Design of a computer controlled speed control system for wound-rotor inducion machines

This study introduces a novel and powerful speed control system with computer interface for wound-rotor induction machines (WRIM). In order to improve the sensitivity and stability of the control process, a high-speed digital signal processor (DSP) is used as the main controller. A serial resistor is connected to rotor side of WRIM to control the output power of the machine. The power consumed on the serial resistor is continuously controlled by PWM signals generated from DSP. A zero-crossing detector is used for calculating the rotor frequency. Thus, the rotor speed is obtained without using a mechanical sensor like external encoders. Thanks to using this method, measurement accuracy is increased and the total cost is decreased as well. After calculating the mechanical speed using the measured rotor frequency, the rotor speed is fixed to the reference value by a PI controller. In addition to speed control system, a graphical user interface (GUI) is also designed to set the reference speed through a computer screen. On this GUI, users can also observe and monitor the some parameters in real time such as rotor frequency, rotor slip, actual rotor speed, actual effective value of the serial resistor, switching ratio of PWM signals.