Anti-windup Scheme Research Articles

FRT Capability of Grid-Forming Power Converters: An Antiwindup Scheme

FRT Capability of Grid-Forming Power Converters: An Antiwindup Scheme

Investigation of anti-windup Proportional-Integral controller with semi-decoupled tuning gains in motor speed control

Abstract Integral windup refers to a prevalent phenomenon that can occur in Proportional-Integral-Derivative (PID) control systems that employ integral control where the control output generated exceeds the operating limit of an actuator. Despite the system’s inability to respond further due to control output limitations, the integral controller perseveres in accumulating errors. The accumulation of error can lead to system instability and undesirable oscillations. Additionally, the dynamic response of the PID controller is also limited by the coupled tuning gain characteristics, complicating the process of gain tuning. The coupling and decoupling of the tuning gains are depending on the separation of the gains in the error dynamics of the system. In this study, a concept of semi-decoupled tuning gains in anti-windup controllers is proposed. The performance of the proposed controller was investigated through hardware simulation against conventional PI and existing anti-windup schemes and has demonstrated an overall improvement in its dynamic behaviour such as faster settling time and its ability to tune the system without significantly altering its damping ratio.

Switching Anti-Windup Synthesis for Linear Systems With Asymmetric Actuator Saturation.

This article proposes a switching anti-windup strategy for linear, time-invariant (LTI) systems subject to asymmetric actuator saturation and L2 -disturbances, the core idea behind which is to make full use of the available range of control input space by switching among multiple anti-windup gains. The asymmetrically saturated LTI system is converted to a switched system with symmetrically saturated subsystems, and a dwell time switching rule is presented to govern the switching between different antiwindup gains. Based on multiple Lyapunov functions, we derive sufficient conditions for guaranteeing the regional stability and weighted L2 performance of the closed-loop system. The switching anti-windup synthesis that designs a separate anti-windup gain for each subsystem is cast as a convex optimization problem. In comparison with the design of a single anti-windup gain, our method can induce less conservative results since the asymmetric character of the saturation constraint is fully utilized in the switching anti-windup design. Two numerical examples, and an application to aeroengine control (the experiments are conducted on a semiphysical test bench), demonstrate the superiority and practicality of the proposed scheme.

Sliding mode active disturbance rejection control for manipulator considering actuator saturation

<p style="text-align: justify;">Considering the issue of low control accuracy in joint trajectory tracking control for manipulator systems with actuator saturation due to external disturbances, modelling inaccuracies, and joint friction, a sliding mode active disturbance rejection control approach was proposed. An improved extended state observer is employed to observe and estimate the lumped disturbances affecting the system, providing feedback compensation. A variable gain reaching law is devised, coupled with a fast non-singular terminal sliding mode to design the system control law, which mitigates chattering inherent and ensuring precision control. Additionally, a novel output error compensation-based anti-windup scheme is introduced to compensate for the detrimental impacts caused by actuator saturation. Simulation results collectively demonstrate that the proposed tracking control algorithm exhibits better control performance and robustness against disturbances.</p>

Two-stage anti-windup compensation for systems subject to actuator quantization and saturation

This paper proposes a two stage anti-windup compensation scheme for systems subject to both input saturation and input quantization. The paper makes two main contributions: (i) it proposes a new partitioning of the saturation/quantization nonlinearity; and (ii) it formulates and solves a two-stage anti-windup problem on the basis of this partitioned nonlinearity. The anti-windup compensator contains two distinct elements: one to assuage the effects of quantization, the other to do the same when saturation occurs. Theoretical results provide conditions which must be satisfied in order for the two-stage anti-windup compensator to bestow stability on the resulting closed-loop system. These results are expressed as linear matrix inequalities and naturally lead to algorithms for anti-windup design. Simulation examples illustrate the effectiveness of the techniques.

Anti-windup strategy for interval positive linear systems with input saturation

Anti-windup strategy for interval positive linear systems with input saturation

Control of the RMS Output Current in Series Resonant Converters

In this work the problem of regulation of the Root Mean Square (RMS) value of the current for Series Resonant Converter (SRC) is addressed. The self-oscillating behavior is ensured by an amplitude modulation like control law and the RMS value is estimated with a proposed hybrid system. The closed-loop regulation is done with a Proportional-Integral (PI) controller with anti-windup scheme, and a set of Linear Matrix Inequalities (LMIs) is introduced to tune the gains. The knowledge of a reference trajectory is not needed to implement the controller, and it is shown to be effective in simulation considering uncertain parameters.

PID and Model Predictive Control Approach for Drug Dosage in Anesthesia During Induction: a Comparative Study

In this paper, a PID controller is compared to an extended moving horizon estimator coupled with a model predictive control approach for the problem of dosing propofol and remifentanil during the induction of anesthesia. For the PID controller, taken from the literature, a fixed ratio is considered between propofol and remifentanil flow rates and an anti-windup strategy is used to prevent integration wind-up. The optimal control approach uses an MHE to estimate both the states and the pharmacodynamic parameters of the system, followed by a non-linear model predictive controller to compute the optimal drug rates according to the model. Both controllers are tuned using the same criterion, and are compared by simulating 500 uncertain patient models for the induction phase.

Neuron-based back-calculation anti-windup strategy: first results

Back-calculation is an anti-windup strategy that consists in adding a feedback path to act on the integrator of a proportional-integral-derivative (PID) controller when the actuator causes a saturation. Neuromorphic control (NC) uses neuron models to encode the control signal into pulses. This paper is a first attempt towards using basis of NC as an anti-windup method in a PID controller. More precisely, a neuron is utilized to encode the saturation error (namely, the difference between the controller and the actuator outputs) into pulses, causing that the back-calculation works in lapses according to error intensity. A classical control problem with saturation is given as illustrative example of application of the proposed strategy.

Event-triggered anti-windup strategy for time-delay systems subject to saturating actuators

<p>This paper investigates the anti-windup synthesis problem for linear control systems subject to time-varying state delay and saturating actuators. To alleviate the redundant data transmission, the dynamic event-triggered mechanism is adopted. Moreover, to abate the inherent conservatism, novel delay-dependent sector conditions containing double integral terms are explored. Then, using augmented Lyapunov-Krasovskii functionals and several less conservative inequalities, delay-dependent anti-windup synthesis criteria are obtained in accordance with the feasibility of linear matrix inequalities. Subsequently, the optimization of the initial condition set is addressed. Finally, a simulation example illustrates the availability and technique advantages of the proposed results.</p>

Real-world application of a discrete feedback control system for flexible biogas production

Using renewable energy is increasingly prevalent as part of a global effort to safeguard the environment, with a reduction in {mathrm{CO}}_{2} being one of the primary objectives. A biogas plant provides an opportunity to produce green energy, but its profitability prevents it from being utilized more frequently. A suitable response to this economic issue would be flexible biogas production to exploit fluctuating energy prices. Nevertheless, the complex nature of the anaerobic digestion process that proceeds within the biogas plant and the wide range of substrates that may be utilized as the plant’s feeds make it challenging to achieve flexible biogas production truly. Most plant operators will rely on their experience and intuition to run the plant without knowing exactly how much biogas they will produce with the feed substrate. This work combines a system model estimation and feedback controller to provide an intuitive yet precise feedback control system. The system model estimation represents the biogas plant mathematically, and a total of six distinct approaches have been compared and evaluated. A PT1 model most accurately approximated the step-down and the step-up by the time percentage method, with the Akaike Information Criterion as the primary evaluation criterion for selecting the best model. The downward model was controlled by a discrete PI controller modified with the Root Locus Method and an Anti-Windup scheme, and the upward model was controlled by a state space controller. The quality of the controller was evaluated in both simulation and at the actual biogas plant in Grub, and the controller was able to reduce the biogas production rate approaching the setpoint in the expected period. Furthermore, the developed feedback control system is effortless enough to be installed in many biogas plants.

Dynamic global power extraction of partially shaded PV system using a hybrid MPSO-PID with anti-windup strategy

Particle Swarm Optimizer (PSO) has three main drawbacks in case of partially shaded photovoltaic systems. First, it converges slowly to the global peak (GP). Second, because PSO is a time invariant, it cannot adhere to a dynamic GP in the presence of various temporal shading patterns and instead, sticks to the first GP. Third, it exhibits high oscillations around GP. To overcome these shortcomings, this paper proposes a novel hybrid modified PSO-PID (MPSO-PID) with anti-windup strategy based maximum power point tracking. The anti-windup strategy aims to guarantee the robustness of the PID controller and eliminate the PID windup outcome. Two anti-windup structures were applied to PID namely: anti-windup using back calculation and anti-windup using conditional integration. For validation purpose, the hybrid MPSO-PID with anti-windup has been compared with conventional PSO and three modified PSO versions namely: PSO with random numbers eliminated (PSO-RNE), PSO with linearly varying parameters (PSO-LVP), and PSO with fixed maximum iterations (PSO-FMI). The obtained simulation and experimental results revealed that the proposed MPSO-PID with anti-windup overcome the previous shortcomings providing outperformance to track dynamic GP with a less convergence time and small oscillations around GP compared to other algorithms. The proposed MPSO-PID technique has a minimum average response time; 0.026 s; to catch the GP under various shading patterns compared to the other PSO versions; CPSO, PSO-LVP, PSO-RNE, and PSO-FMI; where the average response time are 0.026 s, 0.531s, 0.446 s, 0.763 s, and 0.494 s respectively. Finally, the results proved the robustness and effectiveness of PID design for enhancing both the PSO and PV system performance.

Incremental control as an enhanced and robust implementation of gain scheduled controllers avoiding hidden coupling terms

This paper proposes a new and simple method to combine incremental control with the classical proportional-integral (PI) control in order to increase the robustness properties of the resulting control law. The proposed method avoids hidden coupling terms in a similar manner to the differential PI controller implementation (DPI) and hence allows for fast gain scheduling. The integral action is accomplished by feedback of actuator measurements and therefore avoids integrator windup without complicated anti-windup schemes. The control law obtains an increase in robust performance with a response less sensitive to variations in flight dynamic parameters when compared to the equivalent PI controller. Improvement in disturbance rejection is also obtained with a faster and more robust response. Increased robustness toward input time delay is observed by example. The trade-off between increased robustness and sensitivity to sensor noise and delay can be adjusted with an intuitive tuning parameter. The novel method, denoted incremental DPI (iDPI), is investigated in the context of fixed-wing flight control. The concept is verified as a retrofit for an industry-level PI baseline controller for the longitudinal motion of a fixed-wing aircraft using a high-fidelity simulation model.

Delay partitioning approach to the delay-dependent stability of discrete-time systems with anti-windup

ABSTRACT In this digital era, the basis of every smart instrument is discrete signal models e.g. in Networked control systems, Cyber physical systems etc. It has been shown that time-delays are unavoidable during the digital implementation of an engineering system. Therefore, the stabilization of discrete time delayed systems is gaining the high importance [1–10]. Although a lot of literature is found on the stabilization of time delayed systems for a long time using the construction of proper non-negative Lyapunov functional. Recalling some existing results on this issue, the LMI-based stability conditions are obtained by its forward difference negative-definite in direction to claim the less conservative results [15–25]. In order to seek less conservative stability criteria, this paper introduces an anti-windup scheme appended with Wirtinger inequality, reciprocal convex approach and delay partitioning of a discrete-time delayed systems by using Lyapunov Krasovskii functional. To accomplish this task, delay partitioning technique may be utilized to develop improved stability conditions for the considered system. The Wirtinger-based inequality and reciprocal convex approach has been employed to derive less conservative results. On employing the delay partitioning, a novel linear matrix inequality-based criterion is proposed to stabilize such systems. The considered Lyapunov-Krasovskii functional includes the information of intermediate delay to acknowledge the delay information implicitly that ensures the considered system to be regular, impulse free and stable in terms of linear matrix inequalities. The estimation of the attraction basin is to ensure that the state remains inside the level set of a certain Lyapunov function. Numerical simulation verifies that the presented method reduces conservatism than the existing results.

Switching Anti-windup Control for Aircraft Engines

In this article, we propose a switching anti-windup scheme for the aircraft engine control. The linear engine model with asymmetric saturation is first transformed into a switched system, each subsystem of which is subject to symmetric saturation. A state-dependent switching logic is presented to orchestrate the switching among multiple anti-windup compensators. We then establish the sufficient condition to guarantee the regional stability and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathcal {L}_{2}$</tex-math></inline-formula> performance of the resulting closed-loop system. This condition is less conservative since the non-symmetric nature of the saturation nonlinearity can be fully exploited in the control design. Optimization algorithms are further developed for the anti-windup gain design. The theoretical aspect of the proposed method is analyzed rigorously, and the effectiveness is validated through experiments performed on a semi-physical test bed.

Advanced Motor Control for Improving the Trajectory Tracking Accuracy of a Low-Cost Mobile Robot

Accurate trajectory tracking is a paramount objective when a mobile robot must perform complicated tasks. In high-speed movements, time delays appear when reaching the desired position and orientation, as well as overshoots in the changes of orientation, which prevent the execution of some tasks. One of the aspects that most influences the tracking performance is the control system of the actuators of the robot wheels. It usually implements PID controllers that, in the case of low-cost robots, do not yield a good tracking performance owing to friction nonlinearity, hardware time delay and saturation. We propose to overcome these problems by designing an advanced process control system composed of a PID controller plus a prefilter combined with a Smith predictor, an anti-windup scheme and a Coulomb friction compensator. The contribution of this article is the motor control scheme and the method to tune the parameters of the controllers. It has been implemented in a well-known low-cost small mobile robot and experiments have been carried out that demonstrate the improvement achieved in the performance by using this control system.

Modeling proportional–integral controllers in tracking and economic model predictive control

In industrial applications, model predictive control (MPC) is typically installed in a hierarchical operational framework above regulatory layer proportional–integral (PI) controllers. Traditional MPC implementations do not include a dynamic model of the regulatory layer PI controller in the MPC optimization problem. This paper presents case studies to illustrate the advantages of modeling the PI controller in the MPC optimization problem. A PI controller implemented with an antiwindup scheme introduces significant nonlinearity into the MPC model that can be challenging to optimize with standard nonlinear solvers. Therefore, an approximate linear PI control law model is proposed for use in the MPC optimization problem. Hard constraints of the plant actuator manipulated by the PI controller are also included in the MPC problem. We illustrate using simulation studies that this PI controller modeling approach in the MPC optimization problem provides the following advantages: (i) systematic constraint handling in the presence of an unmeasured disturbance in the PI feedback loop, (ii) disturbance rejection forecast of the PI controller in the MPC optimization problem for a slow PI feedback loop, and (iii) optimizing plant economics of a cascade control architecture in which the PI controller manipulates a variable that directly influences the economic objective. Case studies on a continuous stirred tank reactor (CSTR) and heating, ventilation, and air-conditioning (HVAC) system are presented to highlight these advantages of modeling the PI controller in the MPC optimization problem.

Thermodynamic based robust regulation of a heat exchanger

In this work, a robust regulation problem based on thermodynamic principles is developed to control a heat exchanger. The system is regulated through a nonlinear output error dependent on the total entropy production within the heat exchanger; this error is a function of the output variable and its reference, but it can also be affected by parametric uncertainties and disturbances, so a geometric controller with a high-gain observer and an anti-windup scheme is proposed. Finally, the numerical simulation of the controller shows compliance with stability and robustness criteria.

Disturbance-Observer-Based Feedback Linearization Control for Stabilization and Accurate Voltage Tracking of a DC–DC Boost Converter

The nonminimum-phase property of the dc–dc boost converter can create difficulties in designing a stable, robust, and fast control for the output voltage. In this article, these difficulties are reduced by modifying the state model of the boost converter in such a way that it behaves like a minimum-phase system. More specifically, the control input entering the state equation for the output voltage is treated as an unknown disturbance to make the relative degree of the system equal the system’s order. As a result, the modified model does not exhibit zero dynamics, so that it can be treated as a minimum-phase system for the control design. The modified model is, then, used to derive a dynamic compensator for the output voltage regulation. More explicitly, the dynamic compensator is designed based on combining linearizing feedback control with a disturbance observer. The latter is employed to compensate for model uncertainties and unknown load with a view to ensure asymptotic regulation under the composite controller. The asymptotic regulation is achieved due to the integral action property characterizing the disturbance observer. More interestingly, after simple algebraic manipulation, it turns out that the composite controller reduces to a dynamic state feedback control plus an antiwindup scheme to mitigate the effect of control saturation during transients. The performance of the proposed controller is verified by experimental tests. The experimental results demonstrate the ability of the proposed controller to achieve good transient and steady-state performances.

Coordinated Control Strategy for Hybrid off-Grid System Based on Variable Speed Diesel Generator

In this article, the control of hybrid <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> -grid configuration based on a variable-speed diesel generator and solar photovoltaic array, is implemented. To ensure a stable operation with the ac voltages and system frequency regulation, back-to-back connected converters are controlled using vector-based control, and stator flux-oriented frame-based control. To adjust the speed of diesel engine according to specific fuel consumption, an effective control strategy is developed. In addition, to compensate for the slow dynamics of variable speed operation and to balance the power in the system the dc-link voltage and battery current are controlled using a double-loop control strategy. Furthermore, the dynamic model of the dc–dc boost converter is integrated with the perturbation and observation method for obtaining smooth and efficient maximum power point tracking (MPPT). To prevent overshoots during the sudden transition, all proportional-integral controllers are reinforced with a back-calculation antiwindup scheme. The performance is obtained using MATLAB/Simulink and validated on real-time hardware to demonstrate the effectiveness of coordinated control under variations of loading and weather conditions.