## 5 Simulation Experiment and Result Analysis
### Simulation Experiment
When the model is mismatched, only when the temperature of the refrigerant inlet fluctuates, a 0.5 step disturbance is added to interference channel 3 when the simulation reaches 200 s, and the simulation effect is shown in Figure 15.  
When the model is mismatched, the three channels of hot fluid flow, hot fluid inlet temperature, and refrigerant flow are disturbed, and the output of the control system in the simulation to 200 s is shown in Figure 16.  
In the case of model mismatch, it can be seen from the simulation diagram that, compared with the scheme with PID as the main controller, the proposed control scheme can better suppress the disturbance and produce little fluctuation. For the feedforward controllers with more accurate parameter settings, such as feedforward controller 1 and feedforward controller 3, the interference can be corrected or minimized before it enters the process. The disturbance does not affect the controlled object. Figure 14: Simulation curve of system output under thermal fluid inlet temperature disturbance under model mismatch. Figure 15: Simulation curve of system output under refrigerant inlet temperature disturbance under model mismatch. (3) Controlled object model mismatch  
To demonstrate the control effect of the control scheme when modeling errors occur in the transfer function of the controlled object, the adjustment parameters of the master and slave controllers, the parameters of the feedforward controller, and the parameters of the disturbance channel are kept unchanged, and the mathematical model parameters of the controlled object are changed and set as: \(G_{PC}(s)=\frac{2}{110.8s^{2}+20.56s+1}e^{-6.166s}\). The same disturbance as the model matching was added to observe the control effect. When the model is mismatched, the step disturbance of 0.5 is added to interference channel 1 only when the hot fluid flow is disturbed. The simulation effect is shown in Figure 17.  
When the model is mismatched, the step disturbance of 0.5 is added to interference channel 2 only when the thermal fluid inlet temperature is disturbed. The simulation effect is shown in Figure 18.  
Figure 13.0 Under the model mismatch, the output curve of the system is disturbed by three inputs simultaneously. Figure 13.1 System output curve under thermal fluid flow perturbation. When the model is mismatched, a step disturbance of 0.5 is added to interference channel 3 only when the refrigerant inlet temperature is disturbed. The simulation effect is shown in Figure 13.2  
In the case of model mismatch, when the three interference channels of hot fluid flow, hot fluid inlet temperature, and refrigerant flow are disturbed, the output of the control system is shown in Figure 13.3  
Figure 13.4 System output curve under refrigerant inlet temperature perturbation. Figure 13.5 The output curve of a system is disturbed by three inputs simultaneously. Figure 13.6 System output curve under thermal fluid inlet temperature perturbation. When a model mismatch occurs in the transfer function of the controlled object, the corresponding simulation curves under different types of disturbance are shown in Figures 17-20. The corresponding dynamic performance indicators are shown in Figure 13.7  
It can be seen from the simulation diagram and dynamic performance indicators that when the mathematical model of the controlled object is mismatched due to modeling errors or other disturbances, the feedforward cascade compound control scheme based on the PID controller has a poor control effect, large overshooting, a long adjustment time, and a poor suppression effect on the disturbance of the three groups of hot fluid flow, hot fluid inlet temperature, and refrigerant inlet temperature. However, the feedforward cascade compound control scheme based on IPFC proposed in this paper has a good control effect, a short regulation time, a small overkill, and a strong inhibition effect against the disturbance of the three groups of input variables, which can make the system quickly restore to a stable state.