Coordinated DC voltage control strategy of hybrid HVDC with multi‐infeed MMC inverters considering commutation failures

Abstract

Summary This paper investigates the hybrid HVDC with cascaded multi‐infeed MMCs' basic control characteristic and designs the coordinates control strategy considering the DC voltage control and commutation failures of the LCC inverters. The complete basic UI curves of the hybrid HVDC are obtained, and the interaction mechanism of each converter is also clarified, which is in master‐slave control mode. Through the obtained basic characteristic, to reduce the commutation failures of the LCC inverter, the coordinated DC voltage control strategy with dynamic limiter is designed to enhance the AC voltage stability. And the coordinated DC voltage control method coped with the dynamic limiters is also designed. Based on the proposed method, the DC voltage can be stable and unbalanced active power can also be distributed reasonably by the DC voltage control strategy, while much more reactive power can simultaneously be released from VSC to support the stable operation of the LCC inverter. Such that the DC side operation and AC side voltage stability of the hybrid HVDC can both be improved. Finally, the simulations verify the theoretical analysis done in the paper.

Interaction Mechanism and Coordinated Control of Commutation Failure Prevention in Multi-Infeed Ultra-HVDC System

“…Ultra-HVDC (UHVDC) transmission technology has been extensively utilized around the world due to its well-known advantage of long-distance bulk power transmission and lower operating power losses [1]. And commutation failure (CF) is a frequent and adverse event in LCC-HVDC systems, usually occurring as the consequence of the short-circuit fault in the AC system on the inverter side [2,3]. Statistics show that a total number of 60 CFs were recorded in East China Power Grid from 2011 to 2018, and up to four HVDC lines suffered from a temporary interruption of the power transmission and misoperation of the protective relays in the severest cases [4,5].…”

“…In addition to the CF mechanism analysis, various CF mitigation methods have been developed. At present, the commonly used strategies mainly fall into the following categories: (1) modifying the layout, capacity allocation, and switching control of reactive power compensation devices [21][22][23][24], (2) reforming the converter topology [25], and (3) optimizing the DC control scheme [6,10,26,27]. Reactive power compensation equipment is not only expensive but also increases short-circuit current of the AC system.…”