Event-Driven Control of a Speed Varying Digital Displacement Machine

The design and analysis of feedback controllers for digital displacement machines requires a control oriented model. The displacement throughput of a full stroke operated machine is altered on a stroke-by-stroke basis at fixed rotation angles. In the case of a fixed speed operation, it may be treated as a Discrete Linear Time Invariant control problem with synchronous sampling rate. To make synchronous linear control theory applicable for a variable speed digital displacement machine, a method based on event-driven control is presented. Using this method, the time domain differential equations are converted into the spatial (position) domain to obtain a constant sampling rate and thus allowing for use of classical control theory. The method is applied to a down scaled digital fluid power motor, where the motor speed is controlled at varying references under varying pressure and load torque conditions. The controller synthesis is carried out as a discrete optimal deterministic problem with full state feedback. Based on a linear analysis of the feedback control system, stability is proven in a pre-specified operation region. Simulation of a non-linear evaluation model with the controller implemented shows great performance, both with respect to tracking and disturbance rejection.