In position-sensorless brushless direct current (DC) motors (BLDCMs) fed by a four-switch three-phase (FSTP) inverter, only two phases are fully controlled, while the remaining phase is tied to the midpoint of the split DC-link capacitors. The voltage pulses required by inductance-based initial position detection can cause unequal discharge of the series capacitors, shifting the neutral-point voltage away from half of DC-link voltage (Udc/2). This neutral-point drift breaks the spatial symmetry of the inverter voltage vectors, so the 360° electrical period can no longer be evenly partitioned into six sectors during initial rotor position detection. To address this issue, this paper proposes a detection-pulse injection sequence that explicitly accounts for the asymmetric voltage vectors of the FSTP inverter. With the proposed sequence, the initial rotor position can be identified within a 30° electrical sector. The method requires no additional voltage or current sensors, and experimental results confirm its feasibility.

Owing to the multi-degree-of-freedom characteristics and inherent ault-tolerant capacity, six-phase motors have been widely adopted in high-power applications, such as electric vehicle propulsion and aerospace systems. This paper presents the fault-tolerant control strategy of symmetrical six-phase permanent magnet synchronous motor (SSPMSM)under an isolated neutral point topology and proposes a fault diagnosis scheme based on joint diagnosis of multiple variables. First, two mathematical models of SSPMSM and their relationship are established. Subsequently, the current vectors in the torque subspace and harmonic subspace of the two winding sets under fault conditions are analyzed, and the cause of postfault torque ripple is explained as resulting from controller conflict. In addition, a multivariate fault diagnosis scheme based on voltage threshold in the x-y subspace and current trajectory characteristics in the α-β subspace is proposed to enhance the diagnostic accuracy. Finally, the feasibility and stability of the proposed control and diagnosis methods are verified by experiments.

Magnetically suspended rotor (MSR) systems have gained widespread industrial adoption owing to their frictionless operation and exceptional reliability. However, harmonic current generated by unbalanced mass and sensor runout threatens the system stability. Repetitive control (RC) effectively suppresses harmonic current, but its parameter design relies on an accurate decoupling model of the system. The decoupling model for the MSR system is often simplified to a second-order linear system. Such a simplification, however, necessitates explicit consideration of system uncertainties caused by unmodeled nonlinearities during the RC design process. Especially under strong gyroscopic effects, the parameter uncertainty is further increased. In this article, an active disturbance rejection controller (ADRC) based on phase compensation (PC) is used to suppress coupling disturbances and improve the control performance of harmonic suppression. Firstly, the dynamic model of the MSR system is established, and both internal and external disturbances are thoroughly analyzed. Then, the RC-PCADRC scheme is designed, integrating the complementary strengths of RC and ADRC, with a particular emphasis on PC to improve stability margins. A comprehensive stability analysis is conducted, along with parameter optimization guidelines. Finally, the effectiveness and superiority of the proposed scheme are validated through both simulations and experiments.

Abstract—This paper proposes a collaborative design method for enhancing the power factor and torque of electric motors. First, the intrinsic relationship between flux linkage analysis of the permanent magnet (PM) and armature field and the power factor is explored. Then, the connection between flux linkage and harmonics is established, clarifying the mechanism for improving power factor and torque. Improvements are focused on the PM and permeance. Regarding the PM structure, employing a Y-shaped PM structure effectively increases PM utilization, reduces leakage flux at the outer ends, and enhances the PM flux linkage. Concerning permeance, stator tooth design is optimized to cooperatively improve permeance harmonics, reduce the non-working flux linkage of the armature field, and enhance the fundamental modulation wave of the armature field responsible for torque generation. This improves the power factor while maintaining motor torque. Finally, through PM structural design, the motor torque performance is optimized. Furthermore, the performance of the Y-shaped PM motor is evaluated. A prototype was manufactured and tested. Theoretical analysis and experimental results demonstrate the effectiveness of the proposed method to a significant extent.

In this paper, a precise and computationally efficient method for estimating multiparameter of permanent magnet synchronous motors (PMSMs) is proposed. This method can realize decoupling estimation with a small amount of data at a single speed, and considers the inductance correlation to improve the estimation accuracy. The saturation in the stator frame is first modeled, and then the related inductance model in the rotating frame is derived. The estimation model is established based on the related inductance model, which is modeled by polynomials of d-axis current (Id) for a given q-axis current (Iq). Then, the influence of permanent magnet (PM) flux linkage on inductance estimation can be eliminated by using the partial derivative of the correlated inductance model. The estimation model fully explores the inductance correlation and can realize the decoupling of PM flux linkage (λ0) and inductance, which greatly improves the inductance estimation accuracy, especially when Id is small. Moreover, this paper realizes the estimation of distortion voltage, PM flux linkage, and stator resistance based on the derived electrical model and mechanical model. Compared with the existing method, this method can use a small amount of data at a single speed to model voltage, which can effectively reduce the influence of measurement noise and improve the calculation efficiency. Experimental verification on a laboratory PMSM prototype shows that the method’s performance of the proposed method is better than existing methods under various working conditions.

Integration of renewable energy sources into power systems requires efficient multilevel inverters, capable of producing high-quality output voltage with low total harmonic distortion (THD). Conventional multilevel inverters often suffer from high component count, high switching stress, low voltage gain, and increased cost, limiting their practical application. This paper introduces a high-gain novel topology for multilevel inverters with reduced number of total components per level count, low voltage stress on power conductive devices, and minimizing a cost function, which depends on the number of components, standing voltage on switches and diodes, output voltage levels, and gain. The designed topology, which can be applied in photovoltaic (PV) systems, utilizes only one direct current (DC) input supply and a modular structure with the ability of capacitor’s voltage self-balancing. The high gain property and low THD of the proposed topology are two advantages that provide sine output waveform, with no need to a high DC input voltage source. Moreover, generalized topology, consisting of cascaded basic units, has been proposed. A comprehensive method has been proposed to determining the values of DC supplies in this configuration, aiming to minimize redundant switching modes and maximize the voltage levels count. The comparison with some other multilevel inverters confirms the desired performance of the basic version given inverter. A prototype has been also implemented and the experimental results have been obtained to verify the advantages of the proposed 25-level topology.

For hybrid-electric unmanned aerial vehicles (UAVs), the stable power supply from the onboard permanent magnet synchronous generator (PMSG) is critical. Overheating in the confined compartment can directly lead to power interruption and system failure. Therefore, proactively improving the thermal management is not only a key technical prerequisite for ensuring flight reliability and mission success, but also enhances the machine’s efficiency and the overall power density of the system. Targeting the stringent spatial constraints in UAV applications, novel self-air-cooling heat dissipation topologies are investigated and highlighted on the rotor sidewall for compact outer-rotor generators. A systematic optimization framework, centered on a multi-objective genetic algorithm, is developed to Pareto-optimize the fin geometries, balancing thermal performance against aerodynamic penalty. The proposed topologies are innovatively deployed on the rotor sidewall, uniquely combining the structural space of an outerrotor machine with self-air-cooling to generate directed airflow of varying patterns that directly enhance the cooling efficiency of the stator. The parameters of the designed self-air-cooled heat dissipation topologies are optimized via a multi-objective genetic algorithm. A temperature rise test under windless conditions shows that the proposed self-air-cooled structure reduces the stator temperature of the generator by 37.1 ℃ at 5000 r/min, confirming the effectiveness and engineering feasibility for practical applications.

In this paper, electrically excited synchronous machines (EESMs) using copper (Cu) and aluminum (Al) windings are compared for the feasibility of replacing Cu windings with Al windings in electric vehicle (EV) applications since Al windings have lower mass density and cost per weight, but higher resistivity and lower thermal conductivity than Cu windings. The EESMs with four winding configurations are optimized with an electromagnetic-thermal co-optimization method. The optimized EESM with only Cu windings is considered as the baseline in this study. Results show that the EESM with stator-Cu/rotor-Al windings has the least torque reduction (12.1%) compared to the baseline among the three EESMs with Al windings and the highest torque mass density among all EESMs. Meanwhile, although the new European driving cycle efficiency of the stator-Cu/rotor-Al EESM is 1.8% lower than that of the baseline, the torque per cost is 71% higher, and the maximum rotor mechanical stress is 8% lower. Therefore, the EESMs with stator-Cu/rotor-Al windings are prospective substitutions of those with only Cu windings for EV applications considering the trade-off between performance and cost.

Optimizing the rotor pole-shoe structure of large salient pole synchronous motors is critical for improving their performance and efficiency, allowing for enhanced responsiveness to grid demands and adjustments in operating conditions. This paper provides a comprehensive review of various pole-shoe structures for salient pole synchronous motor rotors and their associated optimization techniques. First, it outlines the role of the pole-shoe structure and examines the theoretical theories of key electromagnetic parameters, including the pole-arc coefficient, voltage waveform coefficient, and armature reaction coefficient. Regarding structural design, this paper explores several configurations, including the threesegment arc, five-segment arc, single eccentric pole-arc combined with two chordal surface sections, and asymmetric poles. The effects of these designs on the air-gap magnetic field distribution and voltage waveform are evaluated. In terms of methodology, this paper reviews the application of numerical solutions to electromagnetic field inverse problems and the use of optimization algorithms for electrical machine structural optimization. This study illustrates the application of improved simulated annealing algorithms, tabu search algorithms, and particle swarm optimization algorithms for single-objective optimization of five-segment arc pole-shoe structures. Additionally, this paper discusses the use of vector tabu search and multi-objective quantum evolutionary algorithms for the multi-objective optimization of five-segment arc pole-shoe structures. The study concludes that multi-objective optimization algorithms are underutilized for pole-shoe structure optimization and suggests that multi-objective particle swarm optimization could be more extensively employed for this purpose. Furthermore, the potential application of topology optimization methods for the design of salient-pole synchronous motor rotor magnetic poles is proposed.

Modern/distributed electric energy systems, with ever larger penetration of renewable (photovoltaic, wind, wave, and hydro) energy sources and time-variable outputs, are in need of stronger/higher frequency and alternating current (AC) (direct current (DC)) voltage control. In fact, faster and more stable active and reactive power in the presence of frequency and voltage sags and swells is needed. Power electronics-controlled variable speed generators do not have enough energy storage (inertia) for the scope (static synchronous compensators (STATCOMs) included). This is because power electronics tends to decouple the generator from the power system. While virtual inertia control in doubly fed induction generators (DFIGs) offers a partial solution to these problems, a more robust and comprehensive framework is required for advanced grid support. This is how, by extending the dual-excitation principles, the dualaxis excited electric synchronous generators (DE-SG) provide superior flexibility in two variants summarized here: as a multifunctional DFIG and dual-axis vs. single-axis excited synchronous generator (SG), and as a synchronous condenser (SC), with dual DC and AC excitation (as a no-load DFIG with inertia wheel), where variable speed is used to accelerate/decelerate the SC and thus provide additional assistance in frequency stabilization. These solutions, good for short-time transients, are not meant, however, to replace the large bidirectional energy storage systems (pump-hydro, hydrogen, batteries, etc.) which are crucial for the daily inherent variations of output energy in modern power systems with multiple power sources. The present paper offers a summary of techniques used in the dual-axis excited vs. single-axis excited SGs (SE-SGs), and SCs topologies, modeling, and control for better stability in modern multiple-source energy systems. This survey includes multiple case studies to shed light on prominent methods.