Abstract:The charging method of lithium-ion batteries used in electric vehicles (EVs) significantly affects its commercial application. This paper aims to make three contributions to the existing literature. (1) In order to achieve an efficient charging strategy for lithium-ion batteries with shorter charging time and lower charring loss, the trade-off problem between charging loss and charging time has been analyzed in details through the dynamic programing (DP) optimization algorithm; (2) To reduce the computation time consumed during the optimization process, we have proposed a database based optimization approach. After off-line calculation, the simulation results can be applied to on-line charge; (3) The novel database-based DP method is proposed and the simulation results illustrate that this method can effectively find the suboptimal charging strategies under a certain balance between the charging loss and charging time.
--This paper describes a computationally efficient approach for mapping the rotor power loss in permanent magnet (PM) machines. The PM loss mapping methodology discussed here utilises a small number of time-step finite element analyses (FEA) to determine the parameters of a functional representation of the loss variation with speed (frequency) and stator current, and is intended for a rapid evaluation of machine performance over entire torque-speed envelope. The research focus is placed on field-oriented controlled brushless AC PM machines with surface-mounted PM rotor construction, although the method could be adapted for other rotor formats. The loss mapping procedure accounts for the axial-segmentation of PM array through the use of an equivalent electrical resistivity of the segmented PM array, obtained from 3D FEA. The PM loss can be accurately mapped across the full operational envelope, including the field weakened mode, through a single three-dimensional (3D) and four two-dimensional (2D) time-step FEAs. The proposed methodology is validated on an 18 slots, 16 poles surfacemounted brushless AC PM machine design. The loss mapping procedure results agree closely with the computationally demanding alternative of direct 3D FE prediction of the PM power loss undertaken at each of the machine's operating points.Index Terms-PM power loss, surface-mounted brushless AC PM machines, computationally efficient methodology, loss mapping, finite element analysis (FEA), segmented PM array.
I. INTRODUCTIONHE accurate prediction of loss and its variation with load is an important element in the design of electrical machines . Vehicle propulsion applications are particularly demanding as the understanding of machine efficiency over the entire working envelope and under specific control and operating conditions is usually required - . Typically an electric propulsion motor operates under constant torque and field-weakened control regimes. Further the motor input voltage at a given operating point can be highly variable, depending on the battery state of charge. The loss derivation, in such cases, is a time demanding and computationally intensive process requiring numerous analyses to predict each component of loss over the full range of operation.In general, the sources of loss present within an electric machine can be categorised as mechanical and electromagnetic. Mechanical loss is attributed to the frictional effects within the bearing assembly (bearing loss) and fluid dynamics or aerodynamics effects within the motor body (windage or drag loss) . Electromagnetic losses are usually associated with active parts of the motor assembly and include the iron, winding and permanent magnet (PM) loss components - .Recently, there has been increased interest in methods for accurate and computationally efficient derivation of the electromagnetic loss components , , , that can be easily incorporated within design software tools. Of particular interest is the automated generation of loss/efficien...
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