# An Improved Data-Driven Integral Sliding-Mode Control and Its Automation Application
## 4 Simulation and Experiment
### Experiment 2: Water-Level Control of CFB  
The second group of experiments selected the water level of the steam drum in a CFB boiler as the research object. This simulation study demonstrates the effectiveness and application prospects of ISMC based on an FFDL data model. The bubble water-level system of a CFB boiler refers to an important set of equipment and technology used to control the boiling state and monitor the water level in the boiler. CFB is an efficient and low-polluting form of boiler, characterized by the circulation and fluidization of particulate materials to achieve the combustion process. The bubble water-level system plays a role in monitoring and controlling the internal water level of fluidized bed boilers, ensuring their normal operation and safe operation. Specifically, the bubble water-level system mainly consists of the following components:  
1. Water-level measurement sensor: used to detect changes in the water level inside the CFB boiler and convert the signal into an electrical signal sent to the control system, usually using pressure or a capacitance-type water-level sensor. 2. Control system: receive the water-level signal sent by the sensor, and according to the difference between the set value and the actual value, automatically adjust the amount of supply water or discharge steam in order to maintain the water level in the safe range. 3. Water-supply system: according to the signal of the control system, adjust the working status and water inflow of the water-supply pump to maintain the level inside the CFB boiler. 4. Exhaust system: the exhaust valve is adjusted to control the discharge or recovery of steam in order to maintain the airtightness and stable working conditions of the CFB. The design and operation of the CFB boiler system plays an important role in improving the boiler efficiency, safe operation as well as reducing energy consumption and pollutant emissions. The goal of controlling the steam-water system of a CFB boiler is to track the boiler feedwater flow rate and maintain the steam temperature within a given range while also ensuring the safety of the boiler and the stability of the steam turbine. By monitoring the water level and automatically controlling the water supply and steam discharge, it can ensure the normal operation of the CFB boiler and effectively prevent boiler accidents caused by too high or too low water levels. In the steam-water system of a CFB boiler (as shown in Figure 5), the steam-water system in the red-dashed box in Figure 5 is simplified to the flow diagram in Figure 6. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Methods** & **FFDL-SMC** & **FFDL-ISMC** \\ \hline Rise time (s) & 6 & 3 \\ Adjust time (s) & 32 & 10 \\ MAE & \(3.32\times 10^{-2}\) & \(8.15\times 10^{-3}\) \\ MSE & \(1.73\times 10^{-2}\) & \(2.27\times 10^{-3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Performance indexes of each control method. Since the physical properties of the boiler body change with time, the turbine water-level system is regarded as a slow time-varying system. Due to the difference in boiler tank capacity and volume, it takes a short time for the change in valve position to be reflected in the change in water level, which shows that there is a time delay in the system, and there is also the problem of interference in the system. Overall, the control problem of the steam-drum water level not only needs to solve the problem of nonlinear and difficult modeling, but also the problem of accompanying disturbances [30,31]. Above all, the turbine water-level system does not have an accurate model and is accompanied by disturbances. The balance between boiler load and water supply is represented by the drum water level in CFB boilers. Therefore, it is crucial to maintain the water level at an acceptable working area in order to guarantee the stability and efficiency of the boiler operation.