Filter and sensor delay synchronization in incremental flight control laws

Abstract

This paper introduces and investigates several methods of filtering and delay synchronization in incremental control law structures. It is shown that proper filter and delay synchronization is of great importance for both the performance and stability of the control laws. It is derived how to synthesize complementary filters in case of sensor dynamics, sensor delays and internal control law filtering such as roll-off filters and notch filters. The complementary filters are compared to common synchronization approaches previously applied in incremental control laws. It is shown that the proposed methods are beneficial for Multiple Input Multiple Output (MIMO) systems in case that different delays and filtering is present in the different measurement signals. In case of strongly coupled input effectiveness, the synchronization on the actuator feedback may become even unstable, where the complementary filter approach recovers the design closed-loop behavior. In addition, it is derived how to initialize the complementary filters for a transient-free engagement in non-steady-state conditions. The results are compared in simulation with a roll rate control law for a fixed wing aircraft.

Parameter Tuning Approach for Incremental Nonlinear Dynamic Inversion-Based Flight Controllers

“…Decreasing the cutoff frequency, on the other hand, results in a phase delay which also significantly influences the aircraft dynamics. Thus, a complementary filter, as shown for example in [24], is used in order to determine the angular acceleration with minimum noise and also no phase delay with regard to the already filtered variables. The complementary filter uses, on the one hand, an additional lowpass filter, and then derives the filtered angular velocity.…”