Delphine Riu

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.

Robust optimal control strategies for a hybrid fuel cell power management system

In this paper several optimal control strategies are proposed for the power management subsystem of a hybrid fuel cell/supercapacitor power generation system. The control strategies are based on different control configurations involving the power converters associated to the hybrid source. Given certain desired performances, Linear Matrix Inequalities methods are used to solve the controller design problem that is written as an optimization problem with inequalities constraints. The solution to the optimization problem yields a simple PID controller with H∞ desired performance. For the several control strategies proposed, robustness is a primary issue. Time simulations and robustness analysis shows the effectiveness of the proposed strategies when compared with the classic control strategies used for this type of hybrid power generation system.

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.

Energy storage design for primary frequency control for islanding micro grid

This paper presents a methodology which allows designing an energy storage device to prevent frequency instability of islanding power network. Then, energy storage will be able to stabilize frequency of the power system by limiting the frequency deviation to be within an acceptable range after occurrence of any disturbance. Principle of energy storage had been first elaborated to select a suitable model. Trials on influencing variables, such as rated power, droop value, and technology of energy storage were undertaken to find out their effects. The results show that the energy storage is likely to be an effective device for the controlling of frequency deviation. Its effectiveness is depending upon the earlier mentioned variables. However, proper calculation for a suitable value of the rated power happened to be the prime requirement of the design for an appropriate energy storage system.

An LPV control approach for a fuel cell power generator air supply system

In this paper, the control of the air supply system of a fuel cell power generator is addressed. The management of the air dynamic entering the fuel cell is assured by the control of the air flow of a compressor. The air supply subsystem is controlled to keep a desired oxygen excess ratio, this allows to improve the fuel cell performance. Linear Matrix Inequalities (LMI) tools are extensively used in this paper as a solution to the multivariable robust control problem. Robust multivariable H∞ controllers are considered. A special interest is also given to reduced order controllers, specifically simple PI structures with desired H∞ performances. The models used for control implementation were identified from measures on a real test-bench set-up. Two control strategies are proposed, first a speed controller for the air compressor is designed; then the problem of a robust control of the system subject to some model uncertainties is solved using the Linear Parameter Varying (LPV) approach. The validation of the closed-loop control strategies is achieved using time-domain simulation analysis and the gain scheduled approach.

On the Robust Control of DC-DC Converters: Application to a Hybrid Power Generation System

Abstract In this paper a complete robust control synthesis is performed for a hybrid power generation structure composed by a Fuel Cell and a Supercapacitor. The control strategies are applied to the DC-DC boost power converters associated to each power source. Multivariable PI control with H ∞ performance, H ∞ full and reduced order controllers are designed and compared. The multivariable PI controller is designed through an optimization procedure based on solving some Linear Matrix Inequalities. A μ-analysis and frequency/time response performances results shows the advantages of the different proposed control strategies.