Control of mixed-flow grain driers; testing of a feedback-plus-feedforward algorithm

A feedback-plus-feedforward controller, originally designed using a computer simulation, was tested on a laboratory-scale mixed-flow grain drier. The response to large step changes in the input moisture content (m.c.) of re-wetted wheat was investigated over the range of input wheat moistures 0·19 to 0·27 dry basis (d.b.) and drying air temperatures 60 to 120 °C, and was found to be stable, uniform over the range of operating conditions, sufficiently fast, and tolerant of large errors in the fixed control parameters. The contribution from the feedforward term made possible much better control than could have been achieved by feedback alone, but the accuracy of the feedforward action was limited by systematic errors in the measurements of input moisture.