A phase compensator to prevent pilot induced oscillations by actuator rate limiting

In modern fly-by-wire control system, pilot induced oscillations (PIOs) have long been an aviation safety problem. The violation of actuator rate saturation is known to be a leading cause of PIO and has long been linked with performance and stability degradation of an aircraft. This paper proposes a phase compensator designed to reduce the adverse effects of rate saturation of the control surfaces. Without changing the structure of original control scheme in the design process, this proposed phase compensator reduces the effective time delay by minimizing the error of derivatives between the commanded input signal and the actual input signal, as well as minimizing the error of altitudes between these two signals. Simulations on the pilot-aircraft closed-loop system model with rate limiter are used to check the properties of the designed compensator. The pitch angle and roll angle rate commands, which are easy to induce PIO to a pilot, are chosen as references. Results from the simulation evaluation demonstrate that this compensator has good capability of decreasing the occurrence possibility of PIO, including the severity and duration of PIO, introduced by control surface rate limiting.