Abstract
This paper concerns digital speed control for high performance industrial drives (paper machines, rolling mills etc.) based on a novel principle for frequency measurement.In sections 1-2 the principle and theory for digital measurement of angular velocity by means of a low resolution pulse transmitter and the new frequency-to-digital convertor is presented. This system gives high measurement accuracy and resolution combined with short measuring time within a wide speed range at a low ripple content. Further, in section 3 it is shown how this F/D convertor, consisting of a binary rate multiplier, an up/down counter and a register can be built with a few digital integrated circuits.The next section describes the design of the speed control system for a thyristor controlled DC motor drive based on the new F/D convertor. Significantly better steady state accuracy and linearity (better than 0.01 %) compared with present analogue systems has been achieved. The dynamic control performance is also better than that of most analogue systems available (response time better than 30 ms for a 100 kW drive). These characteristics are documented by experimental performance curves.In the last section, two industrial applications of such drives are described - one for a paper machine and one for a wire rod mill. In both cases microprocessor-based program-controlled electronics is used for digital overriding (higher level) control.
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