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Optimization of Powertrain in EV
Department of Power Electronics and Energy Control Systems, AGH University of Science and Technology,
30-059 Krakow, Poland;
[email protected]
Abstract: The method for preliminary powertrain design is presented in the paper. Performance of
the EV is realized by motor torque–speed curve and gear ratio optimization. The typical two-zone
mechanical characteristic of a PMSM traction motor is included in the optimization program. The
longitudinal vehicle model is considered in the paper. Some examples try to show the calculation
possibilities in application to existing vehicles: Tesla Model S and Mini Cooper SE.
Keywords: electric vehicle; electromechanical systems; optimization; multi-objective optimization;
field weakening; traction motors; kinematics; motor torque; gear
1. Introduction
The conversion of electrical energy into mechanical is very important for the drive in
an Electric Vehicle (EV) and optimization of the car performance is discussed in the article.
The path from battery to a traction force FT on the car wheels is called powertrain [1,2].
The presented optimization problem can be used to design preliminary powertrain
in a EV. The torque–speed curve (mechanical characteristics) [3] of PMSM (Permanent
Magnet Synchronous Motor) is introduced. This type of motor is the most popular in car
manufacturers (Toyota, Nissan, BMW, Renault), but Tesla induction motor characteristics
are also considered. The EV mathematical model is presented more precisely than in [4].
Two design examples are included in the paper: gear ratio optimization in Tesla Model S,
traction motor, and gear ratio optimization in the Mini Cooper SE.
The optimization is considered as a Nonlinear Programming Problem because the
objective function (performance index) is nonlinear, and a longitudinal model of motion is
also nonlinear. The value of the objective function is calculated after car race simulation.
Hence, the objective function is not explicit and the Simplex Method (Nelder–Mead Method
or Downhill Simplex Method) [5] is very useful because derivatives of the objective function
are unknown. In the Matlab environment, fminsearch is a Simplex Method without
constraints.
The method of the powertrain optimization shows Figure 1.
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