Switching-based Control Research Articles

Evolvable Hardware Based Optimal Position Control of Quadcopter

Trading off performance metrics in control design for position tracking is unavoidable. This has severe consequences in mission-critical systems such as quadcopter applications. The controller area and propulsion energy are conflicting design parameters, whereas the reliability and tracking speed are related metrics to be optimized. In this research, a switching-based position controller was co-simulated with the quadcopter model. Performance analysis of the Field Programmable Gate Array (FPGA)-based controller validates a better scheme for tracking speed, propulsion energy, and reliability optimization under similar error performance. To improve the computation power and controller area, the dynamic partial reconfiguration(DPR) approach has been adapted and implemented on FPGA using the Vivado Integrated Development Environment (IDE), where a ranking-based approach brings into action either proportional derivative, sliding mode, or model predictive controllers for each dimension of position tracking. It is verified by analyzing the cumulative tracking speed, reliability, controller area, and propulsion energy metrics that the proposed controller can optimize all these metrics within three successive iterations of tracking either in the same direction or in any combination of directions. Concerning the implementation results of the controller with the switching-based controller, there is 6 % computation power and 30 % resource savings due to DPR .

A Brief Survey of Recent Advances and Methodologies for the Security Control of Complex Cyber-Physical Networks.

Complex cyber-physical networks combine the prominent features of complex networks and cyber-physical systems (CPSs), and the interconnections between the cyber layer and physical layer usually pose significant impacts on its normal operation. Many vital infrastructures, such as electrical power grids, can be effectively modeled as complex cyber-physical networks. Given the growing importance of complex cyber-physical networks, the issue of their cybersecurity has become a significant concern in both industry and academic fields. This survey is focused on some recent developments and methodologies for secure control of complex cyber-physical networks. Besides the single type of cyberattack, hybrid cyberattacks are also surveyed. The examination encompasses both cyber-only hybrid attacks and coordinated cyber-physical attacks that leverage the strengths of both physical and cyber attacks. Then, special focus will be paid to proactive secure control. Reviewing existing defense strategies from topology and control perspectives aims to proactively enhance security. The topological design allows the defender to resist potential attacks in advance, while the reconstruction process can aid in reasonable and practical recovery from unavoidable attacks. In addition, the defense can adopt active switching-based control and moving target defense strategies to reduce stealthiness, increase the cost of attacks, and limit the attack impacts. Finally, conclusions are drawn and some potential research topics are suggested.

Switched electromechanical dynamics for transient phase control of brushed DC servomotor.

Robotic tasks often exceed the scope of steady-state or periodic behavior, which necessitates generally-applicable models of actuators intended to generate transient or aperiodic motion. However, existing electromechanical models of servomotors typically omit consideration of the switching power converter circuits required for directional, speed, or torque control. In this study, a multi-domain framework is established for switched electromechanical dynamics in servomotor systems for their analysis and control in general aperiodic tasks including transient phases. The switched electromechanical dynamics is derived from the individual models of the internal DC motor, gear train, and H-bridge circuit. The coupled models comprehensively integrate all possible distinct switching configurations of on-state, off-state, and dead time. A combination of cycle averaging with piecewise analytical solutions of the non-smooth dynamics is introduced to handle different temporal scales from high-frequency electrical to low-frequency mechanical variables. System parameters were estimated from experimental data using a dual-servomotor test platform. The model was validated for predictive accuracy against measured data in two distinct tasks-dynamic braking of a pendulum system and sinusoidal trajectory following. The model was also used to formulate the servomotor power consumption, which was implemented for optimal control demonstration and energy analysis. In particular, the servomotor power consumption model provided true optimality (minimization) when compared with the squared rotor torque and the positive rotor mechanical power that are commonly used as proxy models. While the focus of this work is on permanent-magnet, armature-controlled brushed DC servomotors, the approach is applicable to general electromechanical systems with switching-based control.

A Switching-Based Control Method for the Fairing Separation Control of Axisymmetric Hypersonic Vehicles

For hypersonic-vehicle fairing separation, the reliable separation of the fairing and rapid suppression of the separation disturbance are required in scenarios where there is high dynamic pressure and there are abrupt changes in the aerodynamic shape of the aircraft as well as overall parameters. A switching-based control method is proposed in this paper for the interference suppression of hypersonic-vehicle fairing separation, aiming to ensure the stability of the control system in cases of abrupt changes in the controlled object. First, an unsteady-flow calculation method is adopted to clarify the aerodynamic interference characteristics of the aircraft in fairing separation, and the aerodynamic calculation model of the hypersonic-vehicle fairing-separation process is established; then, two states of the aircraft, with and without fairing, are transformed into a subsystem with switching characteristics. The attitude-stability problem in the fairing-separation process is transformed into a problem of solving the arbitrary switching of the switched system by using the linear matrix inequality (LMI) approach. Meanwhile, the control system for interference suppression of the fairing separation is designed by considering the aerodynamic interaction of the fairing movement with the aircraft during the separation. The simulation results showed that the designed control system can realize the reliable separation of the fairing under high dynamic pressure and effectively suppress interference in the separation process.

Closed-Loop Torque and Kinematic Control of a Hybrid Lower-Limb Exoskeleton for Treadmill Walking.

Restoring and improving the ability to walk is a top priority for individuals with movement impairments due to neurological injuries. Powered exoskeletons coupled with functional electrical stimulation (FES), called hybrid exoskeletons, exploit the benefits of activating muscles and robotic assistance for locomotion. In this paper, a cable-driven lower-limb exoskeleton is integrated with FES for treadmill walking at a constant speed. A nonlinear robust controller is used to activate the quadriceps and hamstrings muscle groups via FES to achieve kinematic tracking about the knee joint. Moreover, electric motors adjust the knee joint stiffness throughout the gait cycle using an integral torque feedback controller. For the hip joint, a robust sliding-mode controller is developed to achieve kinematic tracking using electric motors. The human-exoskeleton dynamic model is derived using Lagrangian dynamics and incorporates phase-dependent switching to capture the effects of transitioning from the stance to the swing phase, and vice versa. Moreover, low-level control input switching is used to activate individual muscles and motors to achieve flexion and extension about the hip and knee joints. A Lyapunov-based stability analysis is developed to ensure exponential tracking of the kinematic and torque closed-loop error systems, while guaranteeing that the control input signals remain bounded. The developed controllers were tested in real-time walking experiments on a treadmill in three able-bodied individuals at two gait speeds. The experimental results demonstrate the feasibility of coupling a cable-driven exoskeleton with FES for treadmill walking using a switching-based control strategy and exploiting both kinematic and force feedback.

A Switching-Based Adaptive Dynamic Programming Method to Optimal Traffic Signaling

The work presented in this paper concerns a switching-based control formulation for multi-intersection and multiphase traffic light systems. A macroscopic traffic flow modeling approach is first presented, which is instrumental to the development of a model-based and switching-based optimization method for traffic signal operation, in the framework of adaptive dynamic programming (ADP). The main advantage of the switching-based formulation is its capability to determine both “when”’ to switch and “which” mode to switch on without the need to use the cycle-based average flow approximation typical of state-of-the-art formulations. In addition, the framework can handle different cycle times across intersections without the need for synchronization constraints and, moreover, minimum dwell-time constraints can be directly enforced to comply with minimum green/red times in each phase. The simulation experiments on a multi-intersection and multiphase traffic light systems are presented to show the effectiveness of the method.

Force feedback control for bilateral teleoperation system with unknown Prandtl-Ishlinskii hysteresis

Hysteresis nonlinearity is a common phenomenon in mechanical actuators. Specially, it appears when the direction of motion of mechanical actuated joint is reversed in robotic manipulator. This paper focuses on the force feedback control problem for bilateral teleoperation system with unknown Prandtl-Ishlinskii (PI) hysteresis. First, an improved sliding mode observer with adaptive gains is provided for estimating the external force signals acting on the manipulators. This removes the need for force sensors and reduces hardware-cost. Next, to improve transparency and guarantee the passivity of the communication network, a four-channel wave variable transformation scheme including force information is introduced. Then, an adaptive switching-based control framework is proposed to deal with Prandtl-Ishlinskii hysteresis dynamics. Finally, the theoretical findings are supported by simulation and experiment results.

A multi-switching mode intelligent hybrid control of electro-hydraulic proportional systems

The electro-hydraulic proportional system is a highly non-linear system owing to the fact that the system is composed of components from different disciplines such as electric, hydraulic and mechanical disciplines. In general, a switching-based controller is suitable to the control of such a system. In this paper, a switching-based controller is proposed, which is called multi-switching mode intelligent hybrid control, for electro-hydraulic proportional systems. The novelty of the multi-switching mode intelligent hybrid control is that it integrates the PID control law, the neural-fuzzy control law, and the expert-based control law. To demonstrate the effectiveness of the proposed multi-switching mode intelligent hybrid control, both experiment and simulation were conducted. It is shown that the experimental result corresponds well with the simulation result. Further, the proposed control system was compared with the traditional ones such as PID and neural-fuzzy controller for a trajectory tracking task with an electro-hydraulic proportional, which shows that the proposed one is far superior to these traditional ones. Overall, there is evidence that the proposed multi-switching mode intelligent hybrid control is very effective. It is noted that though the idea of the switching-based control system to electro-hydraulic proportional systems may not be new, the specific integration of the member control laws along with specific control laws developed in this work to electro-hydraulic proportional systems is not reported in the literature and multi-switching mode intelligent hybrid control is potentially useful to other electro-hydraulic proportional systems.

Positioning control of an underwater robot with tilting thrusters via decomposition of thrust vector

Positioning control of an underwater robot is a challenging problem due to the high disturbances of ocean flow. To overcome the high disturbance, a new underwater robot with tilting thrusters was proposed previously, which can compensate for disturbance by focusing the thrusting force in the direction of the disturbance. However, the tilting motion of the thrusters makes the system nonlinear, and the limited tilting speed sometimes makes the robot unstable. Therefore, an optimized controller is necessary. A new positioning controller is proposed for this robot using a vector decomposition method. Based on the dynamic model, the nonlinear force input term of the tilting thrusters is decomposed in the horizontal and vertical directions. Based on the decomposition, the solution is determined by a pseudo-inverse and null-space solution. Using the characteristics of the decomposed input matrix, the final solution can be found by solving a simple second-order algebraic equation to overcome the limitations of the tilting speed. The positioning was simulated to validate the proposed controller by comparing the results with a switching-based controller. Tracking results are also presented. In future work, a high-level control strategy will be developed to take advantage of the tilting thrusters by focusing the forcing direction toward the disturbance with a limited stability margin.

A Novel Switching-Based Control Framework for Improved Task Performance in Teleoperation System With Asymmetric Time-Varying Delays.

This paper addresses the adaptive control for task-space teleoperation systems with constrained predefined synchronization error, where a novel switched control framework is investigated. Based on multiple Lyapunov-Krasovskii functionals method, the stability of the resulting closed-loop system is established in the sense of state-independent input-to-output stability. Compared with previous work, the developed method can simultaneously handle the unknown kinematics/dynamics, asymmetric varying time delays, and prescribed performance control in a unified framework. It is shown that the developed controller can guarantee the prescribed transient-state and steady-state synchronization performances between the master and slave robots, which is demonstrated by the simulation study.

Injection locking phase rotator for Outphasing transmitter

This paper presents a novel technique of implementing the amplitude information into out-phase mapping, which is a necessary block of the high-efficiency Outphasing transmitter architecture. The proposed technique is based on using injection locking ring oscillator and switching-based control circuit to implement phase rotator. The technique is compatible with digital implementation using DSP. Since, Outphasing transmitters use switching power amplifiers, this implementation is suitable for an all-digital and adjustable transmitter implementation. The modulator system is designed using UMC130nm CMOS technology; and is simulated at 1.8GHz operation frequency, as it is commonly used in multiple mobile applications requiring high power levels. Simulation shows an out-phasing error of 0.41°rms, across the whole input amplitude sweep of 45dB. The power consumption of the single phase rotator is 1.5mW from 1.2V supply.

Linear Parameter Varying Analysis of Switched Controllers for Attitude Control Systems

T HE on-orbit life of a satellite is decomposed into phases, allowing the convergence from the separation state to the mission state, the orbit control, and the safe state in case of fault. For each phase ormode, a specific set of attitude pointing requirements is to be met by using a specific set of actuators and sensors. Inside a mode, several attitude control and estimation algorithms can be designed, for example, to meet increasing performance levels requirements. Over the past 30 years, the number of attitude and orbit control system (AOCS) modes has been reduced so that generic architectures now typically consist of three modes (one safe-hold mode, one mission mode, and one orbit control mode). In the same time, the software complexity has increased to meet ever more demanding requirements. Thus, the switching between different AOCS modes and software requires permanently enhanced robustness levels to cope with more stringent kinematics conditions (satellite angular rate and position)while also improving the pointing accuracy. In this Note, the problem of the reaction wheel control software switching inside the mission mode of the Centre National d’Etudes Spatiales (CNES) microsatellite DEMETER (detection of electromagnetic emissions transmitted from earthquake regions) [1–4] is considered. Because of the limited speed and torque capacities of the reaction wheels, the linear proportional-derivative controller specifically designed for small pointing errors can no longer be used when the latter get too large, which is typically the case when the mission mode is activated. Then, to avoid torque and speed saturations during this phase,whichwill be referred to as the rough pointing phase of the mission mode, a dedicated controller is used to maintain the angular rate around a constant target until the pointing error becomes small enough. More interesting, as soon as the speed target is reached, the commanded torque is null. The parameters of the control system are tuned in such a way that the delivered control input signal remains continuous when switching occurs for prespecified pointing and rate errors. However, because of external perturbations and AOCS sampling constraints, the nominal conditions are rarely met when the control system switches from rough to fine pointing phases, which locally induces some undesirable (and what it is hoped to be transient) behaviors. As a result, it becomes rather difficult to obtain stability and robustness proofs, which have to be addressed through extensive and time-consuming nonlinear simulations campaigns. In this context, the central idea of this Note consists of rewriting the switching-based control law in a quasi-linear-parameter-varying form thanks to which the following properties hold: 1) The continuity of the control signals is guaranteed at anytime, since the new system is based on a smooth transition from rough to fine pointing phases. 2) The stability and robustness proofs for the nonlinear closedloop plant can be obtained via enhanced linear-parameter-varying (LPV) analysis techniques, which are developed in the Note. While many methods are now available to evaluate the stability of LPVplants,most of thewell-established results are numerically quite demanding as soon as the size of the plant increases, togetherwith the complexity of the selected Lyapunov function. In this Note, a new algorithm based on parameter-dependent Lyapunov (PDL) functions is then developed, thanks to which the stability analysis can be performed at a reasonable cost. The key idea of the proposed iterative technique consists of a first step of optimizing the Lyapunov functions on a rough grid of the parameter space and, in a second step, to check the validity on the continuous space. The grid is then updated if necessary until the whole space is cleared. This approach may be viewed as an original adaptation of a similar idea [5], which was exploited 10 years ago in a -based robustness analysis. The Note is organized as follows. After a brief description of the AOCS control loops and switching-based controllers in Sec. II, the quasi-LPV formulation is detailed in Sec. III. Stability analysis of LPV systems via PDL functions is then described in Sec. IV, where the aforementioned algorithm is detailed. Section V is devoted to the presentation of stability analysis and time-domain simulation results. Finally, some concluding remarks end the Note.