Analysis of AC Fault Ride-through Characteristics of the Baihetan-Jiangsu Hybrid Cascaded UHVDC System

The hybrid cascaded ultra-high voltage direct current (UHVDC) system is a system in which the rectifier station is composed of line commutated convertors (LCCs) and the inverter station is composed of an LCC in series with multiple modular multilevel converters (MMCs). The AC fault ride-through characteristics and corresponding influence factors of the Baihetan-Jiangsu hybrid cascaded UHVDC system are studied in this paper. Simulations are carried out from the aspects of the influence of AC faults on the UHVDC system, the influence of the MMC control mode and synchronous condensers on the fault-ride through characteristics. The results show that the dynamics of the inverter side LCC has little effect on the MMCs. The MMC control mode will affect the temporary overvoltage level of the MMCs, and the synchronous condenser can improve the fault ride-through characteristics of the UHVDC system in case of some faults.

I. Introduction

In China, the high voltage direct current transmission technology has become the main technical means for power transmission from west to east. At present, the line-commuted converter (LCC) based ultra-high voltage direct current (UHVDC) transmission is widely used due to its mature technology and low cost [1]. However, the commutation failure at the inverter side may threaten the safety and stability of the system [2]. The modular multilevel converter (MMC) based UHVDC system overcomes the problems of the commutation failure, but its disadvantages are large loss, high cost and weak overload capacity. The LCC-MMC hybrid UHVDC system combine the advantages of the LCC and MMC, adopting the LCC as the rectifier station and the MMC as the inverter station [4]. To further reduce cost, the hybrid cascaded UHVDC system is composed of LCC and MMC in series, which is used in the Baihetan-Jiangsu hybrid cascaded UHVDC project.