Permanent Magnet Excitation Research Articles

THE STUDY OF TRANSIENT PROCESSES OF THE FREQUENCY-REGULATED SYNCHRONOUS ELECTRIC DRIVE

In order to improve the power indices and to simplify the system of frequency speed control the scope of application of synchronous variable-frequency electric drives with independent frequency setting is being expanded. The synchronous motors with electromagnetic excitation and permanent magnet excitation in various industrial settings, including load-lifting machines and mechanisms, are used. As compared with the asynchronous frequency-regulated electric drives the synchronous ones have lower power loss, harder mechanical characteristic without feedback for speed and the simplest law of frequency control, i. e., a proportional one that, however, provides the maximum electromagnetic torque of the motor constant at all frequencies, due to the constant magnetic flux. The article concerns an analytical study of transient processes of synchronous electric drive with consideration of the influence of damping winding when the motor supply voltage frequency varies linearly during the transient time. As a result of the analysis the formulas have been obtained that make it possible to calculate the angular velocity of the rotor and the electromagnetic torque of the motor at start-up, braking, and impingement and discharge of loads, evaluating the quality of the transition process and tracking the maximum value of the electromagnetic torque, that must not exceed the permissible value. Validation of the developed technique of calculation of transient processes of synchronous electric drive has been obtained by comparison of calculations according to the formulas with the simulation results of the electric drive on the basis of the synchronous motor of the SD3 13-34-6 type (power of 500 kW and voltage of 6 kV).

Comparative Study of Partitioned Stator Machines With Different PM Excitation Stators

The partitioned stator (PS) machine adopts two stators to allocate windings and permanent magnets (PMs) separately, increasing the space for PMs as well as armature coils to boost the electromagnetic torque and improving the thermal condition of PMs. In this paper, the PS switched-flux PM (PS-SFPM) machine and the PS flux reversal PM (PS-FRPM) machine are proved to inherently share the same operating principle and similar machine topology but with interior PM (IPM) and surface-mounted PM stators, respectively. Furthermore, four globally optimized PS machines with different inner stator topologies are compared in terms of back EMF, cogging torque, electromagnetic torque, torque per PM volume, and flux-weakening capability. The results reveal that the spoke-shaped IPM (IPM-spoke) inner stator exhibits the highest back EMF and hence the highest average torque, while the I-shaped IPM (IPM-I) stator has the best flux-weakening capability, and the V-shaped IPM (IPM-V) produces the highest torque per PM volume. Furthermore, four machines are redesigned with the same PM usage volume, and the results show that the PS-SFPM machine still exhibits the highest back EMF as well as torque although with sacrificed advantages. The finite-element analyses and experiments are used to confirm the predictions.

Performance Comparison of 10-MW Wind Turbine Generators With HTS, Copper, and PM Excitation

A conceptual structure for large-scale wind turbine generators (WTGs) with high-temperature superconductor (HTS) excitation has been proposed. A novel electrical design method for this concept has been developed that can be also applied to conventional generators with copper coil and permanent magnet (PM) excitation with some modifications. Using the modified design program, electrical designs of 10-MW synchronous WTGs with HTS coil, copper coil, and PM excitation are conducted, and the influence of machine parameters (such as magnetic flux density in rotor iron cores, pole pitch, and stator outer diameter) on the basic generator performance is clarified. Based on these results, the optimized designs of three kinds of WTGs rotating at the low speeds of 8 min <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 10 min <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> are performed, and their basic performance is studied.

Hybrid-Excited Doubly Salient Synchronous Machine With Permanent Magnets Between Adjacent Salient Stator Poles

A novel stator hybrid-excited, parallel flux path, synchronous machine of doubly salient topology is proposed. It has the novel features of: 1) hybrid dc field and permanent magnet (PM) excitation in the stator; 2) magnets placed in the slots between adjacent salient stator poles; and 3) the magnetic poles of PMs arranged, such that the flux premagnetizes the stator, but it is in a direction to oppose the dc excitation flux. The electromagnetic characteristics of the machine are analyzed on open-circuit and load. Since the new machine topology is developed from the variable-flux machine (VFM), a comparison of their electromagnetic torque and machine losses is conducted. The average electromagnetic torque of the hybrid-excited machine can be increased by 18% for fixed copper loss in comparison with the VFM due to the reduction of magnetic saturation in the stator. It is also shown that at high temperatures some risk of PM demagnetization exists when excited with dc and armature currents due to fringing flux that exists between the stator and the rotor poles. However, this affects only a very small area of the PMs. The performance of the hybrid-excited machine is predicted by a 2-D finite-element analysis and experimentally validated.

Optimization of Single Phase E-Core Hybrid Excitation Flux Switching Machine

Research and development on hybrid excitation flux switching machines (HEFSM) for various applications have been carried out in the last years. The designed HEFSM consist of permanent magnet (PM) and DC field excitation coil (DC-FEC) which is located on the stator core as their main flux sources, while a single piece rotor gives the advantages of robust rotor structure. Since most of the designed HEFSMs utilize three-phase windings, more complicated design and control system are required to run the motor. Thus, a new design of single-phase E-Core HEFSM with several advantages of much simpler converter size and smaller battery package due to small voltage capacity when compared with conventional three-phase system is proposed. Consequently, the size of overall configuration systems will also be reduced resulting in reducing total weight and cost. In this paper, initial performances of 4S-4P, 4S-6P, 4S-8P and 4S-10P E-Core HEFSM topologies are analysed. Since 4S-10P design gives highest torque and power performances, deterministic design optimization approach is conducted to enhance much higher and optimum performances. As conclusion, the optimized E-core HEFSM with 4S-10P topology has achieved maximum torque and power of 208.857Nm and 47.31 kW, respectively.

Rotating permanent magnet excitation for blood flow measurement.

A compact, portable and improved blood flow measurement system for an extracorporeal circuit having a rotating permanent magnetic excitation scheme is described in this paper. The system consists of a set of permanent magnets rotating near blood or any conductive fluid to create high-intensity alternating magnetic field in it and inducing a sinusoidal varying voltage across the column of fluid. The induced voltage signal is acquired, conditioned and processed to determine its flow rate. Performance analysis shows that a sensitivity of more than 250 mV/lpm can be obtained, which is more than five times higher than conventional flow measurement systems. Choice of rotating permanent magnet instead of an electromagnetic core generates alternate magnetic field of smooth sinusoidal nature which in turn reduces switching and interference noises. These results in reduction in complex electronic circuitry required for processing the signal to a great extent and enable the flow measuring device to be much less costlier, portable and light weight. The signal remains steady even with changes in environmental conditions and has an accuracy of greater than 95%. This paper also describes the construction details of the prototype, the factors affecting sensitivity and detailed performance analysis at various operating conditions.

Design of the Halbach Hybrid-Excitation Compulsator

Pulsed alternators integrate kinetic energy storage, electromechanical energy conversion, and pulse shaping into one unit, and it is the research focused on the field of pulsed power sources. The electrical excitation and the permanent magnet excitation are contained in one hybrid-excitation pulsed generator together in which the advantages of two different excitation types are integrated. The brush slip ring mechanism with low reliability and high maintenance costs can be cancelled. In addition, the electromagnetic field can be adjusted quickly by external electrical excitation source and correspondingly the performance can be quickly adjusted. An all-iron-core hybrid-excitation compulsator prototype was designed, fabricated, and optimized. The hybrid excitation concept was validated in the research of compulsators. Although compulsator research is mainly focused on the all-air-core electrical excitation topology, there exist some bottleneck technologies that restrict the application of compulsators in actual fields. The hybrid-excitation compulsator can decrease the cost, increase the reliability, and widen the application scope of compulsators, especially in the middle-low power range. The Halbach array is a permanent magnet arrangement structure, which is a combination structure of different direction arrays. The Halbach array offers a number of attractive features in comparison with the normal array. The air-gap magnetic flux can be increased and the rotor yoke magnetic flux is decreased. Based on this, the Halbach array can be designed on the composite rotor core. A part-air-core compulsator that includes an air-core rotor and an iron-core stator was designed. For analyzing the electromagnetic design results, the 3-D model was built and finite element analysis method was used. The performance simulation results of the Halbach hybrid-excitation compulsator were presented.

Novel Electrical Machines Having Separate PM Excitation Stator

In this paper, novel electrical machines having a separate permanent magnet (PM) excitation stator are proposed based on a partitioned stator (PS) flux reversal (FR) PM (FRPM) machine. Different from the conventional FRPM machines with a single stator, the PS-FRPM machines have two stators with PMs surface mounted in one stator and the armature windings located in another stator. This paper investigates the electromagnetic performance of PS-FRPM machines with 12/10, 12/11, 12/13, and 12/14 stator/rotor-pole, together with the influence of leading design parameters. The torque characteristics of PS-FRPM machines are quantitatively compared with the conventional FRPM machines based on their globally optimized designs. It shows that the PS-FRPM machines can generally produce higher torque when the PMs are thicker and exhibit >56% higher torque density than that of the conventional FRPM machines. Even compared under the same PM volume, the proposed PS-FRPM machines can have larger torque due to better utilization of the inner space. The investigation is validated by both finite-element and experimental results.

LINEAR ELECTRIC MOTOR WITH PM EXCITATION FOR A FREIGHT MAGNETOLEVITATION PLATFORM

The paper presents the design of a traction electric drive based on a linear synchronous motor with permanent magnets (PM) excitation. The electric drive is a part of the demonstration mock-up and is intended for the linear movement of a freight platform that is suspended in the air by means of the magnetic field. The drive performs a smooth movement of the platform with a required speed, platform stop, and changing of the direction of the movement. The motor inductor with permanent magnets is fixed on the platform whereas the motor stator is placed on the ground being supplied with power through а semiconductor converter. The stator consists of the independent modules that are sequentially connected to the converter as the inductor moves. Commutation of the modules and commutation the windings inside the active module is performed by the signals from some optical sensors attached to the inductor. Modular design of the motor stator and sectional feeding of its windings from the same converter allow to create a levitation mock-up with an arbitrary length of the motion path. At that all the technical solutions adopted in the drive design are directed to reducing of the drive production cost.

Optimization of the synchronous motor with hybrid permanent magnet excitation system

Purpose – The purpose of this paper is to elaborate an algorithm and the software for the rotor structure optimization of the permanent magnet synchronous motor (PMSM) with a magnet composed of two materials made with the use of different technologies: sintered Neodymium magnets and powder dielectromagnets. To execute of optimization of selected motor structure using the non-deterministic procedure. Design/methodology/approach – The mathematical model of the devices includes: the equation of the electromagnetic field, the electric circuit equations and equation of mechanical motion. The numerical implementation is based on finite element method and step-by-step algorithm. The genetic algorithm has been applied in the optimization procedures. The computer code has been developed. Findings – The elaborated computer software has been applied for the optimization and design of PMSMs. The elaborated algorithm has been tested and a good convergence has been attained. The parameters of two optimal structures of PMSM motors have been compared. Originality/value – The presented approach and computer software can be successfully applied to the design and optimization of different structure of PMSM with different type of rotors.

Magnetic equivalent circuit model for unipolar hybrid excitation synchronous machine

AbstractLately, there has been increased interest in hybrid excitation electrical machines. Hybrid excitation is a construction that combines permanent magnet excitation with wound field excitation. Within the general classification, these machines can be classified as modified synchronous machines or inductor machines. These machines may be applied as motors and generators. The complexity of electromagnetic phenomena which occur as a result of coupling of magnetic fluxes of separate excitation systems with perpendicular magnetic axis is a motivation to formulate various mathematical models of these machines. The presented paper discusses the construction of a unipolar hybrid excitation synchronous machine. The magnetic equivalent circuit model including nonlinear magnetization curves is presented. Based on this model, it is possible to determine the multi-parameter relationships between the induced voltage and magnetomotive force in the excitation winding. Particular attention has been paid to the analysis of the impact of additional stator and rotor yokes on above relationship. Induced voltage determines the remaining operating parameters of the machine, both in the motor and generator mode of operation. The analysis of chosen correlations results in an identification of the effective control range of electromotive force of the machine.

Study on the model of automotive electric starter system on the basis of integrated starter-generator

The paper deals with simulation of an electric starter system of a vehicle on the basis of an integrated starter-generator. As a basic electric machine integrated starter-generator is taken a synchronous machine with permanent magnet excitation. The authors examined the modeling of the integrated starter-generator, where the model is in start-up mode is represented by a single-speed automatic control system consisting of a PI controller to compensate the long time constant of a controlled object - an internal combustion engine.

Effect of Different Winding Switching Methods on Regulating and Energetic Characteristics of Synchronous Motor with Permanent Magnet Excitation

The article contains evaluation of effect of different winding switching methods for synchronous motor with permanent magnet excitation (SMPM) on energetic efficiency, possibility of enlarging the ranges of working speeds and torques, adaptation of regulating characteristics with the aim of using it in particular electric drive. The evaluation is performed at similar values of relative speed and relative inductance. The conditions, which make sensible the usage of 120-degree or 180-degree switching, meanwhile all considered SMPM characteristics are not worse than those under vector control, are defined. It is proved, that there is a possibility to minimize engine's energy consumption by regulating switching angle, as well as change it's mechanical characteristics. In particular, it is possible to get mechanical SMPM characteristic, typical for direct-current motor with series excitation, suitable for usage in electric traction drive.

Development of thrust force 6 kN class transverse flux linear motor with synchronous control for direct drive applications

This study investigates the experimental validation of transverse flux linear motors (TFLMs) with permanent magnet excitation and the dynamic simulation of the developed TFLM created using the optimal design. Our research challenge is to use the developed direct drive TFLM to substitute the rack and pinion in a rotary motor because the rack and pinion lacks speed and thrust. The electromagnetic field characteristics are calculated using 3D finite element method analyses, and the dynamic characteristics are simulated using mechanical balance equations. After calculating the integral parameters, the dynamic behavior of the machine is simulated. The Matlab/Simulink model for solving motion equations is used. The peak currents obtained from simulations and experiments are very closely matched within 1%, which is the estimation error. The structural stability is evaluated using structural analyses that consider the load and moment of a robot. In order to reduce the structure-borne noise radiated from the main driving frame, damping materials are applied and the sound pressure level decreases by approximately 8.5 dB(A). Finally, the repetitive position accuracy is considered and measured using an API laser tracker T3. The measured repetitive position accuracy is within 0.1 mm at a speed of 3 m/s.

Correction of Rotor Rotation Irregularity of Permanent Magnet Synchronous Motor in a Controlled Synchronous Mode

While the permanent magnet synchronous motor (PMSM) operation in the synchronous mode rotor speed average value coincides with current frequency in the windings by definition. However instantaneous value of rotation speed can differ from the average one significantly in the process of oscillations occurring in the PMSM rotor and stator electromechanical system. This article describes a refined mathematical model of permanent magnet synchronous motor (PMSM) operating in the synchronous rotation mode allowing to explore rotor speed oscillations arising in the synchronous mode. On the basis of the mathematical model the article provides a theoretical foundation and the example of specific implementation of one of the oscillation damping ways of the PMSM rotor with permanent-magnet excitation in the synchronous mode by introducing a current feedback to the impact on the stator phase voltage. The transfer function of the compensating device, affecting the voltage phase on the motor windings and providing a significant reduction of PMSM rotor rotation irregularity is synthesized on the basis of matrix transfer function of interrelationship between output variables and input signals.

MEC-Based Sizing of a Hybrid-Excited Claw Pole Alternator

The paper is aimed at a magnetic equivalent circuit (MEC)-based sizing of a novel hybrid-excited claw pole alternator. It consists in a claw pole concept with a NdFeB permanent magnet (PM) excitation in the rotor and a dc one in the stator, with the homopolar flux eradicated owing to a magnetic barrier inserted between the stator yoke and lamination. The proposed MEC considers both linear and saturated magnetic circuit, with a focus on the modeling of the leakage fluxes. The developed model is applied for the prediction of the no-load characteristic which is validated by 3-D finite-element analysis (FEA). Then, a dual FEA-experimental validation is carried out considering the case of a dc excitation. Moreover, the proposed MEC makes the investigation of the influent sizing parameters on the machine back-electromotive force (EMF) production capability easy. This latter is enhanced owing to the integration of two ring ferrite PMs linked to the stator, along with a reduction of the volume of the NdFeB PM in the rotor. It has been found that the gained improvement is better than the benefit yielded by as many pole number ferrite PMs inserted between the claws.

Optimization of Electrically Controlled Permanent Magnet Synchronous Machine to Improve Flux Control Range

This paper presents the design, analysis, control, optimization and experimental evaluation of an Electrically Controlled Permanent Magnet Excited Synchronous Machine (ECPMSM) possessing field-control capability. In order to increase flux control range of the machine a three-dimensional finite element analysis (3-D FEA) and the GOT-It software optimization tool are used. The experimental results of no-load back electromotive force (back-EMF) waveform of the prototype machine and a comparison between the analysis and test results are also presented. DOI: http://dx.doi.org/10.5755/j01.eee.20.10.5934

Bacterial Foraging Based Optimal Design of Transverse Flux Linear Motor for Thrust Force Improvement

—This article presents a novel optimal design for a permanent magnet excitation transverse flux linear motor with an inner mover using bacterial foraging optimization. The target is maximizing the motor thrust force, which is the most important quantity in linear electric drives. The stator pole length, air-gap length, winding window width, and stator pole width define the search space for the optimization problem. The response surface methodology is used to build the mathematical model of the motor thrust force in terms of the design variables. It can create an objective function easily, and great computational time is saved. Finite-element computations are used for numerical experiments on the geometrical design variables to determine the coefficients of a second-order analytical model for the response surface methodology. The bacterial foraging optimization technique is used as a searching tool under the constraints of design variables for design optimization of the transverse flux linear motor to improve the motor thrust force. The effectiveness of the proposed bacterial foraging optimization model is then compared with that of both genetic algorithm and particle swarm optimization models. With this proposed bacterial foraging optimization technique, the thrust force of the initially designed transverse flux linear motor can be increased.

FEA-Based Design Study of 12-Slot 14-Pole Outer-Rotor Dual Excitation Flux Switching Machine for Direct Drive Electric Vehicle Applications

This paper presents an investigation into feasibilities design of 12-Slot 14-Pole outer-rotor dual excitation flux switching machine (ORDEFSM) for direct drive electric vehicle (EV) applications. The stator of the proposed machine consists of iron core made of electromagnetic steels, armature coils, permanent magnet (PM) and field excitation coils (FECs). The FECs in this proposed machine is used as a secondary field mmf source to support the main flux source from PM. Therefore, the proposed machine has extra advantage of variable flux control capability as compared with the conventional flux switching machines (FSMs). The rotor is composed of only stack of iron and hence, it is robust and suitable for high speed operation. The design target for the maximum torque and power density, and the maximum speed are more than 333 Nm, 3.5 kW/kg, and 20,000 r/min, respectively. The results obtained from two-dimensional (2-D) FEA study show that the initial design of the proposed machine has achieved the maximum torque, power density and maximum speed of 244.76 Nm, 3.47 kW/kg, and 20,000 r/min, respectively. Thus, it is expected that the proposed machine potentially to achieve the target performances by implementing optimization process using deterministic optimization method.

Modular Stator High Temperature Superconducting Flux-Switching Machines

Flux-switching permanent magnet (FSPM) machines have advantages of robust rotor, strong permanent magnet (PM) dissipation ability, etc, but its flux-weakening capability is poor for its constant PM flux linkage. High temperature superconducting (HTS) excitation windings can produce higher flux density than PM excitation and modify the airgap flux density easily. But if the HTS coils are placed adjacent to the armature winding in the same slot, the heat produced by the armature winding is difficult to cool down. In this paper, a modular stator HTS flux-switching (HTS-FS) machine is first proposed, and the operation principle is described in details. Second, mathematical equations are proposed and detailed electromagnetic design has been done. Then, the optimization of width of flux barrier, rotor pole arc and split ratio have been made to get higher back-EMF, higher output torque capability, and lower torque ripple. Moreover, the comparisons of key performance indexes between HTS-FS machine and conventional FSPM machines have been made. The results show that the HTS-FS machine can produce higher back-EMF than FSPM machine, and at small armature current, it can produce higher torque with little electromagnetic saturation.