Theoretical And Experimental Research On Overheating Control Of A Gas Engine-driven Heat Pump Heater

With the improvement of citizen living standards in our country, a lot ofhousehold are wildly used now. Currently, about70%of the families are using waterheaters, so energy-saving and environmental protection of water heaters areincreasingly concerned. Main products of water heater include: heat pumpwaters,gas water heaters, electric water heaters and solar water heaters and they havetheir own advantages and disadvantages.The gas engine-driven heat pump water heater is a new kind of efficient andenvironmentally friendly water heater system, based on the gas engine-driven heatpump and heat pump water heater. The system has the characteristic of working underdifferent load, so the refrigerating fluid flow may change a lot and thermal expansionvalve can not meet the system requirements.This thesis took electronic expansionvalve to control the system overheating and conducted its theoretical and experimentalresearch, completing programming using Siemens PLC200as principal computer.The contents are as follows:Obtain the response curve of the system overheating by applying a step signal.Use the least squares method to establish the overheating dynamic response model ofgas engine-driven heat pump water heater system.This paper aims to study the overheating control strategy when the gasengine-driven heat pump heater runs in start-up or normal operating stage and theimpact of gas engine’s variable speed on overheating control result. In theexperimental process, we adopted the strategy of feedforward-fuzzy self-adaptivePID in the start stage and fuzzy self-adaptive PID in normal operation stage to controlthe overheating of gas engine-driven heat pump，and design the fuzzy adaptive PIDcontroller.Apply the strategy of feedforward-fuzzy self-adaptive PID in the start stage andfuzzy self-adaptive PID to the systerm of gas engine-driven heat pump waterheater.The results show that: during the start-up stage, the maximum overshoot ofoverheating is less than5℃and adjusting time is300s or so; In normal operationstage, the fuzzy self-adaptive PID is superior to gain scheduling control when theengine speed and the set value of overheating changes and the overheating control effect is better when the speed is high; fuzzy self-adaptive PID used in gasengine-driven heat pump heater system can effectively overcome the systeminterference and improve control quality.