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...