HVDC Frequency Limit Control and AGC Coordination Strategy for Wind-Thermal-Bundled Islanded System

In the Wind-Thermal-Bundled (WTB) islanded system with HVDC transmission, the frequency limit control (FLC) will be preceded by the automatic generation control (AGC) unit to accommodate the unbalanced power when the wind power fluctuates, which leads to the frequent HVDC actions and frequent switching of HVDC reactive power regulation equipment. In order to solve the coordination problem of FLC and AGC, this paper predicts the frequency deviation peak by the equivalent single machine system to judge the degree of disturbance; then FLC responses in different degrees accordingly, and does not act when wind power fluctuates; finally, after units with AGC function reach the maximum output, dynamic tracking of wind power by HVDC power based on the principle of frequency division is proposed. The strategy reduces the response amplitude of HVDC modulation by setting different limiting amplitude in different frequency bands. WTB islanded system is established by PSCAD/EMTDC to perform time-domain simulation, and the result verifies that this strategy can reduce the times and amplitude of HVDC actions while ensure the frequency stability of the system.