To further improve the safety and reliability of multi-mobile robot systems, this paper investigates the formation control problem with considerations of collision avoidance, communication maintenance and robots’ actuator bias faults. A novel modular formation control scheme, which consists of two modules, is established. In Module I, a formation signal generator is constructed based on graph theory, acting as a virtual multi-agent system through a network of double-integrator dynamic nodes. The outputs of the virtual multi-agent system (i.e., the generator) are designed to asymptotically form the desired formation shape while satisfying some designed specific constraints. Then, in Module II, extended-state observers (ESOs) are firstly employed to estimate and compensate for the actuator bias faults. After embedding the corresponding node within each robot and taking its outputs as formation references, some constrained ESO-based tracking controllers are designed based on back-stepping method. In general, the proposed modular formation control integrates collision avoidance, connectivity maintenance and fault-tolerant functions, while realizing the desired formation shape with bounded convergence of formation errors. Simulations and experiments demonstrate the effectiveness of the proposed modular formation control scheme.

In this article, a novel output voltage tracking control scheme with current constraint capability is designed for disturbed LC-type three-phase inverters based on sliding-mode control, nonlinear mapping and finite-time disturbance observers. In this control scheme, the current constraints are firstly converted into state constraints for the error state equations. Utilizing nonlinear mapping functions, the state constraint problems are further transformed into the boundedness problems of sliding-mode variables. The sliding-mode controllers which are designed on this basis, ensure the boundedness of the sliding-mode variables, thereby preventing the currents from violating the constraints. By employing finite-time disturbance observers to estimate both mismatched and matched disturbances, and incorporating disturbance compensations into the sliding-mode surfaces and controllers, the system's vulnerability to disturbances is mitigated. With the above design, this control scheme can achieve fast output voltage tracking and current constraints in the presence of mismatched and matched disturbances in the system. The efficacy of the proposed method has been confirmed through simulations.

This paper investigates distributed formation control of multi-mobile robot systems with collision avoidance. A novel guidance module based formation control scheme is established, which consists of two main parts. In the first part, on the communication network of the multi-mobile robot system, a distributed guidance module is constructed from some predesigned virtual dynamics scattered in the robots’ feedback loops. By using some proper distributed formation control methods and distributed observer techniques, some formation references are generated by the guidance module. In the second part, by taking these references as the tracking references, some tracking controllers are designed and assigned to the robots such that the robots’ positions track their respective references asymptotically. A “two-layer constraint mechanism” is presented in the above controller design to limit both the formation references and the robots’ tracking errors such that robots’ collision avoidance is guaranteed. In this way, the multi-mobile robot system completes the desired collision-free formation control task. Compared with existing results, the method proposed in this paper has a better plug-and-play function and wider application scope, especially when the practical robots have tight encapsulations such that their pre-equipped tracking controllers cannot be arbitrarily redesigned. Moreover, under the proposed scheme, the asymptotic formation convergence is achieved by the robots without extra limitations on robots’ initial states and the utilization of global information. Some simulations and an experiment are given to validate the effects of the proposed methods. Note to Practitioners—This paper is motivated by controller encapsulation characteristics of practical mobile robot products. To complete various formation tasks, most of the related existing formation control methods require robots’ controllers to be continually updated and redesigned. However, this purpose is sometimes unachievable because actual mature robot products may have tight controller packages for trade secrets and intellectual property, or engineers want to retain robots’ well-adjusted default performances. To overcome this practical limitation, this paper provides a novel “guidance module based formation control scheme”. Under this scheme, engineers only need to put most efforts on a guidance module design to generate desired real-time desired tracking references for robots. A new “two-layer constraint mechanism” is proposed and applied here to guarantee collision avoidance among the robots when using the proposed scheme. With this scheme, engineers can establish required formation control strategies without robots’ pre-equipped controllers changed and the original control performances abandoned, as long as the robots have some basic capability of tracking given trajectories. Theoretical analysis and experiments on this scheme are all shown. In future research, based on the proposed scheme, we will continue to develop application-oriented formation control methods to improve the anti-disturbance performance and robustness of the multi-mobile robot systems.

In this paper, the output voltage tracking control of DC-DC boost converters is studied. To meet the increasing safety requirements and enhance the control system robustness, overcurrent protection and disturbance rejection are investigated simultaneously. A simple and effective control scheme is proposed to achieve all these three goals, which includes two parts. In the first part, a disturbance observer is constructed to estimate multiple disturbances (including the input voltage fluctuations and the load variations). In the second part, a composite current-constrained controller is proposed by embedding the disturbance estimates and the nonlinear penalty term into the passivity-based control law. Under the novel control scheme, rapid tracking performance and safe overcurrent protection are obtained, even in the presence of multiple disturbances. Rigorous stability analysis is conducted to demonstrate the accomplishment of the output voltage tracking task and the strict guarantee of the current constraint. Simulations and experiments are performed to verify the effectiveness of the proposed control scheme.

In this paper, an adaptive event-triggered secondary regulation strategy is investigated for microgrids with loss of effectiveness actuator faults. In order to deal with unknown loss of effectiveness actuator faults, a distributed secondary regulation strategy is proposed, which achieves voltage and frequency regulations, as well as power sharing. Meanwhile, to save system resources and relieve the communication burden, an adaptive event-triggered mechanism is designed. Finally, some simulation results are given to validate the proposed strategy, which indicates that the proposed strategy reduces the controller updates and increases the reliability of system.

This paper addresses the cooperative trajectory prediction problem of multiple UAVs in air combat. By using the historical trajectory information of each UAV and its neighbors, a novel GAN-CI algorithm is designed based on generate adversarial networks. The algorithm is used to generate multiple prediction trajectories through a generative adversarial network, and the input information is analyzed and processed by a cooperative information interaction module. It is shown that the algorithm improves the average prediction accuracy by 45% over the generative adversarial network without cooperative interaction information and 38% over the Long Short-Term Memory algorithm with pooling module.

In this article, the distributed finite-time optimization problem is investigated for second-order multiagent systems with unknown velocities, disturbances, and quadratic local cost functions. To solve this problem, by combining finite-time observers (FTOs), the homogeneous systems theory, and distributed finite-time estimator techniques together, an output feedback-based feedforward-feedback composite distributed control scheme is proposed. Specifically, the control scheme consists of three parts. First, some FTOs are developed for the agents to estimate their unknown velocities and the disturbances together. Second, based on the velocity and disturbance estimates, the homogeneous system theory, and some global information on all the local cost functions' gradients, Hessian matrices, and the velocity estimates, a kind of centralized finite-time optimization controllers is designed. Third, by designing some distributed finite-time estimators and using their estimates to replace the global terms employed in the centralized optimization controllers, the distributed finite-time optimization controllers are derived. These controllers achieve the distributed finite-time optimization goal. Simulations illustrate the effectiveness and superiority of the proposed control scheme.

This article investigates the finite-time distributed approximate optimization problem of higher order multiagent systems, where the local cost functions are considered to be quadratic functions. This problem is solved via penalty-function-based method. First, by the penalty-function method, a global approximate cost function is constructed. Second, nonlinear distributed optimization algorithms are proposed for higher order multiagent systems by the tool of adding a power integrator technique. In the optimization algorithms design, the gradients of the approximate cost function are utilized. Under the proposed optimization algorithms, the agents approach the approximate optimal solution in finite time. Although there exist errors (they may be called approximation errors) between the approximate minimizers and the global accurate minimizer, the approximation errors can be regulated by penalty parameter and the relationship between the bound of the approximation errors and the penalty parameter is given explicitly. Furthermore, the proposed distributed approximate optimization algorithms are applied to the optimal rendezvous problem of wheeled multimobile robots, making the mobile robots achieve approximate optimization rendezvous in finite time. The effectiveness of the proposed distributed optimization algorithms and their applications to optimal rendezvous problem are validated by simulations.

In this article, the distributed finite-time optimization problem is investigated for second-order multiagent systems with disturbances. To solve this problem, a feedforward-feedback composite control framework is established, which contains two main stages. In the first stage, for disturbed second-order individual systems with generally strongly convex cost functions, a composite finite-time optimization control scheme is proposed based on the combination of adding a power integrator and the finite-time disturbance observer techniques and the use of the cost functions' gradients and Hessian matrices. In the second stage, based on the result of the first stage, a distributed composite finite-time optimization control framework is built for disturbed second-order multiagent systems with quadratic-like local cost functions. This framework involves a kind of finite-time consensus algorithm, some novel distributed finite-time estimators designed for each agent to estimate the velocity, the gradient and Hessian matrix for the local cost function of any other agent, and some optimization terms in the form of the optimization controllers proposed in the first stage and based on the estimates from the distributed estimators. The finite-time convergence of the closed-loop systems is rigorously proved. The simulation results illustrate the effectiveness of the proposed control framework.

In this paper, the trajectory tracking control problem is studied for wheeled mobile robots (WMRs) in the cases without and with kinematic disturbances. In the case without kinematic disturbances, a tracking controller based on cascaded system theory is designed, which guarantees asymptotic tracking for the WMR to the reference trajectory. In the case with kinematic disturbances, two kinds of controllers are designed. At first, a PID tracking controller is proposed. Secondly, after designing some generalized proportional-integral observers (GPIOs) to estimate the kinematic disturbances, a GPIO-based composite tracking controller is derived by combining the disturbance estimates with the tracking controller designed for the case without disturbances. Some comparison simulations are given, by which it is demonstrated with the GPIOs' accurate disturbance estimations and compensations, the GPIO-based composite controller has the best performance among the three kinds of controllers on the trajectory tracking for WMRs with kinematic disturbances.

In this article, the distributed optimization problem is studied for second-order multiagent systems with both mismatched and matched disturbances. For this problem, a distributed active antidisturbance control framework is established, which consists of both disturbance estimation/compensation and distributed feedforward-feedback composite control design. In the first stage, some disturbance estimators are utilized to estimate various types of matched/mismatched disturbances for each agent. In the second stage, for each agent, based on the disturbance estimates, the information exchanges between the neighboring agents, and the gradient of the local cost function only accessible to itself, a kind of distributed composite controllers are proposed. Under these controllers, all the agents' outputs asymptotically reach consensus to the minimizer of the global cost function, which is the sum of all the local cost functions. The closed-loop system convergence is proven based on a new Lyapunov function, convex analysis, and an input-to-state stability criterion. Simulations demonstrate the effectiveness of the proposed control scheme.

Under the noncascade structure, a permanent-magnet synchronous motor (PMSM) regulates the speed and current in one loop. On the one hand, fast dynamic performance requires large transient current to provide a high torque. On the other hand, unlike a cascade control, the q-axis current is no longer governed by a reference current signal. In such a system, the nominal controllers cannot guarantee that the q-axis current is within the required range. But an excessively large transient current may threaten the circuit safety. To solve the overcurrent protection problem, the ordinary solution is to choose conservative control parameters, but the dynamic performance inevitably suffers a certain degree of loss. In order to improve this drawback, a simple and effective control scheme is introduced with a current-constrained technique. By constructing a special nonlinear gain, the punishment mechanism for the q-axis current is established in the control action directly. The proposed control approach does not impose limitations on the initial state. Moreover, it has good robustness to load torque uncertainty and undergoes rigorous theoretical analysis. Besides, the proposed current-constrained controller has a very concise structure. It yields a higher reliability of the PMSM control system. Comparative simulation and experimental results between the classic PID and the current-constrained controller on the PMSM servo system verify the feasibility of the presented control scheme.

This paper studies the finite-time output consensus problem of higher-order multiagent systems subject to both mismatched disturbances and unknown state elements, where the disturbances are allowed to be fast time-varying. To solve this problem, an active anti-disturbance control approach is developed based on the disturbance estimation/compensation and the baseline feedback consensus protocols. First, to estimate the matched/mismatched disturbances and the agents unknown state elements, a finite-time generalized state observer is constructed for each agent. Second, by integrating the distributed adding a power integrator feedback control method and the estimates of the matched/mismatched disturbances and the agents unknown state elements together, composite consensus protocols are developed for both leaderless and leader-follower cases. In both cases, the proposed protocols guarantee that the agents outputs reach consensus in finite time. Simulations show the effectiveness of the proposed consensus algorithms.

This paper proposes a block backstepping trajectories tracking control scheme for a class of unmanned helicopters. The control objective is to make the position and yaw angle trajectories of the helicopter track the desired position and yaw angle trajectories. In order to design the controller, the helicopter system is divided into three subsystems at first. Then based on the block backstepping technique, four control inputs which constitute the helicopter controller are designed step by step in three subsystems. The asymptotic stability of the closed-loop helicopter trajectories tracking error system is verified based on Lyapunov stability analysis. Finally, numerical simulations demonstrate the effectiveness of the proposed block backstepping control scheme.

This paper is devoted to solving the output consensus problem of leader-follower higher-order nonlinear multiagent systems subject to mismatched disturbances. The disturbances are allowed to be in higher-order forms. First, by constructing a generalized proportional-integral observer for each follower, estimates of the disturbances and their derivatives are obtained. At the same time, a distributed observer is also developed for the followers to estimate the leader state information. Second, based on the estimates of the disturbances and the leader state, together with the backstepping technique, a feedforward-feedback composite consensus control scheme is proposed. The designed distributed protocols guarantee asymptotic output consensus for the agents. Simulation results validate the effectiveness of the proposed composite control scheme.

The fixed-time synchronization problem fsor a class of second-order nonlinear multi-agent systems with a leader-follower architecture is investigated in this paper. To achieve the fixed-time tracking, the design procedure is divided into two steps. At the first step, a distributed fixed-time estimator is designed for each agent to estimate the leader's state in a fixed time. Then, at the second step, based on the technique of adding a power integrator, a fixed-time tracking controller for each agent is proposed such that the estimate leader's state can be tracked in a fixed time. Finally, an estimator-based fixed-time controller is developed such that the leader can be tracked by all the followers in a fixed time. Simulations are presented to verify the effectiveness of the proposed approach.

In this paper, the distributed finite-time containment control problem for double-integrator multiagent systems with multiple leaders and external disturbances is discussed. In the presence of multiple dynamic leaders, by utilizing the homogeneous control technique, a distributed finite-time observer is developed for the followers to estimate the weighted average of the leaders' velocities at first. Then, based on the estimates and the generalized adding a power integrator approach, distributed finite-time containment control algorithms are designed to guarantee that the states of the followers converge to the dynamic convex hull spanned by those of the leaders in finite time. Moreover, as a special case of multiple dynamic leaders with zero velocities, the proposed containment control algorithms also work for the case of multiple stationary leaders without using the distributed observer. Simulations demonstrate the effectiveness of the proposed control algorithms.