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Cascade control is used in many practical applications. To realize the desired specification of the cascade control systems, accurate mathematical models of the plant are not only inner but also outer loops required. However, there are also many situations where it is difficult to execute ideal experiments for obtaining mathematical models for practical reasons. In such situations, it is expected that the direct usage of the data for control design enables us to obtain desired controllers. From these backgrounds, we propose a controller tuning method for the two controllers in a cascade control system. Here, we apply virtual internal model tuning proposed by the authors to update the cascade control system. In this proposed method, specifications of the inner and the outer loops can be set independently. The optimal parameters of the controller in each loop can be obtained using the least square method. Finally, the validity and usefulness of the proposed method are illustrated using experiments.

In this paper, we propose a cascade control system design based on linear active disturbance rejection control (SMC&A-LADRC) to address the following quadrotor UAV problems: that the path is easily yawed when disturbed, the control parameters are difficult to optimize, and the tracking accuracy is low. The strategy can effectively eliminate external disturbances and adjust the controller parameters online so that the quadrotor UAV always flies on the optimal path to achieve energy optimization and long-endurance flight. The proposed cascade control system combines the advantages of sliding mode control (SMC) and linear active-disturbance rejection control (LADRC), using the linear extended state observer (LESO) to estimate the uncertain external disturbances and unmodeled internal dynamics of the quadrotor system, compensate for the uncertain signals under SMC chattering, optimize the PD controller parameters online using adaptive control to eliminate the effects of parameter deviations, and simplify the parameter adjustment process. Finally, a stability analysis of the quadrotor cascade control system is carried out by using the Lyapunov theorem of stability, and a simulation analysis is carried out using MATLAB to compare the results with those obtained with classical LADRC. The test results indicate that the control strategy of this paper is reasonable for utilization with a quadrotor attitude and displacement control system, allowing the quadrotor to fly on the optimal path with good anti-interference ability and a fast response speed. [ABSTRACT FROM AUTHOR]

The heating pipe network system with such dynamic characteristics as nonlinearity and large time lag may cause hydraulic disorder. To solve this problem, this paper proposes a unit control-based hydraulic equilibrium control strategy, which constructs an equilibrium regulation system for heating pipe networks by optimising the inlet device of each unit and using a novel control theory. By developing a cascade control system to control the return water temperature and the pressure difference between supply and return water of the branches at each unit of the pipe network, we were able to stabilise the pressure and control the temperature. Then, we used the averaging control theory to set the parameters of regulation systems between each unit. The research results indicate that, compared to the traditional single-loop negative-feedback return water temperature control system, the cascade averaging controller has a better control effect than the single-loop PID controller. This is because it has a smaller overshoot and can cope with system interference factors quickly. Therefore, the temperature of return water between each unit can be coordinated and fluctuation is within a smaller range. This effectively eliminates the influence of static and dynamic hydraulic disorder on entire system stability.

In this paper, we propose a cascade control system design based on linear active disturbance rejection control (SMC&A-LADRC) to address the following quadrotor UAV problems: that the path is easily yawed when disturbed, the control parameters are difficult to optimize, and the tracking accuracy is low. The strategy can effectively eliminate external disturbances and adjust the controller parameters online so that the quadrotor UAV always flies on the optimal path to achieve energy optimization and long-endurance flight. The proposed cascade control system combines the advantages of sliding mode control (SMC) and linear active-disturbance rejection control (LADRC), using the linear extended state observer (LESO) to estimate the uncertain external disturbances and unmodeled internal dynamics of the quadrotor system, compensate for the uncertain signals under SMC chattering, optimize the PD controller parameters online using adaptive control to eliminate the effects of parameter deviations, and simplify the parameter adjustment process. Finally, a stability analysis of the quadrotor cascade control system is carried out by using the Lyapunov theorem of stability, and a simulation analysis is carried out using MATLAB to compare the results with those obtained with classical LADRC. The test results indicate that the control strategy of this paper is reasonable for utilization with a quadrotor attitude and displacement control system, allowing the quadrotor to fly on the optimal path with good anti-interference ability and a fast response speed.

The paper aims to enhance the controllability of a standalone cascade control system with Internet architecture and promote the system to be accessible by remote students. The user interactive web page is developed by using platform independent ASP.NET language and enabled with both monitoring and controlling functionalities. The Internet transmission time delays that are associated with both feed-forward and feedback channels are compensated by using model predictive controller. The performance of cascade control system with and without compensation is validated by measuring indices, such as rise time, peak time and settling time, and also integral square error and integral absolute error. Access privileges among web page users have been added to ensure simultaneous operations as well as security. The cascade control system is an engineering laboratory experiment interfaced with a dedicated computer by using MODBUS protocol and it is made available to the remote students. The user perception analysis is carried out by using a set of questionnaire that observes 85% of positive feedback. [ABSTRACT FROM AUTHOR]

Real-time digital image point tracking feedback was used to control a servo-hydraulic load train during the loading of a Glass Fiber Reinforced Plastic (GFRP) cantilever beam. The loading pattern was defined in terms of two translational and one rotational in-plane degrees-of-freedom at a single control point on the beam. Tests were performed with both single-and multi degree-of-freedom controls, using independent and simultaneous control of the actuators, respectively. A reference control system was set up to transfer the displacements of three hydraulic actuators into a theoretical displacement of the control point using an assumption of rigidity. The discrepancies between this theoretical displacement and the actual displacement were addressed through three control configurations that used a linear transfer function, a feedback signal from the digital image point tracking using Proportional and Integral control, and a combination of these two. Performance was evaluated at frequencies ranging from 0.01 – 1 Hz. The combined implementation of the linear transfer function and digital image point tracking feedback showed the greatest improvement over the reference configuration, reducing the error between the desired and measured signal by 51–93%. [ABSTRACT FROM AUTHOR]

To deal with the inconsistency of the minimum variance (MV) benchmark in evaluating non-Gaussian disturbance systems, this paper proposed a new benchmark, which combined entropy with output mean value. For a cascade control system, the new benchmark was constructed by analyzing the weakness of the MV benchmark and the pure Renyi entropy benchmark. In order to estimate the more accurate performance of the unknown system, an improved estimation of distribution algorithm based on entropy criterion is given. It can identify the disturbance distribution and calculate the new index evaluation value. Finally, different disturbance distributions were used to verify the consistency of the new index. The experimental results show that the proposed index and algorithms are consistent and effective in evaluating the performance of the unknown systems with non-Gaussian disturbance.

In view of the problem that the traditional PID fails to realize load tracking control in real time. a fuzzy PID controller is designed by combining traditional PID control with fuzzy control. The real - time load of the generator is used as the response and input to construct a load tracking fuzzy PID main steam temperature control system. Correction values of the three parameters of the PID controller are obtained through a fuzzy algorithm, and the three parameters of the PID are adjusted online by real - Lime tracking load, and the main steam temperature are controlled lo be stable near the set value. Load fluctuation, load mutation and smoke disturbance are performed and the experimental results show that the error between real - time system data and target temperature value is 1 - 2 °C, the overshoot of the system decreases by 1 . 3 % compared with the traditional method, and the adjustment time shortens by 33. 4% . These results indicate that the proposed system has a strong load tracking ability and better robustness to load fluctuation. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the output tracking control and disturbance attenuation for a class of cascade control systems subject to network‐induced delays. In order to indicate the time‐varying characteristics and uncertainty of network‐induced delays, a switched system approach is applied to the cascade architecture. This leads to the simultaneous design of controllers and switching signals in terms of the network transmission. Unlike the traditional cascade control design approach, which needs to first tune the secondary controller and then the primary one, we can provide a simultaneous design method of the double‐loop controllers and switching signals to make the networked cascade control system achieve the output tracking performance with disturbance attenuation. Finally, two examples are proposed to demonstrate the feasibility and the effectiveness of the approach. [ABSTRACT FROM AUTHOR]

• A control strategy of a space thermionic nuclear reactor is proposed. • The cascade control system is designed for electric power and coolant temperature. • The frequency domain analysis method is used to tune the control parameters. • The bumpless switching of control system is studied to realize the wide rang power regulation. Nuclear reactors are gaining increasing attention for use in spacecraft owing to their long life and high power-density. Because the dynamic characteristics and operation strategy of a space nuclear reactor (SNR) are different from those of a traditional reactor, its control strategy must be investigated to design an appropriate control system. In this study, the dynamic characteristics of the time and frequency domains are analyzed. Based on this analysis, a control strategy is proposed. The cascade control method is applied to the design of control systems, including electric power and coolant temperature control systems. The controller parameters are tuned using the frequency-domain analysis method. To verify the control performance, step and ramp disturbances of the electric power and coolant temperature setpoints are introduced, and comprehensive comparisons are made. Additionally, the startup process is simulated; it reveals that the cascade control systems perform better compared with the traditional proportional-integral-derivative (PID) control. Moreover, the control performance of the wide-range power regulation is smooth and steady. Thus, the control strategy and cascade control system designed in this study can be applied to the thermionic nuclear reactors in space. [ABSTRACT FROM AUTHOR]

Balance evaluation during standing is an important issue for diagnosis of disease and determination of training effect. The purpose of this study is to evaluate personal balance characteristics based on a model from the response of human body when the support surface moves horizontally as an external stimulus. The response of human body was defined as posture angle based on a single-link model and the angle was estimated from two kinds of measurement system. One is a motion capture system and the other is force plates mounted on the support surface. We applied the frequency analysis to the response and identified personal balance characteristics in an assumed balance control model. The balance control model was defined as a multiple feedback loop system which is composed of the delayed state feedback control as an inner-loop and target posture definition according to the velocity of the support surface as an outer-loop. To evaluate personal characteristics from the identified parameters, equivalent damping ratio and natural angular frequency were defined from a pair of conjugate complex roots of the system. As a result, we found that inner-loop characteristics were uniform when the posture angle was estimated from force plates. Outer-loop characteristics contributed to reduce the body sway in the frequency range from 0.1 Hz to 0.2 Hz in theory. The result of seven subjects implied that a subject who has less damping effect tends to use outer-loop system actively.

The work analyzes the performance characteristics of a cascade control system when interconnected with various network architectures, such as Internet, mobile and wireless networks. The cascade control system consists of level and flow as primary and secondary variables, respectively. The web-enabled monitoring and control are realized using three techniques namely remote client–server, ActiveX-data socket and web publishing tool. Mobile network is established by interfacing the control system with a GSM modem which enables the monitoring of process parameters through mobile phones. The cascade control system is also monitored wirelessly from remote locations with advent of an indigenous wireless sensor node. The performance analysis proved that wireless monitoring may be considered as an effective alternate technique to the Internet-based communication especially for shorter distances.

The paper presents the strategies involved in making a stand-alone cascade control system as an Internet enabled one without advent of a dedicated instrument server. The cascaded processes, such as level and flow are independently controlled by particle swarm optimized (PSO) proportional, integral-derivative (PID) and proportional-integral (PI) controller, respectively. The wide area network (WAN) is established wirelessly by using an on-chip Wi-Fi enabled microcontroller, CC3200 that is directly interfaced with level and flow transmitters. The time delays, such as feed forward and feedback that are associated with internet communication are successfully compensated by involving model predictive control (MPC). A private web server is created with adequate data security features to publish and subscribe the real time process data. The web page is enabled with graphical user interface (GUI) that supports real-time plots; control and data logging features. The performance of IoT enabled cascade control system is validated through various metrics, such as rise time, settling time, integral square and integral absolute errors. [ABSTRACT FROM AUTHOR]

The aim of this paper is to outline a design process of an attitude control system for unmanned rotorcraft. This small-scale unmanned aerial robot's concept is based on three rotors and one single tilt mechanism. Final design is consisted of mechanical construction, measurement system including navigation algorithm, as well as control structure and algorithm implementation at the last stage. It is important to underline that high attention was focused on the measurements filtering, estimation of the angular position, and in particular the practical aspects of the control implementation. Furthermore, a PID algorithm including various modified loop structures was studied. On the whole, it is worth to mention that the design, analysis and the validation tests were undertaken on the experimental aerial platform. [ABSTRACT FROM AUTHOR]

The work analyzes the performance characteristics of a cascade control system when interconnected with various network architectures, such as Internet, mobile and wireless networks. The cascade control system consists of level and flow as primary and secondary variables, respectively. The web-enabled monitoring and control are realized using three techniques namely remote client–server, ActiveX-data socket and web publishing tool. Mobile network is established by interfacing the control system with a GSM modem which enables the monitoring of process parameters through mobile phones. The cascade control system is also monitored wirelessly from remote locations with advent of an indigenous wireless sensor node. The performance analysis proved that wireless monitoring may be considered as an effective alternate technique to the Internet-based communication especially for shorter distances. [ABSTRACT FROM AUTHOR]

The cascade system for maintaining the level in the steam boiler drum was investigated. Main features of the system are it’s variable structure which changes depending on the load variation relative to its previous value, and the use of the model of the drum level in dependence of the feedwater flow rate.

This work is devoted to the technique of solving the problem of structural-parametric synthesis of typical controllers in a multiloop cascade automatic control system, which is developed on the basis of the alternance method of parametric optimization that provides the maximum degree of invariance of local control loops relative to external perturbations with given limitations on the peak of amplitude-frequency characteristics of closed loops of the synthesized automatic control system. The task of optimizing the subsystem for controlling the fuel oil temperature in a multiloop control system of primary oil refining on an atmospheric and vacuum crude distillation unit is considered as an example, which is of independent interest. [ABSTRACT FROM AUTHOR]

In order to facilitate DO (dissolved oxygen) monitoring for a scaled aquaculture pond, a DO intelligent monitoring system was developed based on a wireless sensor network, which could realize distribution measurement, intelligent control, and centralized management. The system consists of a three-layer structure including data acquisition and control, water quality monitoring, and water management. The data acquisition and control layer was composed of data acquisition and control terminals, routing nodes, and a coordinator node based on ZigBee technology. They were deployed in the sensing area for an aquaculture pond's waters, and they constituted a wireless monitoring network for water quality environmental parameters by self organization to collect water quality parameters and adjust control devices. The water quality monitoring layer included a water quality monitoring terminal and a communication computer, which realized water quality supervision and aquaculture equipment intelligent control. The water quality management layer contained mainly a water quality management terminal, a system database, and a Web server end. The water quality management end was responsible for analysis and processing for the water quality data. The monitoring system concentrated wireless data acquisition, intelligent control, and centralized management for water quality parameters to improve scale aquaculture benefit and information management level. Aiming at low adaptive ability for conventional fuzzy PID controller, a variable universe fuzzy PID controller was proposed, which comprises an adjustment unit for expansion factors, variable universe fuzzy control unit and PID controller, the extension factor α1, α2 and β for input and output domain of fuzzy control unit were adjusted constantly by an expansion factor regulating unit according to DO error and DO error change rate. PID controller parameters were tuned online by a variable universe fuzzy control unit to realize the purpose for DO adaptive control. According to the DO change characteristics with nonlinear, large delay and large inertia in a pond, the cascade control system was constituted by a variable universe fuzzy PID controller and an aerator speed PID controller. DO was the main controlled variable, and the aerator speed was the secondary controlled variable. If the DO concentration deviates from the setting value, a DO control loop will operate. Its output is the control loop input of the aerator speed, and the output of the aerator regulator changes the aerator speed to make DO concentration fast track the setting value of system target. The cascade control system can timely and accurately adjust the DO concentration to meet aquacultural needs. According to the changing trend of the DO data sequence for multiple pond monitoring sites, a combination grey DO forecasting model was constructed based on grey theory and weights to predict DO concentration and the feedback value for a variable universe fuzzy PID controller. This achieved DO prediction control and beforehand adjustment, and DO overshooting was well restrained. The test pond and the contrast pond respectively used a variable universe fuzzy PID controller and a fuzzy PID controller to regulate DO in the ponds, and the DO target value was 7.10 mg/L. In the dynamic response phase, DO response time for the contrast pond extended about 15 min more than the test pond, and the overshooting expanded 2.96 times. After the system entered steady process, the standard deviation, the mean variance, and the maximum error and minimum error enlarged by 3-4 times. The testing results showed that the adjustment process for the test pond had characteristics with fast response, small overshooting, high control precision, and good stability compared with the contrast pond. The adjusting factors for the variable universe fuzzy PID controller better solved contradictions between the quantity of fuzzy control rules and DO control precision, and realized self tuning for PID parameters, and improved dynamic performance, and raised steady accuracy and quality of the fuzzy PID controller. It can effectively restrain many uncertain factors of interference affecting DO stability to meet aquaculture requirements for DO and provide a new control method to solve control problem for complex objects with a nonlinear and large time delay. [ABSTRACT FROM AUTHOR]

The aim of this research is to examine the different control strategies for the unmanned aerial vehicles (UAV). The control task is formulated as an angular stabilization of the four rotor platform, and also as a tracking problem of chosen state variables. The PID algorithm has been considered in three structures in respect of the optimal control signal applied to the actuators. For better performance of the quadrotor in hover mode the cascade control system has been proposed. The simulation results of attitude control with different PID controller architectures are presented, and confirm the effectiveness of the proposed control structure and theoretical expectations. Moreover, the design and the practical realization of the control architecture on the experimental aerial vehicle are described. The fast prototyping method together with Matlab/Simulink software and DAQ hardware are used for both evolution and validation of control algorithms. The capacity of the attitude stabilization system is important in the development process of more advanced functionality of autonomous flying vehicles; therefore it needs to be highlighted and taken into careful consideration. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the experimental validation procedure of a simple cascade control system through number of architectures, such as SCADA, PLC, OPC and internet. The performance and effectiveness of individual architecture is evaluated on the basis of data rate, rise time, peak time and settling time. In this study, PID is implemented on Micrologix-1200 PLC and RSView-32 SCADA has been used with RSLinx communication software. The PLC–SCADA control loop is implemented with the functionalities such as, real time data analysis, set point modifications, automatic report generation and integration of data with MS-Excel and MS-Access. The enhancement in project data analysis is effectively done through the integration of PLC with Labview. The remote monitoring and control of process parameters is done using NET-ENI. The obtained result proved that the conventional SCADA based control system can be enhanced further more with PLC as well as NI-OPC server significantly. [Copyright &y& Elsevier]

Abstract: This paper is concerned with an improved model free adaptive predictive control (MFAPC) schemer. The controlled system is linearized dynamically to build a predictive model by using the notion of pseudo-partial-derivative. The new control method is applied to the main steam pressure cascade control system, which is a typical controlled process with large time constant and large time-delay parameters in a thermal power plant. The main control loop is implemented by the MFAPC algorithm and the inner control loop is implemented by a conventional PID controller. Simulation results have convinced that the MFAPC-PI cascade control method has good adaptability to overcome disturbances and track point. [Copyright &y& Elsevier]