The Development of Neural Network Based System Identification ...

52 CHAPTER 2 LITERATURE REVIEW
wide range of environments. Although the implementation of NN based direct adaptive
controller is simple, the design and tuning of the controllers are difficult, requiring a
retraining of the NN controller each time the controller parameter is altered [Norgaard,
2000].
The indirect adaptive type controller such as NN based MPC is much more flexible
in implementation where only the model is identified by the NN while the controller
action (MPC) is calculated at each time step. The MPC controller with its anticipated
benefits have been employed successfully to control helicopter based UAS and is expected
to work well with the desired control performance. The NN based system identification
techniques reviewed in the previous section are suitable to be used to identify the
dynamic plant. Considering the convergence and computational speed issues of the NN
based MPC, an approximation based NN-MPC can be used to speed up the computation
speed. Based on the findings from the literature, the NN based MPC seems to fit our
common goal to develop a general adaptive flight controller that can be developed with
less time and effort.
2.5 SUMMARY
In this chapter, a brief literature review about the definition, application and classification
of the rotorcraft UAS is provided as a basic introduction to the research topic.
An overview of various autonomy components that enable the rotorcraft based UAS to
perform autonomous missions is presented. This research project will focus mainly on
the development of automatic flight control components since the automatic control
component is the first key component that needs to be addressed in order to enable a
UAS to be autonomous.
A brief literature review on the helicopter dynamics modelling and NN based
system identification is presented. Various factors that influence the NN prediction
and training performance such as the model structure selection and the choices of
training algorithms are discussed and highlighted. Available literature on the different
AFCS design techniques is explored with special emphasis given to flight control system