Disturbance Rejection Response Research Articles

Robust-augmentation nonlinear dynamic inversion control of over-actuated coaxial high-speed helicopter in transition mode

As the elevator and rudder can be used actively for control, in addition to the rotors, Coaxial High-speed Helicopters (CHHs) have the problems of control redundancy and changing control authority in the transition mode. This paper presents a robust-augmentation transitioning flight control design for a CHH under the adverse conditions of parametric uncertainties and external disturbances. First, based on control characteristic analysis, an Adaptive Filtered Nonlinear Dynamic Inversion (AFNDI) controller is proposed for the angular rate to handle the effect of unknown unstructured uncertainties and external turbulence. Theoretical analysis proves that the presented angular rate controller can guarantee steady-state and transient performance. Furthermore, the attitude angle and velocity controllers are also added. Then, an Incremental-based Nonlinear Prioritizing Control Allocation (INPCA) method is designed to take into account control surface transition and changing control authority, which efficiently distributes the required moments between coaxial rotors and aero-surfaces, and avoids the control reversal problem of the yaw channel. In the proposed control architecture, the low-pass filter is introduced to alleviate the adverse influence of time delay and measurement noise. Finally, the effectiveness of the proposed controller is demonstrated through nonlinear numerical simulations, and is compared with existing methods. Simulation results show that the proposed control law can improve both capabilities of disturbance rejection and fast response, and works satisfactorily for the CHH transitioning control characteristic.

Optimal design of I-PD controller for disturbance rejection of time delayed unstable and integrating-unstable processes

Disturbance rejection has always been a major phenomenon in control theory. Disturbances that arise in control of unstable or integrating unstable processes with time delay present considerable difficulties for classical PID controllers. This paper supplies analytical tuning rules, derived from optimum disturbance rejection responses to minimise the error signal according to several integral performance criteria to identify the tuning parameters of the I-PD controller. The provided analytical rules offer the advantage of calculating controller parameters without the necessity of employing an optimisation algorithm. This simplifies the tuning process and allows for a straightforward determination of the controller's parameters, making it more convenient and efficient for practical implementation in control systems. Comprehensive simulations were performed to validate the effectiveness of the proposed I-PD controller in terms of disturbance rejection responses, control signals, perturbation in process parameters, measurement noises, TV values, Ms values, and integral performance indicators. Overall, the outcomes demonstrate that the introduced method for the tuning of I-PD controllers offers notable advantages when compared to other tuning methods found in the literature.

Fractional‐order LC filter modeling, implementation, and analysis for distributed power generation system

SummaryThis paper proposes a comprehensive mathematical modeling and analysis considering fractional‐order LC filters (FOLCF) in the utility grid‐connected mode (UGCM) and the standalone mode (SM) of operation for the distributed power generation system. The fractional‐order behavior of LC filter elements helps to more properly depict a practical inductor or capacitor than the integer‐order LC filters (IOLCF) in the distributed power generation system. The fractional‐order model of UGCM and SM is obtained in the synchronously rotating reference frame using coordinate transformation. A detailed stability and time domain analysis is performed on the developed FO UGCM and SM mathematical models. The stability of fractional‐order LC filters increases for orders less than 1, based on the performance evaluation of the FO and IO mathematical models for UGCM and SM with the corresponding designed controller gains. The FOLCFs are approximated using the constant phase element method, which gives a compact and exact approximation of the fractional‐order inductor and capacitor elements. The implementation of FOLCF with UGCM and SM operations verifies the effectiveness of the proposed model in real‐time simulation. The results show the FOLCF model provides better dynamic tracking and disturbance rejection response than the IOLCF model. Hence, the FOLCF model imparts immunity against local load disturbances to regulate the point of common coupling voltage and frequency in standalone mode. Furthermore, a significant improvement in % total harmonic distortion is also observed in grid current and load voltage.

Development of Intelligent Controlled Microgrid for Power Sharing and Load Shedding

An online trained intelligent voltage controller is developed in this article to improve the transient responses of the voltage and frequency of an islanded microgrid with droop control and achieve fast load shedding. Although the droop control algorithm has been extensively adopted in microgrid, some shortcoming of the droop control, such as poor disturbance rejection and slow transient response, seriously affect the power quality and stability in islanded microgrid. Moreover, when the power consumption of the demand exceeds the generated power of the distributed generators in microgrid, the decreased frequency will lead to the microgrid blackout owing to the slow load shedding characteristics of the droop control. Hence, in this article, an online trained Petri probabilistic wavelet fuzzy neural network (PPWFNN) controller is developed as the voltage controller to replace the traditional proportional--integral controller in a battery energy storage system for an islanded microgrid with droop control to achieve fast load shedding. The network structure and the online learning algorithm of the proposed PPWFNN are detailedly introduced. Finally, some experimental results are provided to validate the effectiveness of the microgrid using the proposed PPWFNN controller for the improvements of the power sharing and load shedding.

Iterative Design of Centralized PID Controllers Based on Equivalent Loop Transfer Functions and Linear Programming

This paper deals with the design problem of multivariable Proportional-Integral-Derivative (PID) controllers for square and stable multivariable processes when a linear margin at the Nyquist plot is considered as robustness specification for each closed loop. A tuning method is developed based on the new concept of equivalent loop transfer function, which is proposed for centralized control and allows an independent design for each loop considering the interactions with the other loops through an iterative procedure. For the k-th loop, the PID parameters of the k-th column of the control matrix are calculated in each iteration by a linear programming optimization that maximizes the integral gains while fulfilling the robustness specification and achieving static decoupling. The method uses a frequency response array as representation of the process, which allows its applicability to systems with multiple time delays without requiring model reductions or approximations. The effectiveness of the method is illustrated by means of two simulation examples with dimensions <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 \times 2$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3 \times 3$ </tex-math></inline-formula> . Comparisons with other centralized control methodologies show that the proposed approach achieves similar or greater performance and a remarkable better disturbance rejection response.

A novel modified Lévy flight distribution algorithm to tune proportional, integral, derivative and acceleration controller on buck converter system

In this paper, an optimal proportional, integral, derivative and acceleration (PIDA) controller design based on Bode’s ideal reference model and a novel modified Lévy flight distribution (mLFD) algorithm is proposed for buck converter system. The modification of the original Lévy flight distribution (LFD) algorithm was achieved by improving exploration and exploitation capabilities of the algorithm through incorporation of opposition-based learning mechanism and hybridizing with simulated annealing algorithm, respectively. The modified algorithm was used to tune the gains of the PIDA controller in order to operate a buck converter system that is mimicking the response of the Bode’s ideal reference model. Both the proposed novel algorithm and its PIDA controller design implementation for buck converter were confirmed through various tests and extensive analyses of statistical and non-parametric tests, convergence profile, transient and frequency responses, disturbance rejection, robustness, and time delay response. The comparative results with the state-of-the-art algorithms of manta ray foraging optimization, arithmetic optimization algorithm and the original LFD algorithm have shown that the proposed mLFD algorithm performs better than the compared ones in all assessments even when different well-known performance indices are used. The proposed Bode’s ideal reference model-based optimal PIDA control design with novel mLFD algorithm was also compared with other design approaches using the same buck converter system available in the literature. The proposed mLFD algorithm-based design approach has also shown greater effectiveness compared to other available methods, as well.

Experimental validation of optimized fast terminal sliding mode control for level system

This research article presents a process control application of a single-input single-output (SISO) level control system using the combination of fast terminal sliding mode control (FTSMC) and optimization method. Non-dominated sorted genetic algorithm-ii (NSGA-ii); a modern optimization technique is used to optimized the parameters of FTSMC. Here, a comparative analysis of conventional sliding mode control (SMC), FTSMC, NSGA tuned FTSMC and NSGA-ii tuned FTSMC has being carried out through MATLAB/ Simulink. The performance indices such as integral absolute error (IAE), integral square error (ISE), and integration of weighted errors have been considered as the objective functions. The robustness of the controller is tested through real-time experimentation. The stability is obtained by using Lyapunov stability criteria. Simulation and experimental results show that NSGA-ii tuned FTSMC method outperforms the conventional methods and the error is converging to zero in a finite-time. Also, NSGA-ii tuned FTSMC provides better-estimated setpoint and disturbance rejection responses.

Closed Loop Tuning of Cascade Controllers Based on Setpoint Experiment

This study presents online PI/PID controller tuning rules for cascade control configuration. The necessary process data are determined with the help of a simple setpoint experiment in a single closed-loop mode with the proportional controller only. The obtained process data is recorded in terms of the overshoot, controller gain, peak time, and relative output change. The data is then utilized to establish a correlation with PI/PID settings through simulations. Further, the proposed PI/PID controller tuning rule for a single loop has been extended to the cascade control configuration. The inner loop controller is tuned first, and then the primary loop is tuned by considering a well-tuned inner loop as a part of the primary plant. Finally, simulation examples demonstrate that the proposed method delivers significant disturbance rejection and better setpoint response when compared to the recently reported methods from the literature. The proposed method is also able to deliver stable closed-loop performances when subjected to large parametric uncertainties and measurement noise.

Asymmetries in the Disturbance Compensation Methods for the Stable and Unstable First Order Plants

This paper analyzes the first-order and first-order time-delayed systems control approaches, focusing mainly on unstable systems. First, it discusses asymmetries between the disturbance observer-based (DOB) control with decoupled tracking and the disturbance rejection responses, stressing applications to stable and unstable plants. The paper analyzes some DOB-based control solutions for unstable systems which do not use internal closed-loop stabilization. The novelty of the paper is thorough study accompanied with a comprehensive explanation of the differences between two distinct approaches: the transfer-function- and the closed-loop-based feedforward control approach from the point of view of control constraints. It is clearly illustrated that the main cause of instability of DOB-based approaches, applied to unstable systems, is given by their effort to impose on the system the unstable dynamics of the chosen nominal process model. It is also shown that the closed-loop stability of the DOB-based control, applied to the unstable systems, can be restored by using the supervising reference model control (RMC). The main novelty of the proposed approach is that its eliminates the mentioned stability problems while maintaining the full functionality of the chosen control structures. RMC has so far only been implemented for generating a setpoint feedforward signal. However, by generalization of this approach for disturbance rejection, the methodology of DOB design, based on nominal models, can be extended to the control of unstable systems. Without the use of disturbance reference models, the interactions of the master stabilizer with disturbance compensation cannot be eliminated. Without the internal stabilization, the stable transients can only be achieved by designing controllers based on stable models, instead of unstable ones. The existing modifications of DOB-based schemes for unstable plants, proposed in some references, are shown to lead to traditional Proportional-Integrative (PI) control, thus losing all the advantages over the PI controllers. In all the considered structures, the role of integrating models is also emphasized.

Critical Analysis of Optimization Techniques for a MRPID Thermal System Controller

In this paper, critical analysis of performance comparison of various optimization techniques for a MRPID (Multi Resolution Proportional Integral Derivative) thermal system controller is presented. This controller controls the uncertainty or mismatch between real and reference temperature. Wavelet coefficients of error between the two temperatures and their corresponding gains are added to produce a control signal for the thermal system. The main purpose of the proposed method is to optimize the tuning parameters of a wavelet-based MRPID controller to regulate the switching pulse of the thermal system. Modeling and simulations are carried out using MATLAB/Simulink@2015. Figures-of-merit such as disturbance rejection, system stability and transient response are also compared using various techniques like Particle swarm optimization (PSO)-MRPID, Genetic Algorithm (GA)-MRPID (existing techniques), Firefly-MRPID controllers and Elephant herding optimization (EHO) based Recurrent neural network (RNN)-MRPID algorithm. Firefly-MRPID and EHO with RNN-based MRPID are proposed for determining unique (best) operating conditions of the thermal system in this paper.

Predictive In-Cycle Closed-Loop Combustion Control with Pilot-Main Injections

This paper studies the use of predictive in-cycle close-loop combustion control to reduce the stochastic cyclic variations of diesel combustion. The combustion metrics that fully define the pressure trace with a pilot-main injection i.e. pilot and main start of combustion, burned pilot mass, and engine load are used as the set-point reference. These metrics are in-cycle predicted by calibrated models as functions of the current cylinder state, estimated by in-cylinder pressure measurements. The proposed approach uses four individual controllers for the set-point error minimization, which respectively regulate the injection’s timing and duration of the pilot-main injection. The controllers are implemented in a FPGA and tested in a Scania D13 engine. The steady-state error reduction, disturbance rejection and transient response are discussed. The results confirm the error reduction in both, cycle-to-cycle and cylinder-to-cylinder variations. The error dispersion, measured by the 95% confidence interval, was reduced between 25% and 75% for all the controlled parameters. By on-line adaptation, the controllers are robust against model uncertainties and fuel types.

New hybrid‐microgrid topology using a bidirectional interleaved converter as a robust power interface operating in grid‐connected and islanded modes

This study presents a new microgrid topology that uses a bidirectional interleaved converter performing a power interface between DC buses in a hybrid microgrid allowing for both grid-connected and islanded modes. The authors propose a new control strategy and controllers' design method aiming at achieving a high-performance dynamic response regarding the converter load and generation disturbance rejection capability. In the grid-connected mode, the interleaved converter operates in the buck mode providing a high-power-quality DC microgrid voltage. In the islanded mode, the interleaved converter operates in the boost mode and it is responsible for regulating the DC link of the back-to-back converter that connects the main grid to the AC microgrid. A detailed mathematical model is presented to obtain a MIMO system that takes into account the system's disturbances to analyze both stability margins and disturbance-rejection response. Simulations of the proposed topology are carried out in PSCAD/EMTDC in a microgrid operating in grid-connected and islanded operation modes. Experimental results are provided in order to validate the proposed control tuning method.

The Sliding-Mode Control Based on a Novel Reaching Technique for Permanent Magnet Synchronous Motors

In order to improve the robustness, disturbance rejection and dynamic response performance of permanent magnet synchronous motor (PMSM) speed servo system, a novel sliding mode control (NSMC) strategy is adopted to replace the traditional proportion integral (PI) regulator in the design of speed controller. The mathematical model of PMSM is analyzed and a sliding mode controller based on a novel reaching technique is proposed. The integral of speed error is introduced into sliding mode surface to avoid the requirements of acceleration signal and reduced the steady-state error of the system. Meanwhile, a variable speed reaching method is imported to make the approaching speed correlate with the change of system state |s|, so as to improve the dynamic quality. In addition, the sigmoid function is used to replace the sign function in the conventional SMC, which further reduces chattering phenomena. Simulation and experimental results show that the proposed NSMC method based on the new reaching technique can realize precise speed control. Compared with the conventional PI and SMC control, this method not only achieves a fastest and best response speed, but also has a strongest robustness of resisting the external disturbance.

The two-degree-of-freedom parallel control for inverse response plus time delay

ABSTRACTA two-degree-of-freedom (2-DOF) control method with parallel control structure (PCS) is proposed for inverse response process plus time delay. The parallel control structure decouples the set-point tracking response from disturbance rejection response. Set point tracking control uses the method of internal model control (IMC) based on PCS. This method not only eliminates the non minimum phase parts in the denominator of the characteristic equation, but also has only one adjustable parameter which sets controller parameter using dynamic performance index, which makes the system have a good tracking performance. Disturbance rejection controller uses the principle of internal model controller, and the maximum sensitivity function is also applied to set the controller parameter. It avoids the blindness of parameter selection and improves the robustness and disturbance rejection performance of the system. Theoretical analysis and simulation results show that the proposed method presents good set-point tracking performance, disturbance rejection performance and robustness.

Accurate Trajectory Tracking of Disturbed Surface Vehicles: A Finite-Time Control Approach

In this paper, accurate trajectory tracking problem of a surface vehicle disturbed by complex marine environments is solved by creating a finite-time control (FTC) scheme whereby the nonsingular fast terminal sliding mode (NFTSM) and finite-time disturbance observer (FDO) techniques are deployed. Salient features are as follows. By devising an FDO, complex disturbances arising from marine environments can be exactly identified within a short time, in conjunction with the defined NFTSM manifold, and thereby contributing to exact trajectory tracking. Finite-time disturbance observation is completely decoupled from the nominal FTC scheme, and achieves stronger disturbance rejection and faster transient response, simultaneously. Both disturbance observation and trajectory tracking errors can exactly reach to zero in a finite time. Simulation results and comparisons are comprehensively conducted on CyberShip II and demonstrate remarkable superiority of the FTC scheme.

Adaptive Neural Network Control and Optimal Path Planning of UAV Surveillance System With Energy Consumption Prediction

A surveillance system is one of the most interesting research topics for an unmanned aerial vehicle (UAV). However, the problem of planning an energy-efficient path for the surveillance purpose while anticipating disturbances and predicting energy consumptions during the path tracking is still a challenging problem in recent years. The optimal path planning and the disturbance rejection control for a UAV surveillance system are investigated in this paper. A trained and tested energy consumption regression model is used to be the cost function of an optimal path planning scheme, which is designed from a clustered 3D real pilot flight pattern with the proposed K-agglomerative clustering method, and is processed via A-star and set-based particle-swarm-optimization (S-PSO) algorithm with adaptive weights. Moreover, an online adaptive neural network (ANN) controller with varied learning rates is designed to ensure the control stability while having a reliably fast disturbance rejection response. The effectiveness of the proposed framework is verified by numerical simulations and experimental results. By applying the proposed optimal path planning scheme, the energy consumption of the optimal path is only 72.3397 Wh while the average consumed energy of real pilot flight data is 96.593Wh. In addition, the proposed ANN control improves average root-mean-square error (RMSE) of horizontal and vertical tracking performance by 49.083% and 37.50% in comparison with a proportional-integral-differential (PID) control and a fuzzy control under the occurrence of external disturbances. According to all of the results, the combination of the proposed optimal path planning scheme and ANN controller can achieve an energy-efficient UAV surveillance systems with fast disturbance rejection response.

PI Controller Based Load Frequency Control Approach for Single-Area Power System Having Communication Delay

The modern power systems are becoming complicated day by day because of the delays introduced by the communication networks. Due to this reason, the traditional load frequency control (LFC) design scheme depicts a destabilizing impact and an unacceptable performance. Therefore, this paper proposes an analytico-graphical approach for designing PI controller for a single-area LFC system having communication delay. The concept is based on extracting stability region in parameter space (kp,ki) with predefined gain and phase margins. Further, the values of optimal kp and ki are selected using integral error criterion. The proposed scheme gives faster disturbance rejection response as compared to the recently developed LFC scheme. The controller also works well when the system parameters are perturbed from their nominal values.

Positive- and Negative-Sequence Current Controller With Direct Discrete-Time Pole Placement for Grid-Tied Converters With LCL Filter

Traditionally, the current control of grid-tied converters with LCL filter is based on proportional-resonant or proportional-integral controllers, which often need an additional active damping method to achieve stability. These solutions do not permit to place the closed-loop poles in convenient locations when dealing with such high-order plants. This constraint results in degraded reference-tracking and disturbance-rejection responses. On the other hand, the existing methods based on direct pole placement or other modern control strategies, do not control with zero steady-state error both positive and negative sequences of the grid current, but only the positive one. This limitation is undesirable under unbalanced grid conditions. This paper presents a current controller for grid-tied converters with LCL filters based on direct discrete-time pole placement. The proposed controller makes it possible to control both positive and negative sequences of the grid-side current with zero steady-state error. Contrarily to the classical resonant controllers, the closed-loop poles can be placed in convenient locations, yielding a fast response with negligible overshoot and low controller effort. Moreover, no additional damping methods of the resonance are necessary to achieve stable operation, regardless of the switching frequency and LCL filter used. Simulation and experimental results that validate the proposal are presented.

A Combined Voltage Control Strategy for Fuel Cell

Control of output voltage is critical for the power quality of solid oxide fuel cells (SOFCs), which is, however, challenging due to electrochemical nonlinearity, load disturbances, modelling uncertainties, and actuator constraints. Moreover, the fuel utilization rate should be limited within a safety range during the voltage regulation transient. The current research is usually appealing to model predictive control (MPC) by formulating the difficulties into a constrained optimization problem, but its huge computational complexity makes it formidable for real-time implementation in practice. To this end, this paper aims to develop a combined control structure, with basic function blocks, to fulfill the objectives with minor computation. Firstly, the disturbance, nonlinearity and uncertainties are lumped as a total disturbance, which is estimated and mitigated by active disturbance rejection controller (ADRC). Secondly, a feed-forward controller is introduced to improve the load disturbance rejection response. Finally, the constraints are satisfied by designing a cautious switching strategy. The simulation results show that the nominal performance of the proposed strategy is comparable to MPC. In the presence of parameter perturbation, the proposed strategy shows a better performance than MPC.

The magnitude optimum tuning of the PID controller: Improving load disturbance rejection by extending the controller

The Magnitude Optimum (MO) tuning method for PID controllers, applied on stable and non-oscillating plants, usually gives fast tracking responses and offers very good process output disturbance-rejection performance, even if the process contains significant dead time. On the other hand, when an exogenous disturbance affects the process indirectly, for example, via the plant input, slow disturbance rejection responses may be obtained. The paper proposes a way of removing this problem by means of adding two first-order filters into the control loop, without modifying the controller parameters. The filter parameters are determined so that the disturbance lag is partially compensated and the stability margin properties of the MO tuning are preserved.