Brushless Machine Research Articles

Thermal and Mechanical Fields Analysis of Superconducting Magnet and Dewar System for Double-Stator Superconducting Brushless Machines

The double-stator superconducting brushless machine (DS-SCBM) combines high torque density and excellent static sealing characteristics, as well as advantages in reliability and cost-effectiveness. To ensure the long-term stability of the superconducting magnet and Dewar (SCMD) system, this study evaluates the pressure-bearing capacity and heat leakage from the support frame, selecting appropriate materials and dimensions. Furthermore, a model of the thermal and mechanical fields for the SCMD system is developed using finite element analysis which assesses the impact of various reinforcement structures on the mechanical and thermal properties of the superconducting (SC) magnet. Based on this analysis, the dimensions of the reinforcement structures, Dewars, and vacuum interlayer are optimized. Subsequently, efforts are made to manufacture the designed system and its performance is tested.

A Comprehensive Comparison of Double-Stator Superconducting Brushless Machines Using Two Typical Field-Excitation Stator Topologies

A Comprehensive Comparison of Double-Stator Superconducting Brushless Machines Using Two Typical Field-Excitation Stator Topologies

Loss and Thermal Analysis of a High-Power-Density Permanent Magnet Starter/Generator

Reducing heat and improving the overall operation stability of the motor play a key role in the design of a starting engine. This paper focuses on the loss and thermal analysis of a permanent magnet (PM) brushless machine used in starter generators. The loss of the starter generator was calculated through a combination of theoretical analysis and the finite element method. A thermal analysis model was established based on the division of the fluid domain, boundary grid, heat source setting, and so on. The temperature fields of the whole motor and the main components were calculated and analyzed. The main factors affecting the air cooling effect were analyzed, including air flow rate, air temperature, and motor speed. A prototype experimental platform of the SG motor was built. The efficiency and temperature rise in the motor were tested. The temperature values were compared with the calculated values. The experimental results show that the performance of the motor is excellent, and the error between the temperature and the design calculation is less than 10% under each load torque. The accuracy of the thermal analysis method is verified. The correctness of the motor transient model was also confirmed through a temperature rise experiment under rated conditions, providing a research basis for improving operation efficiency.

Investigation of Five-Phase Flux-Switching Permanent Magnet Machines for EV and HEV Applications

As a member of stator permanent magnet (PM) brushless machines, flux-switching (FS) PM machine features outstanding advantages, e.g., robust rotor structure, easy temperature management, high torque density, etc. In this paper, the five-phase FSPM machines for electric vehicle (EV) and hybrid electric vehicle (HEV) applications are investigated. Firstly, the working principle of such machine is analyzed by air-gap field modulation theory. Then, the feasible slot/pole combination is discussed, considering flux leakage, back electro-magnetic force (EMF) quality and unbalanced magnetic force (UMF). Besides, in order to further choose the recommendable slot/pole combination, the torque performances are studied and compared by taking the 20-stators-slot FSPM machines as examples, such as rated torque, overload capability, flux weakening capability and fault tolerance capability. Further, in order to optimize the slot/pole combination which suffers from severe UMF, two different techniques for UMF reduction are proposed, including chamfering both in stator and rotor side. Finally, finite element analysis is employed to verify the analytical analyses. Meanwhile, a 20/18 prototyped machine is manufactured and tested. It is found that the experimental results verify the effectiveness of the analytical analyses.

Magnetic Decoupling: Basis to Form New Electrical Machines

Abstract Magnetic decoupling principle when applied to electrical machines states that if two windings are configured for different number of pole pairs, they would not interact with each other magnetically even though they share a common magnetic core. This principle forms the basis for developing special machines where two or more machines can be integrated with the same magnetic circuit. This paper deals with formulating the mathematical analysis that determines the validity of this principle during practical conditions (i.e. non-sinusoidal winding distribution, flux saturation, etc.). Extensive Finite Element Method (FEM) simulation results from the Ansys Maxwell-2D software platform closely obey the conclusions derived from the mathematical analysis. As an example, new brushless and magnetless synchronous machines (SMs) have been developed by using this principle. It is designed by embedding an induction machine (IM) with a SM. Experimental investigations conducted on the laboratory prototype support the mathematical analysis dealt with in this paper.

Relationship between Slot-Pole Combination and Performance of Partitioned-Stator Field-Excitation Brushless Machines by Air-Gap Field Modulation Principle

Relationship between Slot-Pole Combination and Performance of Partitioned-Stator Field-Excitation Brushless Machines by Air-Gap Field Modulation Principle

Performance analysis of sandwich switched flux switching permanent magnet motor using modular rotor

Conventional flux-switching permanent magnet brushless machines (PMFSM) gained a lot of attraction due to their high torque densities, simple and robust rotor structure, and the permanent magnets and coils on the stator. The sandwich PMFSM machine has been proposed to improve the torque density of the machine in which two PM pieces are sandwiched in one stator pole to enhance the PMs usage efficiency. 2D finite element analysis (2DFEA) method is employed to compare the performance of sandwich PMFSM with salient rotor topology with that of sandwich PMFSM with modular rotor, in terms of flux linkage, flux distribution, flux strengthening, induced back EMF, cogging torque and average torque. From the results it is shown that the salient sandwich PMFSM and sandwich PMFSM modular rotor produces 9.28Nm and 6.7Nm, respectively.

Design of 6 slots/10 poles modular rotor sandwich switched flux switching permanent magnet motor

Conventional flux-switching permanent magnet brushless machines (PMFSM) gained a lot of attraction due to their high torque densities, simple and robust rotor structure, and the permanent magnets and coils on the stator. The sandwich PMFSM machine has been proposed to improve the torque density of the machine in which two PM pieces are sandwiched in one stator pole to enhance the PMs usage efficiency. 2D finite element analysis (2DFEA) method is employed to compare the performance of sandwich PMFSM with salient rotor topology with that of sandwich PMFSM with modular rotor, in terms of flux linkage, flux distribution, flux strengthening, induced back EMF, cogging torque and average torque. From the results it is shown that the salient sandwich PMFSM and sandwich PMFSM modular rotor produces 9.28Nm and 6.7Nm, respectively.

Control of Cascaded/Brushless Doubly-Fed Induction Motors With Real-Time Torque Optimization

Brushless doubly-fed induction machines offer a potential alternative to regular doubly-fed induction generators for wind turbines, due to higher reliability and lower maintenance costs. As motors and generators, the brushless machines could also be part of new technological solutions for hybrid-electric propulsion, including aircraft propulsion. A main advantage is that most of the power would be transferred from generators to motors without electronic conversion. The paper proposes a new speed control algorithm that maximizes the available torque within the limits of the control winding currents and ensures anti-windup protection. The maximum torque and the control variables are obtained through simple analytical computations. The derivations of the paper are based on a complex-variable representation that simplifies the mathematical model and the control algorithm. Compact formulas specify the controller parameters as functions of the machine parameters and of the desired closed-loop behavior. The results are tested on a laboratory testbed using a cascaded doubly-fed induction motor and demonstrate fast responses reaching torque limits that are computed in real-time by the algorithm. While control is achieved through the converter interfaced with the control windings, the data shows that most of the active and reactive power is exchanged directly through the power windings. Similar results are obtained in simulations of a larger brushless doubly-fed induction motor.

Design of a Wound Rotor Brushless Doubly-Fed Machine With 1/5 Pole-Pair Combination

The brushless doubly-fed machine (BDFM) can be used in the variable speed constant frequency field. For BDFM, the choice of the pole-pair combination and the design of the rotor are significant. The output factor of the BDFM with 1/5 pole-pair combination is higher than that of the 2/4 pole-pair counterpart. However, the rotor of the BDFM with 1/5 pole-pair combination is hard to design for its wide pole-pair ratio. This paper presents a 1/5 pole-pair combination BDFM used in hydro power with a three-phase symmetrical wound rotor to solve the design challenge. First, the magnetic field modulation theory of the BDFM and the optimal output power in terms of different pole-pair combinations are introduced. Then, the slot-number phase diagram and the ampere-conductor wave method are applied to design windings of a BDFM with 1/5 pole-pair combination. Finally, the finite element (FE) models of the 1/5 and the 2/4 pole-pair combination BDFMs are established for comparison. A prototype of the 1/5 pole-pair combination is manufactured based on the proposed design scheme. Simulated and experimental results verified the feasibility of the design scheme.

Novel Dual Inverter Sub-Harmonic Synchronous Machines

Sub-harmonic synchronous machines are a relatively new bread of brushless wound field synchronous machines considered alternatives to many electric machines in transportation electrification applications. This paper presents two dual inverter sub-harmonic synchronous machines having unique two-layer and three-layer stator winding topologies. The two inverters provide the stator windings with two sets of balanced three-phase currents. These two and three-layer windings are arranged in such a way that they can generate both fundamental and sub-harmonic magnetomotive force. Furthermore, the fundamental MMF component of this machine is four times the sub-harmonic MMF component used for the brushless operation. In contrast, the sub-harmonic magnetomotive force is used for field excitation, which leads to brushless operation. Two 8-pole, 48-slot, 2-inverter, 2-layer and 3-layer sub-harmonic machines are designed to validate the concept through a 2-D finite element analysis of these new topologies, showing a better overall torque profile and performance as compared with the other sub-harmonic and brushless wound field synchronous machines.

High-Efficient Nonlinear Control for Brushless Doubly-Fed Induction Machines

The brushless doubly-fed induction machine (BDFIM) is suitable for applications that need adjustable speed within limited ranges. It is a promising machine if its control strategies, such as the maximum torque per total copper losses (MTPCL) control, are well designed. A BDFIM has two stator windings, a power winding (not controllable) and a control winding (CW) (controllable through a partially rated back-to-back converter). Unlike singly-fed electrical machines, which are fully controllable and the MTPCL can be easily implemented to them, implementing the MTPCL control in a BDFIM is challenging. In this paper, the model-based MTPCL control strategy in the presence of a nonlinear controller in the BDFIM drive is developed. To realize this strategy, we first determine an expression in terms of the angle of the CW's current as a controllable variable. The optimal angle of the CW's current, which guarantees the realization of the MTPCL strategy, is then mathematically obtained using the numerical minimization approach. Next, the proposed passivity-based nonlinear controller regulates both the MTPCL criterion and the electromagnetic torque directly as the output variables. The proposed strategy is validated by a TMS320F2833 microcontroller synchronized with a personal computer for a 3 kW prototype D132s-BDFIM.

Performance Evaluation of Stator/Rotor-PM Flux-Switching Machines and Interior Rotor-PM Machine for Hybrid Electric Vehicles

A three-phase interior permanent magnet (IPM) machine with 18-stator-slots/12-rotor-poles and concentrated armature winding is commercially employed as a 10 kW integrated-starter-generator in a commercial hybrid electric vehicle. For comprehensive and fair evaluation, a pair of flux-switching permanent magnet (FSPM) brushless machines, namely one stator permanent magnet flux-switching (SPM-FS) machine, and one rotor permanent magnet flux-switching (RPM-FS) machine, are designed and compared under the same DC-link voltage and armature current density. Firstly, a SPM-FS machine is designed and compared with an IPM machine under the same torque requirement, and the performance indicates that they exhibit similar torque density; however, the former suffers from magnetic saturation and low utilization of permanent magnets (PMs). Thus, to eliminate significant stator iron saturation and improve the ratio of torque per PM mass, an RPM-machine is designed with the same overall volume of the IPM machine, where the PMs are moved from stator to rotor and a multi-objective optimization algorithm is applied in the machine optimization. Then, the electromagnetic performance of the three machines, considering end-effect, is compared, including air-gap flux density, torque ripple, overload capacity and flux-weakening ability. The predicted results indicate that the RPM-FS machine exhibits the best performance as a promising candidate for hybrid electric vehicles. Experimental results of both the IPM and SPM-FS machines are provided for validation.

Investigation of Bessel Functions in Analytical Modeling of Rotor Eddy Current Losses in PM Machine Rotor With Copper Shield

In high-speed surface-mounted permanent magnet (SPM) brushless machines, time- and space-harmonic excitations can induce significant eddy currents flowing in the rotor conductive parts. An effective measure to suppress the eddy currents is to employ a copper shield between the magnets and the retaining sleeve. In this article, a Fourier-based analytical model is proposed to evaluate the rotor eddy current losses. The model is set up in the cylindrical coordinate system and is able to compute the eddy current fields and losses in all rotor domains, that is, the sleeve, shield, magnets, and shaft. Although it is generally believed that both ordinary Bessel functions (OBFs) and modified Bessel functions (MBFs) are workable for solving the magnetic vector potential, it is argued in this article that only the MBF-based models are numerically stable when the high-conductivity domain (e.g., the copper shield) exists, while the OBF-based models may result in irrational results. Both the OBF- and MBF-based analytical models for a prototype motor are established and comparatively studied, with verification of the finite-element (FE) method. Moreover, the cause of losing analysis accuracy in the OBF-based models is revealed.

Model-Based Field Winding Interturn Fault Detection Method for Brushless Synchronous Machines

The lack of available measurements makes the detection of electrical faults in the rotating elements of brushless synchronous machines particularly challenging. This paper presents a novel and fast detection method regarding interturn faults at the field winding of the main machine, which is characterized because it is non-intrusive and because its industrial application is straightforward as it does not require any additional equipment. The method is built upon the comparison between the theoretical and the measured exciter field currents. The theoretical exciter field current is computed from the main machine output voltage and current magnitudes for any monitored operating point by means of a theoretical healthy brushless machine model that links the main machine with the exciter. The applicability of the method has been verified for interturn faults at different fault severity levels, both through computer simulations and experimental tests, delivering promising results.

Concept and Implementation of Embedded Magnetic Encoder in Flux-Switching Permanent-Magnet Machines

Rotor angle is essential in permanent-magnet (PM) brushless machines. Recently, an embedded magnetic encoder (EME) scheme, consisted of linear Hall sensors installing inside of the PM machines, has been proposed to sense the flux density and consequently provides rotor position. Compared with traditional optical encoder and resolver, the linear Hall sensor prevails over in both space and cost. The aforementioned scheme is employed successfully in rotor-PM machines, where a PM-excited field rotates at the synchronous speed. In this article, the feasibility of EME in stator-PM flux-switching machine is validated, where PMs are located in stator, resulting in a stationary PM field. The stator slots are selected as installation position of linear Hall sensors to avoid changing the existing structure of machines. The variation of linear Hall signal is due to the changing reluctance of rotor rather than rotating PMs. Then, a decoding algorithm is designed based on an add-up operation, a complex coefficient filter, and a synchronous reference frame phase-locked loop. Finally, experiments on a prototype machine are conducted to validate the effectiveness of EME scheme under both speed-varying and load-varying conditions.

Overview of the Optimal Design of the Electrically Excited Doubly Salient Variable Reluctance Machine

The Electrically Excited Doubly Salient Variable Reluctance Machine (EEDSVRM) is a new type of brushless machine designed according to the principle of air gap reluctance change. There is neither permanent magnet steel nor excitation winding on the rotor. The rotor is made of silicon steel sheets, thus the structure of the variable reluctance machine is very simple. There are many optimization methods for this type of machine optimal design, such as novel machine topology optimization, finite element simulation-based optimization, mathematical analysis-based optimization, intelligent algorithm-based optimization, and multiple fusion-based optimization. Firstly, this article introduces the basic structure and working principle of the EEDSVRM and analyzes both its common regularity and individual difference. Then, the different optimization design methods of EEDSVRM are reviewed, the advantages and disadvantages of the different optimization methods are summarized, and the research interests of the optimization design of variable reluctance machines in the future are prospected.

Spiral vector modeling of brushless doubly-fed induction machines with short-circuited rotor windings

A unified spiral vector model is presented that can be used to assist the finite element method-based performance analysis of brushless doubly-fed induction machines with various short-circuited rotor windings. Specifically, magnet-free brushless doubly-fed induction machines working in doubly-fed or singly-fed synchronous mode are investigated. A dynamic model in spiral vector notation is developed, based on which the torque-angle and power-angle characteristics are derived. It is shown that the investigated brushless machines are equivalent to a traditional non-salient-pole synchronous machine with brushes. By introducing a conversion factor, they can also be analyzed with methods similar to the conventional phasor theory. A comparison is made between the brushless doubly-fed induction machine and non-salient-pole wound-field synchronous machine with brushes, revealing that the performance of the brushless machine degrades faster when the laminated core is saturated. A scaled-down prototype is tested to validate the effectiveness of the theoretical analysis.

Novel Single Inverter-Controlled Brushless Wound Field Synchronous Machine Topology

This paper proposes a novel brushless excitation topology for a three-phase synchronous machine based on a customary current-controlled voltage source inverter (VSI). The inverter employs a simple hysteresis-controller-based current control scheme that enables it to inject a three-phase armature current to the stator winding which contains a dc offset. This dc offset generates an additional air gap magneto-motive force (MMF). On the rotor side, an additional harmonic winding is mounted to harness the harmonic power from the air gap flux. Since a third harmonic flux is generated in this type of topology, the machine structure is also modified to accommodate the third harmonic rotor winding to have a voltage induced as the rotor rotates at synchronous speed. Specifically, four-pole armature and field winding patterns are used, whereas the harmonic winding is configured for a twelve-pole pattern. A diode rectifier is also mounted on the rotor between the harmonic and field windings. Therefore, the generated voltage on the harmonic winding feeds the current to the field winding for excitation. A 2D-finite element analysis (FEA) in JMAG-Designer was carried out for performance evaluation and verification of the topology. The simulation results are consistent with the proposed theory. The topology could reduce the cost and stator winding volume compared to a conventional brushless machine, with good potential for various applications.

Advances in Fault Diagnostics and Post‐Fault Operation of Electrical Drives

Advances in Fault Diagnostics and Post‐Fault Operation of Electrical Drives