Intelligent Control Of Vehicle Air Conditioner Based On Fuzzy Theory

Vehicle air conditioner is an adjustment device which changes air quality of the vehicle compartment. In spite of the weather condition outside of the vehicle, it can also keep the temperature, humidity, flowing rate and cleanliness degree of the air inside the vehicle in a comfortable range of the passenger's sense. With the development of the people's growth in the living standard and automotive industry as well as high-tech and electronical technology, vehicle air conditioner as an important part to improve the ride comfort of the vehicle, it is universally applied to many types of vehicles. Strong nonlinearities, large disturbance system as vehicle air conditioner, it's not only difficult to be expressed by an exactitude mathematics model, but also hard to get the perfect controlling objectives. If we adopt fuzzy logic control theory, then we needn't have the mathematical model of the system, also it has a strong adaptation to parametric changes. So towards this kind of time-variating, non-linearity, large disturbance system, we have many advantages applying fuzzy control. On the basis of analyzing and researching fuzzy logic control theory, the discussion to the fuzzy control technology of the vehicle air conditioner was carried on.Fuzzy controller's design: First of all, we took the difference between the compartment temperature and the established temperature, and the rate of changing regard of the difference as input parameters to fuzzy control, and carried on fuzzy processing and quantization to the input parameters. Then we established fuzzy subjection degree of the inputs according to their fuzzy membership functions. Second, we established fuzzy outputs according to their fuzzy control rule. Finally, we translated the fuzzy outputs to precise value according to output fuzzy membership functions, and then we can control output wind speed of air-blower and the open degree of blending damper.Simulation of the compartment temperature: First of all, we proceeded a thermodynamic analysis to the compartment temperature and established asimple mathematical model. Second, we used fuzzy control tool box in Matlab/Simulink and established fuzzy control module of the vehicle air conditioner including output wind speed of air-blower and the open degree of blending damper. Finally, we used the fuzzy controller to simulate the compartment temperature about summer; the result proved that the compartment temperature could approach the established temperature quickly. Although it had a steady-state error, but it already met the index to this type of system as vehicle air conditioner that isn't strict to the precision.Designing of hardware circuit and software program: Using PIC16F873 chip microprocessor as vehicle air conditioner's electronic control cell to design the hardware circuit. It includes sensor information collecting circuit such as temperature sensor, radiation sensor of the sun and so on, a keyboard scan and input circuit consisting of seven press-key, driving and displaying circuit of the liquid crystal, power circuit, driving and controlling circuit of the step motor including blending damper and wind direction damper, driving and controlling circuit of the fan blower's speed control module. Finally, we designed the control flow about main program and each subprogram of the system.