Thermocompression multi-effect water distiller system and its control method

A thermocompression multi-effect water distiller system, comprising a distillation unit and a control unit;

• the distillation unit comprises a multi-effect evaporator;
• the multi-effect evaporator is a horizontal tube falling film evaporator and is arranged side by side, the shell side of the former-effect evaporator is connected with the tube side of the latter-effect evaporator;
• the control unit controls the distillation unit during the working process, the control unit is a feedforward cascade fuzzy PID model predictive control system, which comprises an inner loop control system and an outer loop control system;
• the inner loop control system is fuzzy PID control, for controlling the flow rate via the pump and controlling the steam pressure via a valve opening, according to a deviation and a deviation change rate of a current controlled quantity, a fuzzy control method is used to form a fuzzy control rule;
• a control system for industrial steam pressure P_steam fluctuation is arranged on the inner loop control system;
• the outer loop control system is model predictive control, and a system performance, a reference trajectory tracking performance and a change degree of the inner loop setting value are taken as an optimization objective, based on the inner loop setting value and the state constraint conditions of the thermocompression multi-effect water distiller system, a rolling optimization model is established:
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• where J(k) is a set optimization objective function;
• EX(rsp) is a system performance evaluation function;
• w(k+i) and yp(k+i|k) are a reference trajectory for the moment of k+i moment and a predicted output for k+i moment at k moment, respectively;
• xmin and xmax are minimum and maximum values of key state parameters of the system;
• x(k+i|k) is a predicted value of the system state parameters at k moment for k+i moment;
• rsp,min and rsp,max are minimum and maximum values of the output value of the model predictive controller to the inner loop controller;
• rsp(k+j) is an output value of model predictive controller to the inner loop controller at k+j moment;
• Δrsp,min and Δrsp,max are minimum and maximum change rates of the output values of the model predictive controller to the inner loop controller;
• Δrsp(k+j−1) is a change rate of the output value of the model predictive controller to the inner loop controller at k+j−1 moment;
• P is a prediction time domain;
• i is a ith moment of the prediction time domain;
• M is a control time domain;
• j is a jth moment of the control time domain;
• pi, λi and qi are weight coefficients at the ith moment.