Dr Alejandro Donaire

In this work we present a port-Hamiltonian supported control system design aimed at stabilizing a DC-DC Buck converter driving a nonlinear dissipative load. A desired closed-loop dynamics in the form of a port-Hamiltonian system is proposed, whose parameterization enforces the asymptotic stability of the desired equilibrium point. Moreover, the closed loop incorporates a first order dynamic extension allowing to reject constant disturbances on the load side. We prove that the closed loop is ISS respect to unmatched disturbances. To extend this property to disturbances acting on the supply side we add a standard PI output regulator to the previous closed loop. The performance of the closed loop is verified via simulation.

In this paper, a switched controller for the Chaplygin Sleigh system based on passivity and energy shaping is presented. The Chaplygin sleigh cannot be asymptotically stabilised with a smooth control law, since Brockett's necessary conditions for smooth stabilisation is not satisfied. To asymptotically stabilise the origin, two potential energy shaping control laws are developed that render the system asymptotically stable to two equilibrium manifolds, which intersect at the origin. A switching strategy between the energy shaping controllers is derived that ensures the system converges to the intersection of the equilibrium manifolds.

In this paper, we address the problem of stabilisation of robots subject to nonholonommic constraints and external disturbances using port-Hamiltonian theory and smooth time-invariant control laws. This should be contrasted with the commonly used switched or time-varying laws. We propose a control design that provides asymptotic stability of an manifold (also called relative equilibria) - due to the Brockett condition this is the only type of stabilisation possible using smooth time-invariant control laws. The equilibrium manifold can be shaped to certain extent to satisfy specific control objectives. The proposed control law also incorporates integral action, and thus the closed-loop system is robust to unknown constant disturbances. A key step in the proposed design is a change of coordinates not only in the momentum, but also in the position vector, which differs from coordinate transformations previously proposed in the literature for the control of nonholonomic systems. The theoretical properties of the control law are verified via numerical simulation based on a robotic ground vehicle model with differential traction wheels and non co-axial centre of mass and point of contact.

© 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.This paper presents a Hamiltonian model of marine vehicle dynamics in six degrees of freedom in both body-fixed and inertial momentum coordinates. The model in body-fixed coordinates presents a particular structure of the mass matrix that allows the adaptation and application of passivity-based control interconnection and damping assignment design methodologies developed for robust stabilisation of mechanical systems in terms of generalised coordinates. As an example of application, we follow this methodology to design a passivity-based tracking controller with integral action for fully actuated vehicles in six degrees of freedom. We also describe a momentum transformation that allows an alternative model representation that resembles general port-Hamiltonian mechanical systems with a coordinate dependent mass matrix. This can be seen as an enabling step towards the adaptation of the theory of control of port-Hamiltonian systems developed in robotic manipulators and multi-body mechanical systems to the case of marine craft dynamics.

© 2015 IFAC.The main purpose of this paper is to investigate the robustness of tracking controllers for mechanical systems vis-a-vis external disturbances. The controllers designed are obtained by modifying a change of coordinates recently proposed for robust energy shaping controller. This type of change of coordinates allows to assign damping in all the states when the closed loop is written in port-Hamiltonian form. This feature simplify the stability analysis by ensure that the Hamiltonian function is a strict Lyapunov function of the closed loop. Moreover, robustness of the closed loop against external disturbances is ensured. This result is also extended for mechanical systems interacting with elastic environments and linear deformation. The robust properties are preserved adding terms in the control law via the new change of coordinates.

Control of underactuated mechanical systems via energy shaping is a well-established, robust design technique. Unfortunately, its application is often stymied by the need to solve partial differential equations (PDEs). In this paper a new, fully constructive, procedure to shape the energy for a class of mechanical systems that obviates the solution of PDEs is proposed. The control law consists of a first stage of partial feedback linearization followed by a simple proportional plus integral controller acting on two new passive outputs. The class of systems for which the procedure is applicable is identified imposing some (directly verifiable) conditions on the systems inertia matrix and its potential energy function. It is shown that these conditions are satisfied by three benchmark examples.

As Unmanned Aircraft Systems (UAS) grow in complexity, and their level of autonomy increases-moving away from the concept of a remotely piloted systems and more towards autonomous systems-there is a need to further improve reliability and tolerance to faults. The traditional way to accommodate actuator faults is by using standard control allocation techniques as part of the flight control system. The allocation problem in the presence of faults often requires adding constraints that quantify the maximum capacity of the actuators. This in turn requires on-line numerical optimisation. In this paper, we propose a framework for joint allocation and constrained control scheme via vector input scaling. The actuator configuration is used to map actuator constraints into the space of the aircraft generalised forces, which are the magnitudes demanded by the flight controller. Then by constraining the output of controller, we ensure that the allocation function always receive feasible demands. With the proposed framework, the allocation problem does not require numerical optimisation, and since the controller handles the constraints, there is not need to implement heuristics to inform the controller about actuator saturation. © 2011 by The University Of Newcastle, Australia and Boeing Defence Australia. Published by the American Institute of Aeronautics and Astronautics, Inc.

This paper presents a method for the estimation of thrust model parameters of uninhabited airborne systems using specific flight tests. Particular tests are proposed to simplify the estimation. The proposed estimation method is based on three steps. The first step uses a regression model in which the thrust is assumed constant. This allows us to obtain biased initial estimates of the aerodynamic coefficients of the surge model. In the second step, a robust nonlinear state estimator is implemented using the initial parameter estimates, and the model is augmented by considering the thrust as random walk. In the third step, the estimate of the thrust obtained by the observer is used to fit a polynomial model in terms of the propeller advanced ratio. We consider a numerical example based on Monte-Carlo simulations to quantify the sampling properties of the proposed estimator given realistic flight conditions.

This paper presents the formulation of Port- Controlled Hamiltonian Models from Bond Graphs. For this, the general abstract field representation of BG and its associated standard implicit form are used in order to establish a connection among variables in both domains. This correspondence can be useful to translate energy- and powershaping control system design methods available on one domain into the other. Some examples illustrate the techniques and formulæ presented.

A speed-tracking problem is solved on a series DC-motor via a bond graph based backstepping technique. A switched excitation circuit allowing for field-weakening demands two designs, each of them being accomplished via a basic methodology combining backstepping and an elementary tracking design. A Lyapunov-redesign method is further applied in order to assure closed loop asymptotic stability of the whole system. The essential BG concepts and techniques used in the methods are minimal paths, bicausality and I-O inversion. The bond graph technique gives physical insight into the choice of the intermediate variables for the backstepping design. The controller performance is shown with the help of digital simulation results.

In this letter we identify, and propose a solution for, the string stability problem that may arise in frequency droop control schemes for a type of inverter-based microgrid. We consider a previously proposed frequency droop control with secondary control loop and we investigate the effect on the performance due to an increase in the number of inverters connected to the microgrid. To mitigate the observed performance deterioration, we propose a new controller that guarantees string stability of the inverter-based microgrid and show its performance via simulations.

This paper presents a control design with integral action for vehicle platoons with disturbances that ensures string stability of the closed-loop system and disturbance rejection. The addition of integral action and a coordinate change allows the development of sufficient smoothness conditions on the closed-loop system to ensure that the closed-loop system using the proposed controller is string stable when subject to time-varying disturbances, while rejecting constant disturbances. In addition, bounds for the tracking error of the platoon configuration are also given. A case study is considered together with a suitable controller structure, which satisfies the required smoothness conditions. Simulation results illustrate the performance of the closed-loop system.

The authors address the problem of tuning a non-linear energy-based regulator for the positioning of a surface marine craft. Interconnection and damping assignment passivity-based control (IDA-PBC) is used for the control design, resulting in passive target dynamics that can be expressed as a port-Hamiltonian system (PHS). The IDA-PBC methodology has been successfully utilised in several applications, however, there has been minimal development in tuning methods that can analytically assist the designer to achieve desired response characteristics. It is demonstrated that eigenvalue assignment of the linearised target dynamics in PHS form can significantly aid the tuning process. Based on this analysis, the authors propose a systematic tuning approach to achieve certain performance and response characteristics. A comprehensive demonstration of the proposed tuning method is provided for the position regulation of an underwater vehicle in the horizontal plane in a case study, where numerical analysis of robustness is also¿conducted.

This paper investigates the control problem for soft continuum manipulators that operate on a plane and that are subject to unknown disturbances. In general, soft continuum manipulators have more degrees-of-freedom than control inputs and are characterised by nonlinear dynamics. Thus, achieving high position accuracy with these systems in the presence of disturbances is a challenging task. In this paper we present the design of a new partial-state feedback controller by using the port-Hamiltonian formulation and we develop a variation of the Integral Interconnection and Damping Assignment Passivity Based Control methodology for a class of soft continuum manipulators. The system dynamics on the bending plane is described by using a rigid-link underactuated model with n elastic virtual joints. The proposed control law regulates the tip rotation to the desired value while compensating unmodelled disturbances and only depends on the tip rotation, which is measurable, hence it is implementable. The effectiveness of the controller is demonstrated with simulations and with experiments on a soft continuum manipulator prototype that employs pneumatic actuation.

To extend the realm of application of the well known controller design technique of interconnection and damping assignment passivity-based control (IDA-PBC) of mechanical systems two modifications to the standard method are presented in this article. First, similarly to Batlle et al. (2009) and Gómez-Estern and van der Schaft (2004), it is proposed to avoid the splitting of the control action into energy-shaping and damping injection terms, but instead to carry them out simultaneously. Second, motivated by Chang (2014), we propose to consider the inclusion of dissipative forces, going beyond the gyroscopic ones used in standard IDA-PBC. The contribution of our work is the proof that the addition of these two elements provides a non-trivial extension to the basic IDA-PBC methodology. It is also shown that several new controllers for mechanical systems designed invoking other (less systematic procedures) that do not satisfy the conditions of standard IDA-PBC, actually belong to this new class of SIDA-PBC.

In a recent contribution, it was shown that a class of mechanical systems, which contains many practical examples, can be stabilized via energy shaping without solving partial differential equations. The proposed controller consists of two terms, a partial linearizing state-feedback and a linear PID loop around two new passive outputs. In this brief note we prove that the first, admittedly non-robust, step can be obviated leaving only the linear PID. A second contribution of the note is to propose a slight modification to the controller to go beyond regulation tasks - being able to follow ramp references in the actuated coordinates.

Poor scalability arises in many vehicle platoon problems. Bidirectional strings appear to show some promise for mitigating these problems. In some cases these solutions have the undesirable side effect of non-scalable response to measurement errors. We examine this problem and show how information exchange between neighbouring vehicles may eliminate scalability difficulties due to measurement errors.

Abstract This paper presents a motion control system for tracking of attitude and speed of an underactuated slender-hull unmanned underwater vehicle. The feedback control strategy is developed using the Port-Hamiltonian theory. By shaping of the target dynamics (desired dynamic response in closed loop) with particular attention to the target mass matrix, the influence of the unactuated dynamics on the controlled system is suppressed. This results in achievable dynamics independent of stable uncontrolled states. Throughout the design, the insight of the physical phenomena involved is used to propose the desired target dynamics. Integral action is added to the system for robustness and to reject steady disturbances. This is achieved via a change of coordinates that result in input-to-state stable (ISS) target dynamics. As a final step in the design, an anti-windup scheme is implemented to account for limited actuator capacity, namely saturation. The performance of the design is demonstrated through simulation with a high-fidelity model. Crown

This paper presents a motion control system for guidance of an underactuated Unmanned Underwater Vehicle (UUV) on a helical trajectory. The control strategy is developed using Port-Hamiltonian theory and interconnection and damping assignment passivity-based control. Using energy routing, the trajectory of a virtual fully actuated plant is guided onto a vector field. A tracking controller is then used that commands the underactuated plant to follow the velocity of the virtual plant. An integral control is inserted between the two control layers, which adds robustness and disturbance rejection to the design.

In this paper, we show how heterogeneous bidirectional vehicle strings can be modelled as port-Hamiltonian systems. Analysis of stability and string stability within this framework is straightforward and leads to a better understanding of the underlying problem. Nonlinear local control and additional integral action is introduced to design a suitable control law guaranteeing l2 string stability of the system with respect to bounded disturbances.