The problem of performance optimization in current controlled switched reluctance motor (SRM) drives is investigated. Two controllers are proposed that determine the optimal turn-on and turn-off angles, respectively, for improving motor efficiency and torque ripple. The suggested controllers are simple, do not affect the complexity of the drive, and are easily implemented since the knowledge of torque-angle-current characteristics or magnetization curves is not required. The proposed control scheme is demonstrated on a prototype experimental system.

Performance optimization in switched reluctance motor drives with online commutation angle control

A novel two-phase switched reluctance machine (SRM) with a stator comprised of E-core structure having minimum stator core iron is proposed. The E-core stator has three poles with two poles at the ends having windings and with the center pole containing no copper windings. The center stator pole in the E-core is shared by both phases during operation. The air gap around the common pole has constant and minimum reluctance irrespective of rotor position by its unique design and the two remaining stator poles at the ends experience variable reluctance with respect to rotor position. The stator is constructed with two independent and physically separate E- cores and the rotor is comprised of ten poles. Other pole combinations are possible. Phase excitation in the novel SRM gives short flux paths, hence reducing the magnetomotive force (MMF) required to drive the machine resulting in significant reduction of copper wire and core-losses compared to existing two-phase SRMs with flux-paths that traverse the entire stator back iron. The concept and principle of operation of this novel SRM and its comparison and contrast to existing two-phase SRMs are detailed in this paper. Comparison between finite element simulations and magnetic equivalent circuit analysis for inductance are made and compared to experimentally measured characteristics. Furthermore, a comparison between a conventional two-phase SRM and the novel SRM is be made in terms of its weight and output torque. Manufacturability and cost savings of the unique SRM structure are presented. It is shown that E-core SRM using common-pole SRM has 50% less iron in the magnetic path compared to the conventional two- phase SRM.

Novel Two-phase Switched Reluctance Machine using Common-Pole E-Core Structure: Concept, Analysis, and Experimental Verification

Low torque ripple in electrical machines is generally required to reduce acoustic noise and mechanical resonance vibration. To design for low torque ripple, however, affects the average torque and the power rating of the machine. In this paper, the effect of stator winding chording and rotor skewing on the average torque, power factor, and torque ripple of the normal laminated, internal flux barrier rotor reluctance synchronous machine is investigated. The two-dimensional finite-element time-step method together with the basic machine equations are used in the analysis. It is shown that to design, in general, for low torque ripple and minimal effect on torque rating of the reluctance synchronous machine, full-pitch stator windings must be used, the rotor must be skewed by a stator slot pitch, and a low number of stator slots must be avoided.

Effect of stator chording and rotor skewing on performance of reluctance synchronous machine

A control system for power smoothing using a switched reluctance machine (SRM) driving a flywheel is presented in this paper. Power smoothing is achieved by controlling the SRM to operate as a motor/generator, storing or retrieving energy from a rotating flywheel. In order to increase the rotational energy stored in the flywheel, the SRM operates at high rotational speed, and the machine phase current is controlled using single-pulse mode. To control the SRM output power, a two-dimensional lookup table is used to store the switching angles. The control strategies proposed in this paper have been experimentally implemented in a 2.5-kW prototype based on an 8/6 SRM. Experimental results are presented and discussed

Power Smoothing Using a Flywheel Driven by a Switched Reluctance Machine

Low-cost motor drives are being sought for high-volume energy-efficient home appliances. Key to the realization of such low-cost motor drives is the reduction of the power electronic converter to the barest in terms of its components, particularly the active devices, finding the motor with the least complexity for manufacturing and a controller that can extract the desired performance from the machine and converter combination. These and other factors such as self-starting, speed control over a wide range, and, most of all, the crowning aspect of four-quadrant operation with a bare minimum number of controllable switches remain as formidable challenges for low-cost motor drive realization. An innovative four-quadrant switched reluctance motor (SRM) drive with only one controllable switch is realized in this paper, for the first time, in the opinion of the authors. The motor drive is realized using a two-phase machine and a single controllable switch converter. The theory and operation of the proposed four-quadrant SRM drive with the proposed control algorithm for its realization are described. The motor drive is modeled, simulated, and analyzed to verify its feasibility for self-starting, speed control, and for four-quadrant operation, and the simulation results are presented. Experimental results confirm the validity of the proposed control algorithm for four-quadrant control of the SRM drive. The focus of the paper is mainly directed toward the control algorithm for realizing the four-quadrant operation of the two-phase SRM drive with a single controllable switch converter.

Theory and operation of a four quadrant switched reluctance motor drive with a single controllable switch- the lowest cost four quadrant brushless motor drive

The paper discusses the design of optimised current waveforms, to give the lowest RMS current per phase for a given mean torque The waveforms are constrained to be within the converter VA rating Current waveforms and the associated voltage waveform, over a wide speed range, are given for a representative motor

http://ieeexplore.ieee.org/iel1/2194/6870/00277975.pdf

Computer-optimised current waveforms for switched-reluctance motors

Reluctance motors, both singly and doubly salient, are receiving ever increasing interest because of their low cost, rugged construction, and high performance. This is particularly true when the reluctance motors are excited by currents which are synchronized with the rotor position, as is the case in this paper. The doubly salient reluctance motor, with position-synchronised excitation, is commonly referred to as a Switched Reluctance Motor (SRM). The paper compares a singly salient reluctance motor (SSRM), an SRM, and an 'off the shelf induction motor (IM). Every attempt has been made to make this comparison fair'. All three motors have the same cooling, use the same frame, have the same temperature rise, use the same air gap, and use the same steel. The paper concludes that both of the reluctance motors have superior performance to the IM and that the SRM has superior performance to the SSRM. The comparison is for D80 sized motors with a nominal top speed of 1500 rpm.

Comparative performance of singly salient reluctance, switched reluctance, and induction motors

The evolution of a novel form of single-phase switched reluctance motor, suitable for example for high-speed fans is described. The motor has four stator and four rotor poles, but only two coils. The new motor is derived by simple analysis from the basic 2-pole machine using sweeping assumptions. It is predicted to have only half the core length, less copper loss, but significantly more iron loss than the 2-pole form. These conclusions are tested using computer-based analysis, and test results from a prototype motor are presented which confirm the attractiveness of the design. Attention then turns to the starting problem of all such machines, and a method using permanent magnets is shown to be particularly appropriate for the new motor. The operation of this method is analysed, and simulated starting responses are compared with experimental results.

Single-phase switched reluctance motor design

An improved dynamic model of the switched reluctance machine for use in design has been developed. The specific requirement was for the incorporation of iron losses, but a secondary benefit has been the inclusion of the magnetic interaction between phases. The work is described in two stages: (i) modelling of iron loss and its effect on current waveform in a rudimentary one-phase static SR machine, and (ii) the development of a dynamic model, including instantaneous torque, of a three-phase machine with eddy-current, hysteresis and additional iron losses. Both stages include experimental verification. Coupling between the phases through shared portions of the magnetic circuits and also through 'leakage flux' is included. Model results are compared with measured values for a three-phase, 12/8-pole motor.

Dynamic modelling of switched reluctance machines with iron losses and phase interactions

The paper describes the first phase of a project to improve the prediction and modelling of iron loss for use in the design of switched-reluctance (SR) machines. Earlier models are reviewed and the development of a comprehensive model is described. Its parameters are obtained from commonly available manufacturers' data and this allows the prediction of not only average loss but also instantaneous power flow for a given flux waveform. Its validation against experimental measurements for sinusoidal and triangular fluxes up to 2 kHz, including superimposed DC bias, is demonstrated. The measurement work using toroidal specimens reveals some unexpected behaviour and a challenge to the measurement technique.

J.M. Stephenson

Papers

Computer-optimised current waveforms for switched-reluctance motors

Comparative performance of singly salient reluctance, switched reluctance, and induction motors

Single-phase switched reluctance motor design

Dynamic modelling of switched reluctance machines with iron losses and phase interactions

Modelling and prediction of iron loss with complex flux waveforms