Digital Control Law Research Articles

Design of microprocessor-based system for positioning servomechanism with induction motor

Digital control algorithms are proposed for a position-controlled system with an inverter-fed induction motor. Two structures for the positioning servomechanism are suggested in which the appropriate digital control laws are applied and a straightforward method for adjusting of controller parameters is developed. The method enables the designer to match the desired dynamic performance and to eliminate the steady-state position error due to the presence of a constant or a slowly varying load disturbance. Particular attention is paid to the nonlinear position control design, which preserves the desired response even in the case when electrical torque reaches limits imposed by the inverter current capacity. To illustrate the proposed design procedure and to verify the efficiency of the nonlinear control laws, simulation results and waveforms from an experimental setup are presented. >

Optimal digital redesign of continuous-time controllers

This paper proposes a new optimal digital redesign technique for finding a dynamic digital control law from the available analog counterpart and simultaneously minimizing a quadratic performance index. The proposed technique can be applied to a system with a more general class of reference inputs, and the developed digital regulator can be implemented using low cost microcomputers.

Adiabatic Control of a Bomb Calorimeter using Electric Heaters.

As an available method to precisely control the temperature of the outer pool of a bomb calorimeter, a method using electric heaters is considered. The operating characteristics are experimentally investigated and compared with those of the Nenken-style method using hot water. The heaters are long and fine in shape and are uniformly set in the pool. They are subject to a digital control law composed of a time-scheduled control and a finite-time settling control. It is consequently confirmed that the heaters can be superior to the hot water method in controllability, accuracy in controlling, uniformity in heating, and ease in setting up. Also, it is found that this system provides the outer pool with far better follow-up characteristics to the inner one on temperature than the existing Nenken-style automatic calorimeter.

Digital robust control law synthesis using constrained optimization

Development of digital robust control laws for active control of high performance flexible aircraft and large space structures is a research area of significant practical importance. The flexible system is typically modeled by a large order state space system of equations in order to accurately represent the dynamics. The active control law must satisy multiple conflicting design requirements and maintain certain stability margins, yet should be simple enough to be implementable on an onboard digital computer. Described here is an application of a generic digital control law synthesis procedure for such a system, using optimal control theory and constrained optimization technique. A linear quadratic Gaussian type cost function is minimized by updating the free parameters of the digital control law, while trying to satisfy a set of constraints on the design loads, responses and stability margins. Analytical expressions for the gradients of the cost function and the constraints with respect to the control law design variables are used to facilitate rapid numerical convergence. These gradients can be used for sensitivity study and may be integrated into a simultaneous structure and control optimization scheme.

Locally optimal-digital redesign of continuous-time systems

The authors present a novel optimal digital redesign technique for finding a dynamic digital control law from the given continuous-time counterpart by minimizing a local quadratic performance index. The quadratic performance index is chosen as the integral of the weighted squared difference between the states of the original closed-loop system and those of the digitally controlled open-loop system at any instant between each sampling period. The developed optimal digital redesign control law enables the states of the digitally controlled open-loop system to match closely those of the original closed-loop system at any instant between each sampling period, and it can easily be implemented using microcomputers with a relatively large sampling period. An illustrative example is presented to demonstrated the effectiveness of the proposed method. >

Synthesis of Type-1 Optimal Digital Servosystems

In the design of digital control systems, the time delay due to computation time of a processor cannot be often neglected. In this paper, we consider the problem of synthesizing a type-1 optimal digital servosystem taking account of controller delay of one sampling period.It is first shown that the optimal digital servo problem in which a quadratic criterion function is defined for a given continuous-time plant can be reasonably reformulated to a discrete optimal regulator problem. To assure the solvability of this problem, some conditions for the preservation of stabilizability and detectability of the plant under sampling are given. In the discrete optimal regulator problem considered here, not only control input but also the initial state of the servocompensator are referred as free design parameters. The obtained optimal digital control law contains a feedforward term of reference signal in addition to a feedback term. It is also shown that the optimal control law has a function of estimating the state variables at the following sampling period in order to recover the controller delay.

Performance enhancement of a solid particle heat exchanger using adaptive control

Two classes of feedback controllers, proportional-integral control and adaptive control, were applied to a counterflow solid particle heat exchange prototype. The primary objective was to optimize process start-up performance of the heat exchanger. The two most significant factors affecting the controllers were: (a) limited input control effort in terms of energy; and (b) deadtime of the process which was a function of the heat exchanger design. The adaptive controller, based on parameter estimation and a digital control law derived using controller synthesis, outperformed the conventional controller during start-up by as much as 11% with respect to a performance measure comprised of both error and energy components. Proper design and implementation of the adaptive controller was crucial for successful regulation.

Estimation and control with cubic nonlinearities

The nonlinearities in a dynamic system and its measurement equations are assumed to be cubic and small, i.e., all proportional to a single scalar small parameter e. The optimal digital nonlinear feedback control law is carried through the first power of e, taking into account the non-Gaussian character of the state conditional distribution. The optimal law involves cubic and linear terms in the state estimate, as well as higher moments of the state conditional distribution.

Robust digital dead time compensator controller for a class of stable systems

A simple way to design a robust digital dead-time compensator controller for a class of common stable processes is suggested. The method requires limited and possibly inaccurate information on the step response of the process. The underlying idea is to model the process by a gain, lag and a dead-time, a common practice in control design. In its simplest form the algorithm reduces to the robust regulator introduced by Åström. The design process and the performance of the digital control law are illustrated by a detailed example.

Perturbation guidance laws for perfect information interceptors withsymmetrical nonlinearities

The nonlinearities in a dynamic system are assumed to be cubic and small, i.e., all proportional to a single scalar small parameter e. The optimal digital nonlinear feedback control law in the case of perfect state knowledge, but with dynamic noise input, is carried through the first power of e. The control law involves cubic as well as linear terms in the state and depends on the prior covariance of the process noise. The theory is applied to a constant-speed coplanar model of a saturated interception and the numerical investigation shows a considerable advantage of the present nonlinear control law over the linear law (e = 0) as applied to the same system.

Time-delay compensation in active control algorithms

SummaryIn this paper a direct digital control law algorithm is proposed which in addition to providing tight non-interacting tracking behaviour and excellent disturbance-rejection characteristics, provides for the compensation of finite-time delays in implementation. The control-law algorithm is defined and system stability is proved in the case of multi-input multi-output linear systems. The theory is synthetic and leads directly to the determination of the appropriate controller matrices.The theory is illustrated by the presentation of simulation results in which the aircraft is represented by an analogue computer and the digital control system is implemented on a microprocessor. In the simulation study the controller is required to effect fuselage pitch pointing and vertical translation manoeuvres for the analogue computer representation of the YF-16 aircraft. It is shown that tight non-interacting control is achievable even when the control implemented is delayed by 0·1 seconds.

Design and flight testing of digital direct side-force control laws

Three-input/three-output command augmentation control laws have been designed and tested in flight using Princeton's Variable-Response Research Aircraft. Controllers were based upon algebraic model-following, a fast and efficient method of direct digital synthesis for advanced control modes. Pilot opinions of several command modes and controller-to-command pairings are presented in this paper. Flat turns, lateral translation, and roll control were investigated. Of the command modes tested, foot pedals-to-yaw rate, lateral stick-to-roll rate, and thumb lever-to-sideslip angle provided the best overall ratings.

A digital adaptive control law for a parabolic distributed parameter system

This paper deals with the design of a digital adaptive controller for a parabolic distributed parameter system. The space of inputs and the space of outputs are both one dimensional. After introducing an input-output representation, a digital adaptive control law is presented and analyzed.

Controller Designs for Power System Stability Enhancement Using Static Phase Shifters

This paper presents a digital simulation study of the use of a static thyristor-controlled phase shifter as an effective power controller to enhance system stability and to damp the line electromechanical oscillations, hence to improve AC tie line capacity. A dynamic model of the static phase shifter is incorporated in the integrated power system dynamics; the unified state space form is used to investigate digital and analog control laws to transform static phase shifters into viable tools in enhancing interconnected power system steady state stability.

Digital Control Loops for Telecom 1 AOCS

The attitude and orbit control system for the TELECOM 1 geostationary satellite is described. Hardwired electronics is used for the operational normal mode while a programmable digital electronics is used for all the other mission phases. Digital control laws implementation is shown for the attitude acquisition modes.

Test demonstration of digital control of wing/store flutter

Methods of digital control have been applied to a demonstration of the suppression of wing/store flutter. Digital control laws were developed by applying a modified Jordan canonical transformation to a state variable formulation of a control law synthesized originally for an analog system. A real-time simulation of the components of the control system served to develop the concepts. This was followed by a wind-tunnel demonstration which evaluated the system in detail. The results of the test showed that the performance of the digital controller was comparable to that of analog controllers. Attention during the test was focused on the insertion of adequate antialiasing filters, the effects of sample time, and the compensation for phase lags introduced by the digital control process.

Microcomputer control algorithms for weapon pointing and stabilization

Since late 1978. technology efforts have been underway within the Fire Control and Small Caliber Weapon Systems Laboratory. Dover. NJ. to exploit state-of-the-art advances in modern control theory and microprocessors for weapon pointing and stabilization. Results to date have been quite encouraging and serve to emphasize the importance of these two emerging technologies in the design of future high performance armament systems. This paper describes the discrete-time regulator microprocessor algorithms which have been implemented and tested on a microcomputer-based servo control system located in the Stabilization Research Laboratory facility at ARADCOM. These algorithms include reduced-order observers for estimating system states and disturbances. and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LQ</tex> - based digital control laws for precision stabilization in the presence of external disturbances.

'Direct' Wiener-Hopf solution of filter/observer and optimal coupler problems

Most approaches to optimal stationary linear stochastic control depend upon time-domain techniques for both theoretical foundations and computational algorithms. In contrast, this paper discusses a WienerHopf approach which avoids several difficulties occurring in time-domain methods (e.g., those which arise in connection with singular regulator and filter problems). Emphasis is placed upon solution properties in distinction to derivations. The following points of the direct Wiener-Hopf approach are emphasized: 1) linear regulator, filter/observer problems can be solved using linear algebraic equations (in distinction to solving nonlinear Riccati equations) once solution eigenvalues are obtained; 2) the control weighting matrix need not be positive definite nor is it necessary that its inverse exist; 3) the state/output weighting matrix need not be positive semidefinite; and 4) singular regulator and filter/observer problems (e.g., the cheap control problem) can be handled with a minimum of special consideration. In addition, a new class of problem is solved using the Wiener-Hopf approach. The solution specifies both the optimal (discrete) digital control law and the optimal (continuous) data hold for the case of a continuous cost function, a continuous plant, and sampled measurements. (T) ( • ) ' ( • ) * ( • ) T <PXY' Nomenclature

Algorithms for the weighting matrices in sampled-data linear time-invariant optimal regulator problems

In this paper we develop Algorithms For Weighting Matrices required to implement the Sampled-Data Linear Optimal Regulator Problems. The knowledge of Continuous Optimal Regulator designs helps in producing digital state variable feedback control laws which satisfy the continuous system performance specifications on one hand, and are equally useful for implementing the equivalent Sampled-Data System on the other hand. Howeve, the difficulty in applying the Sampled-Data Regulator Theory lies in the fact that certain digital performance index weighting matrices need be computed. In this paper, a general form of the dynamical system is considered (including system disturbances). Infinite series representation is used. Only Time-Invariant Linear Optimal Sampled-Data Regulator Systems are considered. Results of error bounds are given. A typical Example is presented. Details of these and Computer program can be found in Ref. [11].

Automatic flare transition penetrating wind shears

In this paper, the development of a digital three-dimensional automatic control law designated to achieve an optimal transition of a large commercial aircraft between the glideslope conditions and the desired final touchdown condition is presented. The linearized equations representing the perturbed motion of the aircraft from the nominal glideslope trajectory are presented. A method of incorporating the spatial, low-level wind shears into these perturbed equations of motion is indicated. It is shown that the system equations then assume the familiar form of the linear regulator problem, acted upon by a constant disturbance. A design procedure is presented to compute a digital, time-invariant, optimal control law for the discrete regulator problem acted upon by a constant disturbance. The response trajectories presented demonstrate the capability of this controller to perform optimal flare maneuvers in the presence of various wind shear conditions.