Showing papers by "Maarouf Saad published in 2018"

Adaptive Leader–Follower Formation Control of Underactuated Surface Vessels Under Asymmetric Range and Bearing Constraints

Abstract: This paper deals with the problem of leader–follower formation control for a group of underactuated surface vessels with partially known control input functions. In the proposed scheme, the problem is formulated as an adaptive feedback control problem for aLine-Of-Sight (LOS) based formation configuration of a leader and a follower. To account for LOS and bearing angle time-varying constraints, asymmetric barrier Lyapunov functions are incorporated with the control design. Furthermore, in order to alleviate required velocity information on the leader, a reconstruction module is designed to estimate the vector velocity of this leader. This reconstruction is accomplished in finite time with zero error, which allows the injection of accurate estimation into the formation controller. The controller is then developed within the framework of the backstepping technique, with the parametric uncertainties and the unknown gains being estimated by a novel structure identifier. The overall closed-loop system, is proved to be semiglobally uniformly ultimately bounded by Lyapunov stability theory. Furthermore, we show under the proposed control scheme that the constraints requirement on the LOS range and bearing angle tracking errors are not violated during the formation process. Finally, the effectiveness and the robustness of the proposed strategy are exhibited through simulations.

Adaptive Tracking Control of an Exoskeleton Robot With Uncertain Dynamics Based on Estimated Time-Delay Control

Abstract: In this paper, we present a backstepping approach integrated with time-delay estimation to provide an accurate estimation of unknown dynamics and to compensate for external bounded disturbances. The control was implemented to perform passive rehabilitation movements with a 7-DOF exoskeleton robot named ETS-Motion Assistive Robotic-Exoskeleton for Superior Extremity. The unknown dynamics and external bounded disturbances can affect the robotic system in the form of input saturation, time-delay errors, friction forces, backlash, and different upper-limb's mass of each subject. The output of the time-delay estimator is coupled directly to the control input of the proposed adaptive tracking control through a feed-forward loop. In this case, the control system ensures a highly accurate tracking of the desired trajectory, while being robust to the uncertainties and unforeseen external forces, and flexible with variation of parameters. Due to the proposed strategy, the designed control approach does not require accurate knowledge of the dynamic parameters of the exoskeleton robot to achieve the desired performance. The stability of the exoskeleton robot and the convergence of its state errors are established and proved based on Lyapunov–Krasovskii functional theory. Experimental results and a comparative study are presented to validate the advantages of the proposed strategy.

Super-twisting algorithm with time delay estimation for uncertain robot manipulators

Abstract: This paper proposes a super-twisting algorithm (STA) with time delay estimation (TDE) for the problem of high-accuracy tracking trajectory of robotic manipulators in the presence of uncertainties and unexpected disturbances. The TDE method is known for it capability to estimate uncertainties simply without an exact knowledge of the system dynamics. Using the estimated uncertainties, the control law is then designed based on STA to ensure robustness, finite-time convergence and chattering reduction. The stability analysis of the closed-loop system and the finite-time convergence are proved using Lyapunov theory. In order to show the effectiveness of the proposed method, simulations and experimental results were carried out on a 2-DOF rigid robot manipulator and on the 7-DOF ANAT robot arm, respectively.

Robust Observer-Based Dynamic Sliding Mode Controller for a Quadrotor UAV

Abstract: In this paper, a novel robust backstepping-based approach combined with sliding mode control is proposed for trajectory tracking of a quadrotor UAV subject to external disturbances and parameter uncertainties associated with the presence of aerodynamic forces and possible wind force. To enhance robustness, a nonlinear disturbance observer (NDO) is employed alongside the controller. A sliding surface is introduced, which shares intermediate control goals with a conventional backstepping scheme. The closed-loop system comprising the sliding mode and backstepping controllers is finally combined with the NDO to track the desired position and attitude trajectories. Good tracking is achieved in the closed loop if the controller and observer gains are selected correctly. The system performance exhibits much better robustness than the existing backstepping control methods, which are not equipped with nonlinear disturbance estimators. The simulation results are confirmed in terms of real laboratory experiments. Prior to the implementation of the control method, the real system has been identified and calibrated.

Robust adaptive path-following control of underactuated marine vessel with off-track error constraint

Abstract: In this paper, a new robust adaptive controller is investigated to force an underactuated surface marine vessel to follow a predefined parameterised path at a desired speed, despite actuator satura...

Passive and active rehabilitation control of human upper-limb exoskeleton robot with dynamic uncertainties

Abstract: This paper investigates the passive and active control strategies to provide a physical assistance and rehabilitation by a 7-DOF exoskeleton robot with nonlinear uncertain dynamics and unknown bounded external disturbances due to the robot user's physiological characteristics. An Integral backstepping controller incorporated with Time Delay Estimation (BITDE) is used, which permits the exoskeleton robot to achieve the desired performance of working under the mentioned uncertainties constraints. Time Delay Estimation (TDE) is employed to estimate the nonlinear uncertain dynamics of the robot and the unknown disturbances. To overcome the limitation of the time delay error inherent of the TDE approach, a recursive algorithm is used to further reduce its effect. The integral action is employed to decrease the impact of the unmodeled dynamics. Besides, the Damped Least Square method is introduced to estimate the desired movement intention of the subject with the objective to provide active rehabilitation. The controller scheme is to ensure that the robot system performs passive and active rehabilitation exercises with a high level of tracking accuracy and robustness, despite the unknown dynamics of the exoskeleton robot and the presence of unknown bounded disturbances. The design, stability, and convergence analysis are formulated and proven based on the Lyapunov–Krasovskii functional theory. Experimental results with healthy subjects, using a virtual environment, show the feasibility, and ease of implementation of the control scheme. Its robustness and flexibility to deal with parameter variations due to the unknown external disturbances are also shown.

Attitude Tracking of a Tri-Rotor UAV based on Robust Sliding Mode with Time Delay Estimation

Abstract: The paper presents a robust sliding mode with time delay estimation method for controlling the attitude of a tri-rotor unmanned aerial vehicle (UAV) in presence of uncertainties and disturbances. The proposed control algorithm allows high accuracy tracking since a good disturbance estimation is provided using time delay estimation method and allows chattering reduction. The stability analysis of the closed-loop system is presented using the theory of Lyapunov. Finally, two numerical simulations are presented in the presence of disturbances to show the effectiveness of the proposed nonlinear control scheme.

Novel Approach for Optimizing the Transformer’s Critical Power Limit

Abstract: Massive penetration of plug-in electric vehicles (EVs) may create challenges in the near future for the distribution network. Moreover, this may lead to an increase of the transformers’ aging rate and a reduction of the financial profits. In this paper, a novel approach is proposed, in which the operational margin of the transformer is optimized based on the transformer’s internal characteristics, its loss of life, and the variation of the ambient temperature. This operational power limit should not be exceeded to guarantee that the loss of life of the transformer is equal to or less than the one provided by the manufacturer. For validation purposes, a comparative study between the conventional method and the suggested one is presented. This paper is applied to a parking lot for charging EVs, which is supplied by a distribution transformer. In contrary to the conventional method, the one suggested in this paper can guarantee a predefined transformer loss of life. Simulation results show that the proposed method increases the transformer lifetime, reduces the loss of life, and reduces its depreciation cost by 63% in certain conditions. In addition, it increases the financial profit for the parking lot’s owner up to 10% during cold weather.

An Impedance-Based Method for Distribution System Monitoring

Abstract: This paper presents a new approach in monitoring of a power distribution system. It uses the bus voltage and injected current to extract the apparent impedance seen from the measuring unit location. Then the apparent impedance variation is used for the monitoring of different electrical quantities of the feeder such as feeder power factor, and the minimum and maximum of active and reactive power flow. This paper also presents the mathematics for defining the monitoring zone on the R-X plane to detect those parameters variations. The proposed method was tested with the unbalanced distribution system feeder loading, distributed and lumped model of solar, and wind power generations. OpenDSS and MATLAB are used to test the effectiveness of the method with the IEEE 8500 node test feeder. The dynamic performance of the proposed method is studied for online monitoring of the reactive power capability requirement of a Canadian utility for a wind farm integrated to the system. The results show that the monitoring method based on the apparent impedance has a good capability to detect different operation conditions. In addition, the simplicity of the proposed method allows easy application of it in smart grid and traditional distribution system.

Compliant control for wearable exoskeleton robot based on human inverse kinematics

Abstract: Rehabilitation robots are a new technology dedicated to the physiotherapy and assistance motion and has aroused great interest in the scientific community. These kinds of robots have shown a high p...

Speed Control of a Five-Phase Induction Motor Drive using Modified Super-Twisting Algorithm

Abstract: Field oriented control, with an outer speed loop and inner current loops, has been the most common control strategy for multiphase drives. For the inner current control, the proportional-integral pulse-width modulation and finite-control-set model predictive control have been the most analyzed implementations. The present work proposes an alternative for the inner current control based on the modified super-twisting algorithm with time delay estimation. Simulation results were carried out to verify the performance of the proposed robust control strategy for a five-phase induction motor drive. A stability analysis is also presented.

Homogeneous finite-time consensus control for higher-order multi-agent systems by full order sliding mode

Abstract: This paper investigates the distributed finite-time consensus tracking problem for higher-order nonlinear multi-agent systems (MASs). The distributed finite-time consensus protocol is based on full order sliding surface and super twisting algorithm. The nominal consensus control for the MASs is designed based on the geometric homogeneous finite time control technique. The chattering is avoided by designing a full order sliding surface. The switching control is constructed by integrating super twisting algorithm, hence a chattering alleviation protocol is obtained to maintain a smooth control input. The finite time convergence analysis for the leader follower network is presented by using strict Lyapunov function. Finally, the numerical simulations validate the proposed homogeneous full-order sliding mode control for higher-order MASs.

An Optimal Approach for Offering Multiple Demand Response Programs Over a Power Distribution Network

Abstract: Playing a significant role in the operation of the modern electric grid, Demand Response Programs (DRPs) balance the demand on the consumer level with the supply through the deployment of specific measures. An important undesirable phenomenon may occur when simultaneously launched DRPs on a same network interact negatively between each other. Therefore, an optimal coordination is necessary in order to optimize a preset objective function. Within this context, and as a new approach for solving this issue, this paper suggests to perform an optimal clustering applied on the network gathered data. Based on published results, the importance of synchronization between different DRPs is proved. It is shown how the suggested clustering would improve the synchronization process. As a demonstration for this new approach, clustering simulations are applied on a set of a real data built through measurements performed on the distribution network of a university campus.

Distribution power factor monitoring in presence of high RES integration using a modified load encroachment technique

Abstract: This study presents a new approach in application of distance relay in distribution system. During the heavy load conditions, the load encroachment of impedance into the distance relay protection zones is a well-known reason for distance relay mal-operation. Therefore, all the modern digital distance relays are equipped with the load encroachment scheme. This study proposes the idea of using the load encroachment scheme of distance relay for monitoring purpose in the presence of renewable energy resources (RES) integration. Furthermore, it will be presented that based on the defined monitoring zones some alarms can be defined. The OpenDSS and Matlab software are used to test the effectiveness of the method with the IEEE 8500 node test feeder. The proposed method is tested with the unbalanced distribution system feeder loading and distributed model of solar generations. The dynamic performance of the proposed method is studied for on-line power factor monitoring of the feeder with the sun irradiation dynamic. The results show the necessity of power factor monitoring in the distribution system with RES integration. In addition, the simplicity of the proposed method allows its easy application in the digital distance relay.

Impact of Considering Variable Battery Power Profile of Electric Vehicles on the Distribution Network

Abstract: In the literature, many papers consider a constant value of the battery power profile while charging Plug-in Electric Vehicles (PEVs). In fact, the battery power profile is not constant; it varies depending on the energy present in the battery. When the State Of Charge of the battery is low, the charging power profile has the highest value. It starts to decline when the battery is approaching its full energy capacity. The consideration of a constant battery power profile may create inaccuracy in the optimization results and lead to eventual instability on the distribution network. Therefore, in this paper, we are going to study the impact of considering or not considering the variable battery power profile on the distribution network and on the end-user financial profits. Simulations are done with OpenDSS and MATLAB using IEEE 13 distribution test feeder.

Discrete-Time Sliding Mode with Time Delay Estimation of a Six-Phase Induction Motor Drive

Abstract: This paper investigates the problem of stator current control in presence of uncertainties and unmeasurable rotor current for a six-phase induction motor drive. An inner control loop based on a robust discrete-time sliding mode with time delay estimation method is proposed to ensure the finite-time convergence of the stator currents to their desired references while the proportional-integral controller is used for the outer speed control. Sufficient conditions are established to ensure the stability of the closed-loop system. Simulation results were carried out to verify the performance of the proposed robust control strategy for a six-phase induction motor drive.

Composite Control Strategy for a PV-Wind-Diesel based Off-Grid Power Generation System Supplying Unbalanced Non-Linear Loads

Abstract: In this paper, a composite control strategy is investigated for a photovoltaic (PV), wind turbine (WT) and diesel engine (DE) generator based off-grid power generation system to achieve high performance while supplying unbalanced nonlinear loads. To operate the WT efficiently under variable speed condition and maximum power point tracking (MPPT) without speed sensors, a root-finding algorithm (secant method) is integrated with perturbation and observation (P&O) technique. A DC/DC buck-boost converter is controlled for bidirectional power flow through battery energy storage system (BESS) and to obtain maximum power from PV system without using any MPPT method. Power management, synchronization and the power quality improvement at the point of common coupling (PCC) are achieved by controlling the four-leg voltage source converter (VSC) using AC source current estimation from the generated and consumed power in the system. The robustness of the developed composite control strategy is tested by performance simulation of the proposed off-grid configuration using Matlab/Simulink and validated through hardware prototyping.

Optimal PMU placement for reverse power flow detection

Abstract: The integration of renewable energy sources alter the radial nature of the conventional distribution network and causes the power flow to reverse in some periods. As the voltage regulator is normally designed for unidirectional power flow, this may cause voltage violations on the distribution feeder resulting in faults and cuts. To solve this problem, monitoring of the distribution network is essential before taking any control or protection measures. From this fact emerges the importance of reverse power flow detection. In this paper, the optimal phasor measurement placement for reverse power flow detection is discussed. An extensive literature review and a comparison among a wide range of existing optimization algorithms is done. Then genetic algorithm is selected to solve this problem. Global Optimization Tool of Matlab are used to test the proposed algorithm on IEEE-14 and IEEE-39 node test feeders.

Real-Time Voltage Stability Monitoring in Smart Distribution Grids

Abstract: As electric distribution grids continue in hosting high penetration levels of renewable Distributed Generation (DG), several challenges will be brought to system operation and stability. When distribution networks face either an outage (or unavailability) of DG unit or an increasing in load demand, the loss of voltage stability may result. Moreover, some types of DGs, especially fixed speed induction generators, can cause voltage instability since they always consume reactive power. This paper uses a nodal model for voltage stability monitoring, which is applicable for online voltage control in distribution networks. The load impedance can be easily calculated and the entire distribution system can be simplified as an equivalent impedance based on SCADA and PMUs data. Since the proposed method is based on nodal method, the equivalent impedance will reflect the nonlinear dynamic nature of the load of multi bus power system. An index based on impedance matching theorem will be derived to calculate the voltage stability margin and determine the weak buses, and enable a warning in case of voltage instability detection. The proposed voltage stability monitoring will be performed on a 77-bus, 11 kV radial distribution system under different operational conditions.

Sliding Mode Controller and Hierarchical Perturbation Compensator in a UAV Quadrotor

Abstract: The commercial small Unmanned Aerial Vehicle (UAV) quadrotor is very sensitive to perturbation due to its relatively small size and because of being an under-actuated system. In general, some non-modeled parameters, wind disturbance, sensor noise and miscellaneous uncertainties cannot be easily quantified in UAV quadrotor systems. Changes of mass and inertia parameters for pick and place operations add more uncertainties to the system. Traditional controllers might not be robust enough to handle all aforementioned perturbation types. This arises the need of some perturbation compensation for guidance and stability. In this article, the complete system is synthesized as a combination of Hierarchical Perturbation Compensator (HPC) and a Sliding Mode Controller (SMC). With this compensation system, better tracking performance is demonstrated through analysis and simulation. The simulation response shows enhanced performance compared with other conventional methods.

A new integral second-order terminal sliding mode control with time delay estimation for an exoskeleton robot with dynamics uncertainties

Abstract: This paper presents a new Integral Second-Order Terminal Sliding Mode Control incorporating Time Delay Estimation applied to passive rehabilitation protocols of an exoskeleton robot with dynamics uncertainties and unknown bounded disturbances. The use of second-order sliding mode is due to its attractive characteristics of accuracy, attenuation of chattering and fast convergence. However, its problem is that the unknown dynamics of the exoskeleton robot and external disturbances caused by its different wearers can be amplified by the second derivative of the sliding surface, which leads to instability of the exoskeleton system. Using Time Delay Estimation will estimate the uncertain dynamics while overcoming the main limitation of second-order sliding mode. The stability analysis is formulated and proved based on Lyapunov function. Experimental results with a healthy subject confirm the effectiveness of the proposed control.

Multivariable Super-Twisting Control in a Vision-based Quadrotor Utilized in Agricultural Application

Abstract: In this paper, a stereo visual-based control is designed by using virtual image projection and actual depth calculation on a quadrotor system. Super-twisting nonlinear control is supported with time delay disturbance estimation algorithm to estimate disturbance and to drive the system to track the desired trajectory. This proposed super-twisting algorithm ensures the finite time convergence of the system states to the selected sliding surface. The stability analysis of the control is confirmed in the closed loop. The effectiveness of the proposed system is shown by carrying out simulation, using real quadrotor parameters.

Model-based sliding functions design for sliding mode robot control

Abstract: This paper introduces a novel manifold design for sliding mode control, applicable to second-order mechanical systems in which nonlinear dynamics can be formalised into that of robotic manipulators. The new approach shows that model-based sliding manifold design substantially simplifies the torque control law, which ultimately becomes linear in terms of joint angles and rates. Additionally, this approach allows the decoupling of the chattering effect on the torque inputs on each axis. A new property related to the gravity term is introduced and is used for stability analysis and model validation. Simulation results compare the introduced approach to the conventional linear manifold design and demonstrate that the new approach reduces transient constraints on torque input and is more robust to matched uncertainties for low inertia robots.

Finite-time altitude and attitude tracking of a Tri-Rotor UAV using modified super-twisting second order sliding mode

Abstract: This paper presents the problem of robust altitude and attitude trajectory tracking of a tri-rotor Unmanned Aerial Vehicle (UAV) based on a finite-time second order sliding mode control algorithm. The chosen algorithm is a modified super-twisting control with double closed-loop feedback regulation that provides fast finite-time convergence even when the system trajectories are far from the sliding surface, robustness against a wide class of uncertainties and disturbances. Moreover, this algorithm eliminates the major disadvantage of the classical sliding mode, the well-known chattering phenomenon. The stability analysis of the closed-loop system and the convergence time are given based on a strong Lyapunov function. To show the effectiveness of the used method, simulation results of different scenarios are presented for the considered tri-rotor UAV.

Improved control method of HVAC system for Demand Response

Abstract: Demand side management (DSM) is a technical program that have the purpose of smoothing the load curve by reducing its peaks and filling its valleys, and of ancillary services and frequency regulation. Many demand response programs (DRP) are used for this purpose. The thermostatically controlled load (TCL) are the most efficient programs used for DSM and especially for ancillary services. In this work, we study the heating ventilation air conditioning (HVAC) system as one of appliances that fall under the category of TCL. In literature, the chiller power variation due to direct control of HVAC supply fan speed is not considered for DSM. This paper fills this gap and increases the participation capacity of HVAC. Therefore, the HVAC system is remodeled in order to express with more accuracy the chiller power variation. The new model relates the chilled water temperature to the leaving air temperature. Simulation results shows the improvement provided by this method.