Two-phase Switched Reluctance Machine Research Articles

Analysis of Two-phase E-core Switched Reluctance Machines Using Magnetic Equivalent Circuit Technique

The modification of magnetic structures for an E-core switched reluctance machine (SRM) comprising two segmented stator cores or a monolithic stator core is presented for ease of assembly, good manufacturability, mechanical robustness, and electromagnetic performance improvement. The E-core stator has four small poles with phase windings and two or four large poles (hereafter referred to as common poles), in between. The common poles are shared by both phases for positive torque generation during the entire operation. The E-core SRMs are compared to a conventional two-phase SRM. The comparison includes cost savings, torque, copper and core losses, and efficiency in order to validate the distinct features of the E-core SRMs. Magnetic equivalent circuit (MEC) technique is employed for proving the benefits of the E-core common-pole structure.

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

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.

New Designs of a Two-Phase E-Core Switched Reluctance Machine by Optimizing the Magnetic Structure for a Specific Application: Concept, Design, and Analysis

Three new magnetic structures for an E-core switched reluctance machine (SRM) comprising two segmented stator cores or a monolithic stator core are proposed for good manufacturability, mechanically robustness, ease of assembly, and electromagnetic-performance improvement. The E-core stator has four small poles with phase windings and two or four large poles (hereinafter referred to as common poles) in between. The common poles do not have copper windings or permanent magnets. The common poles are shared by both phases for positive-torque generation during the entire operation. The air gap around the common pole has constant and minimum reluctance, irrespective of rotor position, by its unique design, and the two small stator poles experience variable reluctance with respect to rotor position. The segmented stator can be constructed with two independent and physically separate E-shaped cores with L- or I-shaped yokes so that the straight back iron in the stator rather than the curved back iron is suitable for assembly with other parts like end bells or brackets. The monolithic stator also has an L-shaped yoke for the same reason, and the new E-core SRMs are designed by means of pole-arc optimization. The novel E-core SRMs are compared to a conventional two-phase SRM. The comparison includes cost savings, torque, copper and core losses, efficiency, and radial force in order to validate the distinct features of the E-core SRMs. For experimental verification, laboratory testing of a segmented E-core SRM is conducted, and the simulated and measured phase currents and voltages correlate well.

Two-Phase SRM With Flux-Reversal-Free Stator: Concept, Analysis, Design, and Experimental Verification

The demand for high-efficiency electric motor drives at low cost is increasing, particularly, in high-volume applications, such as household appliances. Single- and two-phase machines are viable under such constraints. Between them, two-phase switched reluctance motor drives are preferred from the viewpoint of performance. This paper presents a novel two-phase switched reluctance machine (TPSRM) that is conceived for high-efficiency operation and full-load starting performance for any initial rotor position. The principle of operation of the proposed TPSRM and its unique features such as the flux-reversal-free stator for reducing core losses, the utilization of only two thirds of the stator core for each phase operation, and the resulting low noise are presented. The machine is analyzed with the 2-D finite-element analysis method. Self-starting in the proposed machine is developed with rotor pole shaping, and a unique technique to provide the desired torque characteristics is described. The effect of varying pole arcs, the number of turns per pole, asymmetric pole placement, and rotor pole shaping on torque and phase inductance is evaluated to find the best machine dimensions for a required performance as well as to understand qualitatively the influence of each variable on the machine performance. Experimental results from a 2.2-hp laboratory prototype correlate the performance predictions and validate the claims for this novel TPSRM.

Comparison of the acoustic noise of a flux-switching and a switched reluctance drive

This paper describes the results of a comparison between the acoustic noise produced by a two-phase switched reluctance drive and a flux switching motor and drive. For the comparison, two external rotor machines were constructed from identical mechanical parts, and the same lamination stacks. Test results show that there is over 2 dB less acoustic noise from the flux switching topology relative to the equivalent two-phase switched reluctance machine. Finite element analysis is used to calculate the radial force profiles of the two motors during normal rotation and it is shown that further analysis of this data provides supporting evidence to the measured data and confirms the experimental results. The improved acoustic noise and vibration characteristics, coupled with the dramatic simplification of the power converter offered by the flux switching drive makes it a very attractive, low cost, low acoustic noise, variable speed drive.

High-speed performance improvements of a two-phase switched reluctance machine utilizing rotor-conducting screens

The two-phase 4/2 switched reluctance machine is suitable for high-speed operation. It has a simple and robust construction and can be operate from power converters that have no shoot-through mode. In this paper, conducting screens are incorporated in the rotor of a prototype 400 W, 7500 rpm two-phase switched reluctance machine. The effect of the conducting screens on current response, output torque, output power and efficiency of the machine are experimentally evaluated and explained. The conducting screens improve the torque at higher speeds, increase the output power and improve drive efficiency. At low speeds, the conducting screens improve rate of change of inductance and hence torque. At high speeds, enhancements in performance are due to a lowered unaligned inductance that provides an improved initial current response. At rotor speeds greater than base speed and below a breakpoint speed it is found that the conducting screens are detrimental to the performance of the machine. A reason for this phenomenon is given.

High-Speed Performance Improvements of a Two-Phase Switched Reluctance Machine Utilizing Rotor Conducting Screens

The two-phase 4/2 switched reluctance machine is suitable for high-speed operation. It has a simple and robust construction and can be operated from power converters that have no shoot-through mode. In this paper, conducting screens are incorporated in the rotor of a prototype 400 W, 7500 rpm two-phase switched reluctance machine. The effect of the conducting screens on current response, output torque, output power, and efficiency of the machine are experimentally evaluated and explained. The conducting screens improve the torque at higher speeds, increase the output power, and improve drive efficiency. At low speeds, the conducting screens improve rate of change of inductance and, hence, torque. At high speeds, enhancements of performance are due to a lowered unaligned inductance that provides an improved initial current response. At rotor speeds greater than base speed and below a breakpoint speed, it is found that the conducting screens are detrimental to the performance of the machine. A reason for this phenomenon is given.

Bidirectional starting of a symmetrical two-phase switched reluctance machine

The mechanical and electrical properties of the two-phase 4/2 switched reluctance machine make it suitable for high-speed operation. Its adoption in such applications has been hindered by a perceived starting problem especially if starting in both directions is required. A starting technique is proposed which exploits the natural magnetic asymmetry in the symmetrical machine geometry and provides for bidirectional torque production at start-up. The approach utilizes mutual coupling in the machine, an effect not previously identified for starting. The technique requires no modifications to either stator or rotor poles, and is suitable for fan applications which require only low starting torques. The starting technique is described and tested with nonoriented silicon steel and GOSS rotors, and starting torque from machine experimentally determined.