This work presents a comprehensive set of steady state models to be included in power flow simulation studies of DC railway networks. This simulation framework covers all important aspects and features of each element of modern DC railways. The proposed models are simplified to achieve the maximum simulation speed while keeping the required accuracy. Not only non-reversible, controlled and uncontrolled reversible substations are considered, but also on-board and off-board accumulation systems. The train model can consider the low network receptivity (overvoltage protection for trains equipped with regenerative braking) and overcurrent protection. It is also possible to include in the simulation DC/DC links between nodes of the railway network at the same or different voltage. To date, there is no other work able to conjugate all the mentioned models in a complex multi-train scenario.
Abstract-In a smart micro-grid (MG) each generator or load has to take part into the network management, joining in reactive power supply/voltage control, active power supply/frequency control, fault ride-through capability and power quality control. The present 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 (PC) 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 labs (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.
Abstract-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 Kirchhoff' s current law (KCL) and Kirchhoff' s 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 and the IEEE 123 Node Test Feeders with different transformer connections and balanced and unbalanced lines and loads.
Abstract-This paper proposes a combined distributed/centralized architecture for the control and monitoring of a hybrid DC/AC microgrid with energy storage capabilities. The monitoring system is based on an own developed C++ framework for the measurement and real-time state estimation of the microgrid. Calculations running at sampled values (SV) frequency (10kHz) are implemented into a set of distributed measurement and processing units which have a TCP/IP communication link with a central server running the powerflow (PF) algorithm. The architecture is fully scalable, with the only restrictions of the signal processing capabilities of the distributed units, LAN bandwidth and central server calculation capabilities. The proposed system includes the hardware and software architecture for the monitoring of the microgrid, the communications scheme, the implementation of real-time algorithms for grid state estimation, a graphical user interface including different visualization alternatives and data storing/retrieving capabilities.
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