Experimental Research on Parallel Conversion Control of Drying Temperature in a Closed-Loop Heat Pump Dryer

Abstract

The paper proposes a method to handle the challenge of temperature control in a closed-loop heat pump dryer that can operate both in heating cycle and refrigeration cycle. It is hard to avoid the violent fluctuations of drying temperature as the operation mode changes. Hence, the parallel conversion control is introduced to realize the accurate control of drying temperature. The main idea of the controller design lies in the use of different membership functions and fuzzy control rules for the two operation modes. Experimental results show that the temperature fluctuations are reduced when using parallel conversion control with fast and stable response as compared to the fixed-frequency and PID control system. One of the parameters, R _f , representing the value of undershoot ratio is 0.4, 0.48, and 0.64 when drying temperature is fixed at 30, 35, and 38°C, respectively, with a parallel conversion controller. In order to study the application prospects of the parallel conversion control system, a comparison experiment with different compressor frequency ranges was also conducted.

Keywords:

• Closed-loop dryer
• Compressor frequency range
• Heat pump drying
• Parallel conversion control

ACKNOWLEDGMENTS

This research is supported by the National Natural Science Foundation of China (Grant No. 51076112) and National Natural Science Foundation of China (Grant No. 51276124), Science and Technology Project of Tianjin City (Grant No. 12ZCDGGX49400).