Conceptualization and Multi-Objective Optimization of the Electric System of an Airborne Wind Turbine

Transcription

1 1/81 1/82 Conceptualization and Multi-Objective Optimization of the Electric System of an Airborne Wind Turbine J. W. Kolar et al. Swiss Federal Institute of Technology (ETH) Zurich Power Electronic Systems Laboratory

2 2/81 2/82 Pareto-Optimal Design of Airborne Wind Turbine Power Electronics J. W. Kolar, T. Friedli, F. Krismer, A. Looser, M. Schweizer, P. Steimer, J. Bevirt Swiss Federal Institute of Technology (ETH) Zurich Power Electronic Systems Laboratory

3 3/81 3/82 Basics Electronic Power Processing Power Electronics Performance Trends Design Process Multi-Objective Optimization

4 4/81 4/82 Basic Electronic Power Processing System - Electronic Switches / Power Semiconductors - Filter Circuits / Inductors, Capacitors - Heat Management / Heatsink - Sensor Circuits - Digital Signal Processing

5 5/81 5/82 Basic Electronic Power Processing System - Highest Efficiency - Highest Dynamics - Highest Compactness - Highest Compatibility - Highest Reliability Voltage Frequency Power Semiconductors Filter Circuits Interconnections Voltage Frequency EMC EMC Sensors Control Communication

6 6/81 6/82 Basic Electronic Power Processing System - Highest Efficiency - Highest Dynamics - Highest Compactness - Highest Compatibility - Highest Reliability Example of a Three-Phase AC/AC Matrix Converter

7 7/81 7/82 Three-Phase AC/AC Matrix Converter Prototype Output connectors Control boards Input filter Fans Heatsink 2.9 = ~ kw/dm 2.9 kw/dm 48 W/in 3 3 Input RMS voltage 400V Efficiency 95.5% Output Power Rectifier Switching Frequency Inverter Switching Frequency 6.8 kva 12.5 khz 25 khz

8 8/81 8/82 Power Electronics Performance Trends Performance Indices Power Density [kw/dm 3 ] Power per Unit Weight [kw/kg] Relative Costs [kw/$] Relative Losses [%] Failure Rate [h -1 ] Understand the Mutual Coupling of Performance Indices

9 9/81 9/82 Abstraction of Power Converter Design Process Performance Space Design Space Mapping of Design Space into System Performance Space

10 10/81 10/82 Mathematical Modeling of Converter Design Multi-Objective Optimization

11 11/81 11/82 Multi-Objective Design Optimization/ PARETO-Front Sensitivity to Technology Advancements Trade-off Analysis

12 12/81 12/82 Example Efficiency / Volume Trade-off of Inductors Scaling of Core Losses Operating Conditions and Parameters L, fp, I LI 2 P ( ) Core fp V 1 A PCore ( ) l 2 l l Scaling of Winding Losses PWdg I R I 1 P Wdg l l 2 2 Wdg A Wdg

13 13/81 13/82 Converter Performance Evaluation Based on η-ρ-σ-pareto Surface σ: kw/$

14 14/81 14/82 Converter Performance Evaluation Based on η-ρ-σ-pareto Surface Technology Node

15 15/81 15/82 Out-of-the-Box Wind Turbine Concepts Power Kite & Ground-Based EE-Generation Power Kite & On-Board EE-Generation

16 16/81 16/82 Conventional 100kW Wind Turbine Characteristics - Tower 35m/18 tons - Rotor 21m / 2.3tons - Nacelle 4.4 tons Large Fraction of Mechanically Supporting Parts / High Costs

17 17/81 17/82 Air Rotor Wind Generator Helium or Hydrogen Inflated Magnus Effect - Additional Lift

18 18/81 18/82 Revolutionize Wind Power Generation Using Kites / Tethered Airfoils [2] M. Loyd, 1980 Wing Tips / Highest Speed Regions are the Main Power Generating Parts of a Wind Turbine

19 19/81 19/82 Controlled Power Kites for Capturing Wind Power Replace Blades by Power Kites Minimum Base Foundation etc. Required Operative Height Adjustable to Wind Conditions M. Loyd, 1980 Wing Tips / Highest Speed Regions are the Main Power Generating Parts of a Wind Turbine

20 20/81 20/82 Controlled Power Kites for Capturing Wind Power Wind at High Altitudes is Faster and More Consistent Operate Kites at High Altitudes or Even in the Jet Stream Source: kw/m 2 120m 700m

21 21/81 21/82 Controlled Power Kites for Capturing Wind Power Wind at High Altitudes is Faster and More Consistent Operate Kites at High Altitudes or Even in the Jet Stream

22 22/81 22/82 Pumping Power Kites Source: M. Diehl / K.U. Leuven Ground-Based EE-Generation

23 23/81 23/82 Basics of Power Kites Kite s Aerodynamic Surface Converts Wind Energy into Kite Motion Source: M. Diehl / K.U. Leuven Generated Force Could be Converted into Useful Power by Pulling a Load / Driving Turbines via a Tether

24 24/81 24/82 Pumping Power Kites Maximum Power M. Loyd, 1980 Source: M. Diehl / K.U. Leuven

25 25/81 25/82 Pumping Power Kites for Capturing High Altitude Wind Power Lower Electricity Production Costs than Current Wind Farms Generate up to 250 MW/km 2, vs. the Current 3 MW/km 2 Research at the

26 26/81 26/82 Pumping Power Kites for Capturing High Altitude Wind Power Lower Electricity Production Costs than Current Wind Farms Generate up to 250 MW/km 2, vs. the Current 3 MW/km 2 Research at the Carousel Configuration

27 27/81 27/82 Airborne Wind Turbine Source: M. Diehl / K.U. Leuven On-Board EE-Generation

28 28/81 28/82 Alternative Concept Airborne Wind Turbine Power Kite Equipped with Turbine / Generator / Power Electronics Power Transmitted to Ground Electrically M. Loyd, 1980

29 29/81 29/82 Alternative Concept Airborne Wind Turbine Power Kite Equipped with Turbine / Generator / Power Electronics Power Transmitted to Ground Electrically M. Loyd, 1980 Source:

30 30/81 30/82 Basic Physics of Wind Turbines Maximum Achievable acc. to Lanchester / Betz High Crosswind Kite Speed Very Small Turbine Area

31 31/81 31/82 Comparison of Conventional / Airborne Wind Turbine Numerical Values Given for 100kW Rated Power

32 32/81 32/82 SkyWindPower AWT Concept Tethered Rotorcraft Quadrupole Rotor Arrangement Inclined Rotors Generate Lift & Force Rotation / Electricity Generation Artist s Drawing of 240kW / 10m Rotor System Named as One of the 50 Top Inventions in 2008 by TIME Magazine

33 33/81 33/82 AWT Concept Reinforced Tether Transfers MV-Electricity to Ground Composite Tether also Provides Mechanical Connection to Ground

34 AWT Concept 34/81 34/82

35 Demonstration Plan 35/81 35/82

36 Flight Modes / Parked 36/81 36/82

37 37/81 37/82 Future Prospects Source: M. Diehl / K.U. Leuven Example for Thinking Out-of-the-Box!

38 38/81 38/82 Future Prospects Source: M. Diehl / K.U. Leuven Example for Thinking Out-of-the-Box!

39 39/81 39/82 Technical Feasibility of AWT Electrical System AWT Electrical System Structure Multi-Objective Optimization (Weight vs. Efficiency) Controls Aspects

40 40/81 40/82 AWT Basic Electrical System Structure Rated Power 100kW Operating Height m Ambient Temp. 40 C Power Flow Motor & Generator El. System Target Weight 100kg Efficiency (incl. Tether) 90% Turbine /Motor 2000/3000rpm

41 41/81 41/82 Design of Electrical Power System Clarify Practical Feasibility of AWT Concept Clarify Weight/Efficiency Trade-off / Multi-Objective Optimization / PARETO-Front

42 42/81 42/82 Tether Design DC Voltage Level η-γ-pareto Front

43 43/81 43/82 Tether DC Transmission Voltage Level P th,1 = 100kW / l th = 1000m Strain Relief Core Kevlar (F th = 70kN, d=5mm) Cu or Al Helical Conductors - ½ U th Isolated Outer Protection Jacket (3mm)

44 44/81 44/82 Tether η-γ-pareto Front Tether Voltage V th,1 = 8kV Total Weight of Tether: 320kg

45 45/81 45/82 System Overview

46 46/81 46/82 Possible AWT Electrical System Structures Low-Voltage or Medium-Voltage Generators / Power Electronics Decision Based on Weight/Efficiency/Complexity

47 47/81 47/82 Generator / Motor Design Dimensions Number of Pole Pairs η-γ-pareto Front

48 48/81 48/82 Generator / Motor η-γ-pareto Front Medium Voltage vs. Low Voltage Machine V th,1 = 8kV - PMSM Radial Flux Internal Rotor - Slotted Stator / Concentrated Windings Air Cooling - Analytical EM and Thermal Models for Weight / Efficiency Optimization - P = 16kW / 2000rpm Thermal Model LV Machine HV Machine LVG: Diameter 17cm (excl. Cooling Fins) / Width 6.0cm / p = 20 / η = 95.4% / Weight 5.1kg

49 49/81 49/82 CAD Drawing of LV and MV Machine Fixed Parameters and Degrees of Freedom

50 50/81 50/82 Generator / Motor η-γ-pareto Front Selected Design η = 95.4% γ = 3.1 kw/kg Medium Voltage Machine Not Considered Further

51 51/81 51/82 Comparison to Commercial Motors Motors Employed for Electric Propulsion of Glider Airplane Power Speed Cooling P = 10kW n = 2200rpm v L = 25m/s Diameter 22cm Width 8.6cm Weight 12kg Pole Pairs 10 Efficiency 91%

52 52/81 52/82 System Overview

53 53/81 53/82 Rectifier / Inverter Design Chip Area Heatsink Volume η-γ-pareto Front

54 54/81 54/82 Rectifier / Inverter Design 2-Level or 3-Level Bidirectional Voltage Source Rectifier - S = 19.3kVA - V DC = 750V - f S,min = 24kHz - T J = 125 C - Foil Capacitor DC Link 1200V T&FS Si IGBT4s / 1200V SiC Diodes 600V T&FS Si IGBT3s / 600V Si EmCon3 Diodes Maximization of Heatsink Thermal Conductance / Weight (Volume) - Max. CSPI

55 p F [N/m 2 ] p F [N/m 2 ] 55/81 55/82 Heatsink Optimization Maximize Thermal Conductance / Weight (Volume) P V d c d c n = 5 P V n = 5 t t p F,MAX p F,MAX k. p F k. p F operating point operating point v Air 5m/s s b b/n s b b/n p CHANNEL p CHANNEL V F [m 3 /s] V F [m 3 /s] V F,MAX V F,MAX Highest Performance Fan Fin Thickness / Channel Width Optimization

56 p F [N/m 2 ] 56/81 56/82 Heatsink Optimization Maximize Thermal Conductance / Weight (Volume) P V /n P V d c/2 d R th,fin c R th,d R th,a R th,fin n = 5 t p F,MAX k. p F operating point R th,a R th,a t T CHANNEL p CHANNEL s s b b/n V F [m 3 /s] V F,MAX Highest Performance Fan Fin Thickness / Channel Width Optimization

57 R th [K/W] 57/81 57/82 Heatsink Optimization Optimum L x b x c= 80x40x40mm Al with th = 210W/Km 0 n=34 n = [6, 10, 14,..., 42, 46, 50] n=50 X X n=6 n= k = s/(b/n) sub-optimum: n=16 / k=0.60 s=1.5mm / t=1.0mm R th,sub =0.30 optimum: n=26 / k=0.65 s=1.0mm / t=0.54mm R th,sub =0.26 Highest Performance Fan Fin Thickness / Channel Width Optimization

58 58/81 58/82 Rectifier / Inverter η-γ-pareto Front - Switching Frequency Range khz - Heatsink Temperature Range C (T amb = 40 C) Selected Design η = 98.5% γ = 19 kw/kg 3-Level Topology Does Not Show a Benefit

59 59/81 59/82 System Overview

60 60/81 60/82 8kV DC /750V DC DAB Converter Design Switches / Topology Transformer η-γ-pareto Front

61 61/81 61/82 DC/DC Converter Topology Bidirectional Energy Transfer - Dual Active Bridge - Weight 25kg - f S = kHz f S,m = 100kHz - Phase-Shift Control (φ = π/4) 0.8 kv 8 kv Implementation of Electronic Switches - SiC

62 62/81 62/82 DC/DC Converter Topology Bidirectional Energy Transfer - Dual Active Bridge - Weight 25kg - f S = kHz f S,m = 100kHz - Phase-Shift Control (φ = π/4) 0.8 kv 8 kv Implementation of Electronic Switches - SiC 10kV Si/SiC SuperCascode Switch

63 63/81 63/82 Si/SiC Super Cascode Switch C / R HV-Switch Controllable via Si-MOSFET * 1 LV Si MOSFET * 6 HV 1.7kV SiC JFETs * Avalanche Rated Diodes Ultra Fast Switching Low Losses Parasitics * Passive Elements for Simultaneous Turn-on and Turn-off * Stabilization of Turn-off State Voltage Distribution Synchronous Switching MOSFET JFETs

64 64/81 64/82 Si/SiC Super Cascode Switch C / R HV-Switch Controllable via Si-MOSFET * 1 LV Si MOSFET * 6 HV 1.7kV SiC JFETs * Avalanche Rated Diodes Ultra Fast Switching Low Losses Parasitics * Passive Elements for Simultaneous Turn-on and Turn-off * Stabilization of Turn-off State Voltage Distribution Synchronous Switching MOSFET JFETs

65 65/81 65/82 Selected Multi-Cell Converter Topology MV-Side Series-Connection / LV-Side Parallel-Connection P i = 6.25kW V th,1,i = 2kV Winding Arrangement & Efficiency / Weight Optimization of Transformer

66 66/81 66/82 Transformer Design MV-Winding Arranged Around Inductor Cores Cooling Provided by Heatpipes Stacked Cores - Scalable Arrangement Optimization - Weight / Efficiency Trade-off

67 67/81 67/82 Transformer Optimization Degrees of Freedom / Parameter Ranges

68 68/81 68/82 Transformer η-γ-pareto Front Selected Design η = 97% γ = 4.5 kw/kg Transformer Volt-Second Balancing - Series Capacitor or Magnetic Ear Control

69 69/81 69/82 Transformer Volt-Second Balancing Magnetic Ear Magnetic Ear Magnetized with 50% Duty Cycle Rectangular Voltage Winding Measured Aux. Current i aux / Voltage v m Indicates Flux Level Enables Closed-Loop Flux Control N27 E55 Ferrite

70 70/81 70/82 System Overview

71 71/81 71/82 Overall System Consideration Total Weight Overall Efficiency η-γ-pareto Front

72 72/81 72/82 Determination of Overall System Performance Consideration of the η-γ-characteristics of the Partial Systems Pout Overall η-γ-characteristic m Efficiencies of the Partial Systems Need to be Taken into Account P D /P R = Overrating Ratio (8x16kW/100kW)

73 73/81 73/82 Overall System Performance Final Step: System Control Consideration

74 74/81 74/82 Electric System Control Stability Reference Response Disturbance Response

75 75/81 75/82 System Control Control of Flight Trajectory / Max. Energy Generation Generator (Motor) Speed / Torque Control etc. Control of DC Voltage Levels is Mandatory! Simplified Control-Oriented Block Diagram of the Electric System

76 76/81 76/82 Control Block Diagram Ground Station Controls the Tether Voltage Control Objectives: LV DC Bus V; MV (Tether) < 8kV Only Tether Voltage at Ground Station is Measured (I Th Feedforward) Motor AND Generator Operation Must be Considered

77 77/81 77/82 Tether Voltage Control Plant Motor Operation (100kW)

78 78/81 78/82 Voltage Control Reference Step Response Overshoot Could be Avoided with Reference Form Filter

79 79/81 79/82 Voltage Control Disturbance Response Motor Operation 100kW 0 Gen. Operation 100kW 0

80 80/81 80/82 Conclusions AWTs are Basically Technically Feasible AWTs Realization Combines Numerous Challenges - Aircraft Design - MVDC Transmission - MV/HF Power Electronics - etc. AWTs are a Highly Interesting Example for η-γ Trade-off Studies AWTs are Examples for Smart Pico Grids or MEA Power System Analysis AWTs is a Clear Example of Thinking Out-of-the-Box!

81 81/81 81/82

82 Questions? 82/81 82/82