A Coordinated Voltage-Frequency Support Method for VSC-MTDC Integrated Offshore Wind Farms System

Voltage and frequency stability is one of the major concerns with the continuously increasing penetration of offshore wind farms (OWFs) integrated into onshore grid via VSC-MTDC system, and it is a challenge to coordinate its low voltage ride-through (LVRT) and frequency regulation (FR) control when a local fault or large disturbance occurs in onshore grid. To address this challenge, a coordinated voltage-frequency support (CVFS) method for the VSC-MTDC integrated OWFs system is proposed in three parts: 1) an adaptive maximum power point tracking (MPPT) strategy is developed for wind turbines (WTs) to satisfy the power demands for LVRT and FR; 2) an active and reactive power quantification strategy, which firstly considers the static load characteristics of nodes nearest the grid side VSC (GSVSC) stations, is proposed for GSVSC stations to support LVRT and FR respectively; 3) an adaptive power allocation strategy, which considers the capacity constraint and the coordination factor with deviation and rate of change of voltage and frequency of different GSVSC stations, is conducted to achieve differential power distribution between LVRT and FR. Extensive test results have validated the effectiveness and performance of the proposed CVFS method.