Research on the adaptive proportional-integral control method of a direct-expansion photovoltaic-thermal heat pump system

An adaptive proportional-integral control method (APCM) of a direct expansion photovoltaic-thermal heat pump (DX-PVTHP) system is proposed. First, the APCM was adopted and the proportional and integral factors were determined by experiments. Then, a universal engineering model combined the 10-factor model and temperature prediction model is built. The initial electronic expansion valve (EEV) opening during start-up under different working conditions is predicted and the EEV opening under dramatic irradiance changes is corrected under the APCM. Multiple experiments were conducted to evaluate the effectiveness of the APCM and test the performance of DX-PVTHP system under the APCM. The results reveal that the stability of superheat improved under typical cloudy skies and the maximum overshoot value was 3.2 °C. The overshoot time percentage of superheat was 27.54% with a decrease of 36.12% relative to the conventional control method. Moreover, the average coefficient of performance and photoelectric conversion efficiency were 3.51 and 13.25% in household mode, and 3.16 and 13.78% in commercial mode. Furthermore, the comprehensive coefficient of heating and electricity generation (CHE) is proposed to evaluate the comprehensive coefficient of the DX-PVTHP system. The CHE of the system was obtained 34.92% in household mode and 32.83% in commercial mode. •An adaptive control method for photovoltaic-thermal heat pump was proposed.•Engineering model was used to predict the opening of electronic expansion valve.•Comprehensive coefficient of thermal and electricity generation was defined.•Overshoot of superheat was determined less than 3.2 °C under typical cloudy skies.•CHE of system was obtained 34.92% in household and 32.83% in commercial modes.