Project 1J.1: Hydraulic Transmissions for Wind Energy

Transcription

1 Georgia Institute of Technology Milwaukee School of Engineering North Carolina A&T State University Purdue University University of Illinois, Urbana-Champaign University of Minnesota Vanderbilt University Project 1J.1: Hydraulic Transmissions for Wind Energy Researchers: Biswaranjan Mohanty, Feng Wang, Brad Bohlmann, Mike Gust PI: Professor Kim A. Stelson Center for Compact and Efficient Fluid Power Department of Mechanical Engineering University of Minnesota FPIRC, Chicago, October 14-16, 2015

2 Outline 1. Introduction 2. Research topics Hydrostatic turbine control Short-term energy storage Hydro-mechanical transmission 3. Power regenerative wind turbine test platform 4. Conclusions 2

3 Introduction Fastest growing clean and green energy sources 370 GW by 2014, 5% of the global electricity demand Denmark has goal of 50% wind by GW till June 2015, 5.13% of the U.S. electricity demand DOE set goal of 20% of U.S. energy from wind by

4 Turbine Components Two or three stages of planetary or parallel shaft gear train Three actuators: Yaw motor, Pitch motor & Generator Synchronous or asynchronous generator 4

5 Components reliability WindStats Data - 5,000 turbines from Denmark, 24,000 from Germany & 1,200 from Sweden Electrical system has highest failure rate Gear Box has longest downtime per failure Drive train repairs are more expensive due to the crane costs. 5

6 Potential of HST wind turbine Generator Power converter Grid Motor Generator Grid Pump Rotor fixed ratio gearbox Conventional gearbox turbine Rotor Hydrostatic transmission Hydrostatic wind turbine Performance Objective Maximize captured power Minimize loads Reduce downtime Reduce maintenance cost Hydrostatic transmission (HST): Simple system structure Continuous variable transmission ratio No need of power converter All power transmitted through a fluid link; hence less stiff Improves reliability and reduce cost 6

7 HST wind turbines 1. ChapDrive (Norway) 2. Windera Power System (Florida) 3. WindSmart (Canada) 4. Mitsubishi Heavy Industry Aachen University IFAS 1 MW HST wind power test stand Mitsubishi 7MW Sea Angel offshore turbine Core technology: Digital displacement technology by Artemis 93.5% peak efficiency from shaft-to-shaft, and also very efficient in part load too 7

8 Midsize HST turbine in CCEFP CCEFP target: midsize wind (100 kw-1 MW): Community wind - cost-effective way for farms, communities or factories Relatively easy permitting process Few midsize turbines in the market today Commercially available hydrostatic units Mid-size turbines can be designed as locally distributed type, eliminating the costly electric power transmission and improving energy use efficiency. Community wind 8

9 Turbine Control Turbine power Rated power Cut-in speed P w = 1 2 ρau3 Rated speed Region 1 Region 2 Region 3 Four control regions: Region 1: Standby mode Region 2: Control to maximize power Region 3: Control to rated power Region 4: Turbine shut down Cut-out speed Wind speed Region 4 Rotor power coefficient (Cp) is the fraction of wind power captured by the rotor: C P = P r = C P P (λ, β) w Rotor tip speed ratio: λ = ω rr u According to Betz Law, the maximum energy that can be captured by the rotor is 59.3% of the kinetic energy of the wind * Johnson, K. E., Pao, L. Y., Balas, M. J., Fingersh, L. J. Control of variable-speed wind turbines: standard and adaptive techniques for maximizing energy capture. IEEE Control Systems Magazine, Vol. 26(3), pp.70 81,

10 Region 2 Control (Existing) Objective: Maximize power captured Strategy: Constant pitch angle β and use τ g to operate turbine at optimum point Torque control law - control rotor reaction torque: τ g = τ c = Kω r 2 where the gain K is given by blade parameters. K = 1 2 ρar3 C pmax λ 3 Dynamics of the rotor ω r = 1 2J ρar3 ω r 2 ( C p λ 3 C pmax λ 3 ) u The beauty of the kω 2 law: bring the turbine to optimal point only with rotor speed and it does not require wind speed information. Rotor power coefficient C p C p max Acceleration C C p pmax 3 3 * Optimum point * Tip speed ratio C C p pmax 3 3 * Deceleration C C p pmax 3 3 * 14 10

11 HST turbine control in region 2 Rotor Hydrostatic transmission Kω 2 law Pressure sensor torque cmd Torque/ pressure conversion Generator pressure - cmd + HST turbine control scheme in region 2 motor disp. cmd PI controller Rotor reaction torque generated by the pump The relationship between the pump torque command and the line pressure command: p c p c D where η p is the pump mechanical efficiency. To give accurate control, the pump mechanical efficiency is estimated by previewing the pump efficiency map from the historical rotor speed and line pressure data. p Control strategy 1. Use rotor speed to generate rotor reaction torque (pump torque) command (kω 2 law) 2. Convert pump torque command to line pressure command 3. Track the line pressure by adjusting motor displacement through PI controller F. Wang and K. A. Stelson, Model predictive control for a mid-sized hydrostatic wind turbine, 13th Scandinavian International Conference on Fluid Power, SICFP2013, June 3-5, 2013, Linköping, Sweden,

12 Dynamic simulation model Hydrostatic wind turbine Main features of the simulation model: 1. Physical equation based components model; 2. Use bond graph method to determine the causality; 3. Use FAST code to generate rotor efficiency map; 4. Use pump/motor efficiency map to determine the HST losses; 5. Use distributed line model to simulate line dynamics and losses. 6. Take the charge pump power into consideration. total motor displacement fraction pitch angle Controller Wind profile rotor speed pump output flow motor inlet pressure motor torque Aerodynamic rotor Generator Radial piston pump High pressure pipeline Bent/axial piston motor pump torque motor input flow pump outlet pressure motor speed pump input flow motor outlet pressure motor output flow pump inlet pressure Low pressure pipeline Charge pump charge flow Valve manifold total input flow to low pressure line 12

13 Short-term energy storage To increase the energy capture of an HST wind turbine, a short-term energy storage system using a hydraulic accumulator is proposed. Turbine power Rated power Store P wind = 1 2 ρau3 Energy storage regime Release Wind turbulence: Gaussian distribution - mean wind speed Cut-in speed Rated speed Cut-out speed Region 1 Region 2 Region 3 Wind speed Captures excess energy when the wind speed is above rated (region 3) Release stored energy when the wind speed is below rated (region 2). 10 minutes turbulent wind profile * R. Dutta, F. Wang, B. Bohlmann and K. A. Stelson, Analysis of short-term energy storage for mid-size hydrostatic wind turbine, in Proc. ASME Dynamic Systems and Control Conference, Fort Lauderdale, FL, USA, 2012, selected as top 20 outstanding finalist papers. 13

14 % increase Short-term energy storage Rotor o 4.5% 4.0% 3.5% D p P o P Fixed pump Displacement control M1 M2 Energy storage configuration Accumulator Generator M1 Variable motor M2 Variable pump/motor Generator power with and without storage Sensitivity study: accumulator size on annual energy production (AEP) in a 50 kw turbine: 3.0% 2.5% 2.0% Accumulator Volume (liter) % increase in AEP 40 liter accumulator increases AEP by 3.4% 60 liter accumulator increases AEP by 4.1% A cost analysis is required to determine whether the AEP increase will offset the cost increase of implementing the system. * R. Dutta, F. Wang*, B. Bohlmann, K. Stelson, Analysis of short-term energy storage for mid-size hydrostatic wind turbine, ASME Transaction, Journal of Dynamic Systems, Measurement, and Control, 136(1),

15 Hydro-mechanical wind turbine A hydro-mechanical transmission combines the advantages of high efficiency of a gearbox and variable function of an HST. HMT vs HST (real-world components data) 1 v Rotor T r r R1 C1 S1 Mechanical power T d p Q T p D p p D m x p T Hydro-mechanical transmission Hydraulic power T m m R2 C2 S2 T g g Hydro-mechanical wind turbine (PGS+HST) R- ring gear C- carrier S- sun gear Generator Drivetrain efficiency Generator power (W) Simulated (HMT) Simulated (HST) Wind speed (m/s) x Simulated (HMT) Simulated (HST) Wind speed (m/s) * F. Wang, B. Trietch and K. A. Stelson, Mid-sized wind turbine with hydro-mechanical transmission demonstrates improved energy production, Proc. 8th International Conference on Fluid Power Transmission and Control (ICFP 2013), Hangzhou, China,

16 A. Power Regenerative Test Platform 105 kw 160 kw Virtual rotor Turbine output Virtual wind simulated by hydrostatic drive Real HST under test M Hydrostatic Transmission (HST) To Investigate the performance of hydrostatic transmission To test the advanced control algorithm 1. Capable of simulating a turbine output power of 105 kw VFD Variable Frequency 55 kw Drive Hydrostatic Drive (HSD) 2. Small electric motor (55kW) to compensate for losses in the components (assuming overall efficiencies of the pump and motor are 90% each) 16

17 A. Power Regenerative Test Platform Virtual rotor 2512 cc Hagglunds motors (act as pump) Turbine output 2512 cc Hagglunds motors 135 cc Linde variable motor Electric power input 180 cc Bosch variable pump 17

18 A. Power Regenerative Test Platform (Status) Charge Circuit(HST) VFD Motor(HST) Electric Motor Torque Sensor Pump(HSD) Cooler Pump(HST) Rotor Motor(HSD) 18

19 A. Wind turbine rotor simulation Aerodynamic torque is a function of pitch angle, rotor speed and wind speed To simulate real dynamics of the rotor of a turbine, the effect of the large blade inertia will be virtually simulated and the modified torque is applied on the rotor of the test platform τ d = τ r (J r J s ) ω r Design a controller to track desired torque using HSD circuit To generate aero dynamic torque for 105 kw turbine by modifying the blade dynamics of the FAST code 19

20 Conclusions The proposed HST turbine control strategy based on torque control law is applicable to the real world HST turbine. Short-term energy storage with hydraulic accumulator can improve the turbine energy production. A cost analysis is required to determine whether the energy increase will offset the cost increase of implementing such system. A hydro-mechanical transmission combines the advantages of high efficiency of a gearbox and variable function of an HST, resulting a high turbine energy production. The cost and reliability analysis is still required. The power regeneration wind turbine test platform enables simulating the real word HST turbine behaviors in the lab, providing a powerful tool to investigate research topics. New improvements could come from advanced turbine control strategies, more efficient hydraulic transmissions and new hydraulic fluids. 20

21 Kim A. Stelson University of Minnesota Mike Gust University of Minnesota Brad Bohlmann University of Minnesota Thank you! Feng Wang University of Minnesota Biswaranjan Mohanty University of Minnesota Ching-Sung Wang National Taiwan University 21