Topology Optimization Of Single-Phase Induction Motor For Rotary Compressor For Reducing OCR

The oil circulation rate (OCR) of the rotary compressor is a crucial factor affecting the performance and reliability of air-conditioning systems. In this paper, topology optimization of the single-phase induction motor of rotary compressor is carried out for reducing the OCR. The nonlinear transient characteristic of single-phase induction motor for rotary compressor is analyzed by using FLUX2D. The topology optimization for electromagnetic systems is developed using the finite element method (FEM). The proposed method is applied to a single-phase induction motor for reducing the OCR. For validation, optimized induction motors are manufactured and tested. NOMENCLATURE A : Vector potential s J : Current density μ : Permeability λ : Adjoint vector potential A~ : Space of virtual vector potential λ : Virtual adjoint vector potential H : Magnetic field intensity B : Magnetic flux density P : Penalization factor ρ : Density function INTRODUCTION The oil circulation rate (OCR) of the rotary compressor is a crucial factor affecting the performance and reliability of air-conditioning systems. The flow circulating in refrigeration systems is a mixture of the refrigerant and lubricating oil. The primary function of the lubricating oil is reducing friction to minimize wear at the journal bearing of the compressor. The oil pumped out of the compressor causes problems both in the unit and the compressor. The oil concentration in the unit may have significant effects on the hydrodynamic and heat transfer performance of the condenser and the evaporator, because of changes in the thermodynamic and transport properties [1]. So it negatively affects the unit efficiency by lowering effectiveness of coil heat transfer. And high OCR may lead the compressor to bearing failure in split, multi-evaporator split and heat pump. Recognizing these important effects of oil in a refrigeration system, the OCR must be kept at minimum level. Stator core cut area and rotor vent hole, which are related with pressure drop across motor, are major factors to reduce OCR as paths are related with gas velocity as shown in Figure 1 [1]. In this paper, the topology optimization of the single-phase induction motor is obtained to reduce the OCR and the results of the topology optimization are validated by the experimental tests. The study of the topology optimization on the electromagnetic systems began few years ago [2-3]. The principle of the topology optimization on electromagnetic systems is the same with that of structural systems. Researchers applied the topology optimization methodology into the electromagnetic system using the density method. Hence, this paper aimed on the development of theory and the application into the single-phase induction motor for the rotary compressor. In this paper, the torque properties of the single-phase induction motor are calculated by using a commercial finite element analysis (FEA) program, FLUX2D, because FLUX2D can easily express the effect of the squirrel cage in the induction motor. However, the topology optimization is obtained by using a different FEA program, ANSYS, because the access and change of ANSYS files for reanalysis and optimization are much easier than those of FLUX2D. To obtain the meaningful topology optimization, the magnetostatic analysis of ANSYS uses all information calculated from the magneto-transient analysis of FLUX2D. The sensitivity equation is derived using the continuum method [4], and the sensitivity is calculated by using the software of topology optimization for electromagnetic systems [5]. In the optimization program, the optimization routine is implemented using SLP in DOT [6]. A single-phase induction motor is optimized to reduce the OCR while maintaining the current torque. The optimized design shows improved OCR without losing the torque after they are manufactured and tested. TOPOLOGY OPTIMIZATION Sizing Design Sensitivity Analysis of Electromagnetic Systems Design sensitivity analysis (DSA) [4] is widely used in structural systems. Mostly DSA for electromagnetic systems are related with shape design variable [6] because sizing variable case like thickness was rare in electromagnetic devices. Consider a measure of electromagnetic performance that may be written in integral form as ∫∫∫Ω Ω ∇ = d u A A g ) , , ( ψ (1) where A is the vector potential, T s J u ] , [ μ = is the design vector of current density and permeability. Using the variational form of objective function of (1) and direct differentiation result [4], the sizing design sensitivity equation is [5]