Comparison of electrical drives for road vehicles

The low storage capacity of presently available galvanic batteries restricts the effective use of electrically driven vehicles to a limited range of transportation jobs. For this application any change from vehicles driven by internal combustion engines to vehicles driven by electric motors can only be justified if the use of electrical drives results in an overall cost reduction. This criterion means that a direct current, separately excited motor with its speed controlled by field weakening is the best solution. In a conventionally designed motor the attainable speed range is limited to approximately 1:3. In most cases additional means for the extension of the driving range are required. If, however, the motor is equipped with an additional compensation winding, a controllable speed range of close to 1:8 is obtainable by field weakening. Acceleration characteristics are applied to evaluate the various drive units which provide advantages in energy consumption and disadvantages in the acceleration time, and vice versa. On the basis of test vehicles with various drive systems, design of the required control is explained. Additional requirements for automatic control are partially offset by the additional protective devices required to restrict the effects of faulty handling of a manually controlled drive.