Variable speed drive with hydraulic boost

This paper studies a variable speed drive with two hydraulic pump motors connected to an actuator. The torque load of the pump motors is reduced by connecting different pressures to the inlets of the pump motors. A method for real-time selection of the inlet pressures is developed. A linearized model is derived, and a robust control approach is used for the controller design of the variable speed drive. Simulation results indicate excellent controllability and robustness together with good energy efficiency. When three supply pressures — one being a pressurized tank line — are used, the peak torque is reduced by 52 per cent compared to the traditional solution.