Enrico Carpaneto

Induction motor high frequency model

In this paper, an accurate high frequency model of an induction motor is presented. The proposed model allows analysis, at the same time, of both high frequency phenomena up to some MHz due to the static supply, and low frequency phenomena usually analyzed by means of the dq motor model. The high frequency model has been obtained by means of a frequency and time domain analysis and has been verified on a wide spread of induction motors starting from 4 up to 55 kW. The proposed model can be used to evaluate the high frequency leakage currents, which are the cause of electromagnetic interference to electronic and electric equipment.

Convergence of the backward/forward sweep method for the load-flow analysis of radial distribution systems

This paper presents a study on the convergence characteristics of the backward/forward sweep method, which is one of the most effective methods for the load-flow analysis of the radial distribution systems. After revisiting the theoretical background, the convergence conditions and the evolution of the iterative process are investigated in detail for different load models. A dedicated study of the properties of the backward/forward sweep method is performed, taking into account different line X/R ratios and different types of voltage-dependent loads. Some useful indicators are introduced to estimate the number of iterations required to reach the convergence of the iterative process under a given tolerance. Test results are included for a tutorial two-node system and for a real 84-node system.

Branch current decomposition method for loss allocation in radial distribution systems with distributed generation

The allocation of the system losses to suppliers and consumers is a challenging issue for the restructured electricity business. Meaningful loss allocation techniques have to be adopted to set up appropriate economic penalties or rewards. The allocation factors should depend on size, location, and time evolution of the resources connected to the system. In the presence of distributed generation, the variety of the power flows in distribution systems calls for adopting mechanisms able to discriminate among the contributions that increase or reduce the total losses. Some loss allocation techniques already developed in the literature have shown consistent behavior. However, their application requires computing a set of additional quantities with respect to those provided by the distribution system power flow solved with the backward/forward sweep approach. This paper presents a new circuit-based loss allocation technique, based on the decomposition of the branch currents, specifically developed for radial distribution systems with distributed generation. The proposed technique is simple and effective and is only based on the information provided by the network data and by the power flow solution. Examples of application are shown to confirm its effectiveness

Ant-colony search-based minimum losses reconfiguration of distribution systems

This paper presents a new application of the ant colony search method to the minimum losses reconfiguration of distribution systems. The optimization problem is formulated by taking into account the operational constraints of the distribution systems. The results of the proposed approach are compared to the ones obtained from other deterministic and heuristic methods (iterative improvement, tabu search and simulated annealing) on two test systems.

Evaluation of the probability density functions of distribution system reliability indices with a characteristic functions-based approach

In reliability analysis of distribution systems, random events like the occurrence of a fault or the time to restore the service after a fault are represented by using random variables (RVs), so that the reliability indices built on the basis of these RVs also become RVs. Existing techniques for the evaluation of the probability distributions of reliability indices are typically based on Monte Carlo and analytical simulations. This paper presents a new method for computing the probability distribution of reliability indices. The random sums introduced by the randomness of the number of fault occurrences in the time interval of analysis are handled by using a characteristic functions-based approach. The direct convolution of the probability density functions is avoided by resorting to the properties of the compound Poisson process. In addition, the direct and inverse discrete Fourier transforms are used to allow for handling any type of probability distribution. The proposed method is an effective alternative to the existing methods, providing a fast and simple computation of probability distributions and moments for local and global reliability indices. Results obtained for large real urban distribution systems are presented.

Characterisation of the aggregated load patterns for extraurban residential customer groups

This paper reports on the results of a study carried out on the basis of information obtained from real case investigations on residential customer behaviour, lifestyle, and usage of the appliances. The aggregated load patterns of single-house customers have been first computed by using a bottom-up approach. Then, the time-dependent uncertainty of the aggregated load power has been assessed from simulations in function of the number of residential customers. Finally, a goodness-of-fit analysis has shown that a Gamma probability distribution, with parameters related to average value and standard deviation of the simulation results, satisfactorily represents the probability distribution of the load power at each time instant.

A dynamic interpretation of the load-flow Jacobian singularity for voltage stability analysis

Abstract In voltage stability analysis, both static and dynamic approaches are used to evaluate the system critical conditions. The static approach is based on the standard load flow equations. For small-disturbance analysis, the dynamic approach is based on the eigenvalue computation of the linearized system, while for large-disturbance analysis a complete time-domain simulation is required. However, both the equilibrium point around which linearization is performed and the initial conditions for the simulation are computed by a procedure which uses the standard load-flow equations. The standard load-flow equations make some implicit assumptions on the steadystate behaviour of dynamic components (generator control systems, loads). These assumptions are not satisfied by the usual dynamic models, and this discrepancy leads to different results in the voltage stability assessment using static and dynamic methods. In the framework of bifurcation theory, this paper discusses the relationships between static and small-disturbance dynamic approaches to find the voltage stability critical condition, with emphasis on system component modelling. A set of hypotheses on generator control systems and load models is given for a multimachine system, according to which the same critical conditions are obtained both from the load flow equations and from the full eigenvalue analysis. These hypotheses are less restrictive than those previously proposed in the literature and make it possible to obtain equivalence between the singularity of the load flow Jacobian and a null eigenvalue of the linearized dynamic system. Following a dynamic argumentation based on small-disturbance analysis, this result may justify the use of simple and fast static methods for voltage stability assessment and shows that the smalldisturbance voltage stability limit depends only on the steady-state characteristics of the dynamic components of the system.

Loss Partitioning and Loss Allocation in Three-Phase Radial Distribution Systems With Distributed Generation

In this paper, the concepts related to loss partitioning among the phase currents in three-phase distribution systems are revisited in the light of new findings identified by the authors. In particular, the presence of a paradox in the classical loss partitioning approach, based on the use of the phase-by-phase difference between the input and output complex power, is highlighted. The conditions for performing effective loss partitioning without the occurrence of the paradox are thus established. The corresponding results are then used to extend the branch current decomposition loss allocation method for enabling its application to three-phase unbalanced distribution systems with distributed generation. Several numerical examples on a three-phase line with grounded neutral and on the modified IEEE 13-node test system are provided to assist the illustration and discussion of the novel conceptual framework.

Stator-Winding Thermal Models for Short-Time Thermal Transients: Definition and Validation

In this paper, four thermal models for the stator-winding temperature prediction in short-time thermal transient are presented and experimentally validated. The lumped-parameter networks, based on physical representation of the stator components, are composed of multiple RC cells in cascade. In particular, starting from a fourth-order thermal network, the model complexity is progressively reduced to a third-, second-, and then down to a first-order system. The proposed models and their predicted temperature evolutions are discussed in detail and validated by means of a full experimental approach on an industrial 7.5-kW induction motor. Finally, the behaviors of the proposed thermal models are corroborated by some considerations drawn by the analytical solution of the models.

Reliability of reconfigurable distribution systems including distributed generation

This paper deals with the reliability analysis of a radial distribution system with local generation sources, considering how the possible formation of intentional islands, associated to the reconfiguration of the distribution systems through redundant branches, could enhance the effectiveness of the service restoration process. A dedicated procedure has been developed to assist the possible formation of intentional islands with fixed or variable extension. The characteristics of the procedure are illustrated by means of a number of examples. Finally, an example showing the possible use of DG resources to defer structural investments for the distribution system expansion is presented