Precision motion control of electro-hydraulic systems with energy recovery
Abstract
Hydraulic systems will continue to play an important role in our society because of their large power to weight ratios and compact actuators. Hydraulic servo-systems will only become more ubiquitous as demands for increased performance, faster production, tighter tolerances and more efficient operation continue to become more stringent. There is a need for energy-efficient hydraulic systems which can deliver the high performance control required in today’s society. In this thesis, the technologies of independent metering valves, cross-port regeneration and accumulator-based energy recovery systems and the reasons why they are able to boost the efficiency of hydraulic systems are discussed. A control methodology including low-level adaptive robust control (ARC) of the flow rates and high-level decision logic is presented for simultaneously achieving high performance and energy-efficient operation for hydraulic systems with these features. An experimental setup consisting of a scaled-down hydraulic excavator arm is used as a case study. Model parameters are identified and a correlated system model for the swing motion is presented. This system is then used to illustrate the control design procedure. The ARC algorithm is quite flexible and is applied without major modification to systems using four different valve configurations. A systematic method is proposed for selecting the controller gains to reduce the amount of trial and error required for this task. The ARC algorithm guarantees high performance motion control even in the presence of uncertainties and disturbances by combining adjustable nonlinear model compensation with robust feedback. The model compensation is adjusted by controlled parameter adaptation. The high-level logic selects the most efficient way to implement the flow rates determined by the ARC algorithm and also determines the pressure level at which the system can operate most efficiently. Simulation results are presented which demonstrate the ability to achieve both precision motion control and increase energy efficiency using the proposed control strategy. These results clearly show the operation and benefits of independent metering, cross-port regeneration and energy recovery. Experimental results were obtained for one of the valve configurations studied. The tracking performance achieved demonstrates the effectiveness of the control algorithm. Additional experimental results are still needed to confirm that the energy efficiency predicted by the simulations can be achieved without loss of performance in practice. The addition of an energy recovery accumulator to a system with an under-utilized constant pressure source can allow the system to approach the efficiency which would be obtained by using a load-sensing pump. There is potential for increased efficiency by using a central energy recovery accumulator on systems with multiple actuators, since the accumulator is able to recover energy normally lost to throttling for actuators with widelyvarying pressure requirements.
Degree
M.S.M.E.
Advisors
Yao, Purdue University.
Subject Area
Mechanical engineering
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