Design for an Six-Phase Synchronous Reluctance Motor Mounted With Centrifugal Compressor Using Multiobjective Optimization Methods

Abstract

This paper describes a two-step design using optimization method for a six-phase synchronous reluctance motor mounted with a centrifugal compressor to achieve minimum cost, lower torque ripple, maximum efficiency and higher power factor. In the first-step optimization, the multiobjective design of adopted altered bee colony optimization (BCO) and Taguchi method combined with finite element analysis (FEA) are used for optimizing the barrier shape and layer number in the rotor to reduce torque ripple and raise power factor. In the second-step optimization, the adopted multiobject design method can be emplyed for optimizing the geometry of stator to achieve minimum cost and maximum efficiency. Experimental results show that these techniques can not only improve the efficiency and power factor but also reduce the material cost and torque ripple. The multiphase machine offers numerous advantages over the conventional threephase motor drives such as increased torque per ampere for the same volume machine, reduction of the stator current per phase, improvement of torque density and increase of the fault tolerance [1–2]. Some of the most suitable applications are electric, hybrid electric vehicles [3] and ship propulsion [4]. An multiobjective optimization design of a six-phase synchronous reluctance motor applied in a centrifugal compressor provides an important role in helping the consumption systems. The factors of design optimization in the six-phase synchronous reluctance motor are minimizing material cost, minimizing torque ripple, maximizing efficiency, and maximizing power factor. One of the popular design methods of the electromagnetic devices is the use of finite-element analysis (FEA) coupled with optimization algorithms. However, the classical optimization algorithms, such as deterministic and stochastic methods, seem to be not very efficient by using the FEA because it needs longer computing time. Therefore, a multiobjective optimization design of a six-phase synchronous reluctance motor used in both the altered bee colony optimization (BCO) [5], [6] and the Taguchi method [7], [8] with FEA [9], [10] in practical methodology is applied in a centrifugal compressor system. In this paper, the motor is rated at a power of 3kW, rotating at 1800r/min. The initial design of the motor consists of a stator having 36 slots that carry two-layer windings, as shown in Fig. 1 and Table I. The losses of the motor include iron loss in the stator, copper loss in the winding, eddy current loss in the rotor, and rotational losses due to friction and wind resistance. The iron and copper losses were the dominant contributor in a centrifugal compressor. The finite-element method with the measurement that combined the BCO and the Taguchi method is a very efficient and effective approach in the robust design of a high-performance motor. This paper presents the optimization design of a six-phase synchronous reluctance motor using two-stage optimization processes, which mainly depends on the stator and rotor regions between cost and efficiency. The stator region is applied to reduce the use of the iron and the winding to minimize cost and maxmimize efficiency in the first stage, while the rotor parameters are kept unchanged. An optimization design based on the altered BCO and the Taguchi method with FEA is employed to further enhance the machine performance. The Taguchi method can optimize the machine parameter of performance characteristics in electrical discharge machining. The experimental results are then converted into a signal-to-noise (S/N) ratio. The S/N ratio can be used to measure the deviation of the show characteristics from the desired values. In the second-stage optimization, the objectives are the maximization of power factor and minimization of toque ripple. while the stator parameters are kept unchanged. An optimization design based on the altered BCO and the Taguchi method with FEA is employed to further enhance the machine performance. In summary, it is seen that the two-stage optimization can reduce both cost and torque ripple, and further increase efficiency and power factor from the experimental values. Finally, the photo view of a six-phase synchronous reluctance motor is shown Fig. 2. The views of stator, rotor and winding combination in the six-phase synchronous reluctance motor mounted with a centrifugal compressor is shown in Fig. 2(a)–(b). This paper has presented an optimization design using the altered BCO and Taguchi method with FEA for tacking multiobjective optimization problems on a six-phase synchronous reluctance motor mounted with a centrifugal compressor compressor. The results of this paper confirm the effectiveness of the proposed technique for obtaining lower cost and better performance characteristics. This technique can be applied to solve multiobjective optimization problems of any electromagnetic devices.