Explain the control systems in modern variable-speed wind turbines.

Wind turbine control hierarchy: Region 1 (below cut-in) - idling. Region 2 (partial load) - optimize tip-speed ratio via generator torque control, pitch fixed, extract maximum power. Region 3 (full load) - pitch control limits power to rated, generator torque constant. Control loops: torque control (fast, tracks optimal tip-speed ratio), pitch control (slower, limits rotor speed and power), yaw control (orients nacelle into wind), and supervisory control (startup/shutdown sequences, fault handling). Advanced controls include: individual pitch control (reduce asymmetric loads), tower damping, and LIDAR-assisted preview control.