Sliding mode control of the temperature of a nonlinear plate heat exchange system

Based on the working process and principles of a plate heat exchange system, a set of differential equations to control the temperature of the system was deduced. Based on analysis and calculation using FLUENT fluid simulation software, as well as repeated experiments using an experimental platform, mathematical expressions for the variable parameters, such as the temperature difference between cold and hot water and the heat transfer coefficient in the equation set, were determined. In the heat exchange model, the temperature of the cold water entering the heat exchanger and the temperature of the hot water exiting the heat exchanger were taken as the state variables, and the degree of opening of the electric control valves for the open-and closed-circulating cold water were taken as the control inputs. The system showed characteristics typical of a multi-input coupled nonlinear system. Using the method of solving the multi-input nonlinear system in the sliding mode variable structure theory, the model was studied as a type of multi-input affine nonlinear system, and the sliding mode variable structure controller was solved. Simulation research using MATLAB/Simulink was carried out on the nonlinear plate heat exchange control system. The results showed that sliding mode variable structure control had several advantages, including limited overshoot, rapid response speed, and strong anti-interference ability.