A prototype knowledge-based system for pavement analysis

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Series interline DC/DC current flow controller for meshed HVDC grids

This paper proposes a DC/DC Current Flow Controller (CFC) for meshed High Voltage Direct Current (HVDC) grids. The CFC has the advantage of a simplified structure that allows to use minimum number of switches when unidirectional current flows through the DC lines are expected. An extended CFC topology able to operate with all the possible current flows is also presented. Then, the operating principle of the CFC is discussed and its structure is compared with a dual H-bridge analysing advantages and disadvantages. The work also details the applied modulation strategy and the control methodology. Finally, a 5-terminal meshed HVDC grid is used to validate the CFC by means of simulations.Peer ReviewedPostprint (published version

Selective operation of distributed current flow controller devices for meshed HVDC grids

In meshed High Voltage Direct Current (HVDC) grids, Current Flow Controllers (CFC) may be required to avoid bottlenecks or line overloads. The present paper proposes the concept of installing Distributed Current Flow Controllers (DCFCs) in different nodes of a meshed HVDC grid that are operated selectively. This concept allows to use simplified DCFC devices to prevent the overloads, with a reduction of the required CFC voltage compared with a single CFC in the grid. First, a methodology to investigate the effect of installing DCFCs in a generic meshed HVDC grid is presented. Several case studies with a 3-terminal and a 7-terminal meshed HVDC grids are conducted and the most suitable topology for the DCFCs is derived based on the previous analysis. Then, this work analyses the increase in the operational area brought by installing DCFCs in a 3-terminal HVDC grid and it is compared with the increase achieved by a Dual H-bridge CFC in one node. The CFC losses and voltage requirement depending on the location of the DCFCs are investigated. Finally, the operation and control of the DCFCs are designed and tested in a 3-terminal meshed HVDC grid using dynamic simulations.Postprint (published version

Advanced vector control for voltage source converters connected to weak grids

This paper addresses an advanced vector current control for a voltage source converter (VSC) connected to a weak grid. The proposed control methodology permits high-performance regulation of the active power and the voltage for the feasible VSC range of operation. First, the steady state characteristics for a power converter connected to a very weak system with a short circuit ratio (SCR) of 1 are discussed in order to identify the system limits. Then, the conventional vector control (inner loop) and the conventional power/voltage control (outer loop) stability and frequency responses are analyzed. From the analysis of the classic structure, an enhanced outer loop based on a decoupled and gain-scheduling controller is presented and its stability is analyzed. The proposed control is validated by means of dynamic simulations and it is compared with classic vector current control. Simulation results illustrate that the proposed control system could provide a promising approach to tackle the challenging problem of VSC in connection with weak AC grids.Peer Reviewe

Series interline DC/DC current flow controller for meshed HVDC grids

This paper proposes a DC/DC Current Flow Controller (CFC) for meshed High Voltage Direct Current (HVDC) grids. The CFC has the advantage of a simplified structure that allows to use minimum number of switches when unidirectional current flows through the DC lines are expected. An extended CFC topology able to operate with all the possible current flows is also presented. Then, the operating principle of the CFC is discussed and its structure is compared with a dual H-bridge analysing advantages and disadvantages. The work also details the applied modulation strategy and the control methodology. Finally, a 5-terminal meshed HVDC grid is used to validate the CFC by means of simulations.Peer Reviewe

THE ACTIVE USE OF DISTRIBUTED GENERATION IN NETWORK PLANNING

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