A system for improving wind turbine generator performance is disclosed. In one aspect a rotary power generation system is provided, including: a rotary power generator for generating variable-frequency alternating currents; a negative sequence current regulator that determines and uses frequency-dependent D-axis and Q-axis negative sequence gains based on an electrical frequency of the rotary power generator; and a system for controlling voltage components for balancing the variable-frequency alternating currents generated by the rotary power generator based on the selected D-axis and Q-axis negative sequence gains.