Energy Control Strategy to Enhance AC Fault Ride-Through in Offshore Wind MMC-HVDC Systems

TL;DR

This paper proposes an energy control strategy for MMC-HVDC systems that improves fault ride-through capability during AC faults, ensuring stable operation and power transfer in offshore wind farm connections.

Contribution

It introduces a novel AC fault ride-through scheme combining surplus power storage in MMC submodule capacitors with energy dissipation, enabling use of low-capacitance submodules and enhancing system stability.

Findings

Effective DC link voltage regulation during faults

Successful demonstration on a 640kV/420MW system

Maintains offshore wind farm connection during AC faults

Abstract

Modular Multilevel Converter-based High Voltage Direct Current (MMC-HVDC) system is a promising technology for integration of offshore wind farms (OWFs). However, onshore AC faults on MMC-HVDC reduce the power transfer capability of onshore converter station, leading to surplus power accumulation in HVDC link. This surplus power causes a rapid rise in DC-link voltage and may hinder safe operation of OWFs. To address such a situation, this paper presents an AC fault ride-through scheme that combines the storage of surplus power in MMC submodule (SM) capacitors and dissipation of residual power in an energy dissipation device (EDD). The proposed energy control facilitates use of half-bridge MMC SMs with low-capacitance, with their storage capacity leveraged to share the surplus power during faults, with a lower-rated EDD. The proposed scheme is tested on a 640kV/420MW MMC-HVDC system. The results show that proposed control scheme effectively maintains DC link voltages, ensuring connection of OWFs.