several impairments as well. Consequently, an optimized discontinuous space vector modulation (ODSVM) strategy is proposed in this article, where the switching action reduction focuses on the multiplexing power legs to reduce the power loss and amplitude of common-mode voltage caused by the above legs. Furthermore, a spatial near state SVM (NSSVM) scheme is proposed to reduce the common-mode voltage from the converter/machine sides. Two proposed discontinuous space vector modulation (DSVM) strategies are verified and compared with traditional continuous SVM (CSVM) and three existing DSVM methods by experimental results. The effective common-mode voltage and/or power loss reduction are verified experimentally in the proposed DSVM strategies.

In order to solve the problems of low ‘power/volume’ or low ‘power/cost’ caused by the low speed of wave energy converter (WEC), a linear-rotary magnetic field modulation generator (LMFMG) is proposed. The three-dimensional structure and working principle of LMFMG are introduced. The air gap flux density of the magnetic gear screw is calculated to verify the magnetic field modulation principle and the speed-up mechanism. After comparative analysis, the optimized parameters and output parameters of the LMFMG are given. The back EMF, loss and efficiency of the rotary generator are calculated. Through magnetic field modulation, the proposed LMFMG can convert the linear motion of 0.5 m/s into a highspeed rotational motion of 10000 rpm. Compared with the existing WEC, the proposed LMFMG has higher ‘power/volume’ and ‘power/cost’, which makes it very potential in WEC. The prototype is manufactured and the experimental platform is built. The thrust, torque, current and back EMF are measured to verify the theoretical calculation results of LMFMG.

Due to their simple structure and high efficiency, various types of linear machines are employed in direct-drive applications such as linear railway traction. The transverse flux linear machine (TFLM) can achieve high thrust density, but it has demerits of severe magnetic flux leakage and large detent force. This article investigates a tubular hybrid excitation TFLM (HE-TFLM) for a linear railway traction system. The structure and working principle of the proposed machine are described in detail. Subsequently, a magnetic circuit analysis is conducted while taking axial magnetic flux leakage into consideration. By optimizing the pole arc coefficient, the magnetic flux leakage of the machine is reduced, and performance parameters such as average thrust are improved. Based on the optimized dimensional parameters, the machine performance with different combinations of primary slots and secondary poles is compared. It is proved that employing cross-connected windings simultaneously in both the circumferential and axial directions can effectively reduce thrust ripple. Moreover, the loss and efficiency analysis and temperature field simulation results are given. Since both the primary and secondary of the HE-TFLM can be axially laminated, the motor exhibits very low eddy current losses. Despite the relatively high copper losses in the motor, its efficiency under rated conditions remains acceptable. An HE-TFLM prototype is manufactured, and an experimental platform is established to measure the no-load back electromotive force (EMF) and on-load thrust of the prototype under two conditions: reciprocal motion with a sinusoidal velocity of the secondary and linear motion with a constant velocity of the secondary. The experimental results are in good agreement with the simulation results. Compared with other TFLMs, the proposed machine achieves relatively high thrust density and extremely low thrust ripple. Additionally, by adopting a hybrid excitation method, the proposed HE-TFLM attains a wide speed regulation range, making it well-suited for application in linear railway traction systems.

The high permanent magnet (PM) eddy-current loss is a key issue for AFPM machines with fractional slot concentrated winding (FSCW). To fast calculate and restrain PM eddy-current loss for AFPM machines, a novel analytical simple model on AFPM machine with radial segmentation design is proposed by considering the time and space harmonics. Firstly, the relationship between PM eddy-current loss and PM radial segmentation is derived and analyzed, and the initial analytical model is presented to evaluate the PM eddy-current loss under different operating conditions. Then, the calculation error is analyzed for the initial analytical model according to the different sources of PM eddy-current loss. In addition, the influence law of time and space harmonics on PM eddy-current loss is obtained and analyzed, and the improved accurate analytical model is established based on the equivalent resistances model. Then, the predicted results are compared with three-dimensional finite element (3-D FE) analysis, which indicates that the improved analytical model shows a quickly and accurately calculation on the PM eddy-current loss under different operating conditions. Finally, a 60kW prototype with segmented PM is manufactured and tested to validate the theoretical analysis and FE simulation.