ABSTRACT
Variable speed electric drives are nowadays utilized in almost every walk of life, from the most basic devices, such as hand-held tools and other home appliances, to the most sophisticated ones, such as electric propulsion systems in cruise ships and high-precision manufacturing technologies. Depending on the application, the control variable may be the motor’s torque, speed, or position of the rotor sha³. In the most demanding applications, the requirement is to be able to control the electric machine’s electromagnetic torque in order to be able to provide a controlled transition from one operating speed (position) to another speed (position). žis means that the control of the drive must be able to achieve desired dynamic response of the controlled variable in a minimum time interval. žis can only be achieved if the motor’s electromagnetic torque can be practically instantaneously stepped from the previous steadystate value to the maximum allowed value, which is in turn governed by the allowed maximum current. Variable speed electric drives that are capable of achieving such a performance are usually called high-performance drives, since the control is e¦ective not only in steady state but in transient as well. Common features of all high-performance drives are that they require information on instantaneous rotor position (speed), operation is with closed-loop control, and the machine is supplied from a power electronic converter. Applications that necessitate use of a high-performance drive are numerous and include robotics, machine tools, elevators, rolling mills, paper mills, spindles, mine winders, electric traction, electric and hybrid electric vehicles, and the like.
