MOD-2 wind turbine farm stability study

The development of large wind turbine generators (WTGs) for operation in utility power systems is accelerating. This report contains the results of an investigation of the dynamics of single and multiple 2.5 MW, Boeing MOD-2 WTGs connected to utility power systems, including the first three-machine cluster connected to the grid of the Bonneville Power Administration. The analysis is based on digital simulation of the complete electromechanical system of single and multiple WTGs, including wind turbine, wind turbine control, drive train, generator, generator excitation control, electrical network and equivalent utility source. Both time response and frequency response methods were used. The results show that the dynamics of WTGs are characterized by two torsional modes, the lightly damped shaft mode at frequencies well below 1 Hz, and the electrical mode at 3-5 Hz. The former is primarily excited by wind speed disturbances, the latter by electrical disturbances. Since the shaft mode falls within the bandwidth of blade pitch control, additional damping for this mode is a prerequisite for good turbine control.