Control of VSC-HVDC for Wind Farm Integration with Real-Time Frequency Mirroring and Self-Synchronizing Capability

Abstract

Voltage source converter based HVDC (VSC-HVDC) is a future trend for integrating the large-scale offshore wind farms to the power grid. Due to fast current vector control of VSC-HVDC receiving-end, offshore wind farms present no inertial response and become unstable when the grid is weak. A novel control strategy for VSC-HVDC system to provide inertial response with offshore wind farm is presented in this paper. With the application of inertial synchronizing control (ISC), self-synchronization is realized in receiving end converter (REC) by utilizing the nature response of DC capacitor with grid frequency well reflected to the DC voltage. At the same time, frequency mirroring control is applied in sending end converter (SEC), with which AC grid frequency is mirrored to the sending-end instantaneously. Then wind farm can realize inertial response, and REC behaves like a synchronous generator with inertia equivalent to the wind farms and VSC-HVDC system. This largely enhances the stability under weak grid condition and frequency supporting ability to the grid. The effectiveness of proposed control strategy is evaluated by comparing to an existing method based on different work scenarios in PSCAD/EMTDC.