Frequency Support

This chapter analyzes frequency support for the surrounding AC systems interconnected through an asymmetric bipole Multi-terminal Direct Current (MTDC) grid with metallic return network. It reviews the fundamentals of frequency control followed by brief discussions on the primary frequency support from wind farms and participation in automatic generation control (AGC). The chapter describes the modification of the power-voltage droop control loop for frequency support. It presents an analytical formulation to compute the post-contingency frequency in an AC-MTDC grid in the presence of frequency droop control. The chapter discusses Small-signal Stability analysis to establish the sensitivity of the eigenvalues with respect to different droop coefficients, control parameters, and change in operating conditions involving converter outage. It demonstrates that the frequency droop control for the converters in an MTDC grid is effective in reducing the deviation in the frequency of the AC system following disturbances on both AC and DC sides.