PROJECT TITLE :

A Control Method of HVDC-Modular Multilevel Converter Based on Arm Current Under the Unbalanced Voltage Condition

ABSTRACT:

This paper proposes an enhanced management method for a high-voltage direct-current (HVDC) modular multilevel converter (MMC). To control an MMC-HVDC system properly, the ac current, circulating current, and submodule (SM) capacitor voltage are thought of. The ac-side current may be a basic frequency part, and the circulating current is a double-line frequency part. Existing management strategies control the ac current and circulating current by separating each element. However, the prevailing ways have an obstacle in that the ac-side current must be separated into the positive and negative sequences for management under an unbalanced voltage condition. The circulating current consists of not only negative-sequence parts however additionally positive- and nil-sequence components under an unbalanced voltage condition. So, a further management method is necessary to contemplate the positive- and 0-sequence components of the circulating current. The proposed control methodology has the advantage of controlling not only the ac-facet current of the MMC but conjointly the circulating current without separating every of this elements to manage every arm current of the MMC. Additionally, it can stably management the positive- and nil-sequence elements of the circulating current under the unbalanced voltage condition.