Yaw and pitch control of a twin rotor MIMO system

This paper addresses the control of the standard twin rotor multi-input-multi-output (MIMO) control system problem. First, nonlinear dynamic model of the system was derived using basic laws of physics. While it was possible to linearize some of the plant nonlinearities, some of them were not, such as squared input. In the conventional approach, this problem has been solved by linearizing the possible nonlinearities, while neglecting the others, at the cost of reduced performance. Most importantly, the latter partially linearized approach demands linearized plant model at every operating point, which makes the controller implementation complicated when considering a wide dynamic operating range. In order to overcome limitations of the partially linearized approach, we derive a nonlinear controller. In that we use the tracking error dynamics to arrive at a compromise between the tracking performances of the pitch and yaw axes control and the smoothness of the actuator input. Furthermore, one of the key features of twin rotor MIMO system is its dynamic cross coupling. Therefore, in order to get rid of the cross coupling a dynamic de-coupler was used. First the plant and the controller was simulated in MATLAB/Simulink™ environment. Then, it was implemented in the hardware to control the pitch and yaw of an actual Twin Rotor MIMO system. The performance assessed using Integrated Absolute Error (IAE) and Accumulated Squared Input (ASI) metrics which represents the tracking performance and the energy input respectively. The performance matrices of the controller were compared with a PID controller tuned to the partially linearized plant model and the results show approximately more than 25% improvement both in terms of IAE and ASI.