Frequency Response of Power Systems With Variable Speed Wind Turbines

As wind penetration levels on power systems increase worldwide and synchronous generation is displaced, the dynamic characteristics of these systems, and hence the protocols for how they are operated, are changing. One issue, of particular concern, is the resulting reduction in system inertia since modern variable speed wind turbines do not inherently contribute to the inertial response of the system. Such devices can, however, be fitted with a control loop which provides an active power response to significant frequency deviations, similar to the inertial response of fixed speed wind turbines and synchronous generation. Unlike conventional machines, however, the response of variable speed turbines is dependent on local wind speeds and so cannot be quantified deterministically by system operators. As a result, it is likely that uncertainty will exist over the inertial response capability of the system at high wind penetration levels. In this paper, the frequency response capability is assessed on a test system and the effectiveness of wind turbines´ contribution to system inertial response is evaluated in the context of future system requirements.