Open-Loop and closed-loop control of electric fractional-horsepower motors

Abstract

Electric drives convert electrical into mechanical energy. Because applications are becoming ever higher demanding with respect to the process of motion in the manufacturing and handling technique, there are also increasing requirements on the open- and closed-loop control of the drives. Therefore, different procedures of the speed adjustment, of rotational speed control and positioning control are described for the different kinds of motors. In addition, references of which procedure is suitable for which application are provided. Besides simple circuits, with the increasing requirements on the quality of the controls, modern and efficient components of information electronics and power electronics are used for the open-loop controls and closed-loop controls. These are special microcontrollers developed for these applications and IPMs (intelligent power modules) with large scale integration. The highest requirements on the sensitivity usually arise for the case of positioning control. In general, for these applications, cascade controls are developed. They consist of a positioning controller with a subcontroller for the rotational speed and another subcontroller for the motor current. For asynchronous machines, this method of control only becomes possible by the application of the field-oriented control, and for synchronous machines by the rotor position-oriented control. For this the system theory of these kinds of motors is necessary. Therefore it is treated in detail. By using the system theory, also the procedures for sensorless motor control are indicated. They are characterised by small costs and by high robustness, and they can be employed when no extremely high demands on the accuracy of the control are imposed.