Energy storage system design and modeling considerations

Transcription

1 Energy storage system design and modeling considerations Dong Wang, Kaiyuan Lu Dept. of Energy Technology, Aalborg University

2 Content Purpose and role in the whole project Hydraulic energy storage design and optimization System topology Verification Case study WaveStar Optimization

3 Purpose and role in the whole project

4 It behaviors likes a filter (buffer) smoothing the energy generated by irregular energy sources (e.g. waves). The output power to the grid is more stable, predicable, and controllable. Secure the energy supply. Purpose Advantages offered by an energy storage system Extra economic benefits like moving off peak power to on peak periods with higher electricity prices. (smart grid)

5 In this project, we need to Role in the project Understand the performances of energy storage systems Understand their interactions with the rest of the Wave Energy Converter (WEC). require a proper model that can be inserted in the complete WEC mode

6 Hydraulic energy storage design and optimization

7 Basic configuration hydraulic accumulator hydraulic pump/motor Reservoir connecting lines controller Hydraulic input / output System topology Accumulator Gas Oil Controller Reservoir Pump /Mot or Shaft Connecting lines Control signal Mechanical input / output Hydraulic energy storage system

8 System modeling Mathematical model is established in Simulink A regeneration system is used for verification [A. Pourmovahed, etc. all, 1992], 8Ref [1]

9 System modeling Mathematical model is established in Simulink A regeneration system is used for verification Hydraulic Energy Regeneration System Acc_v Acc_v Ppm_Qa Leav e Acc Ppm_alpha Scope Ppm_alpha Scope Ppm_Qa Acc_p FW_N Accumulator Control FW_N Ppm_Qa FW_N Ppm_alpha Scope FW_N Scope Acc_p Acc_p Ppm_Ta Ppm_Qa CL_pl CL_pl Eff_rt Ppm_Ta Res_p Scope Eff_rt Pump/Motor Flywheel Connecting Lines Scope Ppm_Ta Ppm_Qa Res_p Reservoir [A. Pourmovahed, etc. all, 1992], 9Ref [1]

10 System modeling Model of hydraulic accumulator

11 Flywheel Speed (r/min) Verification Simulation and reference results comparison P/M Angle = 20 Deg, Cold Oil Time (s) Gas Pressure (MPa) P/M Angle = 20 Deg, Cold Oil Time (s) Round-trip Efficiency, % P/M Angle = 20 Deg, Cold Oil Cycle Number, i [A. Pourmovahed, etc. all, 1992], 11Ref [2]

12 Case study - WaveStar System topology The excessive wave energy enters the energy overflow system, where energy storage system is installed Hydraulic pump/motor works at motor mode only Output power to generator is controlled by adjusting the swivel angle [R. H. Hansen, etc. all, 2011], Ref 12[3]

13 System model Wave_no Wave Type 1, 2 or 3 Ppm_Qa Leav e Acc CC_Qa Acc_p Wav_t Res_p Accumulator Case study - WaveStar Cyl_P CC_Qa CC_P Cylinder and Check Valve Acc_v Acc_p Scope CC_Qa Acc_v Gen_T Ppm_Qa Ppm_Qa CC_Qa Hydraulic Energy Storage System Control Connecting Lines Reservoir Ppm_alpha CL_pl Res_p Scope Ppm_alpha FW_N Ppm_alpha Acc_p CL_pl Res_p Pump/Motor Ppm_Qa Ppm_Ta Scope Ppm_Ta Scope Ppm_Qa Ppm_Ta Electric Generator Gen_Pin Cyl_P CC_P Gen_N Gen_T Gen_Pin Whl_Eff Sy s_ef f Efficiency Calculation Scope Gen_N Scope Gen_T Scope Eff_Sys

14 Work procedure 1. Too much input, relief valve open to limit the system pressure to max; swivel angle (capacity) is limited in order to limit the shaft power output; 2. No input, system pressure drops as stored energy is used; no pump capacity limitation; Case study - WaveStar Gas Volume [m 3 ] x Hydraulic Power [kw] FlowRate [m 3 /s] Pressure [MPa] Shaft Power [kw] Shaft Power and Hydraulic Input Power Time (s) Gas Volume, Flow Rate and Pressure x Time (s) Time (s) 1 3 Fraction of Maximum Unit Capacity Time (s)

15 Optimization Key parameters regarding system efficiency optimization System maximum allowable pressure How much energy can be stored in accumulator How fast hydraulic motor can convert energy Accumulator size How much energy can be stored Hydraulic motor displacement (power) How fast it can convert energy from hydraulic to mechanical

16 Optimization System maximum allowable pressure At sea state 3: At sea state 2: System Efficiency Wave 3, 40kW Generator, System Max. Pressure 35MPa Accumulator Maximum Hydraulic Motor Accumulator Maximum Hydraulic Motor Gas Volume [liter] 0 70 Displacement [cm 3 /rev] Gas Volume [liter] 0 70 Displacement [cm 3 /rev] System Efficiency Wave 2, 40kW Generator, System Max. Pressure 35MPa System Efficiency Wave 3, 40kW Generator, System Max. Pressure 45MPa Accumulator Maximum Hydraulic Motor Accumulator Maximum Hydraulic Motor Gas Volume [liter] 0 70 Displacement [cm 3 /rev] Gas Volume [liter] 0 70 Displacement [cm 3 /rev] System Efficiency Wave 2, 40kW Generator, System Max. Pressure 45MPa

17 Generator rated power At sea state 3: At sea state 2: 30kW is big enough At very small, drops due to waste of energy System Efficiency Wave 3, 30kW Generator, System Max. Pressure 35MPa Accumulator Maximum Hydraulic Motor Accumulator Maximum Hydraulic Motor Gas Volume [liter] 0 70 Displacement [cm 3 /rev] Gas Volume [liter] 0 70 Displacement [cm 3 /rev] Optimization System Efficiency Wave 2, 30kW Generator, System Max. Pressure 35MPa System Efficiency Wave 3, 40kW Generator, System Max. Pressure 35MPa Accumulator Maximum Hydraulic Motor Accumulator Maximum Hydraulic Motor Gas Volume [liter] 0 70 Displacement [cm 3 /rev] Gas Volume [liter] 0 70 Displacement [cm 3 /rev] System Efficiency Wave 2, 40kW Generator, System Max. Pressure 35MPa

18 Optimization Discussions Balance sea state 1, 2 and 3 to obtain the highest possible average system efficiency Relative low hydraulic motor capacity and high system pressure is preferred It can ensure that the hydraulic motor works with a relative high average efficiency and give much smooth output torque Balance the system max. allowable pressure and size to obtain optimal cost High requires high quality component, thus high cost High can reduce the requirement of accumulator size and hydraulic motor displacement, which may reduce cost High can give high system efficiency, which save money

19 Summary Summary The model can be used to analyse the performance of hydraulic energy storage system, and give reasonable accuracy Key parameters regarding system efficiency optimization are found and discussed A system efficiency around 85 percent seems to be an attainable theoretical value. In a real system, system efficiency of 80 percent may be practically expected

20 Reference 1. A. Pourmovahed, N. H. Beachley, F. J. Fronczak, Modeling of a Hydraulic Energy Regeneration System Part I: Analytical Treatment, Journal of Dynamic Systems, Measurement, and Control, vol. 114, pp , Mar A. Pourmovahed, N. H. Beachley, F. J. Fronczak, Modeling of a Hydraulic Energy Regeneration System Part II: Experimental Program, Journal of Dynamic Systems, Measurement, and Control, vol. 114, pp , Mar R. H. Hansen, T. O. Andersen, and H. C. Pedersen, Model Based Design of Efficient Power Take off Systems for Wave Energy Converters, in The 12th Scandinavian International Conference on Fluid Power, May 18 20, Tampere, Finland,

21 Funded by The International Research Alliance