Torque disturbances and their effect on process control

The paper seeks to demonstrate the deleterious effects that torque disturbances can have on an industrial process where close control of speed is required to maintain product quality. The paper also highlights the type of disturbance arising from driven equipment as well as those generated from a variety of different types of drive used for variable speed applications within ICI Films. The need to consider the system in the frequency domain, as opposed to the time domain is encouraged as a useful guide to assessing the capability of the drive system in dealing with torque disturbances. Tuning the drive controller can improve the system bandwidth but practical difficulties in achieving optimal tuning in an industrial environment are discussed. Finally the results of analytical techniques are presented as a means of minimising the effect of torque disturbances. It is suggested that a control algorithm, other than a conventional P+I controller, together with a form of constraint optimisation may be required within the drive controller to achieve the desired level of performance. It is envisaged that this could form part of a model reference adaptive control system or alternatively on a simpler level to be used off line, within an expert system shell