Anti-windup Research Articles

Biaxial Stage Contouring Control with a Novel Anti-Windup PID Controller Strategy

For stage systems performing precision contouring actions under the conventional proportional–integral–derivative (PID) control structures, the phenomenon of actuator saturation is a common problem which can easily lead to the windup effect and cause unexpected results to the overall performance. To conquer this problem, this paper presents a new strategy for suppressing the windup effect in the conventional PID contouring control structures. In the proposed approach, the windup effect is modeled as a disturbance input to the PID controller such that an observer-based auxiliary control is designed to minimize the difference between the computed control force and the actual axial input based on an H-infinite optimization criterion. From theoretical analyses, it can show that the proposed anti-windup (AW) scheme can provide a more robust performance under the effects of windup than the conventional PID AW schemes. Moreover, it can also bring about better noise rejection capability to the controlled systems. Furthermore, the design of the proposed PID AW scheme is system independent and can be formulated based on the original PID controller parameters such that it can utilize a rapid on-line tuning of the controller parameters in order to prevent the windup effect. To validate the approach, a biaxial x-y stage system performing contouring action is applied which originally has obvious windup effect in both axial inputs under the conventional PID scheme. After the implementation, the experimental results show that the proposed PID AW scheme indeed improves the windup effect and also provides a better system robustness performance compared to the original one. It can be obtained that the experimental results are in accordance with the theoretical analyses, and show the effectiveness of the proposed method.

Anti-windup embedded magnetic actuator applied for near-high-speed milling

A fuzzy anti-windup (AW) compensator is proposed and applied to the embedded cylindrical-array magnetic actuator (ECAMA) to ensure the superior performance of spindle position regulation for milling machines under actuator saturation. Since ECAMA is a type of active magnetic bearing (AMB), the supplied coil current and the induced magnetic force are both limited by the maximum current and power output of the AMB and the associated amplifier. Once the magnetic actuator is saturated, the required control input cannot be realized by ECAMA and may lead to drastic tremble of spindle position. In this work, an AW compensator, based on fuzzy logic algorithm, is therefore proposed to rectify the control input to ECAMA. By employing commercial software MATLAB/Simulink and signal processing interface, Module DS1104 by dSPACE, the efficacy of the fuzzy AW compensation is practically verified by intensive experiments.

Anti-Windup Compensation for Embedded Cylindrical-Array Magnetic Actuator

An Anti-Windup (AW) compensator is applied to the Embedded Cylindrical-Array Magnetic Actuator (ECAMA) to sustain the performance of spindle position regulation for milling machines under actuator saturation. Since ECAMA is a type of Active Magnetic Bearing (AMB), the maximum supplied coil current and the induced magnetic force are both limited by their extrema. Once the magnetic actuator is saturated, the required control input cannot be realized by the actuator as long as the magnitude of control input exceeds the upper limit of the actuator output. In this work, an AW compensator is therefore proposed and employed to compensate the output of PID controller to prevent saturation of ECAMA. By employing commercial software MATLAB/Simulink and signal processing interface, Module DS1104 by dSPACE, the efficacy of the AW compensation is practically verified by intensive experiments.

A Microcontroller Implementation of Constrained Model Predictive Control

Model Predictive Control (MPC) is an established con- trol technique in a wide range of process industries. The reason for this success is its ability to handle multivariable systems and systems having input, output or state constraints. Neverthless comparing to PID controller, the implementation of the MPC in miniaturized devices like Field Programmable Gate Arrays (FPGA) and microcon- trollers has historically been very small scale due to its complexity in implementation and its computation time requirement. At the same time, such embedded technologies have become an enabler for future manufacturing enterprisers as well as a transformer of organizations and markets. In this work, we take advantage of these recent advances in this area in the deployment of one of the most studied and applied control technique in the industrial engineering. In this paper, we propose an efficient firmware for the implementation of constrained MPC in the performed STM32 microcontroller using interior point method. Indeed, performances study shows good execution speed and low computational burden. These results encourage to develop predictive control algorithms to be programmed in industrial standard processes. The PID anti windup controller was also implemented in the STM32 in order to make a performance comparison with the MPC. The main features of the proposed constrained MPC framework are illustrated through two examples.

The input amplitude saturation problem in QFT: A survey

In this work the input amplitude saturation problem is analysed in the Quantitative Feedback Theory (QFT) framework. This paper reviews previous works in the literature dealing with the input amplitude saturation problem in the presence of an uncertain plant in the frequency domain using QFT. The objective of this paper is to compare the different available approaches and summarize the design process for each case so that this paper can be used as a tutorial; there are six main approaches to this problem. Two of these approaches use the classical two degrees of freedom control scheme for QFT; in both of these, the design constraints of a linear QFT compensator are added in the loop shaping stage: they are added in the first approach to avoid excitation of the actuator saturation and in the second one to guarantee global stability. The other three techniques are considered as anti-windup (AW) approaches. Starting from a base design in QFT with two degrees of freedom, the first AW approach introduces a third degree of freedom that guarantees the stability of the system, allowing for base designs for high performance. The other two AW approaches also introduce a third degree of freedom, but they take simple stability considerations into account and focus on the performance of the system. The last solution consists of using a reference governor technique, which guarantees the computation of a reference signal for an inner control loop that is shaped using QFT in such a way that robust stability will be guaranteed. The reference governor technique is a time domain approach that implies the resolution of an optimization problem. The rest of the approaches are frequency domain techniques based on a loop shaping method in the traditional QFT sense.

A robust anti-windup design procedure for SISO systems

A model-based anti-windup (AW) controller design approach for constrained uncertain linear single-input–single-output (SISO) systems is proposed based on quantitative feedback theory (QFT) loopshaping. The design approach explicitly incorporates uncertainty, is suitable for the solution of both the magnitude and rate saturation problems, and provides for the design of low-order AW controllers satisfying robust stability and robust performance objectives. Robust stability is enforced using absolute stability theory and generic multipliers (i.e. circle, Popov, Zames–Falb), and robust performance is enforced using linear lower-bounds on the input–output maps capturing the effects of saturation as a metric. Two detailed design examples are presented. These show that even for simple systems, certain popular AW techniques lead to compensators that may fail to ensure robust stability and performance when saturation is encountered, but that the proposed QFT design approach is able to handle both saturation and uncertainty effectively.

A novel robust disturbance rejection anti-windup framework

In this article, we propose a novel anti-windup (AW) framework for coping with input saturation in the disturbance rejection problem of stable plant systems. This framework is based on the one developed by Weston and Postlethwaite (W&P) (Weston, P.F., and Postlethwaite, I. (2000), ‘Linear Conditioning for Systems Containing Saturating Actuators’, Automatica, 36, 1347–1354). The new AW-design improves the disturbance rejection performance over the design framework usually suggested for the coprime-factorisation based W&P-approach. Performance improvement is achieved by explicitly incorporating a transfer function, which represents the effect of the disturbance on the nonlinear loop, into the AW compensator synthesis. An extra degree of freedom is exploited for the coprime factorisation, resulting in an implicitly computed multivariable algebraic loop for the AW-implementation. Suggestions are made to overcome the algebraic loop problem via explicit computation. Furthermore, paralleling the results of former work (Turner, M.C., Herrmann, G., and Postlethwaite, I. (2007), ‘Incorporating Robustness Requirements into Antiwindup Design’, IEEE Transactions on Automatic Control, 52, 1842–1855), the additive plant uncertainty is incorporated into the AW compensator synthesis, by using a novel augmentation for the disturbance rejection problem. In this new framework, it is shown that the internal model control (IMC) scheme is optimally robust, as was the case in Turner, Herrmann, and Postlethwaite (2007) and Zheng and Morari (Zheng, A., and Morari, M. (1994), ‘Anti-windup using Internal Model Control’, International Journal of Control, 60, 1015–1024). The new AW approach is applied to the control of dynamically substructured systems (DSS) subject to external excitation signals and actuator limits. The benefit of this approach is demonstrated in the simulations for a small-scale building mass damper DSS and a quasi-motorcycle DSS.

Robust Anti-windup Compensator Synthesis via Integral Quadratic Constraints

AbstractWe develop an anti-windup (AW) compensator synthesis approach using Integral Quadratic Constraints (IQC). The synthesis finds the AW compensator that achieves a specified robustness against additive or input multiplicative uncertainty, provided there exists a feasible solution. We also incorporate a performance criterion into the AW compensator synthesis to achieve an appropriate trade-off between the performance and robustness. The efficacy of this approach is demonstrated by a numerical example.

Constrained control of hot air blower system under output delay using globally stable performance-based anti-windup approach

This paper describes the design and implementation of a linear controller with an Anti-Windup Compensator (AWC) for a hot air blower system having output delays, under actuator saturation constraint and noise. Traditional Anti-Windup (AW) schemes for timedelay systems are based on either local stability or global stability with performance restrictions. We modify an existing AWC architecture using a time-delay term in the compensator in order to ensure global stability and performance. It is also shown that the existing Linear Matrix Inequalities (LMIs) based optimization schemes for AWC, which are derived using the decoupled architecture and coprime factorization, can be applied to the modified AWC architecture. This modified delay independent AWC scheme is applied to a hot air blower system and practical results are discussed. This paper aims to support the industrial application of the modified AWC ensuring global stability and performance, by applying it to a hot air blower system under actuator situation and output delay as well as electrical and thermal noises.

A new anti‐windup strategy for PID controllers with derivative filters

AbstractThis paper presents a new strategy for suppressing the windup effect caused by actuator saturation in proportional–integral–derivative (PID) controlled systems. In the proposed approach, the windup effect is modeled as an external disturbance imported to the PID controller and an observer‐based auxiliary controller is designed to minimize the difference between the controller output signal and the system input signal in accordance with an H‐infinite optimization criterion. It is shown that the proposed anti‐windup (AW) scheme renders the performance of the controlled system more robust toward the effects of windup than conventional PID AW schemes and provides a better noise rejection capability. In addition, the proposed PID AW scheme is system independent and is an explicit function of the parameters of the original PID controller. As a result, the controller is easily implemented using either digital or analog circuits and facilitates a rapid, on‐line tuning of the controller parameters as required in order to prevent the windup effect.Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

Anti‐windup synthesis for nonlinear dynamic inversion control schemes

AbstractA general anti‐windup (AW) compensation scheme is provided for a class of input constrained feedback‐linearizable nonlinear systems. The controller considered is an inner‐loop nonlinear dynamic inversion controller, augmented with an outer‐loop linear controller, of arbitrary structure. For open‐loop globally exponentially stable plants, it is shown that (i) there always exists a globally stabilizing AW compensator corresponding to a nonlinear generalization of the Internal‐Model‐Control (IMC) AW solution; (ii) important operator theoretic parallels exist between the AW design scheme for linear control and the suggested AW design scheme for nonlinear affine plants and (iii) a more attractive AW compensator may be obtained by using a nonlinear state‐feedback term, which plays a role similar to the linear state‐feedback term in linear coprime factor‐based AW compensation. The results are demonstrated on a dual‐tank simulation example. Copyright © 2009 John Wiley & Sons, Ltd.

Anti-windup synthesis for systems with rate-limits using Riccati equations

This article develops an anti-windup (AW) scheme for systems with rate-limited actuators. The main results show how a full-order AW compensator can be synthesised using an algebraic Riccati equation and several free parameters. A further result then shows how the free parameters may be chosen to influence, in an intuitive way, the local gain of the system and the size of the region of attraction. The results are of interest due to their low computational burden and hence their applicability to the systems of large state dimension.

Analysis and Prevention for Oscillation Failure of Capacitive Micro-accelerometers

As actuator of the force-rebalanced servo loop, the electrostatic force generator of the micro-accelerometer shows high nonlinearity while the interpole of the micro-electro-mechanical system(MEMS) sensor is far away from its balance position. The control system cannot rebalance itself with the limited bandwidth after an external long overload, because the characteristics of the force generator differ from normal case. Although for similar problems, solutions with cascading lead-lag blocks, with the anti-windup(AW) technology, or with the sliding-mode control, are widely reported, the problems such as performance loss or difficulty to synthesize a digital controller still remain. Based on existing researches, remedies are developed by analyzing the characteristic of the system not only near the balance position, but also corresponding to the whole moveable range of the interpole, and a new controller is proposed. The solution is compared with the common solutions of cascading lead-lag blocks method, AW methods, and sliding mode methods. Comparison results show that the proposed solution avoid performance loss, compared to cascading lead-lag blocks solution; the proposed solution is easily synthesized and implemented in the analog servo loop of the micro-accelerometer, compared to digital AW methods; at the same time, the proposed solution avoids suffering the chattering effect problem but just utilize it, compared to the sliding-mode control solution. Nevertheless, comparison results show the solution is lack of commonality, since the solution is only more suitable to micro electrostatic force-rebalance system. The SIMULINK models with and without the proposed solution, taking typical micro-accelerometer parameters, have been set up for simulation; corresponding experiments utilizing electrometric method are also conducted after the successful simulations. Simulation and experiment results verify that the micro-accelerometer will reliably return to normal operation after external long overload with the proposed solution. Therefore, it is expected to design the analog servo loop of high performance micro electrostatic force-rebalance system so as to ensure the rebalance after long overload without performance loss.

An Internal Model Control Anti-Windup Scheme With Improved Performance for Input Saturation Via Loop Shaping

Proposed here is a new approach for synthesizing an internal model control (IMC) anti-windup (AW) compensator for a stable plant subject to input saturation. Built on the conventional IMC AW scheme, which preserves the stability robustness of the unconstrained system, the proposed linear AW compensator improves the performance of the constrained system. The analysis conducted through the loop decomposition of the AW system clearly reveals the impacts of the AW compensator on the closed-loop stability and performance. Loop shaping techniques are executed to design the AW compensator. The effectiveness of this approach is demonstrated using a numerical example.

Design of Antiwindup AVR for Synchronous Generator Using Matlab Simulation

Automatic voltage regulator AVR is designed for synchronous generator utilizing anti windup PI controller, to keep the terminal voltage of the generator to the rated value. The simulation of the synchronous generator is done using Matlab instructions which based on d-q axes models and the designed AVR as anti wind up PI controller. The results shows when an inductive load is applied to the generator the terminal voltage drops , the AVR is automatically increasing the excitation to get rid of this the disturbance as fast as possible. Keyword: Anti windup PI, AVR, Synchronous generator.

Generalized sector synthesis of output feedback control with anti-windup structure

This paper considers the control synthesis problem for linear time invariant (LTI) continuous-time systems with actuator saturation nonlinearities. The control architecture is standard; a nominal LTI output feedback with an anti-windup (AW) mechanism. Traditional approaches have focused on AW synthesis where the nominal controller is first designed to achieve a local performance in the linear region of the actuators and then the AW compensator is added to guarantee stability/performance properties when the actuators saturate. In contrast, this paper proposes a synthesis method to design both the nominal controller and the AW compensator simultaneously. Using the generalized sector (GS) approach in the multiplier setting, a sufficient condition is given in terms of linear matrix inequalities so that a given ellipsoid is synthesized as a domain of attraction for the closed-loop system. Our result is shown to include the existing results on the simultaneous circle synthesis and the anti-windup GS synthesis as special cases. This paper also shows that the direct feed-through term in the AW compensator does not contribute to enlarging the achievable domain of attraction within the multiplier GS framework.

Discrete Robust Anti-Windup to Improve a Novel Dual-Stage Large-Span Track-Seek/Following Method

An application of an advanced anti-windup compensation scheme to a recently developed large-span track-seeking and track-following method for dual-stage actuator systems in hard disk drives (HDDs) is presented. In the original dual-stage servo control approach, micro-actuator saturation was addressed using the Circle Criterion to guide the controller design. However, such an approach does not allow the fine-tuning of seeking and settling speeds and also limits the class of linear controllers for the secondary loop due to the Circle Criterion. Anti-windup compensation removes many of these limitations and improves settling duration, disturbance rejection, recovery from saturation in the secondary actuator loop, and design flexibility. A general anti-windup (AW) compensator is presented in discrete time bringing together a number of AW concepts and results previously given in continuous time. Robustness is taken into account and performance requirements are expressed via frequency weights. The robust performance design is based on an l 2-optimization approach using linear matrix inequalities (LMIs).

Robust performance for an energy sensitive wireless body area network – an anti-windup approach

This paper applies a robust anti-windup (AW) based control scheme to optimise throughput rate for an 802.15.4 wireless body area network (WBAN) that is subject to naturally occurring input saturation constraints. The technique uses an intuitively appealing two step design procedure. Firstly, a robust H∞ loop-shaping linear controller is designed providing nominal (un-saturated) robust performance. Then Weston–Postlethwaite AW compensation techniques are used to minimise the adverse effects of any control input non-linearities on closed loop performance. The methodology provides guaranteed quality of service (in this context taken to mean that sufficient data is always available to reassemble the required biometric waveforms, e.g. ECG) while concurrently minimising power consumption over an extended usage period. This joint robust performance question is validated on an experimental mote based 802.15.4 wireless sensor network.

Flight testing of a rate saturation compensation scheme on the ATTAS aircraft

This paper presents the application of a rate saturation compensation scheme to the DLR Advanced Technologies Testing Aircraft (ATTAS) and the results of the subsequent flight tests. Details of the design philosophy and the flight tests, termed SAIFE (Saturation Alleviation In-Flight Experiment), which employed the HQDT (Handling Qualities During Tracking) test technique, are presented, as well as pilot flight test reports (PFRs). The rate saturation compensators were designed based on the anti-windup (AW) control philosophy, with the aim to reduce the deleterious effects of rate saturation on the piloted aircraft dynamics, and hence provide an increased flight envelope (operating envelope) for acceptable aircraft handling qualities and reduced PIO (Pilot-in-the-Loop/Pilot-involved Oscillation) tendencies. The achievement of this goal was primarily determined by subjective pilot handling qualities ratings and PIO ratings, and secondly by supporting flight test data. The results show that the compensation scheme greatly reduced the level of rate saturation in all instances (flight conditions), making the aircraft less PIO prone in almost all investigated cases, while exhibiting either unchanged or improved handling qualities. Most notably, the flight tests demonstrated the definite potential for well designed AW compensators to improve the safety and handling qualities of aircraft during rate saturation, with some flight conditions exhibiting dramatic improvements.

Nonlinear Dynamic Inversion Based Anti-windup - An Aerospace Application

A recently suggested general anti-windup (AW) compensation scheme is applied to the nonlinear simulation model of the 1/16 scaled BAe Hawk aircraft model used for wind tunnel experiments. The Hawk is modelled as a nonlinear affine system subject to input constraints and has a primary control system consisting of an inner-loop nonlinear dynamic inversion controller and an outer-loop linear PID controller. To address the input constraints a recently introduced nonlinear ℒ2 sub-optimal AW compensation method is applied and compared with a nonlinear version of the internal model control AW scheme. Nonlinear simulation results demonstrate the promise of the approach and indicate the superiority of the optimal AW scheme.