Hasan Mehrjerdi

Formation path following control of unicycle-type mobile robots

This paper presents a control strategy for the coordination of multiple mobile robots. A combination of the virtual structure and path following approaches is used to derive the formation architecture. A formation controller is proposed for the kinematic model of two-degree-of-freedom unicycle-type mobile robots. The approach is then extended to consider the formation controller by taking into account the physical dimensions and dynamics of the robots. The controller is designed in such a way that the path derivative is left as a free input to synchronize the robots motion. Simulation results with three robots are included to show the performance of our control system. Finally, the theoretical results are experimentally validated on a multi-robot platform.

Hierarchical Fuzzy Cooperative Control and Path Following for a Team of Mobile Robots

In this paper, an intelligent cooperative control and path-following algorithm is proposed and tested for a group of mobile robots. The core of this algorithm uses a fuzzy model, which mimics human thought to control the robots velocity, movement, and group behavior. The designed fuzzy model employs two behaviors: path following and group cooperation. Hierarchical controllers have also been developed based on fuzzy and proportional integral derivative to instruct the robots to move in a group formation and follow specific paths. As the robots move along individual predetermined paths, the designed algorithm adjusts their velocities so that the group arrives at their target points within the same time duration regardless of the length of each individual path. The fuzzy rules applied to the robots are defined by the kinematics limitation, which is bounded by both linear and angular velocities and the length and curvature of the individual paths. The experimental results of three mobile robots traveling on different paths are presented to show the accuracy of obtaining control and cooperation by using the fuzzy algorithm.

A Decentralized Control of Partitioned Power Networks for Voltage Regulation and Prevention Against Disturbance Propagation

This paper investigates a secondary voltage control based on a graph partitioning method. The method divides the power system into regions to eventually prevent the propagation of disturbances and to minimize the interaction between these regions. The optimized number of regions is found based on the bus voltage sensitivity to disturbances being applied to loads in each region. Then, a number of representative buses are labelled as pilot buses displaying the critical point for voltage control in each region. The control uses decentralized controllers to eliminate voltage violations resulting from load variations and disturbances in the system. The decentralized controllers are implemented by fuzzy logic which is trained via offline simulations; they inject required reactive power into the regions to correct voltage violations. The methodology is applied to the IEEE 118-bus network. The results show the performance and ability of graph partitioning and fuzzy secondary voltage control to regulate the voltage and to avoid propagation of disturbances between regions.

A survey on multiple unmanned vehicles formation control and coordination: Normal and fault situations

This paper provides a review on the strategies and methodologies developed in recent years for trajectory/path following, coordination and unified group behavior of a team of unmanned vehicles in terms of application and categorization. The unmanned vehicles being studied have a common mission to maintain group formation and reach their target destinations in either known or unknown environments. The ability for a group of vehicles to follow individual paths is the first critical step in achieving group coordination and originates from path following employing a single vehicle. Once this technique is refined then various algorithm constructs can be explored in order to create efficient and harmonious group coordination, which is based on their originality on whether they are employed in a centralized or decentralized system. In this paper, survey and analysis on the various multi-vehicle applications in formation operation and categorizations of existing works are provided based on over 140 published literatures since 1986. A few challenges and future works are also recognized.

A Monitoring Technique for Reversed Power Flow Detection With High PV Penetration Level

The integration of renewable energy resources (RESs) in power systems poses many research challenges. Research shows that the RES output may exceed the consumed power during the day. Consequently, the direction of the power flow on distribution lines can be reversed during some periods. As the voltage regulator is normally designed for unidirectional power flow, this may cause voltage violations on the distribution feeder. Therefore, most utilities try to set a penetration level (PL) limit for safe operation. On the other hand, time varying and unbalanced loading are the main characteristics of distribution systems. Moreover installation of intermittent and nondispatchable photovoltaic (PV) devices increases the control problems of distribution system. This paper presents an impedance-based monitoring method for detection of distribution system current behavior. It will be shown that by utilizing this monitoring technique, not only the small variation of PV PL can be easily detected, but also some fast transients such as the effect of cloud movement on PV system can be monitored. This monitoring technique employs only local measurements of bus voltages and line current to measure the apparent impedance seen at the installation point. The practical application of measured impedance as a monitoring technique shows its effectiveness for distribution system monitoring in presence of various PV PL.

Cascade design for formation control of nonholonomic systems in chained form

This paper presents a constructive method to design a cooperative state and output feedback to steer a group of nonholonomic mobile robots in chained form to form a desired geometric formation shape. The control methodology divides the resulting tracking error dynamics into a cascaded of linear and time-varying subsystems. A basic consensus algorithm is first applied to the linear subsystem which makes the states synchronize exponentially to zero. Once this first linear subsystem has converged, the second cascade can be treated as a linear time-varying subsystem perturbed by a vanishing term from its cascade. A dynamic state and output feedback is constructed to achieve synchronization of the rest of the states. The proof of stability is given using a result from cascade systems. Since time delay appears in many interconnection networks and particularly in cooperative control, its effect on the stability of the closed-loop system is analyzed using Razumikhim theorem. It is shown that the established cooperative controller work well even in the presence of time delay. Numerical simulations are performed on models of car-like mobile robots to show the effectiveness of the proposed cooperative state and output-feedback controllers.

Coordinated Control Strategy Considering Effect of Neighborhood Compensation for Voltage Improvement in Transmission Systems

This paper presents coordinated secondary voltage control based on partitioned power network and decentralized controllers designed for each region. The elements of control are installed on pilot buses (critical point for voltage control in each region). The aim is coordination among elements of control in each region or between different regions to regulate voltage of buses and increase the security of the power network. The elements of control are considered as nodes of a graph and reactive power will be transferred through edges of this graph. This gives capability of transfer of reactive power between regions in case of voltage violations in a special region that cannot be regulated by controllers installed on that region. The control uses decentralized controllers to eliminate voltage violations resulting from load variations and disturbance in the power network. The methodology is applied to the IEEE 118-bus network. The results show and verify the performance of coordinated control scheme to regulate the voltage and to avoid propagation of contingency between regions.

Leader-follower formation control of nonholonomic robots with fuzzy logic based approach for obstacle avoidance

In this paper we investigate the leader follower motion coordination of multiple nonholonomic mobile robots. A combination of the virtual vehicle and trajectory tracking approach is used to derive the formation architecture. A virtual vehicle is steered in such a way it stabilizes to a shifted reference position/heading defined by the leader, the velocity of the virtual vehicle is then provided for further use in designing control law for the follower independent from the measurement of leaders velocity. Position tracking control is then constructed for the follower to track the virtual vehicle using the backstepping and Lyapunov direct design technique. Furthermore and to ensure the safety of robots while moving in a dynamic environment, obstacle avoidance scheme based on sensing the relative distance between follower robots and obstacles is introduced using fuzzy logic. Simulations are provided to show the effectiveness of the proposed approach.

Dynamic tracking control of mobile robot using exponential sliding mode

This paper proposes an exponential sliding mode control for trajectory tracking of nonholonomic wheeled mobile robots. A new solution to the problem of chattering in variable structure control is presented. Exponential sliding mode is defined to reduce chattering and keep high dynamic tracking performance in steady state mode for mobile robot. This algorithm instructs the robot to keep move on the desired path while reduce tracking errors. The simulation results obtained with unicycle mobile robot is presented to demonstrate the performance of exponential sliding mode controller algorithm compare to conventional sliding mode.

Leader-follower based formation control of nonholonomic robots using the virtual vehicle approach

In this paper we investigate the leader follower motton coordination of multiple nonholonomic mobile robots. A combination of the virtual vehicle and trajectory tracking approach is used to derive the formation architecture. A virtual vehicle is steered in such away it stabilizes to a shifted reference position/heading deflned by the leader, the velocity of the virtual vehicle is then provided for further use in designing control law for the follower independent from the measurement of leaders velocity. Position tracking control is then constructed for the follower to track the virtual vehicle using the backstepping and Lyapunov direct design technique. Simulations are provided to show the effectiveness of the proposed approach.