Development of proportional-sum-derivative control methodology

Abstract

A newly developed proportional-sum-derivative (PSD) control methodology is introduced. The need for on-line local controllers that can be adapted to existing proportional-integral-derivative (PID) controllers without additional effort for re-tuning motivates this work. The PSD control methodology is founded on the basis that an increase in energy efficiency and an enhancement in thermal comfort conditions are achieved by means of decreasing both the energy input and the heating/cooling-cycle changeovers. The objectives of this article are to describe the PSD control methodology and to compare the performance of the PSD and PID controllers. For the case where the gain coefficients are equal, the comparison is made using cost indices based on the controller energy and the offset of temperature from the setpoint temperature. The results show that the energy cost for the PSD controller is 64% lower than that for the PID controller. Also, because of fewer oscillations in zone temperature, the change-over to PSD results in better comfort conditions although the steady-state zone temperature is 0.5% higher than that of PID control methodology. The study performed on tuning the PSD controller indicates that various forms of performance objectives, such as lowering energy cost or lowering comfort-penalty, can be achieved. The PSD control methodology is adaptable to PID controllers that are currently in operation and should be considered in new installations.