Standard Control System Research Articles

Analysis of robustness of standard control systems for the electric drive

Many of both ac and dc drives are characterized by variation in parameters, which is sometimes significant, while in operation. This results in worsening of the control property and accuracy and negatively affects the production process. Therefore, analysis of control systems of electric drives aimed at providing low sensitivity of static and dynamic characteristics to parametrical fluctuations remains a pressing issue. Typical current and speed-control systems of electric drives are considered under variation in control-object parameters. Analysis of the main disturbing factors acting in electric drives is performed. Interval models of control objects and elements of interval mathematics are used to study the robust properties of control systems. Integrated interval models of objects in control contours of the current and speed taking into account the variation in major parameters are found. Two variants of current controllers (with object lag compensation and without it) and three speed controllers (P, PI, and PID) with standard tunings are considered. Theoretical analysis of these systems is performed using coefficient evaluations of stability, property, and accuracy. The current controller with control-object lag compensation is shown to be more sensitive to variation in parameters. Complication of the controller in the speed control loop leads to a decrease in sensitivity. Results of mathematical modeling that confirm these conclusions are presented.

Experimental model and analytic solution for real-time observation of vehicle’s additional steer angle

The current research of real-time observation for vehicle roll steer angle and compliance steer angle(both of them comprehensively referred as the additional steer angle in this paper) mainly employs the linear vehicle dynamic model, in which only the lateral acceleration of vehicle body is considered. The observation accuracy resorting to this method cannot meet the requirements of vehicle real-time stability control, especially under extreme driving conditions. The paper explores the solution resorting to experimental method. Firstly, a multi-body dynamic model of a passenger car is built based on the ADAMS/Car software, whose dynamic accuracy is verified by the same vehicle’s roadway test data of steady static circular test. Based on this simulation platform, several influencing factors of additional steer angle under different driving conditions are quantitatively analyzed. Then ɛ-SVR algorithm is employed to build the additional steer angle prediction model, whose input vectors mainly include the sensor information of standard electronic stability control system(ESC). The method of typical slalom tests and FMVSS 126 tests are adopted to make simulation, train model and test model’s generalization performance. The test result shows that the influence of lateral acceleration on additional steer angle is maximal (the magnitude up to 1°), followed by the longitudinal acceleration-deceleration and the road wave amplitude (the magnitude up to 0.3°). Moreover, both the prediction accuracy and the calculation real-time of the model can meet the control requirements of ESC. This research expands the accurate observation methods of the additional steer angle under extreme driving conditions.

Energy-Efficient Control of Evaporative Cooling Towers for Small Steam Power Plants

Forced draft evaporative cooling towers are often used for condenser cooling in small steam power plants. Conventional control strategies keep the cooling pump operating at full speed all the time, and control the cooling water temperature by modulating the tower fan speed. In this work, an energy-efficient control strategy is proposed, that minimizes the combined consumption of the tower fans and circulation pump, while also avoiding the sustained operation of the fans within some forbidden velocity range, to avoid resonance effects. The proposed strategy can be easily implemented within standard industrial control system, and is demonstrated to operate satisfactorily by a simulation study.

Stability analysis of a run-of-river diversion hydropower plant with surge tank and spillway in the head pond.

Run-of-river hydropower plants usually lack significant storage capacity; therefore, the more adequate control strategy would consist of keeping a constant water level at the intake pond in order to harness the maximum amount of energy from the river flow or to reduce the surface flooded in the head pond. In this paper, a standard PI control system of a run-of-river diversion hydropower plant with surge tank and a spillway in the head pond that evacuates part of the river flow plant is studied. A stability analysis based on the Routh-Hurwitz criterion is carried out and a practical criterion for tuning the gains of the PI controller is proposed. Conclusions about the head pond and surge tank areas are drawn from the stability analysis. Finally, this criterion is applied to a real hydropower plant in design state; the importance of considering the spillway dimensions and turbine characteristic curves for adequate tuning of the controller gains is highlighted.

Nonconvex model predictive control for commercial refrigeration

We consider the control of a commercial multi-zone refrigeration system, consisting of several cooling units that share a common compressor, and is used to cool multiple areas or rooms. In each time period we choose cooling capacity to each unit and a common evaporation temperature. The goal is to minimise the total energy cost, using real-time electricity prices, while obeying temperature constraints on the zones. We propose a variation on model predictive control to achieve this goal. When the right variables are used, the dynamics of the system are linear, and the constraints are convex. The cost function, however, is nonconvex due to the temperature dependence of thermodynamic efficiency. To handle this nonconvexity we propose a sequential convex optimisation method, which typically converges in fewer than 5 or so iterations. We employ a fast convex quadratic programming solver to carry out the iterations, which is more than fast enough to run in real time. We demonstrate our method on a realistic model, with a full year simulation and 15-minute time periods, using historical electricity prices and weather data, as well as random variations in thermal load. These simulations show substantial cost savings, on the order of 30%, compared to a standard thermostat-based control system. Perhaps more important, we see that the method exhibits sophisticated response to real-time variations in electricity prices. This demand response is critical to help balance real-time uncertainties in generation capacity associated with large penetration of intermittent renewable energy sources in a future smart grid.

A Novel Piezoelectric Strain Sensor for Simultaneous Damping and Tracking Control of a High-Speed Nanopositioner

This paper presents a novel piezoelectric strain sensor for damping and accurate tracking control of a high-speed nanopositioning stage. Piezoelectric sensors have the benefit of simple interface circuitry, low cost, high sensitivity, and high bandwidth. Although piezoelectric sensors have been successfully used as vibration sensors in smart structures, complications arise when they are used in a feedback loop for tracking. As piezoelectric strain sensors exhibit a capacitive source impedance, a high-pass filter is created, typically with a cut-off frequency of 1 to 10 Hz. This filter can cause significant errors and destabilize a tracking control system. Here, we overcome this problem by using a low-frequency bypass technique to replace the low-frequency component of the strain measurement with an estimate based on the open-loop system. Once the low-frequency filter is accounted for, any standard control system can be applied. In this paper, an analog integral resonant controller together with an integral tracking controller are implemented on a flexure-guided nanopositioner. The resulting closed-loop bandwidth is experimentally demonstrated to be 1.86 kHz. The nanopositioner is installed in an Atomic Force Microscope to obtain open- and closed-loop images at line rates of 40 and 78 Hz. Images recorded in closed loop show a significant improvement due to the elimination of nonlinearity.

Predictive Prevention of Loss of Vehicle Control for Roadway Departure Avoidance

In this paper, we investigate predictive approaches to the problem of roadway departure prevention via automated steering and braking. We assume a sensing infrastructure detecting road geometry and consider a two-layer accident avoidance framework consisting of a threat assessment and an intervention layer. A novel active safety function for prevention of loss of vehicle control is proposed and implemented using the considered accident avoidance framework. Simulation and experimental results are presented, showing that the proposed approach effectively exploits road preview information to prevent the vehicle from operating in regions of the state space where standard electronic stability control systems are normally activated.

Quality Analysis on Clinical Pathway Medical Records

Objective. To investigate the content and method of quality control for clinical pathway (CP) medical records. Methods. The items of quality control for medical records were established according to standardized CP of hospitalization process and treatment chart for patients having acute ST-elevation myocardial infarction. Totally 121 cases of acute ST-elevation myocardial infarction were investigated for medical records quality based on clinical pathway. Results. Out of the 121 medical records of acute ST-elevation myocardial infarction, the length of hospitalization time is the most unconformable item in CP standard with a defect rate of 14.1%, while the admission diagnosis, diagnostic evidence, inspection items, operation time, the discharge evaluation, and variation factors possess a defect rate between 4.1% and 12.4%. Conclusion. The quality control of medical record is closely related to the standardization of CP implementation. It will be helpful in carrying out CP through setting up a standardized CP medical record quality control system and CP medical record quality control measures for implementing focus on CP management.

Maximizing a state convex lagrange functional in optimal control

We consider the maximization problem for an integral functional with a state-convex integrand function along a standard control system. We show necessary and sufficient global optimality conditions related to the Pontryagin's maximum principle. We study the properties of these conditions and their relations with optimal control theory. We also illustrate the efficiency of the resulting conditions on specific examples.

Visual Feedback PID Control for 2DOF Parallel Link Manipulator

This paper investigates the visual feedback control for 2DOF(degrees of freedom) parallel link manipulator with zero steady-state error. Firstly we present the model of visual feedback system of the eye-in-hand configuration. Secondly we consider a novel desired joint angle defined by visual information and joint angles based on the structure of the parallel link, because a desired joint angle cannot be given as a standard robot motion control system. Next we propose the PID control law for the visual feedback system in order to overcome steady-state error with respect to the uncertainty of the position and the orientation for the base frame. For the proposed control law, stability analysis of the closed loop system is discussed in the sense of Lyapunov method with a sufficient condition for the feedback gains. Finally the experimental results are shown in order to confirm the validity of the proposed method by comparing with a previous visual feedback control law.

Adaptive Control of H/N Ratio in Ammonia Production

A system for adaptive control of Hydrogen/Nitrogen (H/N) ratio in ammonia production is proposed. It ensures more accurate, robust control of H/N ratio under varying operating conditions. A short description of the process is presented, and its model based on the first principles is elaborated. The computer simulation tests were performed using software tools created in Matlab ( The MathWorks, Inc. ) program environment. Simulation results of the proposed adaptive control system performing under extreme operating conditions are presented and compared with the performance of the standard control system. Ill. 3, bibl. 10 (in English; abstracts in English and Lithuanian). http://dx.doi.org/10.5755/j01.eee.115.9.756

Design and Analysis of Model Following Control Structure with Nonlinear Plant

Abstract. Linearization methods of the object: input-state and input-output linearization are used usually in a standard feedback control system. However, these systems are sensitive to the changes of nonlinear characteristics of the plant. These changes can be compensated in two types of control systems: in the model following control (MFC) and adaptive. The article presents the first solution and contains: miscellaneous structures of linear control systems with model following, brief description of the linearization’s methods, simulation example of the course control of vessel and the advantages of this solution.

Study on Open Standard Control System of Walking Assistant Robot for the Elderly

To solve the problems of the control system of the working assistant robot for elderly such as lower efficiency and weak complicity. A kind of open architecture, modularity, extensible embedded robot control system is developed. The main contents include: Studied on a rich hardware interface and drivers, function easy-to-modular extended robot development platform. The paper presented the platform features, design concepts and system solutions of the robot control system and gave details of building approaches of the platform. On this basis, the functional modules of the robot were designed and implemented with the modular design approach. Finally a specified working assistant robot was created by loading the completed modules into the control system platform and some experiments were carried out on the robot system. Experiments results show that the system platform can be a convenient and effective way to develop multi-functional working assistant robot for elderly.

A new algorithm for generalized Sylvester-observer equation and its application to state and velocity estimations in vibrating systems

We propose a new algorithm for block-wise solution of the generalized Sylvester-observer equation XA−FXE = GC, where the matrices A, E, and C are given, the matrices X, F, and G need to be computed, and matrix E may be singular. The algorithm is based on an orthogonal decomposition of the triplet (A, E, C) into the observer-Hessenberg-triangular form. It is a natural generalization of the widely known observer-Hessenberg algorithm for the Sylvester-observer equation: XA−FX = GC, which arises in state estimation of a standard first-order state-space control system. An application of the proposed algorithm is made to state and velocity estimations of second-order control systems modeling a wide variety of vibrating structures. For dense un-structured data, the proposed algorithm is more efficient than the recently proposed SVD-based algorithm of the authors. Copyright © 2010 John Wiley & Sons, Ltd.

Model order reduction for large LTI control systems

An overview of model-order-reduction methods for descriptor control system is presented, with the emphasis on the Krylov-subspace-based methods. We used two standard benchmark descriptor problems for an empirical comparison of the methods. The results indicate that the methods perform differently, depending on whether they are used on generalized control systems or on standard control systems.

A robust control of electro hydrostatic actuator using the adaptive back-stepping scheme and fuzzy neural networks

In general, the position control of electro hydrostatic actuator(EHA) systems is difficult because of the large variation of the effective bulk modulus of the working fluid, which is due to the absence of a heat exchanger like a reservoir tank, the friction between the cylinder and piston, and the external disturbance force. Moreover, it is difficult to identify the values of the effective bulk modulus and friction. In this paper, the variation of the effective bulk modulus, friction, and external disturbance are considered as uncertainties of EHA systems. To solve the problems due to these system uncertainties, an adaptive back-stepping control scheme with fuzzy neural networks(FNNs) is proposed. The effectiveness of the adaptive back-stepping control(ABSC) system with FNNs was compared with those of the standard back-stepping control(BSC) system and the ABSC system through computer simulation.

Applied LPV Control with Full Block Multipliers and Regional Pole Placement

A formulation of an LPV control problem with regional pole placement constraints is presented, which is suitable for the application of a Full Block S-Procedure. It is demonstrated that improved bounds can be obtained on the inducedL2norm of closed loop systems, while satisfying pole placement constraints. An application consisting in the 6 degrees of freedom (DOF) control of a space vehicle is developed as an example, with hardware in the loop (HIL) simulation. This shows that the method is appealing from the practical point of view, considering that the synthesized control law can be implemented satisfactorily in standard flight control systems. Conclusions with remarks towards the practical use of the method are presented as well.

ADAPTIVE pH CONTROL SYSTEM FOR FED-BATCH BIOCHEMICAL PROCESSES

In the paper pH control problems in fed-batch biochemical processes are analyzed. Process mathematical model was based on the first principles and identified using available experimental data. An adaptive pH control sys- tem based on gain scheduling approach was proposed. Significant increase in control quality as compared to a standard PI control system was achieved.

An integrated qualitative trend analysis approach to identify process abnormalities: A case of oil export pumps in an offshore oil and gas production facility

Oil and gas production can be largely benefited by minimizing unwanted production losses. This can be done by effective identification of system anomalies and faults. In standard control systems these abnormalities can be observed as gradually deviating trends from the norms. Available tools for monitoring these trends, in some cases, may not be enough to reveal hidden faulty features. In order to interpret these changes accurately, measured data must be visualized as a combination of multiple sensor signals within a particular domain. This article suggests an approach to effectively utilize integrated data from multiple sources, and defines a set of 12 fault features. The approach, in principle, encodes real plant data in the form of logical IF-THEN rules in Microsoft Excel. Confidence values are set based on these interpretations to differentiate between normal and abnormal conditions exhibited by the system. This is to provide an opportunity for the process and maintenance engineers to effectively identify the equipment's health based on the early identification of developing abnormalities.

H∞ and L1 control of a teleoperation system via LMIs

This paper presents a new linear matrix inequality approach to robust H ∞ and L 1 controllers design for a bilateral teleoperation system. The time delay of communication media is assumed to be unknown and randomly time varying, but the upper bounds of the delay interval and the derivative of the delay are assumed to be known. In this approach, an impedance controller is designed for the master side and an open-loop controller is designed for the slave side. Also, an optimal disturbance rejection technique is developed for the slave side. In order to design the slave side controller, the control system is reformulated such that the slave side controller is converted to an equivalent dynamic output feedback controller in a standard control system representation. A Lyapunov–Krasovskii functional is defined for stability analysis. The main results provide sufficient delay-dependent conditions for the stability analysis and control design problem. The criteria are expressed as a set of linear matrix inequalities, which can be easily examined using standard numerical software.