Energy-based Stabilization of Network Flows in Multi-machine Power Systems

This paper considers the network flow stabilization problem in power systems and adopts an output regulation viewpoint. Building upon the structure of a heterogeneous port-Hamiltonian model, we integrate network aspects and develop a systematic control design procedure. First, the passive output is selected to encode two objectives: consensus in angular velocity and constant excitation current. Second, the non-Euclidean nature of the angle variable reveals the geometry of a suitable target set, which is compact and attractive for the zero dynamics. On this set, circuit-theoretic aspects come into play, giving rise to a network potential function which relates the electrical circuit variables to the machine rotor angles. As it turns out, this energy function is convex in the edge variables, concave in the node variables and, most importantly, can be optimized via an intrinsic gradient flow, with its global minimum corresponding to angle synchronization. The third step consists of explicitly deriving the steady-state-inducing control action by further refining this sequence of control-invariant sets. Analogously to solving the so called regulator equations, we obtain an impedance-based network flow map leading to novel error coordinates and a shifted energy function. The final step amounts to decoupling the rotor current dynamics via feedback-linearziation resulting in a cascade which is used to construct an energy-based controller hierarchically.Comment: In preparation for MTNS 201

MediaMTool: Multimedia content management tool

With the proliferation of mobile devices, multimedia streaming over wireless networks has increased in popularity. To overcome a number of challenges as well as to enhance mobile users' experience, much research effort has been placed into multimedia content adaptation and personalisation. Supporting adaptive multimedia can pose itself a number of challenges, especially when considering the fast growing rate at which multimedia content is being produced. This paper explores the idea of automatic multimedia content management and authoring to support adaptive multimedia delivery to mobile devices. A multimedia content management tool (MediaMTool) is presented which automatically creates multiple versions of the multimedia clips based on a set of specified multimedia clip features. For testing purposes, MediaMTool was used in conjunction with EcoLearn, a m-learning system that adapts the quality of the educational multimedia clips in order to save battery power on the learner mobile device

Transverse feedback passivation in control of multi-machine and multi-converter power networks

This thesis investigates the coordinated stabilization for two important classes of power conversion systems in electrical networks: the synchronous generator and the three-phase DC/AC converter. Starting from first-principles, we cast a geometric treatment and arrive at the problem of stabilizing a particular log-polar configuration, corresponding to the optimal network flow in an electrical circuit. The approach is, on the one hand, based on constructing a feedback-equivalent system which naturally decomposes into dynamics on the ray and on the circle. These spaces can be seen as mutual quotients of the Euclidean plane. Upon augmenting the appropriate amplitude-coupling component, the so-called phase-coupled oscillator system is no longer constrained to evolve on the n-torus. On the other hand, a model-matching procedure is proposed to induce dominant dynamics for the radial and the angular coordinates. As in mechanical systems, these simple integrators act as generalized coordinates and are associated with a special potential energy construction. From a power systems perspective, the potential energy function encodes the canonical network objective of inductor current minimization and capacitor voltage maximization. As the rest of the system is naturally damped, a harmonic steady-state behavior emerges, allowing a zero-dynamics refinement procedure. We then explore ways of shaping the energy in the aim of achieving higher-level objectives, such as tracking given active and reactive power set points. Finally, we pose a problem of transverse stabilization, and arrive at a constructive energy function and a feedback law for the synchronous machine and the inverter alike. This unified design methodology further allow us to study the dynamic properties of the most significant circuit elements in power systems

The electronic realization of synchronous machines: model matching, angle tracking and energy shaping techniques

In this paper, we investigate grid-following and grid-forming control strategies starting from the nonlinear dynamics of the DC/AC converter. An electronic synchronous machine is an inverter whose the integral of the DC-bus measurement generates the angle of the instantaneous modulation vector. We show how this minimal augmentation represents an exact physical realization without requiring inner current loops. The DC-link capacitance becomes the equivalent rotational inertia of the converter. Additional features such as a novel phase-locked-loop design, a voltage controller and a power set-point tracking mechanism are then designed via two energy-shaping techniques. One energy function is used to implement a grid-following control scheme, via the inherent synchronizing torque, while the other is used to implement a grid-forming control scheme, by uncovering active-power droop. The results are first derived systematically, and then evaluated experimentally on a front-to-front setup.ISSN:0885-8993ISSN:1941-010

Energy-Based Stabilization of Network Flows in Multi-Machine Power Systems

This paper considers the network flow stabilization problem in power systems and adopts an output regulation viewpoint. Building upon the structure of a heterogeneous port-Hamiltonian model, we integrate network aspects and develop a systematic control design procedure. First, the passive output is selected to encode two objectives: consensus in angular velocity and constant excitation current. Second, the non-Euclidean nature of the angle variable reveals the geometry of a suitable target set, which is compact and attractive for the zero dynamics. On this set, circuit-theoretic aspects come into play, giving rise to a network potential function which relates the electrical circuit variables to the machine rotor angles. As it turns out, this energy function is convex in the edge variables, concave in the node variables and, most importantly, can be optimized via an intrinsic gradient flow, with its global minimum corresponding to angle synchronization. The third step consists of explicitly deriving the steady-state-inducing control action by further refining this sequence of control-invariant sets. Analogously to solving the so called regulator equations, we obtain an impedance-based network flow map leading to novel error coordinates and a shifted energy function. The final step amounts to decoupling the rotor current dynamics via feedback-linearziation resulting in a cascade which is used to construct an energy-based controller hierarchically

Grid-forming control for power converters based on matching of synchronous machines

ISSN:0005-109

On the steady-state behavior of a nonlinear power system model

ISSN:0005-109