Self-organising fuzzy logic control of a hydrostatic transmission

Hydrostatic transmission systems are highly nonlinear and subject to severe model variations. This makes the application of linear feedback control to meet ever more demanding requirements of precision, speed of response and flexibility, challenging. Fuzzy logic has been investigated for such systems but the simple error-driven fuzzy controller suffers rather similar performance shortfalls to linear controllers since the operating point is not determined by the error. The fuzzy controller can be made to take account of the operating point, but this makes the controller more complicated, the rule selection process less intuitive and the benefit of simplicity is lost. In this paper, we consider the application of self-organising fuzzy logic control (SOFLC) to the speed control of a hydraulic motor. In addition to setting the rules, SOFLC automatically makes the rule changes that are needed as the motor changes speed with the accompanying changes in characteristics. This gives the motor good performance over the entire speed envelope.