Simulation And Experiment Study On Automatic Control System Of Gas Engine-driven Heat Pumps

The Gas Engine-Driven Heat Pump (GEHP) is a high performance and environment-friendly equipment that can provide heating or cooling and many scholars have conducted in-depth study on GEHP. In this paper, we have accomplished software/hardware optimization of control system, studied the superheat control, gas engine dynamics characteristics and the variable volume adjustment on aspects of theory and experiment and proposed control strategy for different control loops. The controllers of GEHP developed in this thesis ultimately provide better transient and steady state performance. The main contents of this paper are as follows:The optimization of software/hardware achieves the aims of accurate detection of the controlled variable and the reduction of the execution time of step motor. Control-oriented dynamic models of GEHP have been developed by using mechanism modeling and experiment modeling methods and validated with test data collected from a fully instrumented experiment system, which lay the foundation for automatic control system of GEHP.The theoretical analysis and experiment study on the evaporator superheat control shows that compressor speed is the main factor in determining refrigerant flow and the opening percentage of electronic expansion valve should match the compressor rotary speed. In order to compensate the effects of changes in compressor speed and evaporator nonlinear characteristics on the superheat control, the gain scheduling control strategy of superheat has been proposed, which ensures safe and stable operation of compressor and provides better transient and steady state performance.The engine operation conditions are summarized as four typical conditions according to expert knowledge and the engine rotary speed expert controller has been designed based on operation rules of different conditions and dynamics characteristics of engine. Simulation study has been carried out under different conditions by using constructed control models and ultimately the expert controller has been applied to engine rotary speed control in a GEHP system experimentally with good dynamic performance. Cascade control strategy has been proposed to achieve capacity adjustment based on the analysis of the characteristics of GEHP and cascade control strategy. The temperature control loop is primary loop and engine rotary speed control loop is inner loop. The simulation and experiment results show that cascade controller of GEHP can improve the GEHP operating characteristics, control effect and robustness, and has good performance over a wide range of operating conditions.