Showing papers in "IEEE Transactions on Control Systems and Technology in 1999"

A control engineer's guide to sliding mode control

Abstract: Presents a guide to sliding mode control for practicing control engineers. It offers an accurate assessment of the so-called chattering phenomenon, catalogs implementable sliding mode control design solutions, and provides a frame of reference for future sliding mode control research.

Disturbance observer and feedforward design for a high-speed direct-drive positioning table

Abstract: Design and implementation of a discrete-time tracking controller for a precision positioning table actuated by direct-drive motors is considered. The table has acceleration capabilities in excess of 5 G, positioning accuracy at the micron level, and is used in applications such as semiconductor packaging. The controller proposed uses a disturbance observer and proportional derivative (PD) compensation in the feedback path and a zero phase error tracking controller and zero phase low-pass filter in the feedforward path. The existing disturbance observer design techniques are extended to account for time delay in the plant. Practical difficulties with excessive feedforward gains are examined and a low-order filter design method is proposed. Experimental results for quantized low-order position reference trajectories, which are commonly used in industrial systems, demonstrate the effectiveness of the approach.

PID tuning for improved performance

Abstract: In this paper, a simple PID controller design method that achieves high performance for a wide range of linear self-regulating processes is proposed. Satisfactory responses can be expected for processes with various dynamics, including those with low- and high-order, small and large dead time, and monotonic and oscillatory responses. The method is developed based on a second-order plus dead time modeling technique and a closed-loop pole allocation strategy through the use of root-locus. Simulation examples and real-time experiments are given to show the effectiveness and flexibility of the controller in handling processes of different characteristics.

Sliding mode measurement feedback control for antilock braking systems

Abstract: We describe a nonlinear observer-based design for control of vehicle traction that is important in providing safety and obtaining desired longitudinal vehicle motion. First, a robust sliding mode controller is designed to maintain the wheel slip at any given value. Simulations show that longitudinal traction controller is capable of controlling the vehicle with parameter deviations and disturbances. The direct state feedback is then replaced with nonlinear observers to estimate the vehicle velocity from the output of the system (i.e., wheel velocity). The nonlinear model of the system is shown locally observable. The effects and drawbacks of the extended Kalman filters and sliding observers are shown via simulations. The sliding observer is found promising while the extended Kalman filter is unsatisfactory due to unpredictable changes in the road conditions.

Experiments and simulations on the nonlinear control of a hydraulic servosystem

Abstract: This paper presents the derivation, simulation, and implementation of a nonlinear tracking control law for a hydraulic servosystem. An analysis of the nonlinear system equations is used in the derivation of a Lyapunov function that provides for exponentially stable force trajectory tracking. This control law is then extended to provide position tracking. The proposed controller is simulated and then implemented on an experimental hydraulic system to test the limits of its performance and the realistic effects of friction.

Deadzone compensation in motion control systems using adaptive fuzzy logic control

Abstract: A deadzone compensator is designed for industrial positioning: systems using a fuzzy logic (FL) controller. The FL approach is shown to subsume other approaches that use switching or indicator functions. The classification property of FL systems makes them a natural candidate for the rejection of errors induced by the deadzone, which has regions in which it behaves differently. A tuning algorithm is given for the FL parameters, so that the deadzone compensation scheme becomes adaptive, guaranteeing small tracking errors and bounded parameter estimates. Formal nonlinear stability proofs are given to show that the tracking error is small. The adaptive FL deadzone compensator is implemented on an actual industrial CNC machine tool to show its efficacy.

Robust hovering control of a PVTOL aircraft

Abstract: We study robust hovering control of vertical/short takeoff and landing (V/STOL) aircraft. For hovering control, we can model a V/STOL aircraft as a planar vertical takeoff and landing (PVTOL) aircraft. We use an optimal control approach to design a robust hovering control. The resulting control is a nonlinear state feedback whose robustness is demonstrated by numerical simulations.

Nonlinear control of a heating, ventilating, and air conditioning system with thermal load estimation

Abstract: This paper presents a nonlinear controller for a heating, ventilating, and air conditioning (HVAC) system capable of maintaining comfort conditions under time varying thermal loads. The controller consist of a regulator and a disturbance rejection component designed using Lyapunov stability theory. The mitigation of the effect of thermal loads other than design loads on the system is due to an online thermal load and state estimator. The availability of the thermal load estimates allows the controller to keep comfort regardless of the thermal loads affecting the thermal space being heated or cooled. Simulation results are used to demonstrate the potential for keeping comfort and saving energy of this methodology on a variable-air-volume HVAC system operating on cooling mode.

An H/sub /spl infin// almost disturbance decoupling robust controller design for a piezoelectric bimorph actuator with hysteresis

Abstract: A robust controller design for a piezoelectric bimorph nonlinear actuator is considered. The nonlinear dynamics of the actuator are first linearized using the stochastic equivalent linearization method and reformulated into a standard almost disturbance decoupling problem. Then a robust controller, which is explicitly parameterized by two tuning parameters, is carried out using a so-called asymptotic time-scale and eigenstructure assignment approach. The parameterized controller can be tuned by adjusting the parameters to achieve disturbance decoupling and other design goals for the problem that we consider. Simulation results of time-domain responses show that the design is very successful in terms of steady-state tracking error and settling time as well as other performances.

Centrifugal compressor surge and speed control

Abstract: Previous work on stabilization of compressor surge is extended to include control of the angular velocity of the compressor. A low-order centrifugal compressor model is presented, where the states are mass flow, pressure rise, and rotational speed of the spool. Energy transfer considerations are used to develop a compressor characteristic. In order to stabilize equilibria to the left of the surge line, a close coupled valve is used in series with the compressor. Controllers for the valve pressure drop and spool speed are derived. Semiglobal exponential stability is proved using a Lyapunov argument.

Discrete-time variable structure controller with a decoupled disturbance compensator and its application to a CNC servomechanism

Abstract: This paper develops a new approach in regulation and tracking, combining a disturbance compensator with a controller, both of which are formulated in the discrete-time domain using the variable structure concept. For single-input single-output, linear time-invariant systems, an algorithm for exactly decoupling the disturbance estimation dynamics from the sliding mode dynamics is developed. This allows the two dynamic modes to be tuned separately. It is shown that the developed approach preserves the robustness properties of the sliding mode and asymptotically achieves zero tracking error, in the presence of external disturbances and parametric uncertainties. Both computer simulation results and experimental results using a CNC milling machine are used to demonstrate those properties of the proposed method in both regulation and tracking.

Inertial navigation system aided by aircraft dynamics

Abstract: In this work the possibility of using the model of aircraft dynamics as a means for aiding an inertial navigation system is studied. The method is of particular interest for low-grade inertial navigating system (INS). The aiding formulation is introduced, its corresponding mathematical model is derived and used in the design of an appropriate extended Kalman filter. Sensitivity analysis of the errors caused by perturbations in the parameters of the aircraft dynamics demonstrates the robustness of the scheme. The importance of maneuvers for observability is also presented. Simulations show that the use of aircraft dynamics for aiding a low-grade inertial navigation system yields a navigation system whose performance is considerably better than that of the pure INS. This improvement is made possible by the fact that the errors in the aircraft dynamics model are observable when performing appropriate calibration maneuvers.

Robust automatic steering control for look-down reference systems with front and rear sensors

Abstract: This paper describes a robust control design for automatic steering of passenger cars. Previous studies showed that reliable automatic driving at highway speed may not be achieved under practical conditions with look-down reference systems which use only one sensor at the front bumper to measure the lateral displacement of the vehicle from the lane reference. An additional lateral displacement sensor is added here at the tail bumper to solve the automatic steering control problem. The control design is performed stepwise: an initial controller is determined using the parameter space approach in an invariance plane; and this controller is then refined to accommodate practical constraints and finally optimized using the multiobjective optimization program. The performance and robustness of the final controller was verified experimentally at California PATH in a series of test runs.

Application of Wiener model predictive control (WMPC) to a pH neutralization experiment

Abstract: pH control is recognized as an industrially important, yet notoriously difficult control problem. Wiener models, consisting of a linear dynamic element followed in series by a static nonlinear element, are considered to be ideal for representing this and several other nonlinear processes. Wiener models require little more effort in development than a standard linear step-response model, yet offer superior characterization of systems with highly nonlinear gains. These models may be incorporated into model predictive control (MPC) schemes in a unique way which effectively removes the nonlinearity from the control problem, preserving many of the favorable properties of linear MPC. In this paper, Wiener model predictive control (WMPC) is evaluated experimentally, and also compared with benchmark proportional integral derivative (PID) and linear MPC strategies, considering the effects of output constraints and modeling error.

H/sub 2//H/sub /spl infin// active control of sound in a headrest: design and implementation

Abstract: This paper presents an H/sub 2//H/sub /spl infin// feedback controller design for active sound control in a headrest. The design method which employ an H/sub 2/ performance criterion, with H/sub 2/ and H/sub /spl infin// constraints, was formulated as a convex programming problem using FIR Q-parameterization and frequency discretization, and solved using sequential quadratic programming. The design method was found effective since various objectives and constraints which are useful for this active sound control application were readily included. A robust controller was then designed for an experimental headrest system, and the performance, robust stability, and the multiplicative plant uncertainty model used in the design are presented and analyzed. A reduced-order real-time controller was then implemented on a digital signal processing system, producing the performance predicted in the design.

Tracking control of mechanical systems in the presence of nonlinear dynamic friction effects

Abstract: In this paper, we design an observer-based exact model knowledge position tracking controller for a second-order mechanical system with nonlinear load dynamics and a nonlinear dynamic friction model. Since the controller requires an estimate of the unmeasurable friction state, we demonstrate how the friction dynamics can be exploited to design three different observers which foster different transient response characteristics for the composite closed-loop system. We then present two adaptive controllers which utilize nonlinear observer/filter structures to provide for asymptotic position tracking while compensating for selected parametric uncertainty. Dynamic simulation and experimental results are utilized to illustrate control performance.

Intelligent control for brake systems

Abstract: There exist several problems in the control of brake systems including the development of control logic for antilock braking systems (ABS) and "base-braking." Here, we study the base-braking control problem where we seek to develop a controller that can ensure that the braking torque commanded by the driver will be achieved. In particular, we develop a fuzzy model reference learning controller, a genetic model reference adaptive controller, and a general genetic adaptive controller, and investigate their ability to reduce the effects of variations in the process due to temperature. The results are compared to those found in previous research.

Nonlinear H/sub /spl infin// controller design for a DC-to-DC power converter

Abstract: We present a state feedback controller for the Cuk converter. It is shown that a special type of DC-DC switched mode power supply can be handled by the theory of affine-input systems. The controller design is based on the H/sub /spl infin//-theory of nonlinear systems. Using an appropriate exogenous system, the stationary control error can be made arbitrarily small. Furthermore, this design method leads to a simple controller and the stability of the closed loop can be guaranteed in the sense of Lyapunov. The implementation for a laboratory model shows a good tracking and disturbance behavior, which proves the feasibility of the proposed procedure.

Design of a robust voltage controller for a buck-boost converter using /spl mu/-synthesis

Abstract: Proposes the structured singular value (/spl mu/) approach to the problem of designing an output voltage regulator for a buck-boost converter with current-mode control. This approach allows a quantitative description of the effects of reactive components' tolerances and operating point variations, which strongly affect the converter dynamics. First, a suitable linear converter model is derived, whose parameter variations are described in terms of perturbations of the linear fractional transformation (LFT) class. Then, /spl mu/-analysis is used to evaluate the robustness of a conventional PI voltage regulator with respect to the modeled perturbations. Finally, the approximate /spl mu/-synthesis procedure known as D-K iteration is used to design a robustly performing regulator. Simulation results are presented, describing the small and large signal behavior of a reduced order approximation of the /spl mu/-synthesized controller.

Rail vehicle control system integration testing using digital hardware-in-the-loop simulation

Abstract: Control systems for converter-controlled rail vehicles are orders of magnitude more complex than controllers for previous generations of vehicles. While the dynamic behavior of previous generations of vehicles was to a large extent determined by its power components alone, an important part of the dynamics of modern vehicles is shaped by real-time software, distributed computing and intercontroller communication. To ensure proper operation of the vehicle on track, an integration test of the vehicle control system is performed before initial roll-out. In order to achieve a maximum test depth and to minimize risk and cost, this test is achieved by connecting the original vehicle control system to a real-time dynamic vehicle simulator in closed-loop operation. The paper describes concept, evaluation, and operation of a digital hardware-in-the-loop simulator for testing control-relevant parts of the vehicle. Particular emphasis is put on the hybrid nature of the underlying simulation problem and its inherent causality variations due to the combination of discrete switching effects, e.g., in diodes and controlled converters, with continuous system parts, e.g., differential equations for currents or mechanical system parts.

An overview of rotating stall and surge control for axial flow compressors

Abstract: Modeling and control for axial flow compression systems have received great attention in recent years. The objectives are to suppress rotating stall and surge, to extend the stable operating range of the compressor system, and to enlarge domains of attraction of stable equilibria using feedback control methods. The success of this research field will significantly improve compressor performance and thus future aeroengine performance. This paper surveys the research literature and summarizes the major developments in this active research field, focusing on the modeling and control perspectives to rotating stall and surge for axial flow compressors.

A current control for a permanent magnet synchronous motor with a simple disturbance estimation scheme

Abstract: A current control technique for a permanent magnet synchronous motor (PMSM) with a simple disturbance estimation scheme is proposed. Among the various current control schemes for a PMSM drive, predictive control is known to give a superior performance. This scheme, however, requires the full knowledge of motor parameters. To overcome such a limitation, the disturbances caused by the parameter variations will be estimated by using disturbance observer theory and used for the calculation of the reference voltages by feedforward control. Thus, the control performance can be significantly improved with a relatively simple control algorithm. The proposed control scheme is implemented on a PMSM using DSP TMS320C30 and the effectiveness is verified through the comparative experiments.

High-performance motion control of an induction motor with magnetic saturation

Abstract: Generalizes the authors' work on high-performance control of induction motors to machines that exhibit significant magnetic saturation. The controller design is based on the standard d-q model of the induction motor which has been modified to account for the saturation of the iron in the main (magnetic) path of the machine. An input-output linearization controller is used to provide independent (decoupled) control of the speed and flux. With this controller, the flux reference becomes an extra degree of freedom for the designer to help achieve performance objectives. Taking into account saturation along with the voltage and current constraints, the flux reference is chosen to achieve the optimal torque (maximum for acceleration and minimum for deceleration) at any given speed. Experimental results are given to demonstrate the input-output controller's effectiveness in providing the tracking of a given position and speed trajectory while simultaneously tracking the optimal flux reference. The set of experiments are fast point-to-point motion control moves with an inertial load comparing the input-output controller based on the saturated magnetics model with that based on the linear magnetics model.

Self-tuning control of a nonlinear model of combustion instabilities

Abstract: We present a self-tuning scheme for adapting the parameters of a proportional integral (PI) controller for stabilization of a Culick-type model (1976) of nonlinear acoustic oscillations in combustion chambers. Our adaptation criterion is Lyapunov-based and its objective is the regulation of nonlinear pressure oscillations to zero. We focus on a two-mode model and first develop a design based on an assumption that the amplitudes of the two modes are available for measurement. The adaptation mechanism is designed to stabilize both modes and prevent the phenomenon observed by Candel and coworkers whose adaptive controller stabilizes the first but (under some conditions) apparently destabilizes the second mode. We also prove that the adaptation mechanism is robust to a time delay inherent to the actuation approach via heat release. In order to avoid requirements for sophisticated sensing of the mode amplitudes needed for feedback, we also develop an adaptation scheme which employs only one pressure sensor. In order for the adaptation scheme to be implementable, it is also necessary to know the control input matrix of the system. Rather than performing a linear ID procedure with input excitation, we propose a simple nonlinear ID approach based on limit cycles (internal excitation) which exploits the quadratic character of the nonlinearities. Simulations illustrate the scheme's capability to attenuate limit cycles and its robustness to magnitude- and rate-saturation of the actuator.

Output-feedback global stabilization of a nonlinear benchmark system using a saturated passivity-based controller

Abstract: We address the problem of regulation of the benchmark rotational/translational proof mass actuator using a passivity-based controller, We show that a (relatively straightforward) modification of the output feedback saturated input controller proposed by the authors in a previous paper provides a simple and robust solution to the global asymptotic stabilization problem. The design technique is based on the practically appealing principles of energy shaping and damping injection. Computer simulations show that the performance is comparable, and in some respects better, than the one obtained with a far more complicated full-state unsaturated feedback controller.

Application of l/sub 1/ optimal control to the engine idle speed control problem

Abstract: In this paper, the engine idle speed control (ISC) problem is revisited with the l/sub 1/ optimization design methodology. A controller configuration consisting of a feedback linear quadratic Gaussian (LQG) optimal controller and a feedforward l/sub 1/ optimal controller is chosen to satisfy the design objectives. The main goal of this work is to demonstrate the application of the l/sub 1/ optimal control methodology on a standard automotive control problem and evaluate the advantages and disadvantages of the l/sub 1/ design method. Using the idle bypass valve as the only actuator, the l/sub 1/ optimal feedforward control is shown to be effective in reducing the idle speed errors at the expense of extra control energy being spent during the transient. The controller design process is described along with the simulation and experimental results on a 4.6L 2 valve V8 production engine. A method to address tradeoff issues in evaluating the performance of a feedforward control system is also discussed.

Analysis and design of the integrated controller for precise motion systems

Abstract: Recently, feedforward controllers like zero phase error tracking controllers (ZPETC) and cross-coupled controllers (CCC) have been developed to effectively reduce tracking error and contouring error, respectively. This paper proposes an integrated controller which combines ZPETC and CCC to achieve both tracking and contouring accuracy. Furthermore, studies indicate that ZPETC and CCC can be designed separately in the present integrated control design. In the provided experimental setup with a servo table, an optimal ZPETC and a robust CCC based on the contouring error transfer function (CETF) were designed to achieve desirable frequency responses and stability. Experimental results show that the proposed integrated controller renders significantly improved accuracy in both tracking and contouring.

Robust tuning of power system stabilizers using QFT

Abstract: This paper presents a new method for tuning the parameters of a conventional power system stabilizer. The region of acceptable performance for the stabilizer has been extended and covers a wider range of operating and system conditions. The parametric uncertainty in power systems has been handled using quantitative feedback theory (QFT). The required controller parameters are arrived at by solving an optimization problem that incorporates the control specifications. The robustness of the feedback controller has been investigated on a single machine infinite bus model and the results are shown to be consistent with the expected performance of the stabilizer.

Future needs for control theory in industry-report of the control technology survey in Japanese industry

Abstract: Reports the current situation and future directions of control theory and control technology which have been practically applied to Japanese industries. The control technology committee in the Japanese Society of Instrument and Control Engineering (SICE) conducted a control technology survey of Japanese industry in 1995. The committee sent 300 inquiry letters to Japanese manufacturing companies and received 110 effective answers which included 150 application examples in the practical industries. After the inquiry, the committee visited the leading companies and interviewed process and control engineers to discuss their opinions and comments regarding the inquiry.

Control of nonlinear systems with friction

Abstract: We introduce a continuous dynamic controller for a class of nonlinear systems which includes mechanical system models with a bristle model for nonlinear friction effects. We obtain sufficient conditions for global stabilization using an estimate for bristle defection and present experimental results illustrating the benefits of our dynamic controller in the regulation of a high-speed linear positioning table.