Abstract
This paper presents an efficient multi-objective optimization method for linear induction motors (LIMs). With this modified method, the eddy current analysis and optimization design can be realized with speediness and accuracy. To ensure the consideration of skin effect, transverse end effect and longitudinal end effect, the raw data are obtained from 3D finite element model (FEM). Latin hypercube sampling (LHS) is adopted to facilitate the extraction of data, including every structural parameter of secondary. With these samples, eXtreme Gradient Boosting (XGBoost) is utilized to establish a multiple analysis model. Assuredly, the analysis model of thrust force, vertical force, eddy current and magnetic flux density owns concurrency and precision. Considering the limitation and rationality of designing structure and velocity, an objective function is specified to determine the ultimate optimization scheme.I. INTRODUCTIONAs a vital component of an LIM, secondary induces eddy current and generates thrust force. Therefore, the rectification method and optimization design of eddy current plays a crucial role in performance improvement.Due to the complexity of approximate analytical method, finite element analysis (FEA) is a conventional analysis method for eddy current distribution and magnetic flux density instead. Evidently, 2D FEM is inadequate for eddy current analysis [1]. 3D FEM can ensure the reliability of the calculation, and yet has the fatal flaw of being laborious and time-consuming.Therefore, this paper proposed a modified analysis and optimization method based on XGBoost and LHS. The mathematical modeling method can explore the output characteristic and electromagnetic performance under different secondary topologies with efficiency and accuracy.II. TOPOLOGY AND EDDY CURRENT DENSITY DISTUIBUTIONTo weaken the impact of skin effect and end effect, modifying eddy current path can apparently improve the performance, but the optimization capability is bound up with the selection of secondary topology.Figs. 1(a)-(c) show the topologies and eddy current density distributions of LIMs with different types of secondary. Obviously, the existence of back-iron strengthens the eddy current. Compared with the distribution in single-slit structure, the transverse component of current density at the edge is higher, while the longitudinal component at the active zone and overhang area shows an opposite trend.III. ALGORITHM AND PRINCIPLEConsidering correctness, efficiency and generalization are the core of optimization, the mainstay of proposed strategy is streamlined as follows.As shown in Fig. 2, the optimization process can be divided into five main steps. Objective to determine the general value range of structural parameters, equivalent circuit is effective for preliminary assessment. Then, Latin hypercube sampling (LHS), as a method can ensure the maximum of feature information and minimum of sample points, is adopted to obtain data with good rationality and coverage. Respecting that the analysis model erected by XGBoost has the combination of accurateness and speediness, the relationship between structural parameters and analysis objectives will be observed intuitively [2]. Thereinto, the structural parameters contain overall dimension and ladder structural dimension of secondary; thrust force, vertical force, current density and magnetic flux density are taken into consideration as analysis objectives. The objective function can conveniently judge the comprehensive performance of analysis targets, so as to select the most appropriate optimization scheme.IV. CHARACTERISTIC ANALYSISFigs. 1(b)-(e) show the distributions of eddy current density and the force characteristics of LIMs under different secondary topologies.Through the analysis and optimization method proposed in this paper, both electromagnetic properties and force characteristics achieved modification. Crucially, the ultimate optimization scheme is in good agreement with the FEA result, but the achievement only takes a little time after the analysis model is erected.V. CONCLUSIONIn this paper, the proposed analysis method, which adopts LHS and XGBoost, realizes the speedy and accurate optimization of electromagnetic properties and force characteristics by selecting the most suitable secondary scheme. The superiorities are listed as follows.(1) The proposed method can analyze the relationship between secondary structural parameters and performance indexes with efficiency. Both electromagnetic properties and force characteristics are taken into consideration.(2) With LHS, random samples in the whole range possess a balance of distribution and representativeness.(3) Excluding the speediness of modeling and prediction, XGBoost has a great imputation capability of missing data. Additionally, the autonomy of objective function and evaluation function is a high guarantee for the adjustability of multi-objective optimization.Therefore, this proposed multi-objective analysis method can achieve an efficient, accurate and reliable optimization for LIMs. The detailed analysis will be listed in the full paper. **
Published Version
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