Olivier Deblecker

Impact of the Wind Geographical Correlation Level for Reliability Studies

Following several governmental policies trying to reduce CO emissions, renewable energies have been largely promoted during the last decade. Among the green energies that have been developed, wind can actually be seen as one of the most promising solution if we refer to its past and predicted evolutions. However and, even though wind can be considered as an interesting alternative to fossil fuels, it is imperious to emphasize on problematic situations that could be due to the intermittent behavior of wind generation. Indeed, actually, most of the electric utilities do not consider wind power in the classical units management; consequently involving, in the case of increased wind power penetration, untimely stopping of big thermal (or nuclear) units. It is, therefore, necessary to calculate wind equivalent capacities in order to introduce a coherent evaluation of wind production in the management of the centralized production park. In this paper, wind equivalent capacities are calculated using a nonsequential Monte Carlo Simulation. Moreover, in order to evaluate the importance of the wind correlation level between parks located in the same geographical region, two cases are investigated, respectively considering entirely correlated wind parks and, on the opposite, totally independent wind sites. Finally, simulation results show that durations of simultaneous zero wind power production for each considered wind parks stay, in both cases, very low involving quasi-identical calculated equivalent capacities; what tends to demonstrate the minor importance of the wind parks correlation level for wind power estimation in reliability studies. Note that, here, the proposed conclusions are obtained using the Belgian production park data and that the objective is not to dynamically estimate wind production on the short-term (by the use of an autocorrelation function) but rather to give a simplified way to introduce an hourly evaluation of wind production in the day by day management of the classical thermal (nuclear) units.

System Reliability Assessment Method for Wind Power Integration

Wind power penetration is expected to be largely increased in the near future. Nevertheless, due to the high variability of wind, the increase of the installed capacity in wind energy could sometimes lead to a stopping of nonadjustable power plants if the planning of those units was still decided without considering a realistic estimation of the available wind potential. In that way, and as it is illusory to imagine that all the installed wind capacity will always be produced, this article proposes a new method, based on a discrete convolution process, to compute a two-state probabilistic model for wind generation and to define, so, an equivalent capacity for global wind production in order to introduce it in the predictive peak load covering process. This global model is, in fact, based on the convolution between each single wind park multistates histograms and permits to compute accurate equivalent capacity for the wind production of an entire country.

Comparative Study of Soft-Switched Isolated DC-DC Converters for Auxiliary Railway Supply

In modern railways coaches, the electrical separation between the high voltage side and the auxiliary equipments on the consumer side is realized by means of heavy and bulky 50-Hz transformers. In order to reduce the weight and size of the devices, today new power supply systems are proposed that consist in soft-switched isolated DC-DC converters with a lightweight medium frequency transformer and diverse output modules supplied by a common 600-V dc intermediate circuit. This paper aims to investigate in detail two such solutions of isolated DC-DC converters for auxiliary railway supply where zero-current transitions are achieved for the primary inverter switches. A comparison based on several criteria (overall power rating, losses in power semiconductor devices, operation in the whole range of load, etc.) is presented.

Optimal Wind Clustering Methodology for Adequacy Evaluation in System Generation Studies Using Nonsequential Monte Carlo Simulation

In this paper, several clustering algorithms are investigated in order to group together wind parks with close statistical behavior. Here, the proposed approach is practically founded on a fast incremental algorithm validated by a normalized principal component analysis combined with a k-means process. Both methods are practically based on the definition of a Pearson correlation coefficient. The advantage of such a clustering methodology is mainly perceptible in large-scale electrical systems with increased wind penetration. Indeed, it allows to group together highly correlated wind parks into the same cluster and to integrate them in a realistic way into a nonsequential Monte Carlo adequacy evaluation process. Here, the implemented clustering methodology is applied to 94 wind sites located in Occidental Europe. Then, in order to point out the efficiency of this clustering methodology that is afterwards combined with an original wind speed sampling process, an adequacy study is applied to the Roy Billinton Test System in the particular case of two wind clusters.

A computer‐aided design tool dedicated to isolated DC‐DC converters based on multiobjective optimization using genetic algorithms

Purpose – This paper presents a computer‐aided design (CAD) tool for the design of isolated dc‐dc converters.Design/methodology/approach – This tool, developed in Matlab environment, is based on multiobjective optimization (MO) using genetic algorithms. The Elitist Nondominated Sorting Genetic Algorithm is used to perform search and optimization whereas analytical models are used to model the power converters. The design problem requires minimizing the weight, losses and cost of the converter while ensuring the satisfaction of a number of constraints. The optimization variables are, as for them, the operating frequency, the current density, the maximum flux density, the transformer dimensions, the wire diameter, the core material, the conductor material, the converter topology (among Flyback, Forward, Push‐Pull, half‐bridge and full‐bridge topologies), the number of semiconductor devices associated in parallel, the number of cells associated in series or parallel as well as the kinds of input and output c...

A new efficient technique for harmonic-balance finite-element analysis of saturated electromagnetic devices

The paper presents a new efficient technique for the harmonic-balance finite-element modeling of magnetically saturated electromagnetic devices. It is based upon the transmission-line modeling method that leads to a numerical scheme where the field-circuit coupled problem harmonic solutions are obtained iteratively. A superposition principle applies due to the substitution of a fictitious linear material to the nonlinear one. This amounts to significant savings both in computation time and storage requirements. The method is validated by applying it to a two-dimensional voltage-driven model of a three-phase inductor

A Response Surface Methodology Approach to Study the Influence of Specifications or Model Parameters on the Multiobjective Optimal Design of Isolated DC–DC Converters

Nowadays, the use of mathematical optimization techniques to design power converters has become more and more attractive. This paper goes a step further in studying the influence of some specifications (e.g., the input voltage of the converter) or model parameters (e.g., the transformer heat-transfer coefficient) on the multiobjective optimal design of isolated dc-dc converters. A response surface methodology (RSM) approach is used in combination with a multiobjective optimal design tool dedicated to such power converters and using genetic algorithms. At each time, two factors are studied while two response variables are of interest, namely, the power loss and the weight of the converter. The pairs of factors are: the input voltage and the output power, the current and voltage ripples (through the inductor and across the capacitor of the output filter), and, finally, the convection heat-transfer coefficient and the maximal isolation transformer temperature. It should be pointed out that the full-bridge topology is considered in this paper but the proposed methodology is easily applicable to other topologies. It can also be extended to study other factors or other responses of interest.

Numerical Modeling of Capacitive Effects in HF Multiwinding Transformers—Part II: Identification Using the Finite-Element Method

This paper is the second part of a work which aims at proposing a global approach for the numerical modeling of parasitic capacitances in high-frequency multiwinding transformers. In this part, we focus on the numerical identification using the finite-element method (FEM) of the capacitive circuits which have been introduced in a companion paper in the same issue. An original procedure based on the FEM in 2-D electrostatics is first presented. The validity of the 2-D approximation is thereafter discussed, and a new method which consists in solving two successive 3-D models (an electrokinetic problem in the windings and an electrostatic one in the dielectrics) is then exposed. The two methods are illustrated and experimentally validated on a three-winding transformer.

Multiobjective optimal design of transformers for isolated switch mode power supplies

This paper deals with the multiobjective optimal design of medium frequency (MF) transformers for isolated switch mode power supplies (SMPS). The design problem requires minimizing the weight and the loss of the transformer while ensuring the satisfaction of a number of constraints. These constraints include appropriate limits on efficiency, temperature rise and winding dimensions. The optimization variables are, as for them, the operating frequency, the maximum flux density, the current density in windings as well as the core dimensions. If the first three variables are commonly used as design variables, it is rarer to treat the core dimensions as design variables. Note that the MF transformer model used in the design procedure takes full account of the current and voltage waveforms. In this contribution, a design procedure of MF transformers based on multiobjective Genetic Algorithms (GAs) is proposed and illustrated with the design of a transformer for a full-bridge converter.

High-Frequency Multi-Winding Magnetic Components: From Numerical Simulation to Equivalent Circuits With Frequency-Independent RL Parameters

In this paper, mathematically rigorous RL circuits of high-frequency multi-winding transformers are identified using an original three-step numerical procedure. They are composed of frequency-independent coefficients and can therefore be introduced in classical circuit simulators. First, the finite-element method in 3-D magnetodynamics, together with homogenization techniques which reduce the overall computational burden, are employed to extract frequency-dependent impedances and voltage gains. Then, the identified equivalent circuit is modified by removing the static resistances from the impedances, so as to obtain frequency-independent voltage gains, or coupling coefficients. An algorithm which is valid for any number of windings is proposed to that end. Finally, the frequency-dependent impedances are identified to Foster networks with constant elements using an optimization algorithm. An experimental validation with an impedance analyzer is proposed.