Latency Compensation in an Adaptive Flight Controller

In a flight controller, latency can be defined as the time delay between when the sensor data is collected and the corresponding control command is executed. Latency exists in all real world systems. Although its effects can be negligible under certain operating conditions, the time delay in a system can ultimately create an upper limit on the performance of a controller. The latency problem has been tackled in many ways in the past, and will continue to be a challenge in the pursuit of faster, more responsive, flight controllers. This paper describes two latency compensation techniques that have been implemented in an adaptive flight controller with a dynamic inversion to increase the performance. The first method, the direct compensation technique, incorporates the time delay into the system model and accounts for it directly in the choice of linear gains. The second method, the integrated Smith predictor, is an adaptation of the classic Smith predictor approach, and addresses the latency problem by correcting the feedback through the controller to stabilize the system. The effectiveness of both methods in handling system latency is demonstrated and discussed through simulation and the flighttesting of a small autonomous helicopter, with the results showing an increase in available bandwidth over the equivalent controller without latency compensation.