Maximum Electromagnetic Torque Research Articles

Optimal Design of an Axial-Flux Switched Reluctance Motor With Grain-Oriented Electrical Steel

This paper employs grain-oriented electrical steel (GOES) in an axial-flux switched reluctance motor (AFSRM) to improve its torque characteristic, taking advantages of the material's excellent magnetic properties in the rolling direction. Based on the study on the parameter and switching characteristics of an AFSRM, GOES can be divided into pieces and arranged in the rotor and stator teeth so that the magnetic flux mainly travels along the rolling direction of the material. AFSRMs with different lamination shapes and deviation angles between the magnetic flux and rolling direction of the GOES have been studied to further improve the output performance; the maximum electromagnetic torque of the proposed design shows a 20.5% increase in comparison with that of the conventional nonoriented electrical steel motors under identical conditions. The rotor retaining ring is composed of epoxy resin lamination to constrain the rotor teeth modules. Thermal and stress analyses under fault conditions are analyzed to verify the reliability of the retaining ring. Furthermore, an AFSRM prototype is built and experiments are conducted to validate the calculated data.

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).

Circuits of a pulse-vector controlling alternate current motor drive

A system of classification for methods for pulse-vector controlling ac drives is presented. The resource and energy efficiency are considered in electric drives using pulse-vector control systems with wound rotor induction and synchronous motors. Various examples of pulse-vector control circuits are discussed. The control principles for each circuit are worked out, and instances of their application are given. The choice of the element basis of these circuits is grounded, and the advantages and disadvantages of each circuit are considered. The basic pulse-vector control circuits are compared in terms of the following parameters: the values of the maximum electromagnetic torque for the nominal motor torque and the torque pulses for the nominal motor torque. It is shown that application of pulse-vector control improves the energy- and cost-effectiveness of the electric drive, while using different circuits allows one to eliminate some of its disadvantages.

Comparative analysis of the SRM as an alternative to the PM motor for automotive applications

Purpose – The purpose of this paper is to present comparative analysis of several configurations of the switched reluctance motor (SRM) for an in-wheel drive for a heavy-duty automotive series hybrid system. The SRM motor is regarded as one of the primary candidates for possible replacement of the permanent magnet (PM) motor. Design/methodology/approach – Three SRMs of 10/8, 12/10 and 12/8 configurations have been analysed, where the last two motors had the stator lamination profile taken from the existing PM motor. The analysis is performed using magnetostatic FEM and transient modelling techniques. Findings – The maximum developed electromagnetic torque of the two analysed motors of 12/10 and 12/8 SRM configurations with the stator lamination profile taken from the existing PM motor is limited due to saturation of the stator yoke. Both motor configurations are capable to provide the specified power within the same outer dimensions due to extended speed in the field-weakening region and position independent starting torque. A redesigned stator results in substantial increase in torque developed by the machine and, consequently, ability to provide similar torque-speed performance as the existing PM motor, at cost of increased copper loss at the low-speed regime. Originality/value – The paper proposes several structures of SRMs for the in-wheel drive for a heavy-duty automotive series hybrid system converted from the present expensive PM machine, having the same power density. The “bottleneck” of the direct conversion of the PM machine into the SRM is highlighted.

Determination of Maximum Electromagnetic Torque in PM Brushless Machines Having Two-Segment Halbach Array

This paper develops a 2-D field analytical model for predicting the magnetic field distribution and the corresponding electromagnetic performance in air- and iron-cored permanent magnet (PM) brushless machines having radially or parallel magnetized two-segment Halbach array. A simple equation is derived to directly predict the optimal magnet ratio for maximum electromagnetic torque, while the influence of pole-pair number and magnet thickness on the optimal magnet ratio is investigated for both air- and iron-cored machines. The analytical model is validated by finite-element analyses and also measurements on a prototype 12-slot/10-pole PM brushless machine.

Optimal control of current switching angles for high‐speed SRM drive

PurposeThe purpose of this paper is to propose a method of optimal control of current commutation of switched reluctance motor drive.Design/methodology/approachThe problem of optimal current commutation control is solved by off‐line selection of switching‐on and switching‐off angles. Selection of optimal values of angles is provided on computer model of the drive with help of particle swarm optimisation method. The optimal angle values are detected as functions of phase current and rotor speed. These calculated optimal values are stored in microcomputer control system memory in form of two‐input look‐up tables. The results are validated on laboratory set up.FindingsThree different criteria of optimal control, which are taken into account: the maximum electromagnetic torque for given reference current, the maximum ratio of electromagnetic torque to root mean square value of phase current and the minimum electromagnetic torque ripples, gave a good results validated by simulation and experimental investigations.Practical implicationsA simple control method is proposed to optimise switched reluctance motors drive behaviour. Such an approach can be recommended for practical implementations.Originality/valueThe off‐line optimisation of switching angles, which is realised on computer model, is sufficient to obtain a good control effect.

Rotor‐field orientation with optimal torque‐control strategy for current‐fed induction‐machine system

AbstractField orientation provides the possibility to control torque and flux of the induction machine independently. However, the widely used control strategy for field orientation is based on constant rotor flux. This strategy does not utilize all advantages by using field‐orientation method. This paper reveals a degree of freedom for controlling an induction machine, by controlling both field‐ and torque components. It presents a control strategy based on varying the flux level to provide optimum torque operation irrespective of speed ranges. The freedom for controlling both field‐ and torque components of the stator winding currents can make the inverter induction motor drive superior to DC drives, where proper resolving for the stator current components can provide maximum electromagnetic torque per ampere, optimal efficiency and higher short duty system capability. In this paper, the rotor‐field oriented saturated model of the induction machine is presented. The analysis of the electro‐magnetic torque, in terms of stator current components, is used to find the optimal resolving ratio for maximum torque. This optimal ratio depends on the machine parameters and the saturation level. Investigation and comparison for widely used and the proposed control strategies are given for different cases, namely: neglecting saturation effect case, then taking saturation into account for low‐ (0.75 kW) and high power rating (90 kW) machines. Also, the proposed optimal control strategy and the microprocessor implementation method are presented.

Effects of flux level on a CSI-fed field-oriented induction motor

A definite relation exists between the flux level, torque and slip speed of a vector controlled induction motor. An untuned vector controller generates an inappropriate slip frequency that changes the operating flux of the machine. This affects the electromagnetic torque linearity and dynamic performance of the drive system. For an induction motor with magnetic saturation, the ratio of flux and torque-producing components of stator current differs from unity for the maximum electromagnetic torque. With a linear model this ratio is unity. The dependence of this ratio for maximum torque output is explained for linear and nonlinear models of the machine. The torque characteristic is analysed with three aspects of magnetic state: true saturation curve, hard-limit saturation curve, and constant inductance model. Degradation in dynamic performance due to saturation for a CSI-fed system is presented.