Application And Research Of Model Predictive Control Method On Preventing Category â…¡ Pilot-Induced Oscillations

Flight safety is always a primary issue of concern in aviation area, and the pilot-induced oscillations(PIOs) is a well-known flight accident with disastrous consequences and a serious threat to flight safety. Therefore, how to prevent the PIOs is an important research task in the field of flight. In recent years, many of the typical, serious PIOs are mostly categoryⅡPIOs that caused by the rate-limiter. Modern pilot-aircraft closed-loop system is equipped with rate-limiter for the protection of machinery and equipment performance, but the rate-limiter is always with a fixed limit range of the input signal rate, when the input signal rate is much larger than the limit value of the rate-limiter, the rate limiting will be activated, then it will cause the output amplitude decreases, and generate additional phase lag, morever, cause the misjudgment and over-repeated operations of the pilot, and even lead to categoryⅡPIOs.In this paper, a controller is designed based on the model predictive control(MPC)method and applied to the pilot-aircraft closed-loop system. Because of the MPC algorithm characteristics that can take the system constraints into account and ensure the stability, the limiting conditions of the rate-limiter is converted to the system input constraints, which can guarantee the input values in a reasonable range, thus overcome the negative effects of limiter and prevent the occurrence of category II PIOs fundamentally. In this article, the effectiveness and feasibility of the MPC controller in the prevention of categoryⅡPIOs is validated from two aspects.First, a common gain pilots model and Neal-smith aircraft model are selected to establish the pilot-aircraft closed-loop system, and a model predictive controller programming is designed based on Matlab platform to do a simulation. With sine input signals, the effects of the controller on the phase are analyzed, the results show that the MPC controller enables phase lead relative to the input, in some degree, it compensates the phase lag caused by the rate limiting. By changing the gain value of the pilot model and analyzing the time domain response of the system, we found that before PIOs occuring, the effects of MPC controller are not obvious, but it can eliminates system error and suppress oscillations quickly and effectively under oscillation occurring condition, the effectiveness of the MPC controller on preventing categoryⅡPIOs is proved initially.In addition, applied to the pilot-aircraft closed-loop system with different models, the MPC controller is compared with other four compensation schemes(as DASA, RLF, etc.),based on Simulink simulation platform, to analyze the phase compensation effects and step responses. Simulation results show that with the same input signal and flight conditions, the phase compensation effects of the MPC controller are significantly better than the other four suppressors, and the system responses are also better. The tracking performance of the MPC controller is also compared with other suppressors under the tasks of USA air standard( 1797A-STD-ML), such as sinusoidal tracking、discrete pitch and the step tracking task, the MPC controller can effectively complete the tasks and control results are better, then the validity of MPC approach has been further verified.