The control system of the traction motor for an electric vehicle has different requirements from other systems for common, factory-use motors, because this control system needs to actuate the vehicle at the driver's demand.
The requirements are:

1) To eliminate gear changes at low speeds, constant high torque is needed when starting and accelerating, and at high speeds, a constant power characteristic is preferable.

2) The motor should be able to start the vehicle from a dead stop without any additional mechanisms.

3) The accelerator pedal should have the same feel as that of an internal combustion engine vehicle for the driver's comfort and familiarity.

4) Reversible motor control with no mechanism is preferable.

5) The ability to recharge the battery while decelerating is preferable.

6) The motor should be able to be actuated under wide range of voltages because the power source is a battery.

The internal combustion engine has a constant torque characteristic through its rotational speed range, and is used with a transmission and clutch mechanism. The figure shows that at low speeds, a low gear ratio is used to gain acceleration, and at high speeds, a high gear ratio is used to reduce the rotational speed of the engine.

On the other hand, motor control can easily produce such characteristics as low-speed, constant torque and high-speed, constant power. In addition, an AC motor can be driven at quite high rotational speeds. For these reasons the motor generally needs a reduction gear but not a transmission. The motor can start and stop easily, and needs no mechanism such as a clutch to cut off the idling engine from the drive train when the vehicle stops. However, to start the vehicle from a dead stop, the motor must be able to generate high torque at a standstill, which is particularly important when ascending a steep road.

The other major characteristic of the internal combustion engine is the engine brake. From the driver's point of view, it is better to decelerate by just taking a foot off the accelerator pedal. The motor does not have this mechanism by itself, so a control system will require some kind of decelerating logic. Moreover, the engine torque is in proportion to the opening rate of the throttle valve, which is operated by the accelerator pedal. Drivers are accustomed to this characteristic of the accelerator pedal, so they prefer the proportional torque to the accelerator pedal operation in the case of the electric vehicle motor. The motor control system thus seems to require demand torque logic.