A Double-Stator Switched Reluctance Motor for Direct-Drive Washing Machine Application

Cumhuriyet Üniversitesi Fen Fakültesi Cumhuriyet University Faculty of Science Fen Bilimleri Dergisi (CFD), Cilt:36, No: 3 Özel Sayı (2015) Science Journal (CSJ), Vol. 36, No: 3 Special Issue (2015) ISSN: 1300-1949 ISSN: 1300-1949   A Double-Stator Switched Reluctance Motor for Direct-Drive Washing Machine Application M. ASGAR1,*, E. AFJEI1, M. M. MAHMOODI2, A. R. BAHRAMI2, E. Z. ALIABADI3 1 Department of Electrical Engineering, Shahid Beheshti University, G.C., Tehran, Iran 2 Department of Electrical Engineering, Saveh Branch, Islamic Azad University, Saveh, Iran 3 Department of Technical and Vocational College of Islamic Enghelab, Tehran, Iran Received: 01.02.2015; Accepted: 05.05.2015 Abstract. Switched reluctance motors (SRMs) are known as an economical solution by several unique features such as: simple structure and low cost maintenance. Furthermore, due to the lack of permanent magnet, powerful and economical structure of these types of motors, they are proposed as a good choice for use in household appliances. In this paper, a high power flat-type double-stator SRM with low operating voltage in direct-drive system is introduced. Initially, proportional to the intended application, the acceptable attribute of SRM structure is selected, and was followed by the calculation of the motor design. Next, the magnetic characteristics are analyzed by finite element method (FEM) to determine the efficiency of the motor. Finally, the collection of experimental data is tested to confirm the calculated values and the simulation results and ensure the proper functioning of the obtained collection. Keywords: Switched reluctance motors, finite element analysis, double-stator motors, direct-drive, washing machine. 1. INTRODUCTION Nowadays, SRMs are used for a wide range of applications, such as aerospace industry, propulsion marine equipment, linear drivers, drilling equipment, hand tools and household appliances [1-4]. The main reasons for employing SRMs on scopes which have been mentioned above, is the low cost, the resistance to admitting error and high efficiency via variable speed [5]. Therefore, the SRMs due to the low cost and also easy access to components and electronic equipment required, is proposed as a powerful corrival for other electric motors such as induction motors, brushless DC motors, permanent magnet synchronous motors and universal motors in most applications [6-8]. In practice phase, the configuration of SRMs is supposed to be developed with the fault-tolerant on mechanical and electrical performance on washing machine application. Otherwise, if there is any weakness or defect in the motor, then SRMs technology has the potential to cover or compensate the inherit limitations by closed-loop controller circuits. In this paper, design process of a three-phase DSSRM with 12/8 poles, (12 poles for inner stators, 12 poles for outer stators and 8 double-side poles for rotor), is proposed. Motor structure and its properties are described in Section 2. Details of the design and calculation of the frame sizing are given in Section 3. _____________ *Corresponding author. Email address: Special Issue: The Second National Conference on Applied Research in Science and Technology http://dergi.cumhuriyet.edu.tr/cumuscij ©2015 Faculty of Science, Cumhuriyet University A Double-Stator Switched Reluctance Motor for Direct-Drive Washing Machine Application In Section 4, the equivalent model based on the calculated size, is analyzed. Also, in this study a magnetic analysis is performed in three-dimensional condition by specialized software which is called "Magnet" package [9]. In Section 5, an experimental testing and also field trail is performed on the constructed prototype. Finally, in Section 6, the summary of the obtained results are offered. 2. DESCRIBE THE STRUCTURE OF PROPOSED DSSRM Proportional to the defined application, a DSSRM with 12/8 poles is introduced as an innovation in application. The two-side segmented rotor includes salient poles. The coils are located on both inner and outer stators poles and the poles are linked to each other by means of the yoke. The rotor places between inner and outer stators. In proposed structure of this segmented rotor, yoke is not existed so the detached parts of rotor are interrelated by thin sheets of soft magnetic materials. In proposed rotor structure, the segments of the rotor are located on a supported aluminum plate. In this structure shaft can be eliminated. Selecting such a different configuration of SRMs is customized with respect to intended application and imposed limitations such as: space restriction and obtaining the required torque generated via different speed in washing and drying cycles on washing machines application. The wash program chosen determines the overall time period of the washing cycle [10-11]. As shown in Fig. 7, after completion of the washing cycle, the washing machine starts operation in the spin-dry cycle. The washing machine's drum accelerates to a pre-defined high speed level for a drying cycle where it remains for a short time. Then, the washing machine's drum is ordered to decelerate either to a stop or to proceed to a low speed level. Depending on the wash program chosen, this cycle might be repeated several times [12]. Drum Speed [rpm] Washing Cycle 1500 1250 CW Spin-Dry Cycle CCW 1000 750 500 250 Time [min] 0 250 500 750 Figure 1. Washing machine operating cycles. In SRMs, increase the number of rotor and stator poles causes the reduction of torque ripple. Instead, increasing the number of phases increases the power switches and thus, increases the cost of the motor converter. The new structure is configured in respect to these two points of view. 781     ASGAR, AFJEI, MAHMOODI, BAHRAMI, ALIABADI 3. DESIGN AND CALCULATION OF THE PROPOSED SRM In 5 Kg front-door washing machine, to evaluate the output power of its direct-drive motor, the rotor segments and drum weights are also considered in spine-dry cycle. In this case, the motor speed increases to nominal speed. In washing cycle, due to utilizing the PWM controller, the speed of the motor decreases and stabilizes under about 50 [rpm]. P = Pin + Pout = F × vm (1) The following equation can be used to convert the linear velocity to the angular velocity: Nr = vm 60 × D / 2 2π (2) Calculating process of the parameters which are required in the design of SRMs, followed by design process of double stators SRMs based on the above computed parameters. To achieve an appropriate continuity of torque the minimum stator pole arc is calculated as follows:   β s [min] = 4π Ns × Nr (3) This point is notable, that to achieve maximum power delivered by the motor, the stimulation phase angel must be equal to stators poles arc:   kd = θi × q × Pr 360 (4) As seen in Fig. 2, the outer diameter of the inner stator of a DSSRM is calculated by output power equation as follows: Din = π × Pin 60k e k d k1k 2 (...truncated)