Stepwise inertial control of a wind turbine generator to minimize a second frequency dip

AbstractWind turbine generators (WTGs) in power systems with high wind penetration levels are encouraged or forced to participate in frequency control. A stepwise inertial control (SIC) scheme instantly increases WTG output to arrest the frequency drop for a preset period upon detecting a disturbance. After arresting the frequency drop, the output is rapidly reduced to recover the rotor speed. The reduction could cause a power deficit to the power system, which in turn results in a second frequency dip (SFD). This paper proposes an SIC scheme that can improve the frequency nadir (FN) and maximum rate of change of frequency (ROCOF) while minimizing an SFD. To achieve this, a reference function is separately defined prior to and after the FN. To improve the FN and maximum ROCOF, the output is instantly increased by adding a constant, which is proportional to the rotor speed, and maintaining it until the FN is reached. To minimize an SFD, the output is slowly reduced with the rotor speed. This reduction ensu...