Nicolas Retière

Identification of fractional order models for electrical networks

In this article, the authors propose a new modelling of electrical networks based on fractional order systems, i.e. systems with non-integer derivative functions. The algorithm of identification of such systems has been applied on a particular network presenting a fractal behaviour on a restricted frequency range

Turbine generator modeling by non-integer order systems

The flowing of induced currents in electric machines, especially in the dampers of synchronous machines, implies an increase in the order of the equivalent circuits used to model their frequency response. But physical meanings of the circuit parameters are often lost. Thus, the authors propose to come back over the modeling of skin effect and to define noninteger order equivalent circuits which would accurately and physically represent the development of induced currents. In this paper, the theoretical basis of this approach is presented. Then, an half-order equivalent circuit of a turbine generator is given.

Induced currents modeling by half-order systems application to hydro- and turbo-alternators

The flowing of induced currents in electric machines, especially in the dampers or massive parts of large synchronous machines, implies an increase in the order of the equivalent circuits used to model their frequency response. But physical meanings of the circuit parameters are often lost. Thus, the authors propose to go back over the modeling of induced currents, in order to define noninteger order equivalent circuits which would be closely linked with the consequences of induced currents on the frequency response. In this paper, the proposed equivalent circuit is based on half-order systems. It is used to represent the frequency response of 1101-MVA turbo-alternator and 6-MVA hydro-alternator. The identification results are compared with measurements.

Simulating calculations and optimization design of a new HVDC supply power for light rail system

In this paper, a new HVDC power supply system for light rail systems is presented and compared to classical distribution networks based on AC/DC controlled converters. A simulation tool has been developed to simulate such a complex system, taking into account vehicle motion and HVDC electrical distribution. Then, an optimization of HVDC structure and control will be presented using Lagrangian formulation. All the results are compared to classical distributions, and show the effectiveness of the proposed power supply distribution used for light rail systems.

A generic method for robust performance analysis of aircraft DC power systems

The recent evolution of aircraft power networks makes new design study necessary for solving key issues such as optimal efficiency, reliability, adaptability and performances. Indeed, DC power systems are subject to strong dynamic interactions between the source and the loads. In this paper, the need for a new design method of the power network is explained, and the authors propose to use a robust performance analysis method. The first main result concerns the analysis of the robustness of a classical aircraft DC source where the parameters of the DC bus are unknown. The second one shows the efficiency of the method to evaluate the potential gain in weight from a change in the performance specifications at the system level.

Half-Order Modeling of Saturated Synchronous Machine

Non-integer-order systems are used to model diffusion in conductive parts of electrical machines as they lead to more compact knowledge models and also to improve their precision. In this paper, a linear half-order impedance model of a ferromagnetic sheet deduced from the diffusion of magnetic field is briefly introduced. Then, from physical considerations and finite-element simulation, the nonlinear half-order impedance model of a ferromagnetic sheet is proposed, taking into account both saturation and diffusion effects. Next, it has been proved that this model can be successfully included in the equivalent circuits of a synchronous machine (SM), taking into account eddy currents in massive parts of the rotor or damper bars and of small-signal saturation. The new SM equivalent circuit is validated by stand-still frequency response tests performed on the solid salient-pole SM of 125 kVA for variable field excitation conditions. An example of the SM transfer function computation in relation to different magnetization levels indicates the usefulness of this modeling approach for robust control issues.

Non linear half-order modeling of synchronous machine

Non integer order systems are used to model diffusion in conductive parts of electrical machines as they lead to more compact and knowledge models but also to improve their precision. Nevertheless, non integer order models have been established under linear conditions. It is than interesting to study the influence of saturation on such model parameters. In this article, a linear half-order impedance model of a ferromagnetic sheet deduced from the diffusion of the magnetic field is introduced. Then, a non linear half-order impedance model of the sheet is proposed. It is finally validated by performing 3D finite element simulations and experimentally verified on a 3 kVA saturated synchronous machine.

Half-order modelling of ferromagnetic sheet

This paper presents a half-order modelling approach applied to a saturated ferromagnetic sheet. Several analytical models are then developed and compared for one-dimensional formulation. In order to identify parameters and validate such models, the saturated ferromagnetic sheet has been simulated using Flux® finite element simulation software. The proposed model has been finally validated by performing the impedance measurements on the real ferromagnetic saturated sheet, using Agilent HP 4294A impedance meter. This model takes into account diffusion of the magnetic field in conductive materials and magnetic saturation.

Exploring the Scale-Invariant Structure of Smart Grids

Smart grids are new complex systems used for the optimal delivery of electricity. Their study and design require a better understanding of the interactions between their topological structure and performance. It is proved that the structure of power systems is self-similar and can be characterized by the spectral dimension. The effects of scale invariance on the frequency response of the networks are shown at intermediate frequencies. Impacts on the wideband dynamic equivalent modeling are finally explored. Two IEEE test cases are used for the numerical verifications of the results.

Time domain simulations of synchronous generator modelled by half-order system

This paper presents a methodology which allows to obtain a time domain response of synchronous generator modelled by the half-order systems. The machine is connected to an electrical network composed of RL circuit. From the Park d-q axis equivalent circuit containing impedances modelled by the half-order transmittances, a state space equation system has been built. Then, using the Grünwald-Letnikov approximation of the half-order derivatives, the state space equations have been solved using a program written in the Matlab® software. Simulation results of three phase short-circuit and power restoration have been compared with the corresponding measurements performed on a 3 kVA synchronous generator.