A practical tuning methodology for event-based PI control

This paper is focused on the tuning of an event-based PI controller for first-order plus time delay systems (FOPTD). In this work, a novel design and combination of a controller and event generator with an easy-to-use tuning methodology is presented. The event generator combines the Smith predictor structure with the symmetric send-on-delta (SSOD) sampling scheme to compensate the delay and trigger the events. The controller has an adaptive structure with the purpose of improving the set-point tracking and guaranteeing stability under conditions of uncertainty. The approach is focused on FOPTD systems but can be easily extended to higher order systems. Stability and robustness analyses are conducted, and the experimental results verify the effectiveness of the approach.     

A two-degree-of-freedom PI controller based on events

In this paper, a completely event-based two-degree-of-freedom proportional-integral controller is presented. The architecture of the controller is based on event-based decoupled solutions for the set-point following and the load disturbance rejection tasks. For the first task, the solution is a design procedure that, by considering a first-order-plus-dead-time model of the process and a predesigned open-loop control action, produces an event-based feedforward controller that provides the required process variable transition with just two events. The second task is solved by applying two separate event-based proportional and integral control actions. Because the two tasks are initially solved independently, two solutions for coupling them are described. Illustrative examples of the performance of the controller are included as well as experimental results.     

A new design for a PID plus feedforward controller

In this paper, a new design and tuning procedure for a PID plus feedforward controller is proposed. It consists of determining a feedforward signal in order to achieve a predefined process output transition time assuming a first order plus dead time model of the process. Then, the PID parameters are tuned by any conventional method in order to assure a good load disturbance rejection and the reference signal to the closed-loop system is obtained by filtering appropriately the set-point step signal. Simulation and experimental results show that the method outperforms the typical (inverse) model-based approach despite its simplicity and it is therefore suitable to implement in Distributed Control Systems as well as in single-station controllers.     

A switching control strategy applied to a solar collector field

This work presents a new switching control procedure that has been chosen to deal with the changes in plant dynamics. Several control systems composed of IMC-based PID controllers and feedforward compensators are designed for each operation region and a continuous switching mechanism for the overall control system is defined. Experimental tests which have been performed in a distributed collector field of a solar air cooling system, are presented showing promising results for the proposed strategy.     

Characterization of limit cycles for self-regulating and integral processes with PI control and send-on-delta sampling

This work is focused on the study of limit cycles that appear in a control scheme which is based on the use of a PI controller with an event-based send-on-delta sampling (SOD). The processes investigated are integrator processes plus time delay (IPTD) and first and second order processes plus time delay, which are of interest because they are frequently used to model many industrial processes. The SOD sampling is characterized as a non-linearity of n levels with hysteresis. An algorithm to calculate the limit cycles properties is proposed, and then the results obtained in simulations are compared with experiments performed on a real plant, a distributed solar collector field at the Solar Platform of Almería (PSA, Spain).     

Selective pH and dissolved oxygen control strategy for a raceway reactor within an event-based approach

In this study, we introduce a selective pH and dissolved oxygen control strategy for a raceway reactor with an event-based approach. In such a configuration, the pH value is prioritized over the dissolved oxygen value, since it has a critical influence on process performance. On the other hand, the dissolved oxygen also influences biomass productivity and should be kept within the optimal photosynthesis rate limits. The proposed control scheme has been implemented in a pilot-scale raceway reactor, where it was used for simultaneous pH and dissolved oxygen control. The results demonstrated that the analyzed control algorithm improves the microorganism growth condition and, consequently, overall production is increased.     

RPN tuning strategy for model predictive control

A novel tuning strategy based on RPN for MIMO MPC is presented. The RPN indicates how potentially difficult it is for a given system to achieve the desired performance robustly. It reflects both the attainable performance of a system and its degree of directionality. These system's properties are the basis of the proposed RPN-MPC tuning strategy, which is applied in the controller design of an air separation plant and a CSTR with the Van de Vusse's reaction. Although it was only used a linear nominal model, the results can also be applied at least at some extent for nonlinear systems with uncertainties.     

Cost effective water clarification control using a neurally informed control strategy

The abstraction, treatment and supply of potable (drinking) water presents a range of special problems. Early attempts at introducing and extending the range of automatic control at a water treatment plant were invariably compromised by the poor quality of the instrumentation available. Improved sensor technology and the advent of microprocessor based programmable controllers has allowed the implementation of nonstandard solutions. This paper describes the steps followed in developing an accurate feedforward automatic clarification control strategy. The existing strategy was occasionally compromised when a colour measurement was corrupted, usually under conditions of high turbidity. It should be emphasised that the colour monitor used is being asked to operate at and beyond the range of its original design specification. This occurs because there are no other alternative instruments. The paper shows how the use of an artificial neural network produces a solution to a seemingly intractable problem.     

Decoupling two-degree-of-freedom control strategy for cascade control systems

In this paper, two new two-degree-of-freedom control structures are proposed for cascade control systems, both of which are identical in the controller design procedure. The primary controller used for setpoint tracking is derived in terms of H₂ optimal performance objective. The secondary controller is responsible for rejecting load disturbances that seep into the intermediate process and therefore is called a load disturbance estimator, which is inversely figured out by proposing the desired complementary sensitivity function of the inner loop for disturbance rejection. As a result, the nominal setpoint response is decoupled with the load disturbance response of the inner loop, both of which can be optimized independently. Based on the control system stability analysis, the rule of thumb for tuning the single adjustable parameter of each controller is provided to cope with the process uncertainty in practice. Several illustrative examples are included to demonstrate the superiority of the proposed method.     

基于改进差分进化算法的三相逆变系统分数阶PI控制策略

三相逆变系统在新能源发电、电动汽车等诸多领域都得到了广泛的应用,对三相逆变系统的控制器进行持续的优化改进具有重要意义。针对传统三相双闭环逆变控制系统输出电能质量较低和鲁棒性不强的问题,提出了基于改进差分进化算法的分数阶PI三相逆变控制策略(IDE-FOPI)。该策略将分数阶微积分理论引入到双闭环三相逆变控制系统,并基于此对双闭环分数阶PI控制的三相逆变系统进行数学建模。考虑到三相逆变系统是一个复杂的非线性时变网络,其双闭环PI控制器参数整定复杂,传统的参数整定方法整定效果不佳,该策略将三相逆变系统双闭环分数阶PI控制器参数优化问题转换为一个典型的约束优化问题,引入一种基于自适应多变异操作和参数自调节策略的改进差分进化算法对控制器参数优化问题进行求解。仿真测试表明,相对于遗传算法(GA)、粒子群算法(PSO)、传统差分进化算法(DE),本文提出基于改进差分进化的分数阶PI策略所输出的电压谐波畸变率低,动态性能好,抗干扰能力强。     

Passivity-based control design for a grid-connected hybrid generation system integrated with the energy management strategy

Hybrid generation systems produce electric energy from a wide variety of energy sources, including renewable sources. A hybrid system based on renewable sources usually consists of two or more renewable energy sources with the possibility of including storage units so as to enhance the reliability of the system. The hybrid system requires an energy strategy that determines the operation point of each element of the system depending on multiple variables and subjected to the constraints inherent in this kind of systems. In addition, the system needs controllers to command each of these elements in order to reach the operation point established by the energy strategy. Here, we propose a control design via passivity-based control integrated with an energy management strategy for a hybrid generation system based on solar energy and coupled with the grid. The performance of the control methodology is extensively assessed through computer simulation using a comprehensive nonlinear model of the plant. The results show that the controlled system accomplishes the control tasks with good responses, working under very different atmospheric conditions and required load power.     

New design relations for 2-DOF PID-like control systems

Self-regulating processes can be controlled by internal model control systems where the usual three-parameter model of the process is transformed into a rational model via a parametrized first-order approximant of the apparent dead time. Using feedback and feedforward compensators leads to 2-DOF PID controllers whose time constants cancel that of the rational model. To obtain the desired sensitivity of the actual control loop, the model adaptation parameter and a gain tuning factor in the control system are determined by functions of the normalized dead time. The response to setpoint changes is selected by means of the feedforward compensator or via a prefilter. Plots of the sensitivity and the simulation of step responses to changes in the controller setpoint or to disturbances, show the validity of these design relations for transfer functions representative of typical industrial processes.     

Robust position control design for a cylinder in mobile hydraulics applications

Automation of various agricultural tasks, which are nowadays routinely executed by operators of hydraulically actuated tractors equipped with front-end loaders, is an important open problem. The so-called self-leveling task is considered here, where the lifting and lowering motions of the loader are performed manually while the orientation of the tool must be adjusted automatically. The proposed controller is constituted by a proportional feedback, a disturbance compensator based on an observer and a relay controller. A model-based tuning procedure for the controller parameters is discussed and an implementation is validated experimentally on an industry-standard commercial set-up.     

Gain-scheduling model predictive control of a Fresnel collector field

Model predictive control strategies have been applied successfully when controlling solar plants. If the control algorithm uses a linear model associated only to an operating point, when the plant is working far from the design conditions, the performance of the controller may deteriorate.In this paper, a gain scheduling model predictive control strategy is designed for the Fresnel collector field located at the Escuela Superior de Ingenieros de Sevilla. Simulation results are provided comparing the proposed strategy with another linear MPC controller showing a better performance. Furthermore, two real tests are presented showing the effectiveness of the proposed strategy.     

挠性航天器的非线性PID和PI姿态控制器设计

针对存在模型不确性和常值干扰的挠性航天器, 提出一种不依赖于模型参数的非线性PID姿态控制器. 该控制器在小姿态偏差的情况下近似经典的线性PID控制器. 另外, 考虑到航天器上陀螺失效情况, 设计了一种仅需姿态测量信息的非线性PI控制器. 这两种控制器在局部均对常值干扰有抑制作用, 并能使无干扰作用的姿态控制系统半全局渐近稳定. 闭环系统的稳定性证明采用了奇异扰动理论, 以解决积分项的存在带来的稳定性分析问题. 文章最后用数学仿真验证了控制器的性能.     

基于PI 控制器的线性系统的鲁棒耗散控制

针对参数具有确定性及不确定性的连续系统,给出两种严格耗散PI控制器的设计方法.首先,系统参数确定时,采用线性矩阵不等式方法,导出了类状态反馈和静态输出反馈严格耗散PI控制器存在的充要条件,并由线性矩阵不等式的可行解构造出严格耗散PI控制器增益的显式表达式;然后,考虑系数矩阵均具有范数有界不确定性时的鲁棒严格耗散控制问题,得到相似的结果;最后,通过数值算例表明了所给方法的有效性.     

高带宽无线局域网中PI速率控制算法

针对传统传输控制协议（TCP）在高带宽、无线网络中性能表现不佳的问题, 建立了一个端到端的虚拟路由器模型, 提出了一个端到端的发送端比例积分（PI）速率控制算法。根据RTT的变化, 利用PI控制器计算发送端的发送速率, 使瓶颈节点的队长稳定在一个目标位置, 减少拥塞丢包, 避免无线链路错误丢包引起的对拥塞窗口的错误调整。仿真结果表明, 与传统拥塞控制协议相比, 新机制能较好地控制路由器队长、提高网络负载的稳定性和网络吞吐率。     

Robust reliable control design for networked control system with sampling communication

In this article, the problem of robust exponential stability and reliable stabilisation for a class of continuous-time networked control systems (NCSs) with a sample-data controller and unknown time-varying sampling rate is considered. The analysis is based on average dwell-time, Lyapunov–Krasovskii functional and linear matrix inequality (LMI) technique. The delay-dependent criteria are developed for ensuring the robust exponential stability of the considered NCSs. The obtained conditions are formulated in terms of LMIs that can easily be solved by using standard software packages. Furthermore, the result is extended to study the robust stabilisation for NCS with parameter uncertainties. A state feedback controller is constructed in terms of the solution to a set of LMIs, which guarantee the robust exponential stabilisation of NCS and the controller. Finally, numerical examples are presented to illustrate the effectiveness of the obtained results.