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This paper presents a decentralized hybrid supervisory control approach for a team of unmanned helicopters that are involved in a leader-follower formation mission. Using a polar partitioning technique, the motion dynamics of the follower helicopters are abstracted to finite state machines. Then, a discrete supervisor is designed in a modular way for different components of the formation mission including reaching the formation, keeping the formation, and collision avoidance. Furthermore, a formal technique is developed to design the local supervisors decentralizedly, so that the team of helicopters as whole, can cooperatively accomplish a collisionfree formation task.Greensboro, NC 27411 USA, akarimod@ncat.edu. 2 M. Karimadini is with the

Phase-locked loops (PLLs) are well known tools for synchronisation and measurement of the fundamental parameters of power grid signals. Signals measured in the electrical industry may contain disturbances such as harmonic distortion, dc offset, noise and unbalanced conditions which destroy the pure sinusoidal form of signals. The present study improves the trade-off between PLL disturbance-rejection capability and dynamic-response speed. An improved PLL is proposed based on frequency and initial-phase-angle detectors (FIPD) and moving average filter for measurement of the signal parameters in both single-phase and three-phase applications. The proposed PLL is called improved FIPD-based PLL (IFIP-PLL) and provides satisfactory disturbance rejection and response time. The proposed structure effectively decreases the estimation error. Simulation and experimental results show the superiority of IFIP-PLL over conventional PLLs.

This paper proposes necessary and sufficient conditions for task decomposability with respect to an arbitrary finite number of agents. It is furthermore shown that fulfilling the decomposed local tasks by individual agents guarantees the satisfaction of the original global decomposable task. A divide-and-conquer approach for cooperative tasking among multi-agent systems is proposed. The basic idea is to decompose an assigned global specification (given as a deterministic automaton) into subtasks for individual concurrent agents such that the fulfillment of these subtasks by each individual agent leads to the satisfaction of the global specification as a team. A cooperative scenario involving three robots has been implemented to illustrate the proposed technique. This work provides insights into what kinds of tasks can be achieved distributively, which helps designers specify achievable global tasks for a group of agents and design necessary information sharing among each other for a particular task.