Optimal Power Flow Control in Parallel Operating AC and DC Distribution Links

DC links with back to back voltage source converters are usually built alongside the existing medium voltage ac distribution grids for infrastructure reinforcement. The distribution network operators need to run multiple of such parallel ac and dc links between two substations at optimal efficiency. This article shows that the active power...

Common Mode Currents in DC Power Routers

The grid reinforcement and energy redirection needs have led to the emergence of Back-To-Back Voltage Source Converter (BTB-VSC) based dc power routers. This paper investigates the low frequency Common Mode Currents (CMCs) that arise in the system if the employed BTB-VSCs have an un-isolated ac path connected in parallel to their output ports....

Virtual Resistor Active Damping with Selective Harmonics Control of LCL-Filtered VSCs

LCL filter is widely adopted for strict standard compliance of grid-tied voltage source converters (VSCs). The third order low-pass filtering provides great attenuation for the high frequency harmonics generated by the power electronics guaranteeing low output currents noise injection into the grid. A major concern of the implementation of the...

Boundaries of Operation for Refurbished Parallel AC–DC Reconfigurable Links in Distribution Grids

Hybrid ac–dc reconfigurable link technology can find interesting applications in medium-voltage power distribution. These are networks having dc links operating in parallel alongside ac links with post-fault reconfiguration capability. A given system can operate in different configurations while maintaining equivalent capacity during (n−1)...

Offline Reconfigurability Based Substation Converter Sizing for Hybrid AC-DC Distribution Links

Hybrid ac-dc distribution systems with multiple parallel operating ac and dc links are being developed to maximize system capacity during (n-1) contingencies. This paper shows that offline reconfigurability between such ac and dc links post-fault clearance allows an additional design flexibility of reducing the required substation converter...

Voltage Source Converter Control under Distorted Grid Voltage for Hybrid AC-DC Distribution Links

Back-To-Back (B2B) Voltage Source Converter (VSC) with AC-side LCL filters can be adopted for parallel AC-DC distribution links. In this paper, Grid-side Current Control (GCC) for the inner/fast control loops of the front- and backend power electronics are implemented in order to enhance the system performance against grid disturbances. Herein,...

Zero Sequence Currents Externally Circulating between the Back to Back Modular Multilevel Converters in Parallel AC-DC Distribution Links

During the operation of a three line ac link in parallel with a ac-dc-ac link system that employs Back-to-Back (B2B)Medium Voltage Modular Multilevel Converters (MMC), a path for the low frequency zero sequence currents is shown to exist. Apart from causing additional losses, these currents can result in limitations on power capacity. A...

Number of Levels, Arm Inductance and Modulation Trade-offs for High Power Medium Voltage Grid-Connected Modular Multilevel Converters

There is an increasing focus on integrating flexible dc links for bulk power routing in medium voltage distribution grids. In such applications, the ac-dc Modular Multilevel Converter (MMC) devised for medium voltage and high-power ratings can be an interesting choice. This paper highlights some less explored design trade-offs arising due to...

Suitable Submodule Switch Rating for Medium Voltage Modular Multilevel Converter Design

An important step in Voltage-Source Modular Multilevel Converter (MMC) design is the selection of adequate semiconductor blocking voltage class. This paper highlights that particularly for grid connected medium voltage applications, the choice of suitable switch blocking voltage class is not so straightforward. The market available switch...