A comparison of rate-limit phase compensator to prevent category II pilot induced oscillations

When rate limiter is saturated, the phase lag would occur and the aircraft dynamics would change suddenly, which could cause category II pilot induced oscillations (PIO) and threaten flight safety. The phase compensating method is a practical means to avoid PIO. The dead area stability augmentation(DASA) compensator, feedback with bypass(FWB) compensator and derivative switching(DS) compensator which prevent category II PIO are compared. The open loop properties and phase compensation properties of three compensators are analyzed with describing method in frequency domain. The occurring mechanism of category II PIO is analyzed and the expression to avoid category II PIO is derived. The step, discrete and sine tracking tasks are employed to research the prevention capability of three compensators in closed loop analysis. The simulation results demonstrate that FWB compensator produces the best performance on avoiding category II PIO and reduces the occurrence possibility of category II PIO distinctly.