Adaptive control of the unique mobility EV drive system to account for time-varying battery parameters

Abstract

Unique Mobility developed an electric vehicle drive system which is being used in the BMW E I.This system is comprised of a permanent magnet brushless DC motor, amplifier, and microprocessor controller. The system is capable of high torque (150 Nm) at low speeds « 2000 rpm) and constant power (32 kW) at higher speeds (to 8000 rpm). The design of the system utilizes a 6 step drive in combination with microprocessor control. The topology of the drive was designed to maximize overall system efficiency.The control system was designed to operate smoothly while transltlOning between different regions of operation. The controller must also regulate the torque to stay within all of the safety limits, two of which are under voltage and over voltage. The under voltage limit is used to prevent fully discharging the batteries to prolong their life, and the over voltage limit is necessary to protect the power devices in the amplifier and/or prevent outgassing of the battery. The maximum voltage from the motor in regeneration is a function of the regenerated current, the internal battery impedance in regeneration, and the open circuit bus voltage. The open circuit bus voltage and the internal battery impedance in regeneration varies with each different battery technology, and the batteries' short and long term charge/discharge history. The described drive system adapts to any battery technology by limiting the user to only the maximum instantaneous power that the battery can provide (in motoring) or accept (in regeneration).