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.

As vehicular modern electric technologies imply the need for ever better auxiliary services, small electric actuators with higher energy conversion performance at affordable prices are required. This paper introduces a three-phase inner claw pole ATOMET core stator with outer PM rotor synchronous actuator characterized by a modular structure with one circular shape ac coil per phase, capable of producing high torque per copper loss and enjoy practical fabrication at reasonable cost. As a follow-up to a recent conference paper, this study presents novel 3D-FEM simulations that reveal important aspects related to the magnetic behavior of the machine under both no-load and full-load (rated Iq current) conditions. Additional experimental results for the 125W inner claw pole stator outer permanent magnet rotor machine are also included, specifically demonstrating its inverter-fed motor mode operation using a Field-Oriented Control (FOC) technique up to full torque load.

Conventional E-type linear oscillatory machine (ELOM) suffers from insufficient utilization of air gap flux density and low power density, which limits their wider adoption. In order to improve the power density, this article proposes an innovative double-sided dual-magnet stator-mover LOM (DSLOM) featuring a composite mover structure of permanent magnet (PM)-iron core-PM and a flux switching topology on the stator side, which can greatly improve the overall output power by enhancing the air gap magnetic flux density. First, the topology and operating principle of the DSLOM are presented. Then, considering the differences between the PM magnetic circuit and the armature magnetic circuit of the proposed machine, two separate equivalent magnetic circuit (EMC) models are established, including a PM EMC accounting for center region saturation and an armature EMC considering slot leakage flux. Moreover, comprehensive design guidelines for the key dimensional parameters are established and analyzed in detail. Finally, simulation and experimental results demonstrate that, compared with the conventional ELOM, the proposed DSLOM achieves a 17.65% improvement in permanent-magnet utilization and a significant increase in output power density, thereby validating the superiority and correctness of the proposed topology.

Homopolar linear synchronous motors (H-LSM) represent a viable solution for high temperature superconducting (HTS) maglev requiring low-cost vehicle propulsion systems. However, due to the inherent 3D-field distribution of H-LSM, the necessary 3D finite element analysis (FEA) hinders its rapid design and optimization. This paper proposes for the first time a complete refined hybrid analytical framework model for H-LSM with discrete secondary segments. This model integrates the methods of airgap magnetomotive force-permeance, winding function theory, and conformal transformation, accurately considering the magnetic field modulation effects caused by discrete secondary iron segments and primary slotting, as well as the transverse and longitudinal end effects. The analytical predictions are verified by 3D FEA and a laboratory-scale prototype, demonstrating high agreement, which validates the effectiveness of the proposed model. This model reduces computational time by approximately 98% compared to FEA under the specific conditions, enabling rapid analysis and optimal design of H-LSM with complex 3D-field characteristics under arbitrary pole-slot combinations for HTS maglev applications.

Speed sensorless control is essential for linear induction machines (LIMs) in urban rail transit. However, it is difficult to obtain the accurate speed when the mutual inductance of LIM is changed nonlinearly due to the end effect, especially in high-speed flux-weakening region. To enhance the robustness of the sensorless control system against such parameter changes, an improved speed sensorless control based on full-order terminal sliding mode (FOTSM) observer with adaptive gain is proposed in this article. First, to implement the minimum use of parameters affected by end effect, an active flux observer with improved FOTSM is constructed in the back electromotive force-primary current model. Then, an adaptive gain is designed to guarantee the stability and effectively attenuate the chattering. After acquiring the accurate estimated active flux, a novel speed observer based FOTSM is established, where the mutual inductance and estimated active flux are decoupled. Finally, comprehensive simulation and experimental results have demonstrated the effectiveness and feasibility of the proposed method.

Rare-earth-free Biaxial Excited Synchronous Machines (BESMs) are highly suitable for traction motor drive systems, offering high power density and improved power factor without reliance on permanent magnets. Effective control of BESMs requires coordinated regulation of stator and rotor currents, typically achieved using feedback-based strategies that rely on accurate current sensing. However, in practical applications, sensor faults and degraded operating conditions particularly the loss of rotor current sensing can compromise conventional control approaches. To address this limitation, this paper investigates a current control strategy that employs feedback control of stator currents in the synchronous reference frame and feedforward control of rotor field current, enabling continued operation in the absence of rotor current sensing. While feedforward control is inherently sensitive to parameter variations, it provides a viable fallback solution under fault conditions. Therefore, it is critical to analyze the impact of parameter estimation errors on both steady-state and dynamic performance. This paper presents a detailed implementation of the proposed control architecture along with a comprehensive parameter sensitivity analysis. Analytical expressions for the actual currents under parameter mismatch are derived, and the theoretical analysis is validated through high-fidelity simulations.

The paper presents a higher magnetic saliency-with open rotor flux barriers solution for a four-pole reluctance synchronous machine with transversal laminations anisotropic rotor. The rotor structure is very close to the axially laminated anisotropic rotor, but the manufacturing costs are estimated lower. Key FEM characterization and results for the two proposed solutions are compared in order to evaluate the applicability for power trains.

This paper presents the design and analysis of a PMassisted high-saliency synchronous reluctance machine (SynRM) intended for standalone operation in light vessels, according to industrial requirements. The machine is designed for $40-100 \mathrm{~kW}$, 450-2400 rpm operation, with a regulated $800 \mathrm{~V}_{d c}$ output using a full-power active rectifier. The proposed machine features an axially laminated rotor with embedded permanent magnets on the q-axis, achieving high saliency ratios that enable reduced magnet usage and eliminate the need for overvoltage protection at high speeds. A preliminary analytical design methodology is employed to determine the geometry and operating characteristics, followed by comprehensive validation using the finite element method (FEM). The results demonstrate a peak torque of 932 Nm, high efficiency (up to 0.94), and favorable power factor across the operating range, along with reduced torque ripple through rotor segmentation. The machine maintains high performance under demanding operating conditions, including wide speed variation and constrained voltage operation. The proposed topology offers a practical, cost-effective solution with strong potential for industrial applications Index Terms-variable speed generator, hybrid electric vehicle, key FEM validation, axially-laminated rotor, variable speed drives, traction applications.

Super power wind generators, especially in off shore implementation require voltage boosting to say 60 kV d.c. for a 50+ km off shore sites to reduce cable weight, cost, losses. A d.c. excited synchronous at unity power factor generator designed to deliver directly power in d.c. at 60 kV dc, via a diode 12 pulse rectifier would imply the elimination of full power transformer with its high-cost power interrupter on load and separator on no-load. Also, the diode rectifier reduces the system cost while securing a high efficiency for d.c. output. Building up on an earlier attempt (power former) but suggesting a tooth wound winding with q1=2/5 made of nonoverlapping cable coils and a possible 1000 kW non-contacting induction rotary transformer at 500 Hz to supply the d.c. excitation on the rotor constitutes the core of the present paper. Preliminary analytical model based electromagnetic design of a 24 MW, 60 kV d.c. output synchronous generator (SG) is accompanied by key FEM validation to sustain the feasibility of the proposed solution.

The paper presents a solution for a higher torque density (from 25Nm/litre up to 44Nm/litre) four poles reluctance synchronous machine with axially laminated anisotropic (ALA) rotor. Key FEM validation results for 100kW, 3-6krpm for two rotor structure variants suggest that the proposed solution could be competitive for traction applications.

Electric drives are everywhere, and with the looming promise of electric vehicles and renewable energy, they will become more complex and the demands on their capabilities will continue to increase. To keep up with these trends, students require hands-on knowledge and a keen understanding of the subtleties involved in the operation of modern electr

High Energy conversion control of ac motor drives that considers magnetic saturation and computes, based on the Newton-Raphson method, the “active flux” trajectories for maximum torque per ampere (MTPA), maximum power factor (MaxCosPhi) and maximum torque per flux (MTPF) to cover all the torque-speed envelope points, based on the “active flux” concept is presented in this paper. A case study for ALA-RSM with digital simulations and preliminary experimental results constitutes the contribution of the present paper.

To enhance the linear oscillatory machine system efficiency, it is essential to optimize the operating frequency. Traditional model-based method is constrained by the model accuracy, resulting in limited improvement of system efficiency. Although the traditional search-based method can significantly improve system efficiency, it suffers from an issue of tradeoff between stability and rapidity. In response to these drawbacks, this article first analyzes the qualitative relationship between operating frequency and system efficiency to elucidate the principle of efficiency optimization. Subsequently, a novel efficiency optimization method based on variable universe fuzzy search is proposed, which can achieve rapid and stable optimization of system efficiency by continuously adjusting the frequency search step. Finally, extensive experimental results verify the effectiveness and superiority of the proposed method.

The main goal of this paper is to provide a systematic understanding of hybridization of magnetic circuits in rotary electric machinery to achieve higher performance via optimal profiling of the reluctance and reaction components of the electromagnetic torque. The main performance indices include torque density, torque pulsation, and efficiency. Furthermore, placement and optimal allocation of magnetic saliency and sources of magneto-motive force (i.e., permanent magnets and distributed electromagnets) are used as tuning parameters in this study. Examples from the existing hybrid torque generation and potential alternate solutions are introduced to provide a physically insightful approach to the problem. Simulation and experimental results are presented to validate the claims.

This article presents the optimization study targeting a specific drive cycle for a MAGNUS-type axial-flux permanent magnet vernier machine (AFPMVM). The proposed MAGNUS machine has a novel design with a dual-stator configuration, where only one stator is wound, with a high-polarity spoke permanent magnet (PM) rotor. The machine topology has a 3-D flux path, which necessitates the analysis of a large finite-element (FE) model. However, due to the computational complexity and time required for such a large FE model, a new approach was developed. This approach involves a computationally efficient FE analysis (CE-FEA) model combined with a single-point drive-cycle analysis and the differential evolution (DE) optimization algorithm. The targets of the optimization algorithm are derived by modeling the load operating cycle through a systematic k-means clustering method, identifying specific operating points representing high-energy zones within the drive cycle. The optimized design achieves a wide range of constant power operation, which is desirable for electric vehicle (EV) in-wheel traction. Experimental and numerical results demonstrate a higher torque density in the MAGNUS machine compared with commercially available EV traction motors. In addition, this article explores various flux-weakening methods for the MAGNUS machine, highlighting their respective benefits.

Small electric aircrafts for short range with Li-ion battery (200 Wh/kg) has been investigated aggressively lately for local transport or for pilots training. Quite a few types of permanent magnet motor drives have been proposed for the scope with speeds from 1500 to 5000 rpm, powers of 30-380 kW, with specific calculated weights of 7 to 25 Nm/kg active weight. This paper presents a preliminary design of a pilot-training small aircraft at 20 kW cruising respectively, 80 kW max. at take-off, max. speed of 2000 rpm (direct-drive) at max. 6 kW/kg for a 80 kWh (330 kg) Li-ion battery for an 864 [kg] total aircraft weight. An easy to build single bearing pancake shape interior rotor surface PMSM of 24 slots/20 poles is chosen to perform in cruising at 96 + [%] efficiency. Preliminary design is followed by Key FEM validations of no-load and on load airgap flux density, torque, torque waveform and demagnetization avoidance.

This paper presents a biaxial excitation generator for automobiles (BEGA) in generator mode, three three-phase windings (9 phases), and three diode bridge rectifiers DC parallel-connected for full power. BEGA is a synchronous machine with a biaxial excitation: one along the d-axis produced by the DC excitation coils (fed through brushes or contactless) and another along the q-axis produced by the PMs. The experimental demonstration of fault-tolerant characteristics was conducted under various fault conditions, including interrupted phases, short-circuited coils, and missing or short-circuited diodes. The importance of having all three three-phase windings (star-connection) connected in neutral points is highlighted and discussed. A comprehensive analysis of the impact of these faults on the harmonic spectrum is presented using a fast Fourier transform.

This paper presents a novel rotor current-oriented control concept and simulation results for a small-scale 7.5 kW DFIG system used in standalone applications. The system incorporates a specialized transformer with star and delta connections on the secondary side connected to a 12-pulse rectifier. The primary side of the transformer is connected to the DFIG stator windings. For DFIG rotor-side converter a Rotor Current-Oriented Control strategy is employed, where the dq- axis reference frame rotates with the rotor current's speed (rotor field speed in steady state). By choosing the $\mathrm{I}_{qr}=0$ the cross-coupling effect is minimized for $\mathrm{V}_{dr}$. This strategy requires only rotor current measurements, dc-link voltage, and rotor speed for implementation. The system's performance is analyzed during start-up, steady-state, and dynamic conditions under various loading scenarios. Furthermore, a comprehensive investigation into system efficiency is conducted, considering different rotor (wind) speeds, load conditions, and stator frequencies of the DFIG.

Rare-earth free biaxial excited synchronous machines (BESMs) are well-suited for achieving unity power factor (UPF) at base speed, enabling high power density and costeffective solutions in traction motor drive systems. With dual excitation sources, the rotor field current can be effectively controlled to optimize machine performance across the entire operating range of the motor drive system. This paper proposes a novel algorithm for the generation of optimal stator and rotor current commands, aimed at minimizing copper losses while ensuring UPF operation. The algorithm also guarantees compliance with stator and rotor voltage constraints under all operating conditions. Developed using the machine's analytical model and numerical optimization techniques, the proposed method is validated through comprehensive simulations across a wide range of torque and speed scenarios. The results confirm the algorithm's effectiveness in maintaining UPF and reducing copper losses, providing valuable insights for enhancing BESM efficiency in traction applications.

This paper presents the preliminary experimental characterization of a small 500W, 1pole pair, shaft-less (no shaft through rotor) Axially Laminated Anisotropic - rotor Reluctance Synchronous Machine (ALA-rotor RSM). The dc current decay experiments and the laboratory setup configuration are being presented in detail. The procedure for determining the dq-axis inductance and the method for calculating the power factor (cos q» are also included. The paper presents a comprehensive comparison between the ALA-rotor RSM and a comparable induction machine in terms of efficiency and losses, but more attention should be given to measurement equipment for future experiments. The machine's performance in generator mode is investigated as well, using ac-side connected capacitors, and the results are presented for maximum speed under loading conditions ranging from 0.48 to 1.36 per unit.