In this paper, a global optimization methodology is described to pre-design an electric vehicle powertrain in order to find the best compromises between components. The modeled system includes a transmission, an electric machine, an inverter and a battery pack. The challenge is to find the dedicated formulations, with the vehicle performance requirements, electric range, and cost calculation that include the whole system without exploding computational time. Bi-objective, range/costs, optimizations with performance constraints are performed to find the potential gain with the system model.
Keywords-Electric vehicle powertrain, optimization methodology, electric system design, methodology
Notations:Sp: Vehicle Speed (km/h) t: driving cycle time (s) Sl: Road slope dp: number of operating points that represent a portion of a driving cycle pp: number of operation points that represent a performance requirements ng: number of gears of the transmission Tw: required torque at the wheel (Nm) Ωw: wheel speed (rpm) Tm: required machine torque (Nm) Ωm: machine speed (rpm) Tm max : maximum machine achievable torque (Nm) Tm req : required machine torque for performance (Nm) f: stator frequency (Hz) Um: machine voltage (V) Im: machine current (A) cos(φ): machine power factor J: stator current density (A/mm²) Ib: battery current (A) Ub: battery voltage (V) x i : design variable ns: number of cells in series for the battery pack np: number of cells in parallel for the battery pack SOC: battery state of charge