Abstract
A hybrid of line commutated converters (LCCs) and modular multi-level converters (MMCs) can provide the advantages of both the technologies. However, the commutation failure still exists if the LCC operates as an inverter in a hybrid LCC/MMC system. In this paper, the system behavior during a commutation failure is investigated. Both half- bridge and full-bridge MMCs are considered. Control strategies are examined through simulations conducted in PSCAD/ EMTDC. Additionally, commutation failure protection strategies for multi-terminal hybrid LCC/MMC systems with AC and DC circuit breakers are studied. This paper can contribute to the protection design of future hybrid LCC/MMC systems against commutation failures.
Highlights
Renewable energy, like wind and solar power, is widely accepted as a key solution to cope with anthropogenic global warming and climate change and achieve sustainable development [1]
Hybrid line commutated converters (LCCs)/modular multi-level converters (MMCs) high-voltage direct-current (HVDC) systems combine the merits of both LCC and MMC
This paper investigated the commutation failure in hybrid LCC/MMC HVDC systems with the consideration of different types of MMCs and control and protection strategies
Summary
Like wind and solar power, is widely accepted as a key solution to cope with anthropogenic global warming and climate change and achieve sustainable development [1]. The MMCs deployed in the Kun-Liu-Long project have reached to ± 800 kV with a capacity of 5 GW [6] This provides technical feasibility to combine the two types of HVDC technologies to achieve hybrid LCC/MMC based HVDC and UHVDC systems [10]. Compared with pure MMC-HVDC, the hybrid topology employs LCC as the rectifier and MMC as the inverter can reduce the capital cost and power losses and avoid commutation failures This topology is not suitable for offshore wind integration as the LCC station is too large to be built on an offshore platform [13]. The studies in this paper can provide technical guidance for mitigating commutation failures in future hybrid LCC/ MMC HVDC systems
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