Catalin Arghir


Last Name

Arghir

First Name

Catalin

ORCID

0000-0001-6584-5512

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2016 - 20207
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Publications 1 - 7 of 7
  • On the steady-state behavior of a nonlinear power network model
    Item type: Conference Paper
    Arghir, Catalin; Groß, Dominic; Dörfler, Florian (2016)
    IFAC-PapersOnLine ~ 6th IFAC Workshop on Distributed Estimation and Control in Networked Systems, NECSYS 2016. Proceedings
    In this paper, we consider a dynamic model of a three-phase power system including nonlinear generator dynamics and transmission line dynamics. We derive conditions under which the power system admits a steady-state behavior characterized by an operation of the grid at a synchronous frequency as well as a power balance for each single device. Based on this, we specify a set on which the dynamics of the power grid match the desired steady-state behavior and show that this set is control-invariant if and only if the control inputs to the generators are constant. Moreover, we constructively obtain network balance equations typically encountered in power flow analysis and subsequently show that the power system can be operated at the desired steady-state if and only if the network balance equations can be solved.
  • Grid-friendly matching of synchronous machines by tapping into the DC storage
    Item type: Conference Paper
    Jouini, Taouba; Arghir, Catalin; Dörfler, Florian (2016)
    IFAC-PapersOnLine ~ 6th IFAC Workshop on Distributed Estimation and Control in Networked Systems, NECSYS 2016. Proceedings
    We propose a novel control strategy for grid-forming converters in low-inertia power grids. Our strategy is inspired by identifying the structural similarities between the 3-phase DC/AC converter and the synchronous machine model. We explicitly match these models through modulation control so that they become structurally equivalent. Compared to standard emulation of virtual synchronous machines, our controller relies solely on readily available DC-side measurements and takes into account the natural DC and AC storage elements which are usually neglected. As a result, our controller is generally faster and less vulnerable to delays and measurement inaccuracies. We provide a virtual adaptive oscillator interpretation of our controller various plug-and-play properties of the closed loop, such as passivity with respect to the DC and AC ports as well as the steady-state droop slopes, which we illustrate in simulations.
  • Energy-Based Stabilization of Network Flows in Multi-Machine Power Systems
    Item type: Conference Paper
    Arghir, Catalin; Dörfler, Florian (2018)
    Proceedings of the 23rd International Symposium on Mathematical Theory of Networks and 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
    Item type: Journal Article
    Arghir, Catalin; Jouini, Taouba; Dörfler, Florian (2018)
    Automatica
  • On the steady-state behavior of a nonlinear power system model
    Item type: Journal Article
    Gross, Dominic; Arghir, Catalin; Dörfler, Florian (2018)
    Automatica
  • The electronic realization of synchronous machines: model matching, angle tracking and energy shaping techniques
    Item type: Journal Article
    Arghir, Catalin; Dörfler, Florian (2020)
    IEEE Transactions on Power Electronics
    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.
  • Transverse feedback passivation in control of multi-machine and multi-converter power networks
    Item type: Doctoral Thesis
    Arghir, Catalin (2019)
    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.
Publications 1 - 7 of 7