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

Joostberens Jarosław, Heyduk Adam

Mining Machines

2022

vol. 40, iss. 4

249--257

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.

Frequency Response Testing of Zero-Sequence Current Transformers for Mining Ground Fault Protection Relays

Kuliński Krzysztof, Heyduk Adam

International Journal of Electronics and Telecommunications

2020

Vol. 66, No. 4

701--705

In Polish coal mining, medium voltage power distribution networks operate with an insulated neutral point. Zero-sequence current transformers are the basic sensors that generate input signals for earth-fault protection relays. In the literature, the problem of frequency response analysis of various types of current transformers has been examined many times, e.g. [1] [2], but not for zero-sequence current transformers so far. As part of the work, two types of zero-sequence current transformers in the range from 0.1 Hz to 100 kHz were tested. Both the change of the current ratio and the angular shift between the transformer secondary current and the total primary current were analyzed.