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On the consequences of fixed-force strategies on the efficiency of hydrostatic transmissions

Date: October 11, 2013 at 12:12 GMT

Abstract: This paper focuses on wave energy converters with hydrostatic transmissions, which employ either fixed-force damping or velocity-proportional damping control strategies. Both strategies affect design and complexity of the hydraulic setup and its control algorithm significantly. The power capture of absorbers and the total efficiency of the hydrostatic transmission are strongly influenced by this issue as well.

An analysis of both strategies regarding their impact on the fluid power system, its structure and efficiency is given. To compare the performance of both strategies, a simulation model is set up in Matlab/Simulink. For different sea states optimal damping coefficients for both strategies are derived in order to achieve maximum power capture.

The performance of each strategy with optimal damping coefficients is accounted for by an efficiency analysis of the adapted hydrostatic transmission within DSHplus. Employing a fixed-force strategy instead of a velocity-proportional damping strategy results in an efficiency drop of power capture. This efficiency-gap needs to be compensated by the implemented hydrostatic transmission to make fixed-force strategies e.g. in manifolded systems more applicable concerning economic aspects. 

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