Centralized Pressure Control and Displacement Quantization with Digital Displacement Pumps
DOI:
https://doi.org/10.13052/ijfp1439-9776.2623Keywords:
Digital displacement, hydraulic power units, centralized pressure controlAbstract
Danfoss Power Solutions has developed a centralized pressure control solution for multi-pump hydraulic power units (HPU) in the industrial market. This system architecture has been developed around the use of the Digital Displacement Pump® (DDP) which is highly efficient over a wide range of operating conditions and has typically shown a >
30% decrease in electrical input energy over similar systems using axial piston pumps.
MTS Systems, a leading global supplier of test and simulation systems, expanded this centralized control to work in a harmonized fashion with other pumping technologies housed within unique motor-pump modules; some containing DDP and others containing conventional axial piston pumps. This arrangement provided several benefits and empirically demonstrated the DDP module efficiency over the axial piston pump module in supplying fluid power to dynamic downstream force and motion systems that replicate real-world automotive drive files and test track profiles.
Special consideration was required when implementing DDP in a system with multiple pumps’ (maximum of 6) outlet flow combined in parallel. Allowing each individual pump controller to operate in pressure control mode caused compounding complexity in tuning, and noisy, unstable flow pulsations. As a solution, a centralized pressure control scheme was implemented in which a system level microcontroller evaluated user inputs, pressure signals from a transducer, executed logic, and output displacement commands to each pump controller as required to meet the system demand. What makes this control scheme unique is that in a multi-pump system, one pump has a continuously variable displacement fraction with any value from 0 to 100%. The other pump displacements were controlled in a quantized manner with stepped values of displacement (for example: 0%, 25%, 75%, 100%). Hose resonant frequencies were also avoided in this manner.
Testing and implementation of this control scheme has proven to be effective in reducing system tuning complexity and undesirable flow pulsations in the system. Measured results indicate that the average pressure ripple power was reduced by 28% to 94% and the average pressure ripple band power by 61% to 98% (pump module dependent).
Successful implementation of the centralized control allowed MTS to demonstrate through an energy efficiency study that HPUs equipped with DDP consume up to 37.5% less energy than those with swashplate pumps for a given test cycle.
Downloads
References
U.S. Department of Energy (13 November 2024). Improving Pumping System Performance: A Sourcebook for Industry, 2nd Ed. Publication date May 2006. https://www.energy.gov/sites/prod/files/2014/05/f16/pump.pdf.
Rampen, William. 1992. The Digital Displacement Hydraulic Piston Pump. PhD Thesis. University of Edinburgh. Edinburgh, UK.
Danfoss Power Solutions (13 November 2024). Digital Displacement Data Sheet, DDP096 pump and DPC12 controller. https://assets.danfoss.com/documents/361313/AI332064420016en-000201.pdf.
Williamson, C. and Manring, N. A more accurate definition of mechanical and volumetric efficiencies for Digital Displacement pumps. Proceedings of the ASME/Bath 2019 Symposium on Fluid Power and Motion Control, FPMC2019.
Karnell, S. and Ericson, L. Analysis of a Digital Pump with Variable Speed Drive. Proceedings of the ASME/Bath 2022 Symposium on Fluid Power and Motion Control, FPMC2022.
Huova, M. and Linjama, M. Control of Multi-Pressure Hydraulic Supply Line Using Digital Hydraulic Power Management System. Proceedings of the ASME/Bath 2022 Symposium on Fluid Power and Motion Control, FPMC2022.
Jimenez, C.R., Reinertz, O. and Schmitz, K. A Novel Hydro-Mechanical Control Method for Digital Pumps. The 11th Workshop on Digital Fluid Power. Edinburgh, Scotland, 2022.
Pate, K.; Marschand, J.R.; Breidi, F.; Salem, T.; Lumkes, J. Design and Sensitivity Analysis of Mechanically Actuated Digital Radial Piston Pumps. Processes 2024, 12, 504. https://doi.org/10.3390/pr12030504.
U.S. Department of Energy (13 November 2024). Adjustable Speed DrivePart-Load Efficiency: Energy Tips, Motor System Sheet #11. Publication date November 2012. https://www.energy.gov/eere/amo/articles/adjustable-speed-drive-part-load-efficiency.
Dumnov, D. and Caldwell, N. A cylinder enabling algorithm for reduction in low frequency pulsation from Digital Displacement pumps. Proceedings of the ASME/Bath 2022 Symposium on Fluid Power and Motion Control, FPMC2022.
Szczepaniak, C. and Legarde, J. Hydraulic circuit arrangement and control system for ganged electronically-commutated pumps. PCT patent application WO2022/226026A1, 20 April 2022.
Wiens, T.; Schmidt, M.; Williamson, C. Design of Digital Displacement Pump Systems with Multiple Pumps. Proceedings of the ASME/Bath 2024 Symposium on Fluid Power and Motion Control, FPMC2024.
Pascale, J.; Williamson, C.; Hennen, J.; Rindahl, P. Centralized Pressure Control and Displacement Quantization with Digital Displacement Pumps. Proceedings of the 2024 International Maha Fluid Power Conference. West Lafayette, IN, USA.
