What is integral windup and how is it prevented?

Integral windup occurs when actuator saturates but integral keeps accumulating error, causing large overshoot when error reverses. Prevention methods include: back-calculation (reduce integral when output saturates), conditional integration (stop integrating during saturation), integrator clamping (limit integral term directly), and tracking mode (modify integral based on actual vs commanded output). Most industrial PID controllers include anti-windup logic. The choice of method affects performance during saturation and recovery.