Equivalent Permanent Magnet Research Articles

Equivalent Transformation Between Axial- and Radial-Flux Permanent-Magnet Machines

In this paper, an equivalent transformation approach for permanent-magnet (PM) electrical machines using coordinate transformation theory is presented. With the proposed method, an axial-flux PM (AFPM) machine can be transformed to an equivalent radial-flux PM (RFPM) machine or vice versa. The main purpose of proposing such a transformation method is to simplify the design of AFPM for specific applications. Besides, according to the working space requirement, the shape of PM machines can be changed while maintaining magnetic performances. The proposed transformation theory is based on the basic magnetic theory and the theoretical derivation is presented in detail. The resulted transformation equations for RFPM and AFPM machines with surface-mounted PMs are friendly to engineers. Moreover, an AFPM machine is used to validate the proposed theory, both FEM and experimental results have good agreement with the results of the proposed method. With the equivalent transformation theory, engineers could design, simulate and evaluate the AFPM machines with an exist well-developed machines.

Evaluation of Operating Range of a Machine Emulator for a Back-to-Back Power-Hardware-in-the-Loop Test Bench

Inverter testing using laboratory test benches with rotating machines can be bulky, complex, and maintenance intensive. One solution is to use machine emulator for laboratory testing of inverters. The emulator is controlled in such a way that currents and voltages at the terminals resemble a machine connected to a mechanical load. A machine emulator for a back-to-back power-hardware-in-the-loop (PHIL) test bench is proposed in this article. The PHIL test bench consists of two identical voltage source converters (VSCs) with three single-phase inductors as coupling network. The two VSCs are connected to the same direct current supply. One VSC acts as inverter under test (IUT), while the other is part of machine emulator. Aim of this article is to analyze the influence of coupling inductance on operating range of the emulator. An analytical method to dimension the coupling inductance is introduced and verified in experiments. The operating range of the emulator is also evaluated. The performance of the IUT when tested with an equivalent permanent magnet synchronous motor in simulations and that of a prototyped 60-kW rated machine emulator are compared. Sensitivity of emulator control on parameter estimation is discussed. The experimental results show good agreement with simulations in both steady-state and dynamic conditions.

Prospect of PM Vernier Machine for Wind Power Application

This paper investigates the prospect of permanent magnet vernier machine (PMVM) technology for wind power applications. Two types of PMVMs are defined based on the winding arrangements and resultant gear ratio ranges. A comprehensive design study of the selected PMVM topologies is conducted at 1 and 3 MW power levels. The optimized candidate designs of the PMVMs are then evaluated and also compared against the equivalent permanent magnet synchronous machine (PMSM) in terms of performance, costs, size and mass. While the existing research publications mainly focused on the PMVM designs of (Gr=5), this study reveals that the pole/slot combinations of PMVMs with (Gr≤5) are more appealing as there is a good trade-off between a reasonable power factor and high power density in these designs. It shows, in this paper, that the PMVM is a promising alternative to common PMSM technology for utility-scale wind-turbine drive-train applications.

A Comparative Investigation of Presaturated Core Fault Current Limiters Biased by DC Current and Permanent Magnet

In this paper, the dc biasing magnetomotive force (mmf) in presaturated core fault current limiter (PCFCL) is replaced with permanent magnet (PM) to overcome the well-known drawbacks of the dc biased PCFCLs. These drawbacks are excessively induced voltage across the terminals of the dc coil during fault condition and high total power losses during the steady-state condition. The novel contributions of this paper are the introduction of the selection criteria of PM material and its representation by actual nonlinear $B$ – $H$ hysteresis loop of Jiles-Atherton method, and the use of PM alone as an equivalent to the dc biasing coils for three-phase fault current limiter (FCL), contrary to work reported in earlier papers. Single- and three-phase PCFCLs are modified by replacement of dc saturation coil by the equivalent PM through time-domain finite element (FE) simulation of COMSOL Multiphysics package. Experimental verification shows that the implementation of accurate nonlinear representation of PM demagnetization curve with FE simulation gives a realistic performance of the PM biased PCFCL, especially in the fault condition. The performance of PCFCL can be evaluated through the voltage drop and total power losses during the steady-state condition and the fault current clipping ratio during fault condition of the grid. Furthermore, a comparative investigation of dynamic behavior is considered between dc and PM biased PCFCLs. It is found that the PM biased PCFCL has enriched capability of limiting any type of fault current with leading advantages of reduced voltage drop and power losses significantly together with risk elimination of the high induced voltage across dc coil terminals. Moreover, the governing parameters of PM biased PCFCLs are subjected to performance analysis to study their inherent effects.

Design and Optimization of a Brushless Wound-Rotor Vernier Machine

In this paper, a permanent magnet (PM)-less, brushless, wound-rotor vernier machine (BL-WRVM) is proposed for variable speed applications such as electric vehicles and washing machines. The wound rotor is excited through an already existing brushless topology, which requires a dual inverter configuration to generate an additional subharmonic component in the stator magnetomotive force (MMF). Different from permanent magnet vernier machines (PMVMs), the proposed BL-WRVM provides easy regulation of the rotor flux for variable speed operation. A 24-slot, 4-pole stator, and 44-pole outer rotor were designed, and 2D finite element analysis (FEA) was carried out to determine the performance of the proposed machine. To improve the performance of the proposed machine, optimization of the rotor and stator winding turns was done. The optimized model was further analyzed for wide-speed operation, and its performance was then compared with that of an equivalent permanent magnet vernier machine (PMVM). The proposed machine has the advantage of low cost due to its PM-less structure and is suitable for variable speed applications.

Magnet shape optimization of five‐phase surface‐mounted permanent magnet machine to improve torque performance based on equivalent permanent magnet method

This paper studies the magnet shape optimization of a five‐phase surface‐mounted permanent magnet (PM) machine to improve its torque performance. First, a sinusoidal PM with third and fifth harmonics (sine + third + fifth PM) is presented to enhance the torque. An equivalent PM method is then proposed to avoid the complicated interface conditions between PM and the air gap, making the derivation of torques with magnet shapes using 2‐D analytical models possible. Besides, the influence of PM edge thickness on torque improvement is considered. Moreover, under the condition that the copper losses of machines with different magnet shapes are kept unchanged, optimal harmonics of sinusoidal PM with third harmonic (sine + third PM) and sine + third + fifth PM are analytically derived. Finite element (FE) analysis is performed to validate the equivalent PM method and analytical results. Finally, machines with sine + third PM, sine + third + fifth PM and conventional (without shaping) PM are comparatively studied using nonlinear FE analysis and the experimental results of machine with sine + third + fifth PM are presented, verifying the effectiveness of the analytical optimization of magnet shape. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Dipole Models for Forward/Inverse Torque Computation of a Spherical Motor

This paper presents an alternative method to model a multilayer voice coil or an air-cored electromagnet as an equivalent permanent magnet (ePM) such that its magnetic field can be characterized by a distributed set of multipoles model. We validate the ePM model by comparing the computed results against exact solutions and illustrate its effectiveness in computing the magnetic force using the dipole force equation. Unlike methods that are based on the Lorentz force equation or the Maxwell stress tensor, which require computing the volume or surface integrals to derive the forces, the closed-form dipole force method that replaces integrations with summations dramatically reduces computation time. We compare the dipole force computation against results of the Lorentz force equation and the Maxwell stress tensor method, and validate the comparisons against published experimental data. To demonstrate the effectiveness of the method, we compute the inverse torque model of a 3-DOF orientation stage operated on the principle of a spherical motor that has more controlling inputs than its mechanical DOF.

Five-Phase Permanent-Magnet Motor Drives

A five-phase brushless permanent-magnet (PM) motor is introduced. The proposed motor has concentrated windings such that the produced back electromotive force is almost trapezoidal. The motor is supplied with the combined sinusoidal plus third harmonic of currents. This motor, while generating the same average torque as an equivalent PM brushless dc motor (BLDC), overcomes its disadvantages. The motor equations are obtained in the d/sub 1/q/sub 1/d/sub 3/q/sub 3/0 rotating reference frame. Therefore, the so-called vector control is easily applicable to this kind of motors and the motor has the same controllability as a PM synchronous motor (PMSM). For presenting the superior performance of the proposed five-phase motor, its three and five-phase PMSM and BLDC counterparts are also analyzed. Finite element method is used for studying the flux density and calculating the developed static torque. Also, the developed torque is obtained using the mathematical model in the d-q reference frame. The average torque and the torque ripple for all cases are calculated and compared. Experimental results are in good agreement with the simulation results.

2-D FE analysis of hybrid stepping motor using virtual magnetic barrier

Though full three-dimensional (3-D) analysis is the proper method to analyze the hybrid stepping motor (HSM), it has weaknesses in the computation time and complexity. This paper introduces a two-dimensional (2-D) finite-element analysis (FEA) using a virtual magnetic barrier for the axial cross section to save computation time. For the purpose of 2-D FEA, the virtual magnetic barrier and equivalent permanent magnet model of HSM are proposed. This result is compared with that of experimental and 3-D analysis, considered as reference result.

A Study of the Iron-Core Solenoid Analysis for 3 D.O.F. Motor Control with Experimental Method

In this paper, the experimental modeling of the force between permanent magnet and iron-core solenoid is suggested for more accurate control of 3 D.O.F. motor using the electromagnetic force. In the case of iron-core solenoid, the general equation of solenoid cant be used simply because of its nonlinearity. Therefore, the magnetic flux density is estimated through the concept of equivalent permanent magnet. The force distribution between permanent magnet and iron-core solenoid is more dependent on the magnetization of iron core caused by the permanent magnet than any other parameters. Therefore, the equation of the force estimation between these magnetic systems can be modeled by the experimental function of the magnetization of iron core. Especially, if the distance between iron-core solenoid and permanent magnet is far enough, the force equation through experiment can be expressed from only the current of coil and the distance between iron-core solenoid and permanent magnet. It means that Coulombs law can be used for magnetic systems and it is validated through the experiment. Therefore, force calibration is performed by the concept of Coulombs law.