Tuning fuzzy Bang–bang relay controller for satellite attitude control system

Abstract

Two level Bang–bang controllers are generally used in conjunction with the thrust reaction actuator for spacecraft/satellite attitude control. These controllers are fast acting and firing time dependent; full or no thrust-power to control the satellite attitude in minimum time. Conventional Bang–bang fuzzy controller requires soft fuzzy engine, and a hardware relay to accomplish Bang–bang control action. A new fuzzy Bang–bang relay controller (FBBRC) is introduced in this paper. The new controller is inherently sub-optimal due to its Bang–bang property. The controller has fuzzy decision making capability in its inputs and have two fixed levels Bang–bang output. Consequently, the tuning of FBBRC is restricted to inputs parameters only in comparison to standard fuzzy logic controller (FLC) where the output parameters can also be tuned. The stability of new controller stems from well established Bang–bang sliding mode control theory. The new fuzzy controller is simulated on a three-axis satellite attitude control model and comparison is made with standard fuzzy logic controller. The work presented here demonstrates that tuning only the input membership function is sufficient and simpler than tuning both input and output membership functions in the standard FLC. The controller is tuned on-line with gradient descent optimization method. The Inherent chattering associated with two-level Bang–bang controller produce undesirable low amplitude high frequency limit cycles. The chattering can be easily stopped in propose fuzzy Bang–bang relay controller, hence adding multi-functionality to its simple design. Simulation result shows that the new controller has faster response time and is capable of controlling the satellite attitude system under adverse initial conditions.