Patent ID: 8688303

Claim:
A method for determining motor current capability for a battery powered vehicle, the method comprising: estimating, via an estimation module, a sagged battery voltage for a vehicle battery during operation based on: a) a predetermined maximum expected battery bus current of the vehicle battery during operation, wherein the expected battery bus current is a current to which the battery current rises due to the sagging of the battery voltage, b) an estimated battery open-circuit voltage, and c) an estimated battery open-circuit resistance; wherein the sagged battery voltage is a voltage to which a DC bus of the vehicle battery sags at a maximum expected operating speed of the battery powered vehicle, and the estimated sagged battery voltage for a vehicle battery during operation is estimated in accordance with: V bat â€” sag =V oc âˆ’I bat â€” max *R bat , where V bat â€” sag is the estimated sagged battery voltage, V oc is estimated battery open-circuit voltage, I bat â€” max is the predetermined maximum expected battery bus current, and R bat is the estimated battery open-circuit resistance, and estimating, via the estimation module, motor current capability for the battery powered vehicle based on: d) operational speed of a motor propelling the battery powered vehicle, e) back EMF constant of the motor windings, f) electrical resistance of the motor windings, g) the estimated sagged battery voltage, h) electrical inductance of the motor windings, and i) magnetic pole pair count for the motor; wherein the motor current capability for the battery powered vehicle is estimated in accordance with: I mot â¢ â¢ _ â¢ â¢ max â¡ ( Spd ) = 2 3 * - K e * ï˜ƒ Spd ï˜„ * R mot + V bat â¢ â¢ _ â¢ â¢ sag 2 * [ R mot 2 + ( PP * Spd * L mot ) 2 ] - ( K e * Spd 2 * PP * L mot ) 2 R mot 2 + ( PP * Spd * L mot ) 2 where I mot â€” max is the motor current capability, Spd is the operating speed of the motor, K e is the line-to-line back EMF constant of the motor windings, R mot is the line-to-line resistance of the motor windings, PP is the magnetic pole pair count for the motor, and L mot is the line-to-line inductance of the motor windings.