Anti-windup Research Articles

A Class of Proportional-Integral With Anti-Windup Controllers for DC–DC Buck Power Converters With Saturating Input

In dc–dc buck power converters, a control action which is negative or greater than one has no physical meaning and is noncausal. For the sake of realism, the nonlinearity accompanying input saturation is taken into account in a model of dc–dc buck power converters, for which a Lyapunov function-based class of proportional-integral with anti-windup (PIAW) algorithms is given. Simple tuning guidelines ensure the global asymptotical stability of the closed-loop system. Neither the class of controllers nor the tuning procedure require the exact knowledge of the parameters of the power converter. To illustrate the results, a novel design matching the proposed class of controllers is given and the results of real-time experimental tests are presented, including the implementation of the linear proportional-integral (PI) control and a known anti-windup (AW) approach. The results confirm that the proposed PIAW control has the best performance even though saturation limits are activated and disturbances are present.

Robust control with an anti-windup technique based in relaxed LMI conditions for LTV system

This paper proposes a new technique to address the anti-windup (AW) with model predictive control (MPC) scheme for linear time-varying (LTV) systems. The main advantage of this new approach is the reduced conservativeness compared with other well-known anti-windup techniques and to prevent integration windup in MPC controllers when the actuators are saturated. The control with AW is applied in a three-state switching cell (3SSC) DC-DC converter operating under saturation conditions. The MPC with proposed anti-windup is compared with the MPC technique and with MPC-AW without relaxation. The MPC-AW with relaxation improves the performance when the converter operated in the saturated mode and allows the rational use of the converter. The simulation results validated the efficiency of the proposed approach and showed that the proposed approach not only allows working better with the polytope modeling but also improves the response under LTV disturbance.

Autonomous Landing Design of UAVs using Feedback Linearization Controller with Anti Windup Scheme

This paper presents autonomous landing controller design of unmanned aerial vehicles (UAVs). Feedback linearization approach with anti windup scheme is designed as autonomous landing controller. Anti windup basically controls the integrator component accumulation in the autopilot design and restricts the output within saturation limits. Autonomous landing of a fixed wing UAV consists of approach, glideslope and flare phases. During approach, aerial vehicle aligns itself with runway and reduces its lateral deviations with respect to runway central line. In glide slope phase, aerial vehicle maintains a fixed flight path angle and descends with a constant sink rate. In flare phase, aerial vehicle follows an exponential trajectory and descends with a lower sink rate which keeps reducing further as it goes to lower altitudes. Flare controller is designed with integrator and antiwindup scheme is used to handle the controller output within saturation limits. Landing is primarily a longitudinal mode operation but due to disturbances and coupling lateral and directional modes also gets activated. In this paper pitch angle, roll angle and yaw angle nonlinear dynamic equations are linearized to obtain the control commands in terms of elevator deflection, aileron deflection and rudder deflections. Similarly total velocity of aerial vehicle being an important parameter is controlled using thrust command. A first order linearized model of velocity is used to obtain thrust control command. Autonomous landing of UAV with feedback linearization controller and anti windup scheme is simulated with Six-DOF model of AE2 UAV. The algorithm is implemented with wind disturbances to show the autonomous landing performance of UAV.

On Fault-Tolerant Control Systems: A Novel Reconfigurable and Adaptive Solution for Industrial Machines

Fault-Tolerant Controllers (FTCs) modify system behaviour to overcome faults without human interaction. These control algorithms, when based on active approach, detect, quantify and isolate the faults during Fault Detection and Isolation (FDI) phase. Afterwards, during Control Re-design (CR) phase, the controller is reconfigured and adapted to the faulty situation. This last phase has been approached by a wide variety of algorithms, being Adaptive Controllers (ACs) the ones studied in this paper. Despite their potentiality to overcome faults, industrial manufacturing systems demand robustness and flexibility levels hardly achievable by these algorithms. On this context, the paper proposes to upgrade them introducing novel Digital-Twin (DT) models to increase its flexibility and Anti-Windup (AW) techniques to improve their robustness. These novelties reach their maximum potential when FDI and CR phases merge to generate a novel FTC platform based on a Bank of Controllers (BC), improving the fault avoidance process as controller gains are switched to the ones that recover the machine more efficiently.

A Unified Method for Generic Signal Parameter Estimation of Arbitrarily Distorted Single-Phase Grids With DC-Offset

A unified method is presented which allows to estimate dc-offset, all harmonic components and fundamental frequency in arbitrarily distorted single-phase grids using a Frequency Adaptive Observer (FAO) consisting of modified Second-Order Generalized Integrators (mSOGIs) , an adaptive DC-Integrator (DCI) and a modified Frequency Locked Loop (mFLL) . DCI and mSOGIs are tuned by pole placement which allows for an arbitrarily fast detection of dc-offset and harmonic components if the fundamental frequency is known. If the fundamental frequency must be estimated as well, an mFLL with Gain Normalization (GN) , Rate Limitation (RL) , Anti-Windup (AW) strategy and low-pass filters (LPF) must be employed. The effectiveness of the proposed FAO is validated by experimental results and its enhanced performance is shown and compared to existing estimation methods.

A High Dynamic Range ΔΣ Modulator using Anti-Windup Compensated Integrators

This paper presents a continuous-time (CT) ΔΣ modulator employing an anti-windup (AW) feedback control technique to mitigate integrator overload and maintain an acceptable performance simultaneously. The proposed technique accommodates a large dynamic range and can be applied to multi-loop modulators. According to simulations, using AW augmentations, for a 50% higher dynamic range (DR), integrators do not overload and the signal-to-distortion-ratio (SNDR) drops less than 1dB from the maximum SNDR of the modulator.

Total-Amount Coordinated Finite-Time Control of Multi-Motors With Saturation Constraints

For the multi-motor traction finite-time control (FTC) system with input saturation constraints, considering parameter simplification of “adding a power integrator” (AAPI) and anti-windup (AW), a total-amount coordinated tracking control (TACTC) strategy based on nonsingular terminal sliding mode (NTSM) is proposed to ensure the global finite-time stability and effectively reduce energy consumption. First, a traction model of multiple permanent magnet synchronous motors (PMSMs) with uncertain parameter perturbations and external disturbances was established. Next, a finite-time auxiliary AW system was designed and the auxiliary state was fed back to TACTC. Then, the strong constraint of parameters of AAPI was relaxed, the setting rules of the corresponding parameters were given and the proof of finite-time Lyapunov stability was completed. Finally, the excellent performance of parameter simplification of AAPI and the controller was verified by the Matlab/Simuink simulation and RT-Lab semi-physical experiment of the multi-motor traction system, which shows that the control strategy can suppress the input saturation effect in the multi-motor traction system effectively.

An Advanced Anti-Windup Control Strategy for MMC-HVDC System

The modular multilevel converter (MMC) is an operational switch-mode converter topology which represents a potential solution for high-voltage direct current (HVDC) transmission applications. This paper deals with the dynamic performance of an MMC-based, back-to-back HVDC system. Through an Anti-Windup (AW) control method, an energy control strategy for the MMC is proposed. This approach allows to generate the desired optimal reference signals for the differential current loops with respect to its dynamic constraints. A combination between conventional PI/IP and anti-windup controllers is used to extract the advantages of each one. For MMC linked to HVDC systems, the same advanced controller combined to conventional controller of DC voltage will be applied to generate the desired active power reference and to regulate the DC bus voltage. The effectiveness of the proposed anti-windup control strategy for MMC-HVDC system is then evaluated through SPS Matlab/Simulink. Obtained results, of the two-terminal MMC-HVDC system-based anti-windup approach under different dynamic conditions, presents satisfactory dynamic responses.

Fuzzy Anti-Windup PID Controlled Induction Motor

The Induction motor has been the centre of focus in many industrial applications. This is because the Induction motor has many advantages like high precision and high torque performance. The Induction motor speed control is very essential for various applications. Conventionally induction motor speed control was done using Proportional Integral controller. This project proposes the speed control of IM using Fuzzy- Anti Windup PID controller. Using this controller the saturation effect on the speed response of the Induction motor is reduced. A vector speed control Induction motor by Fuzzy-Anti Windup PID controller is simulated using MATLAB/ SIMULINK. The control system parameters of speed of the induction motor with PI controller, Anti Windup PID controller and the proposed controller are measured and compared. From the test results the Fuzzy-Anti Windup PID controller outperforms the other considered controller performance.

A New Anti-Windup Compensator Based on Quantitative Feedback Theory for an Uncertain Linear System with Input Saturation

This paper devotes to the robust stability problem for an uncertain linear time invariant (LTI) feedback system with actuator saturation nonlinearity. Based on a three degree of freedom (DOF) non-interfering control structure, the robust stability is enforced with the describing function (DF) approach for an uncertain LTI system to avoid the limit cycle. A new type of anti-windup (AW) compensator is designed using the quantitative feedback theory (QFT) graphical method, which results in a simple design procedure and low-order AW control system. One of the most significant benefits of the proposed method is free of the non-convexity (intractable) drawback of the linear matrix inequality (LMI)-based approach. The analysis conducted on the benchmark problem clearly reveals that the proposed QFT-based anti-windup design is able to handle both saturation and uncertainty in a very effective manner.

Sampled-data observer-based anti-windup control for singularly perturbed systems with actuator saturation

In this paper, the problem of sampled-data observer-based anti-windup (AW) control for singularly perturbed systems with actuator saturation is considered. A sampled-data observer-based AW controller consisting of a sampled-data observer, controller and AW compensator is proposed for the first time. Based on an ε-dependent Lyapunov–Krasovskii functional and linear matrix inequalities, the three components of sampled-data observer-based AW controller are designed simultaneously, which can reduce the conservatism. Furthermore, a convex optimization algorithm is formulated to obtain a desired stability bound and enlarge the basin of attraction at the same time. Finally, examples are provided to demonstrate the effectiveness and merits of the obtained results.

Power Generation Control of a Monopile Hydrostatic Wind Turbine Using an <inline-formula> <tex-math notation="LaTeX">$\mathcal{H}_{\infty}$ </tex-math> </inline-formula> Loop-Shaping Torque Controller and an LPV Pitch Controller

We transform the National Renewable Energy Laboratory (NREL) 5-MW geared equipped monopile wind turbine model into a hydrostatic wind turbine (HWT) by replacing its drivetrain with a hydrostatic transmission (HST) drivetrain. Then, we design an $\mathcal {H}_{\infty }$ loop-shaping torque controller (to regulate the motor displacement) and a linear parameter varying (LPV) blade pitch controller for the HWT. To enhance the performances of the pitch control system during the transition region around the rated wind speed, we add an antiwindup (AW) compensator to the LPV controller, which would otherwise have had undesirable system responses due to pitch saturation. The LPV AW pitch controller uses the steady rotor effective wind speed as the scheduling parameter, which is estimated by the light detection and ranging preview. The simulations based on the transformed NREL 5-MW HWT model show that our torque controller achieves a very good tracking behavior, while our pitch controller (no matter with or without AW) gets much improved overall performances over a gain-scheduled PI pitch controller.

Multifrequency Current Control Including Distortion-Free Saturation and Antiwindup With Enhanced Dynamics

Output-voltage saturation (OVS) in voltage source converters can produce current-control windup. Many OVS and antiwindup (AWU) methods exist for a single-frequency current controller, but they cause additional distortion when applied to multifrequency current control. The latter is important, e.g., for reducing losses in various applications or torque ripple in ac drives. In the existing strategies with distortion-free OVS and AWU for multifrequency current control, the nonlinear effect of the OVS to the hexagon (OVSH) on the dynamics is neglected. Thus, the actual system can have bad dynamics or even be unstable. This letter proposes a multifrequency current control with distortion-free OVS and AWU where this problem is solved. An internal-model-control scheme is included to remove the OVSH nonlinear effect from the control loops, yielding better dynamics. Experimental results are provided.

New anti-windup structure for magnitude and rate limited inputs and peak-bounded disturbances

A new structure for the anti-windup (AW) compensation for rate limited actuation is proposed which is less conservative than structures currently used. For peak bounded disturbances or reference inputs, we develop AW augmentation loops for both magnitude and rate actuator saturation. To reduce conservatism further, the proposed technique is combined with a multi-stage AW loops to obtain different gains for different levels of saturation.

Heading tracking control with an adaptive hybrid control for under actuated underwater glider

The underwater glider changes its direction to follow the preset path in the horizontal plane only by flapping its vertical rudder. Heading tracking control plays the core role in the navigation process. To deal with non-linear flow disturbance and saturation in actuator, a new hybrid heading tracking control algorithm was presented, which integrated an adaptive fuzzy incremental PID (AFIPID) and an anti-windup (AW) compensator to improve the adaptability and robustness of underwater glider's heading control. The dynamic model of an underwater glider named as Petrel-II 200 was modeled to serve as a controlled plant. The proposed heading tracking control algorithm was described in detail, where the rudder angle, a control quantum to the controlled plant were calculated to get forces and moments required for the desired glider heading. A closed loop motion control system with desired heading angle as input and actual heading angle output was put forward, which included the dynamic model of the Petrel-II 200 and the given heading tracking control algorithm. The simulations followed three typical mathematical signals and the experimental tests were carried out by taking in the dynamic parameters of the controlled plant. And the effectiveness of the proposed control algorithm was assessed and verified.

Anti-windup control for nonlinear singularly perturbed switched systems with actuator saturation

ABSTRACTThis paper considers the problem of anti-windup (AW) control for nonlinear singularly perturbed switched systems with actuator saturation. An AW controller consisting of a dynamic state feedback (DSF) controller and an AW compensator is firstly constructed. Then, two methods are proposed to determine the AW controller gain matrices by a common Lyapunov function. One of which assumes that the singular perturbation parameter ϵ is available and designs ϵ-dependent AW controller gains simultaneously. The other one, which considers the case that ϵ is unknown but sufficiently small, designs the ϵ-independent DSF controller gain matrices first and then designs the ϵ-independent AW compensator gain matrices. Both of the methods are reduced to solving convex optimisation problems and can achieve larger stability bound and basin of attraction than the existing results. Finally, examples are used to illustrate the feasibility and advantages of the proposed methods.

Enhanced Power Generation in SOFCs Using Artificial Limits on Actuator Control Signals

In this paper, we study a solid oxide fuel cell (SOFC) controlled by a multi-input multi-output (MIMO) compensator, which uses the blower/fan power and cathode inlet temperature as actuators. The usable power of the fuel cell (FC) is maximized by limiting the air flow rate deliberately when an increase in power is demanded. Possible rate bounds on the cathode inlet temperature are also modeled. These bounds could represent the physical limitations (due to slow dynamics of heat exchangers) and/or a control concept for accommodating the power saving objective. Applying proper limits to the amplitude and rate of the actuator signals, and incorporating antiwindup (AW) techniques, can raise the net power of the FC by 16% with negligible effects on the spatial temperature profile.

Local Stability Analysis and Controller Design for Speed-Controlled Wind Turbine Systems in Regime II.5

The paper presents a local stability analysis for machine speed control of wind turbine systems (WTS) in regime II.5, where the control objective is set-point reference tracking of the machine speed via a PI-controller. Stability criteria for the controller parameters are derived. Based on these criteria, the controller parameters are chosen by pole placement. Moreover, a model-based tuning rule is proposed which leads (i) to a stable and (ii) to an accurate and fast control performance. The control system is additionally augmented by anti-windup (AWU) and saturation (SAT) strategies to enhance its performance. Simulation results illustrate stability and tracking performance of the closed-loop system.

Pitch Channel Control of a REMUS AUV with Input Saturation and Coupling Disturbances

The motion of an underwater vehicle is prone to be affected by time-varying model parameters and the actuator limitation in control practice. Adaptive control is an effective method to deal with the general system dynamic uncertainties and disturbances. However, the effect of disturbances control on transient dynamics is not prominent. In this paper, we redesign the L 1 adaptive control architecture (L1AC) with anti-windup (AW) compensator to guarantee robust and fast adaption of the underwater vehicle with input saturation and coupling disturbances. To reduce the fluctuation of vehicle states, the Riccati-based AW compensator is utilized to compensate the output signal from L1AC controller via taking proper modification. The proposed method is applied to the pitch channel of REMUS vehicle’s six Degrees Of Freedom (DOF) model with strong nonlinearities and compared with L1AC baseline controller. Simulations show the effectiveness of the proposed control strategy compared to the original L1AC. Besides, the fluctuation in roll channel coupled with pitch channel is suppressed according to the performances of control tests.

Anti-windup scheme for PI temperature control of an open-loop unstable chemical reactor

The problem of designing a proportional-integral (PI) temperature control with anti-windup (AW) scheme for an open-loop (OL) unstable chemical reactor is addressed. The aim is to improve the systematization of application-oriented designs employed in industrial practice. The combination of nonlinear dynamics and industrial control ideas yields a PI controller: (i) with back-calculation (BC) AW scheme, (ii) with assurance of robust closed-loop (CL) operation with criterion to choose control gain and limits, and (iii) that outperforms existing AW with BC plus conditional integration (CI) scheme. The proposed approach is illustrated and tested with a representative example through numerical simulations.