Influence of nonlinearities in sensor and actuator on the operation of the rotational speed control system of a roadheader cutting head

The paper presents a discussion on the selected nonlinearities existing in sensor and actuator subsystems of the roadheader cutting head speed control system. There have been concerned the most significant nonlinearities - rotational speed encoder and frequency rate limiter in the input of the power electronic converter. These nonlinearities significantly reduce the stability margin of the control system and therefore should be minimized. They have also an influence on allowable speed controller settings range. Reduction in the controller settings can result in a decrease in the quality of operation of the entire control system. The measurement time of the encoder-based speed sensing should be as short as possible, or continuous measurement (like tachogenerator) should be used. The frequency converter should be overmatched to ensure current overload capability – allowing an increase in the permissible rate of output voltage frequency change.