This paper presents the design and implementation of automatic flight controllers for a fixed-wing unmanned air vehicle (UAV) by using a linear-quadratic-Gaussian (LQG) control approach. The LQG design is able to retain the guaranteed closed-loop stability of the linear-quadratic regulator (LQR) while having incomplete state measurement. Instead of feeding back the actual states to form the control law, the estimated states provided by a separately designed optimal observer, i.e. the Kalman filter are used. The automatic flight controllers that include outer-loop controls are constructed based on two independent LQG regulators which govern the longitudinal and lateral dynamics of the UAV respectively. The resulting controllers are structurally simple and thus efficient enough to be easily realized with limited onboard computing resource. In this paper, the design of the LQG controllers is described while the navigation and guidance algorithm based on Global Positioning System (GPS) data is also outlined. In order to validate the performance of the automatic flight control system, a series of flight tests have been conducted. Significant results are presented and discussed in detail. Overall, the flight-test results show that it is highly feasible and effective to apply the computationally efficient LQG controllers on a fixed-wing UAV system with a relatively simple onboard system. On the other hand, a fully automatic 44km cross-sea flight demonstration was successfully conducted using the LQG-based flight controllers. Detailed description regarding the event and some significant flight data are given.

A quality tool for predicting control signals is indispensable for effective harmonic compensation in AC power distribution systems. Notably in the literature, either Back Propagation(BP) or Hopfield neural networks(HNN) has claimed to provide quality control signals to achieve the desired harmonic reduction results. This paper evaluates the predictability of BP and HNN in terms of convergence behaviour and leaming capability, as applied to the reduction of load generated current harmonics in a variable speed DC drive. Using the same real current harmonic data, our test results confirm that BP has a larger dynamic harmonic range whereas discrete H", due to its interconnection structure, needs larger size of memory map.