Sliding mode control with closed-loop filtering architecture for a class of nonlinear systems

It is well known by equivalent control theory, that in the sliding mode a low-pass filter, working as an average operator, can capture the desired control fairly well from the switching control signals. However, directly adding the filtered signals in parallel with the switching control does not warrant any improvement in the control system performance. In this work, we make clear the underlying reason why the sliding mode control (SMC) system does not function properly with such a simple closed-loop filtering structure. The correct way of incorporating the closed-loop filtering into SMC requires a second low-pass filter, which works concurrently with the first low pass filter to scale down the gain of the switching control. The SMC system with the new closed-loop filtering is able to realize the acquisition of equivalent control or estimate the disturbance, effectively reduce the switching gain to the minimum level, and as a result to eliminate chattering. Complementary to existing SMC, the proposed control system can easily incorporate feed-forward control into the closed-loop for bounded system perturbations. In addition, the frequency-domain knowledge can be easily used to construct the two filters.     

Sliding mode control of coupled tanks

The paper deals with the level control of two coupled tanks. A static sliding mode control scheme is proposed for the system. To greatly reduce the chattering problem associated with the static sliding mode control scheme, two different dynamic sliding mode control schemes are proposed. The proposed control schemes guarantee the asymptotic stability of the closed loop system. To illustrate the developed control schemes, the performance of the closed loop system is simulated using MATLAB. Moreover the proposed control schemes are implemented using an experimental setup. The simulation as well as the implementation results indicate that the proposed control schemes work very well. In addition, robustness of the control schemes to change in system’s parameters as well as to disturbances are investigated.     

Sliding mode control of quadruple tank process

The process investigated herein is the quadruple tank system that is stable only within a limited zone of operating parameters. The process model has been developed from fundamentals and tuned with experimental data. A controller design based on feedback linearization has been tested on this process model. Coupling feedback linearization with sliding mode algorithm provides robust control of the process and performs far superior to conventional PI control. A PC based controller interfaced to the experimental quadruple tank experimental set up has been used to implement this algorithm and test its performance. Inserting a ‘boundary layer’ around the sliding surface reduced the ‘chattering’ associated with sliding mode control. The implemented controller provides robust control and excellent set point tracking.     

具有输入饱和的光电伺服平台的滑模控制

为了解决光电伺服平台中的输入饱和问题，采用了基于过渡过程的滑模控制算法。过渡过程算法是基于时间最优理论设计的，将跳变的输入信号变为一个缓慢上升的信号，使系统的初始跟踪误差减小，从而避免了输入饱和现象，提高了系统的稳定性。结果表明，该方法可以有效消除输入饱和现象，适用于光电伺服平台的目标跟踪，具有重要研究与应用价值。     

Sliding mode control design principles and applications to electricdrives

The basic concepts, mathematics, and design aspects of variable-structure systems as well as those with sliding modes as a principle operation mode are treated. The main arguments in favor of sliding-mode control are order reduction, decoupling design procedure, disturbance rejection, insensitivity to parameter variations, and simple implementation by means of power converters. The control algorithms and data processing used in variable structure systems are analyzed. The potential of sliding mode control methodology is demonstrated for versatility of electric drives and functional goals of control     

Sliding mode control with time-varying hyperplane for AMB systems

Deals with sliding mode hyperplane design for a class of linear parameter-varying (LPV) plants, the state-space matrices of which are an affine function of time varying physical parameters. The proposed hyperplane, involving a linear matrix inequality (LMI) approach, has continuous dynamics due to scheduling parameters and provides stability and robustness against parametric uncertainties. We have designed a time-varying hyperplane for a rotor-magnetic bearing system with a gyroscopic effect, which can be considered an LPV plant due to parameter dependence on rotational speed. The obtained hyperplane is continuously scheduled with respect to rotational speed. We successfully carried out experiments using a commercially available turbomolecular pump system and results were reasonable and good     

Sliding mode control and stability analysis of buck DC-DC converter

This paper is proposed to deal with the voltage regulation of buck DC-DC converter based on sliding mode control (SMC) technology. A buck DC-DC converter with parasitic resistance is inherently a bilinear system possessing inevitable uncertainties, such as variable resistive load and input disturbance. First, the buck DC-DC converter is modified into an uncertain linear model. Then, SMC technology is adopted to suppress the input disturbance and reduce the effects from the load variation. In addition, the continuous conduction mode (CCM) for normal operation can be guaranteed by the design of sliding function. Finally, experimental results are included for demonstration.     

Sliding mode multilevel control for improved performances in powerconditioning systems

A novel control technique has been devised to obtain high dynamics responses from a multilevel power conditioning converter. The theory of variable structure control systems with sliding mode has been followed, taking into account several problems that may be encountered in space environments. The analytical study made provides general tools to design AC power conditioning systems for any application. The new control scheme, its mathematical analysis and digital simulation results relevant to a 115 V/400 Hz AC power system are presented and discussed     

时变扰动下的永磁同步电机滑模控制

时变扰动环境下,永磁同步电机(PMSM)采用鲁棒性较好的滑模控制.根据滑模控制中传统指数趋近律,提出一种改进型的趋近律,并基于改进型趋近律设计了一种PMSM调速系统的滑模速度控制器,提高电机的运行性能.通过仿真结果对比分析,设计的基于改进型趋近律的滑模速度控制器不仅可以提高系统的动态性能,而且削弱了系统的抖振现象,使电...     

Sliding mode input-output linearization and field orientation forreal-time control of induction motors

This paper deals with real-time control of an induction motor based on a digital signal processor (DSP) TMS320C31/40-MHz-based system. A sliding mode controller (SMC) is presented and compared with the well-known field orientation and input-output linearization techniques. To estimate the rotor flux, a sliding mode observer is used. Experimental results are given to highlight the performances and disadvantages of these methods with respect to rotor resistance variations     

Technical note Sliding mode control for a class of hydraulic position servo

The present paper discusses a sliding mode control method suitable for controlling a hydraulic position servo with a flexible load. Due to the requirements of the control system, the reference model is designed for the case of a flexible load. The core of sliding mode control is switching surfaces which are specially defined for the system according to the mathematical model and control goal. A novel algorithm is developed, and the simulated and experimental results of the control system are shown. The results show the extremely good robustness of the proposed method.     

新型混联机构结合扰动观测器的滑模控制

针对一种新型混联式汽车电泳涂装输送机构,考虑其在实际控制中存在建模误差、参数不确定性、摩擦力和外部未知干扰,为削弱其对系统产生的不利影响,提高输送机构的控制性能,提出一种结合扰动观测器的滑模控制策略。运用Lyapunov稳定性理论证明了所提出控制算法的稳定性,并对滑模控制和结合扰动观测器的滑模控制进行MATLAB仿真比较。     

Sliding mode based powertrain control for efficiency improvement in series hybrid-electric vehicles

This study involves the improvement of overall efficiency in series hybrid-electric vehicles (SHEVs) by restricting the operation of the engine to the optimal efficiency region, using a control strategy based on two chattering-free sliding mode controllers (SMCs). One of the designed SMCs performs engine speed control, while the other controls the engine/generator torque, together achieving the engine operation in the optimal efficiency region of the torque-speed curve. The control strategy is designed for application on a SHEV converted from a standard high mobility multipurpose wheeled vehicle (HMMWV) and simulated by using the Matlab-based PNGV Systems Analysis Toolkit (PSAT). The performance of the control strategy is compared with that of the original PSAT model, which utilizes PI controllers, a feedforward term for the engine torque, and comprehensive maps for the engine, generator and power converter (static only), which constitute the auxiliary power unit (APU). In this study, in spite of the simple modeling approach taken to model the APU and the optimal efficiency region, an improved performance has been achieved with the new SMC based strategy in terms of overall efficiency, engine efficiency, fuel economy, and emissions. The control strategy developed in this work is the first known application of SMC to SHEVs, and offers a simple, effective and modular approach to problems related to SHEVs.     

一种单连杆机械臂柔性关节的滑模变结构控制

研究一种带柔性关节的单连杆机械臂的跟踪控制问题,其中体现关节柔性的是连接单连杆机械臂和驱动电机的两个仿腱线弹簧。利用Lagrange方程导出跟踪控制问题的数学模型,引进滑模变结构控制技术,给出Hurwitz多项式的确定以及滑模控制器的设计方法,并讨论Hurwitz多项式的根对控制效果的影响。将滑模控制器的表示式代入跟踪控制问题的数学模型中,得到状态变量的非线性微分方程组,利用Matlab进行仿真,得到了理想的控制输出效果。     

Fuzzy logic control of FES rowing exercise in paraplegia

An indoor personal rowing machine (Concept 2 Inc., Morrisville, VT) has been modified for functional electrical stimulation assisted rowing exercise in paraplegia. To successfully perform the rowing maneuver, the voluntarily controlled upper body movements must be coordinated with the movements of the electrically stimulated paralyzed legs. To achieve such coordination, an automatic controller was developed that employs two levels of hierarchy. A high level finite state controller identifies the state or phase of the rowing motion and activates a low-level state-dedicated fuzzy logic controller (FLC) to deliver the electrical stimulation to the paralyzed leg muscles. A pilot study with participation of two paraplegic volunteers showed that FLC spent less muscle energy, and produced smoother rowing maneuvers than the existing On-Off constant-level stimulation controller.     

Sliding mode control for an active magnetic bearing system subject to base motion

This paper describes the application of an active magnetic bearing (AMB) system to levitate the elevation axis of an electro-optical sight mounted on a moving vehicle. In this type of system, it is desirable to retain the elevation axis in an air–gap between magnetic bearing stators while the vehicle is moving. A sliding mode control is applied to increase robustness to model uncertainties and to reduce disturbance responses. To ensure the authority of sliding mode control, model parameter uncertainties of AMB systems are analysed and reachability to sliding surface has been verified. The sliding surfaces are designed such that the poles of the closed-loop system locate at desired locations. The proposed control is applied to a 2-DOF active magnetic bearing system subject to base motion. The feasibility of the proposed technique is verified with experimental results.     

A novel dynamic series compensator with closed-loop voltage and current mode control for voltage sag mitigation

The increased use of voltage-sensitive equipment in the industrial sector has made industrial processes more susceptible to supply voltage quality problems in the form of voltage sags. Series-connected voltage source converter (VSC)-based devices have been gaining popularity in protecting sensitive loads against voltage sags. This paper presents a novel transformerless dynamic series compensator (DSC) to mitigate long-duration voltage sags effectively. A line-side controllable rectifier connected to the proposed DSC maintains the dc-link voltage at a specific value while the DSC compensates voltage sags. The DSC is controlled by a closed-loop voltage and current mode controller which provides better damping and dynamic performance than that of in open-loop controller. The closed-loop controller consists of an outer voltage loop and an inner current loop derived from filter capacitor current. Performance of the proposed DSC is tested under varied voltage sag conditions, and simulated and experimental results are presented to show the effectiveness of the proposed DSC in mitigating long-duration voltage sags.     

Tuning of a nonanalytical hierarchical control system for reachingwith FES

Point-to-point functional movements involve simultaneous shoulder and elbow joint rotations. In able-bodied subjects these movements are fully automatic, and feed-forward control ensures the synergistic activity of many muscles. Synergy between joint rotations was defined and described as a scaling between joint angular velocities (M. Popovic and D. Popovic, J. Electromyog. Kinesiol., vol. 4, p. 242-53, 1994). Similarly, subjects who can control their shoulder movements may be assisted in reaching tasks by functional electrical stimulation (FES) of elbow extensor muscles. The synergistic control paradigm can be implemented in real-time by employing a hierarchically structured production-rules method. The use of production-rules necessitates the acquisition of knowledge and the assembly of a rule-base. A nonparametric technique was designed for the identification of the rules. The identification process was divided into two phases: determination of the scaling parameters, and determination of the stimulation parameters. The scaling parameters, needed for the coordination of movements, were determined in able-bodied subjects. Those depend exclusively on the initial and target positions of the hand. The number of scalings could be reduced by dividing the workspace into 12 zones. The stimulation parameters, needed for the execution of movements, were determined in subjects with paralyzed elbow extensor muscles by identifying triplets: elbow angular velocity, elbow angular acceleration (velocity increments), and the corresponding pulse durations for various classes of movements and loads attached to the hand     

Sliding mode controller by use of neural networks

This paper proposes a method to design a robust controller by use of a neural network. The trained neural network functions as a sliding mode controller which is robust against uncertainties. From the analysis of the neural network, it is proved that the switching surface is not the same as the sliding surface like conventional sliding mode control theory. The neural network shows that the switching surface should be a nonlinear surface because of a hard limitation on control inputs, even if the designed sliding surface is linear. From the result of estimating the robustness of neural networks, we propose that generalization of neural networks which are used as controllers should be measured by the robustness. Numerical simulations show that the controller is robust against uncertainties and robustness can be improved by the proposed method.     

Artificial neural network control of FES in paraplegics for patientresponsive ambulation

Describes a binary adaptive resonance theory (ART-1)-based artificial neural network (ANN) adapted for controlling functional electrical stimulation (FES) to facilitate patient-responsive ambulation by paralyzed patients with spinal cord injures. This network is to serve as a controller in an FES system developed by the first author which is presently in use by 300 patients worldwide (still without ANN control) and which was the first and the only FES system approved by the FDA. The proposed neural network discriminates above-lesion upper-trunk electromyographic (EMG) time series to activate standing and walking functions under FES and controls FES stimuli levels using response-EMG signals. For this particular application, the authors introduce several modifications of the ART-1 for pattern recognition and classification. First, a modified on-line learning rule is proposed. The new rule assures bidirectorial modification of the stored patterns and prevents noise interference. Second, a new reset rule is proposed which prevents “exact matching” when the input is a subset of the chosen pattern. The authors show the applicability of a single ART-1-based structure to solving two problems, namely, 1) signal pattern recognition and classification, and 2) control. This also facilitates ambulation of paraplegics under FES, with adequate patient interaction in initial system training, retraining the network when needed, and in allowing patient's manual override in the ease of error, where any manual override serves as a retraining input to the neural network. Thus, the practical control problems (arising in actual independent patient ambulation via FES) were all satisfied by a relatively simple ANN design