Dynamic Transmission Response of a Hydrostatic Transmission Results measured on a Test Bench J. Schmitz, N. Diepeveen, N. Vatheuer

2 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Outline  Introduction  System design & Control strategy  Efficiency measurements  Dynamic measurements  Conclusion / Outlook

3 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch  Drive train is a key component in a wind turbine  Market is dominated by two concepts  Why developing a hydrostatic system? - Hydrostatic transmission is continuously variable - No frequency converter required - Compactness and good damping Introduction Radial piston pump Axial piston motor Efficient, robust and cost effective drive train

4 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Outline  Introduction  System design & Control strategy  Efficiency measurements  Dynamic measurements  Conclusion / Outlook

5 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Optimized configuration for 1 MW 321  Two hydraulic circuits  Three different modes of operation  Components - 2 pumps (70 & 280 kNm) - 3 variable displacement motors - 1 constant motor - 2 generators  Single motors can be switched off  Big pump and one generator can be switched off

6 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Integration into the test bench  Challenges - High torque at low speed - Dynamic loads - Limited electrical power  Test bench layout - Hydrostatic power feed-back - Generators replaced by electrical motors and axial piston pumps - Turbine simulated by radial piston motor - Controlled by variable displacement pumps

7 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Test bench driveHydrostatic transmission Test bench in the IFAS laboratory

8 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Optimal points of operation  Captured power can be optimized by adjusting the rotation speed  Optimal point of operation does not have the maximum torque Power Torque For a given wind speed

9 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Torque balance on the turbine‘s inertia Torque from windBraking torque transmission  Braking torque is independent from wind speed

10 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Simulation of wind turbine environment Real-Time Simulation Test bench  Inertia of turbine is modelled in real-time simulation  Test bench drive transfers rotation speed to the test bench  Measured braking torque is applied on simulated turbine

11 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Outline  Introduction  System design & Control strategy  Efficiency measurements  Dynamic measurements  Conclusion / Outlook

12 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Measurement result of overall efficiency   Procedure of measurement - Transmission controller set rotation speed - Torque applied dependent on rotation speed  Results for different configurations

13 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Outline  Introduction  System design & Control strategy  Efficiency measurements  Dynamic measurements  Conclusion / Outlook

14 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Analysed load cases  Two different load cases - Torque step - Gust of wind (Mexican hat)  Two different control strategies - Fixed displacement of motors - Torque control depending on rotation speed  Torque files generated with industry standard software “Bladed” by TU Delft

15 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch  Control enables the turbine to accelerate  Torque increases with rotation speed Result of measurement with torque step Constant motor displacementTorque controlled transmission  Torque increases rapidly  Rotation speed slightly increases due to increasing leakage

16 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Result of measurement result with gust of wind Constant motor displacementTorque controlled transmission  Torque peak is smoothened  Inertia of turbine acts as flywheel  Torque curve follows torque from wind with short delay  Overshooting braking torque

17 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Outline  Introduction  System design & Control strategy  Efficiency measurements  Dynamic measurements  Conclusion / Outlook

18 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Conclusion Only pilot plant can convince developers and verify cost of energy  Hydrostatic drive train can be adapted to WEP power-curve  Optimal efficiency even at partial load  Variable transmission ratio  No frequency converter required  Torque control based strategy provides compromise of - Adjusting rotation speed - Robust and reliable operation

19 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Transmission on test bench Pilot plant Outlook VDMA Research project funded by VDMA, Fluid Power Research Fund Research Project  Self-sufficient operation on test bench - Installation of required periphery - Development of controller  Form consortium to realize pilot plant ( ~ 900 kW)  Hydraulic companies  Wind turbine manufacturer

Thank you for your attention. Questions, Suggestions? J. Schmitz, N. Diepeveen, N. Vatheuer

21 of 19Dynamic Response of a Hydrostatic Transmission J. Schmitz, N. Diepeveen, N. Vatheuer Englisch Outlook: proposal for multi-megawatt turbine  Doubling the power  four times more pump displacement  Hydraulic pumps are not available yet  Approach: Upstream mechanical transmission Challenge with multi-megawatt transmissions  Mechanical ratio: 4.5  Four independent hydraulic modules  1.25 MW per module 5-MW-Concept Combining the benefits of mechanical and hydraulic drive trains