Manuel Coto

Unified AC/DC Power Flow for Traction Systems: A New Concept

This paper adds some new contributions to the unified alternating current/direct current (ac/dc) power-flow method that is applied to railway power supply systems. These contributions are mainly focused on the way that the unified power-flow problem is implemented. The authors propose a new technique based on graph theory to model the motion of the trains without varying the system topology and dimensions, as well as the solution vector. Furthermore, a new matrix formulation is developed to provide an easy way of setting out the problem. The combination of these techniques makes the unified ac/dc power flow easier to implement, and the comparison among different instants can directly be done, representing the major contribution of this paper. Finally, as a minor contribution, a new technique based on previous matrix formulation is developed to easily obtain all active and reactive power magnitudes in compact form.

Efficient Energy Management in Smart Micro-Grids: ZERO Grid Impact Buildings

In a smart micro-grid (MG) each generator or load has to take part in the network management, joining in reactive power supply/voltage control, active power supply/frequency control, fault ride-through capability, and power quality control. This paper includes a new concept for building integration in MGs with zero grid-impact so improving the MG efficiency. These aims are shown to be achievable with an intelligent system, based on a dc/ac converter connected to the building point of coupling with the main grid. This system can provide active and reactive power services also including a dc link where storage, generation, and loads can be installed. The system employed for validation is a prototype available at ENEA Laboratories (Italian National Agency for New Technologies). A complete and versatile model in MATLAB/SIMULINK is also presented. The simulations results and the experimental test validation are included. The trial confirms the model goodness and the system usefulness in MG applications.

Unbalanced Power Flow in Distribution Systems With Embedded Transformers Using the Complex Theory in

This paper presents three new contributions to power flow analysis of unbalanced three-phase distribution systems. First, a complex vector based model in αβ0 stationary reference frame is developed to state the power flow equations using a compact matrix formulation. The proposed model is based on Kirchhoffs current law (KCL) and Kirchhoffs voltage law (KVL). Then, a general and exact power transformer model in the αβ0 reference frame is proposed. Finally, this transformer model is incorporated into the power flow problem. It will be shown that the use of an orthogonal reference frame simplifies the modeling of the distribution network components. In this work, both the network and the power transformer, as well as PQ type loads, PQ and PV type generators and a slack bus are modeled. By using the node incidence matrix instead of the admittance matrix, the information about the grid topology and the grid parameters (including power transformers) is separately organized. As it will be demonstrated, the proposed formulation is ready to incorporate other complex models of loads, generators or storage devices. The model is tested by using the IEEE 4-Node and the IEEE 123-Node Test Feeders with different transformer connections and balanced and unbalanced lines and loads.

\alpha \beta 0\;

Many authors have conducted power flow analysis as a tool to operate microgrids in a coordinate manner. Some of them have combined a central management with a back-up distributed control. In this paper, a management system based in this previous concept is studied. What we proposed is an optimum power flow method to be applied to microgrids in which the generators are connected through power converters with droop characteristic based control. In this kind of microgrids, the frequency is not constant and must be considered as a variable to correctly estimate the power flow. The central management is combined with distributed control to guaranty the stability in case of communication failures.

Stationary Reference Frame

The integration of intelligent storage systems in smart micro-grids (MGs) is necessary for the optimal management of the energy flows and to make the grids efficient and self-sustainable systems, further able to provide ancillary service to the main network. The present paper includes a new concept for integrating buildings equipped with intelligent storage systems in MG, making them zero grid-impact and so improving the efficiency of the MG including them. These aims are shown to be achievable with the use of an intelligent system managing the storage, based in a DC/AC converter connected to the point of coupling of the building with the main grid. The system is a prototype available at ENEA (Italian National Agency for New Technologies, Energy and Sustainable Economic Development) labs in Rome. The authors describes it in details, including the control functions. A complete and versatile model in MatLab-Simulink is proposed and the results of simulations are shown.