Mercredi 7 octobre 2009
Jean SUMAILI AKILIMALI
Current decomposition-based loss partitioning
and loss allocation in distribution systems
Thèse de doctorat en Génie Électrique
Politecnico di Torino
Directeurs de thèse :
Prof. Gianfranco CHICCO, Prof. Enrico CARPANETO
Coordinateur du doctorat :
Prof. Mario CHIAMPI
Date de soutenance : 8 mai 2008.
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 in order to send correct signals to the market taking into account the location and characteristics of loads and generations, including the local sources forming the distributed generation (DG). The allocation factors should depend on size, location and time evolution of the resources connected to the system. In the presence of DG, 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 behaviour. 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.
The initial part of this thesis addresses the issues related to loss allocation in radial distribution systems with DG, with a threefold focus. First, the key differences in the formulation of the loss allocation problem for radial distribution systems with respect to transmission systems are discussed, specifying the modelling and computational issues concerning the treatment of the slack node in radial distribution systems. Then, the characteristics of derivative-based and circuit-based loss allocation techniques are presented and compared, illustrating the arrangements used for adapting the various techniques to be applied to radial distribution systems with DG. Finally, the effects of introducing voltage-controllable local generation on the calculation of the loss allocation coefficients are discussed, proposing the adoption of a “reduced” representation of the system capable of taking into proper account the characteristics of the nodes containing voltage-controllable DG units.
A key contribution of this thesis is the formulation of a new circuit-based loss allocation technique based on the decomposition of the branch currents, specifically developed for radial distribution systems with DG. The proposed technique called Branch Current Decomposition Loss Allocation (BCDLA) is only based on the information provided by the network data and by the power flow solution. Examples of application to confirm its effectiveness are provided, showing the time evolution of the loss allocation coefficients for distribution systems with variable load and local generation patterns.
In the last part of the thesis, the concepts related to loss partitioning among the phase currents in three-phase distribution systems are revisited in the light of new findings. 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 BCDLA method for enabling its application to three-phase unbalanced distribution systems with distributed generation. Numerical examples on a three-phase line with grounded neutral and on the IEEE 13-node test system are provided to assist the illustration and discussion of the novel conceptual framework.
branch current decomposition, bus admittance matrix, bus impedance matrix; circuit-based techniques; derivative-based methods; distributed generation, distribution systems, loss allocation, loss partitioning, losses, paradox, unbalanced systems, voltage-controllable units.
Publications based on this thesis
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