Fractional-slot concentrated windings (FSCWs) are widely utilized in six-phase fault-tolerant permanent-magnet synchronous machines (PMSMs). However, FSCWs cause abundant space harmonics of stator magnetomotive force (MMF) and increase the losses of the machine. In this article, in order to suppress the space harmonics of a six-phase PMSM, the six-phase winding is regarded as a combination of two sets of three-phase windings, and the effect of phase-shifting between two sets of three-phase windings on the MMF harmonic suppression is investigated. To achieve more effective suppression of the MMF harmonics, the low-space-harmonic oriented design is further extended to phase-shifting between double six-phase windings while the phase number is not doubled. A low-space-harmonic double-six-phase 15°-shifting winding is designed, in which both J-pole-pair and 5-pole-pair MMF harmonics are suppressed, and its characteristics of losses, permanent-magnet (PM) torque, and reluctance torque are evaluated. A prototype of 24-slot/14-pole double-six-phase 15°-shifting PMSM is manufactured, and the experiments are carried out to verify the performance of the machine.
This study focuses on the phenomenon of rotor beat frequency vibration (BFV) in a 2-pole magnetic levitation induction machine (MLIM), systematically investigating its dynamic mechanisms and subsequently applying an established method for its suppression. First, the BFV synthesis process is described. Subsequently, three primary disturbance sources in the magnetic bearing (MB) system are identified and analyzed, including rotor unbalance, unbalanced magnetic pull (UMP) and magnetostrictive effect. Through numerical solution of a four-degree-of-freedom (4-DOF) rotor dynamic model, the theoretical analysis reveals that MLIM -induced BFV consists of three spectral components: (i) rotor rotational frequency (RRF), (ii) electrical fundamental frequency (EFF), and (iii) the sum of EFF and slip frequency (EFF+SF). Building on these findings, we propose the adoption of a well-established notch filtering technique as an effective means to suppress the BFV. The experimental results confirm the correctness of the analysis of the BFV generation mechanism, and in particular of the EFF disturbance mechanism, and also demonstrate the effectiveness of the vibration suppression method.
This paper investigates an aggregated design and optimization method for permanent magnet hub (PMH) motors, guided by permeance harmonics, to meet low-speed, high-torque requirements. The key lies in establishing the correlation between stator and rotor permeance harmonics and torque. Firstly, contribution equations describing the influence of stator and rotor permeance harmonics on torque are derived. It reveals that the contribution degree is affected by harmonic amplitude and phase. Then, the selection criteria for stator and rotor topology are formulated. The amplitude and phase characteristics of the permeance harmonic group are considered in criteria, which aim to achieve the aggregated design from a permeance harmonic perspective. Furthermore, based on the identified aggregated permeance harmonics, the airgap flux density harmonics directly linked to permeance harmonics are determined. Taking these harmonics as the goal, they are involved in the optimization process for high torque density. Sensitivity analysis and response surface analysis are adopted, respectively, to lock the design variables and their parameter ranges. Then, the motor topology with characteristics of high torque density is obtained through multi-objective optimization. Finally, a prototype experiment is conducted on the optimized PMH motor.
Sustainable motor design is crucial for improving energy efficiency and reducing material consumption. This paper introduces a novel asymmetric interior permanent magnet (IPM) rotor design using topology optimization (TO). The study employs a two-stage TO approach to design IPM rotor. In the first stage, a multi-objective electromagnetic TO is conducted to enhance the average torque and reduce the mass of the magnetically active rotor zone. In the second stage, structural TO is performed to minimize the mass of the magnetically inactive rotor zone while maintaining mechanical integrity, ensuring the rotor withstands operational mechanical stresses. The asymmetric topology-optimized IPM (ATO-IPM) machine is analyzed and benchmarked against the conventional IPM design and the symmetric topology-optimized IPM (STO-IPM) design. The results indicate that the asymmetric flux barriers enhance the torque performance. The ATO-IPM design offers significantly more efficient utilization of permanent magnets (PMs) and improved torque density by approximately 13.3% compared to the conventional IPM motor. Moreover, ATO-IPM design supports the advancement of sustainability by improving efficiency by 2.3% compared to conventional design. Furthermore, ATO-IPM designs save about 46.7% of the amount of silicon steel of the conventional topology.
With the development of onshore power grid projects in desert, Gobi and desertified regions as well as offshore wind power projects, electric energy requires long-distance transmission due to insufficient local consumption. Modular multilevel converter based high-voltage direct current (MMC-HVDC) has become the mainstream transmission technology for large-scale remote wind farm integration. However, MMC-HVDC electrically decouples wind farms from the main grid, and its interaction with wind farms can trigger various oscillations. In addition, the MMC-HVDC connected wind farm system differs from single-converter grid-connected systems in structure, equipment complexity, and fault evolution, leading to problems such as low inertia, wideband oscillations and poor fault ride-through. To address these issues, coordinated control strategies considering dynamic interactions between wind farms and MMC-HVDC have been widely studied. This paper thus reviews such coordinated control strategies from three aspects: first, introducing common engineering symmetrical monopole/bipolar MMC-HVDC system structures; second, summarizing grid frequency sensing methods and inertia support control strategies for MMC-HVDC and wind farms; third, discussing coordinated oscillation suppression and fault ride-through control strategies, considering direct current (DC)-side faults, alternating current (AC)-side grid faults, and wind farm area faults. Finally, it summarizes deficiencies of existing studies for each challenge and prospects future research directions for MMC-HVDC connected wind farm systems.
In the field of high-performance motor control, accurate sampling of motor currents is essential for precise control and stability. To achieve reliable measurement of a motor's three-phase currents, it is typically necessary to install at least two high-precision current sensors. However, using multiple sensors increases the volume and cost of the control system, thereby creating challenges for cost management and controller miniaturization. This paper investigates a phase current reconstruction technique that employs only one current sensor mounted on the direct current (DC) bus. The primary goal is to address the current reconstruction dead zones that occur in low modulation regions and sector boundary regions under space vector pulse width modulation (SVPWM) control. To resolve this issue, two hybrid pulse width modulation (HPWM) methods are proposed: one combining remote state pulse width modulation (RSPWM), near state pulse width modulation (NSPWM), and SVPWM, and the other combining RSPWM and NSPWM. Experiments with different voltage utilization have been conducted for both types of HPWM. Both schemes enable 100% voltage utilization for motor control utilizing only a DC-bus current sensor, and the algorithm for HPWM determination has been introduced.
The segmented power supply scheme for long-stator linear motor facilitates reducing power capacity and achieving a high power factor. However, the segment-switching process leads to overcurrent under high-speed conditions. This paper proposes a novel segment-switching strategy based on the time-optimal control theory. It employs time-optimal feedforward voltage and planned current trajectory during the switching transient process. Thus, it ensures rapid disconnection of the exiting segment and rapid establishment of the current in the incoming segment, while suppressing transient current overshoot. The mathematical model of the long-stator linear motor is established in the process of segment-switching. It derives the minimum times required to force the exiting segment current to zero and to establish the incoming segment current to the reference value by time-optimal control theory. Furthermore, the time-optimal voltages and current trajectories are calculated. The time-optimal current trajectories are used as the reference command for the current loop. The time-optimal feedforward voltages are introduced into the current loop control. Hence, it achieves rapid disconnection of the exiting segment and fast, accurate establishment of the incoming segment current. Experimental and simulation results collectively validate the effectiveness of the proposed segment-switching strategy.
With the rapid development of integrated machine drives (IMDs), hybrid excited asymmetric stator pole double salient machines (HEASPDSMs) have gained widespread attention owing to their flexible flux regulation ability, excellent heat dissipation capacity, and robust structure. As a type of flux modulation machine, HEASPDSMs exhibit numerous magnetic field harmonics due to their double-sided reluctance structure and introduction of asymmetric stator poles and excitation windings. These harmonics cause significant distortions in airgap flux density, back-electromotive-force (back-EMF), and torque. Traditional magnetomotive force (MMF)-specific permeance analytical methods fail to quantify the torque contribution of individual structural-related spatial harmonics, which restricts the torque density improvement of HEASPDSMs. To mitigate the torque distortion and improve torque density, a novel evaluation model for both average torque and torque ripple of HEASPDSMs is proposed in this paper. Different from classical methods, the proposed model directly utilizes stator/rotor MMF and specific permeance as modulation components for torque calculation, which can quantitatively clarify the individual contribution of each modulation harmonic to torque and establish a direct correlation between harmonic contribution and structural parameters. Furthermore, its accuracy is validated via finite element analysis (FEA) by performing single-parameter-scan on four HEASPDSMs with different pole-pair combinations, during which the torque performance and flux regulation ability are analyzed. Finally, experimental validation is performed on a 12s7p HEASPDSM prototype to further verify the proposed model.
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 (U-dc/2). This neutral-point drift breaks the spatial symmetry of the inverter voltage vectors, so the 360 degrees 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 degrees 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 fault-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 post-fault torque ripple is explained as resulting from controller conflict. In addition, a multivariate fault diagnosis scheme based on voltage threshold in the $\boldsymbol{x}-\boldsymbol{y}$ subspace and current trajectory characteristics in the $\boldsymbol{\alpha}-\boldsymbol{\beta}$ subspace is proposed to enhance the diagnostic accuracy. Finally, the feasibility and stability of the proposed control and diagnosis methods are verified by experiments.
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 dual-axis 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.
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 outer-rotor 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 °C at 5000 r/min, confirming the effectiveness and engineering feasibility for practical applications.
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 three-segment 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.
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.
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 (I4). 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 (J.0) 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 .
In this paper, electrically excited synchronous machines (EESMs) using copper (Cu) and aluminum (AI) 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.
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.
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.
Linear flux-switching permanent magnet motors (LFSPMs) have been proposed for long stator applications such as rail transit. However, the conventional linear permanent magnet synchronous motor (LPMSM) suffers from thrust ripple, which degrades the motor performance. The thrust ripple in LFSPMs is mainly caused by detent force and asymmetric electromagnetic parameters, excluding external disturbances. Moreover, the 12/13 slot-pole LFSPM exhibits unique inductance characteristics, which lead to different effects on thrust ripple. First, the detent force in the LFSPM is analyzed through finite element method (FEM). In addition, new finite element (FE) models are proposed for further analysis of the cogging force in LFSPMs. Second, the unique inductance characteristics of the 12/13 slot-pole LFSPM are investigated, and then the thrust ripple caused by asymmetric electromagnetic parameters is calculated by the virtual displacement method. Third, the mathematical model considering the thrust ripple is established for the LFSPM, which provides a foundation for subsequent research on thrust ripple suppression control strategies. Finally, the thrust ripple analysis is validated by comparing FEM results, modeling simulations, and experimental data.
Electric vehicle (EV) drive trains are constantly subjected to an imbalance between demanded torque and generated electromagnetic torque due to unpredictable terrain, traffic, and other external factors. This imbalance leads to significant torsional vibrations and speed fluctuations, which not only compromise passenger comfort but also exert additional mechanical stress on the EVs. Conventional sensorless methods offer speed estimation and control; however, they provide suboptimal performance with sudden load torque disturbances and operational uncertainties, especially at low speeds and across diverse real-world driving cycles. To address these challenges and improve system robustness, this work proposes an advanced sensorless integral sliding mode control (ASISMC) that enhances performance under diverse operating conditions. The proposed ASISMC methodology shows robust performance across a wide speed range, effectively mitigating abrupt load torque disturbances while minimizing the effect of uncertainties within the system dynamics. The approach is experimentally validated for a wide range of speeds and periodic/non-periodic load torque disturbances. Additional validation through the new European driving cycle (NEDC) and urban dynamometer driving schedule (UDDS) demonstrates the method's effectiveness and reliability in real-world driving conditions.
