A new two-degree-of-freedom gain scheduling method applied to the Lynx MK7

Abstract

This paper considers the design of two-degree-of-freedom gain-scheduled controllers for a helicopter system in a new fashion. By taking advantage of a two-degree-of-freedom decoupling scheme, it is possible to generically split the controller synthesis into two parts. One part is concerned with the synthesis of a regulator and the other aims to achieve the tracking requirements. An important feature of the method is that the feedforward filter can be designed by solving a particular full information problem. A robust linear time-invariant (LTI) regulator will be designed and two methods used to synthesize a gain-scheduled feedforward tracking controller will be investigated. The first method is based on a quadratic gain scheduling technique which makes use of a polytopic description of the plant. The second is simpler and uses the concept of linear interpolation of LTI controllers. Both methods are tested on a Lynx MK7 helicopter in simulation. For this application, the benefits and the shortcomings of the respective methods are discussed. Non-linear simulation results show that the gain-scheduled interpolated controller performs remarkably well over the flight envelope.