Multiport Interline Current Flow Controller for Meshed HVDC Grids

Abstract

In meshed High Voltage Direct Current (HVDC) grids, the current of each line cannot be controlled independently, since it depends on the resistances between nodes. Additional devices, such as Current Flow Controllers (CFCs), may be needed to avoid bottlenecks or line overloads. This work presents a multi-port DC/DC based CFC topology to be connected to lines with unidirectional current flows. The device is able to control the DC lines' currents to the desired value by inserting variable voltage sources in series. First, the modelling of the generic -port topology is presented and then, its modulation and control strategy are described. In the first case study, the concept is validated considering a 5-port CFC by means of dynamic simulations using different control methods. Finally, in the second case study, a 3-port CFC prototype is built and tested in an experimental platform in the laboratory considering different control modes.

Technical feasibility of Power Flow Controllers for HVDC grids

“…This work focuses on a third option, the use of seriesconnected PFCs that exchange power between two [7] or more DC lines [10]. They are implemented as DC/DC converters (also called interline PFCs) and appear to be a more costeffective solution than the previous alternatives due to the lack of the AC transformer or the high voltage converter.…”

“…Regarding the passive components, they will depend on the selected topology. Most of the converters include one or more capacitors [7], [10] in order to be able to insert voltages in series with the lines. Some structures include also inductors [8] and/or AC transformers.…”

“…According to [13], the total losses of the PFC are expected to be around 100 kW. Some other works in the literature report values in the same order of magnitude [7], [10]. Although, it corresponds to a lower order of magnitude than the losses in the lines (around 5 MW in [13]), it is a non-negligible value for a medium voltage converter.…”

“…The proposed options can be classified as: series switching resistors [5], full power converters connected between poles and variable voltage sources inserted in series with one line [6] or with several lines [7], [8]. Most of the works are supported by simulations of the power electronic circuits [9] and some down-scaled converters have been built in laboratories to test the concepts [10], [11]. Several control schemes for these converters have been also proposed and their stability inside the HVDC grid has been analyzed [9], [12].…”

Coordination Control of Power Flow Controller and Hybrid DC Circuit Breaker in MVDC Distribution Networks

“…In a MVDC distribution network, PFC is required to be installed to flexibly adjust the power flow (PF) of DC lines [17], [18]. According to the access mode to the MVDC distribution network, the PFC can be divided into parallel, series, and series-parallel types [19].…”