ISOLATED MF DC-DC CONVERTER FOR TRACTION BATTERY APPLICATIONTiago Nabais, Bombardier Transportation, Switzerland
Miloš Stojadinović, Jürgen BielaLaboratory for High Power Electronic Systems, ETH Zürich
Agenda
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• Bombardier Transportation• Catenary free operation (CFO)• Energy solutions• MF DC/DC Building block• Transformer Modeling• Optimization and Design• System Control design• Simulation & measurement results• Standardization & modularity• Talent 3 BEMU DC/DC
BOMBARDIER TRANSPORTATION
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A global player with a European base
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Revenues 2017(1):$8.5 billion US
Employees(2):39,850
Global HeadquartersProduction Sites
Mobility solutions
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Vehicle speed
LocomotivesTRAXX
Monorails, people movers
MetrosMOVIA
Light rail vehiclesFLEXITY
Commute / regional trains
(Very) high-speed trains
Intercity trains
Vehi
cle
capa
city
INNOVIA monorailINNOVIA APM
AVENTRATALENT 3,
TWINDEXX, OMNEO,
BiLevel / Multilevel, AVENTRATALENT 3,
TWINDEXX, OMNEO
ZEFIRO
CATENARY FREE OPERATION (CFO)
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Benefits and Customer value
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“Beautiful place”
Spaceconstraints
Difficultcatenary setup
Safetyconcerns
Points of touristic interest Unobstructed urban skyline
Low bridges Obstructing road sign bridges Very narrow roads
Crossing intersections of wide roads Difficult access to power feeders
Rationale Examples Commercial Value Added
Touristic valueRaising urban quality & valueWinning arguments to obtain public approvals
Less costly civil worksFootprint width of 2 tracks reduces from 7.6 m to 7.05 m.No or simplified mesh wiring underneath tracks
CFO as cost efficient alternative
Risk of contacting wires (by overloaded trucks) Clearing the road in case of power outage Electromagnetic interference (e.g. near hospitals
affecting medical devices ) Fire dep’t: No obstacles for fire truck ladder use
Hazard and damage avoidance
Modes of Operation
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LRV
Mass Transit(Metros)
Main Line(Commuter,Regional, …)
Locomotives
Scheduled CatenaryFree Operation
Catenary free route sections (e.g. historic districts)
Static, dynamic and PRI-MOVE charging schemes
Network extensions covering remote stops via unelectrifiedroutes
Emission free one-seat ride
Last mile Diesel and battery to access sidings and unelectrified routes
Battery-only shunting
Rescue Cases(e.g. power outages)
Movement to next trams top or safe place for passengers to exit
Movement to next metro stop for passengers to exit
Movement to next station to clear the tracks and let passengers exit
Clear the tracks Assistance service to re-move
other locos & trains
Other Modes of Operation
Boosting: Accelerated starting w. limited power
EMI reduction with CFO Energy efficiency increase Increased network stability
Boosting: Energy efficiency increase Increased network stability Sleep mode while parking or
standing (See 1)
Sleep mode while parking or standing (See 1)
Catenary free route sections (e.g. historic districts)
Static, dynamic and PRI-MOVE charging schemes
Boosting: Energy efficiency increase Increased network stability
ENERGY SOLUTIONS
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State of the art
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Diesel
Fuel Cell
Battery
Supercaps
Characteristics
State of the art VS applications
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LRV
Mass Transit(Metros)
Main Line(Commuter,Regional, …)
Locomotives
Diesel
Fuel Cell
Battery
Supercaps
Characteristics
1500V-1800V 10’000kWh (1000litres) 600kW
100V-600V 530kWh (1000litres) 200-400kW
500V-900V 24.5kWh-75kWh 100-200kW
500V-900V 2kWh 600kW
Requirements
100kW 750V Line
200kW 750V Line
200kW 1500V-2000V
200kW 3kV Line
State of the art VS applications
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LRV
Mass Transit(Metros)
Main Line(Commuter,Regional, …)
Locomotives
Diesel
Fuel Cell
Battery
Supercaps
Characteristics
1500V-1800V 10’000kWh (1000litres) 600kW
100V-600V 530kWh (1000litres) 200-400kW
500V-900V 24.5kWh-75kWh 100-200kW
500V-900V 2kWh 600kW
Requirements
100kW 750V Line
200kW 750V Line
200kW 1500V-2000V
200kW 3kV Line
Standardization &Modularity
State of the art VS applications
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Scalable solution: 1 or more energy storage systems per MITRAC propulsion system Standardized hardware independent interfaces to MITRAC propulsion system Applicable for all vehicle families from LRV’s to locomotives ‘Plug and play’ solution – modular and scalable
TractionConverter
Motors
EnergyStorage 1
EnergyStorage 2
EnergyStorage n
Any viable technologies (supercaps, batteries, etc.) and chemistries. Mixed (= hybrid) solutions are possible.
The protection concept is specific to the energy storage units. High re-use on homologation and safety approvals
ENERGY STORAGE
Standardize power and communication protocol interfaces between traction converter and energy storage.
Standardized application interface towards traction converter Software as ‘ad-on package’ to minimize application specific
adaptations.
WELL DEFINED INTERFACES
MF DC/DC BUILDING BLOCK
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Project requirements
Battery Voltage Range 518..835V
Nominal DC Link Voltage 2800V
Regulated DC Link Voltage (peak) 3000V
Unregulated DC Link Voltage (peak) 4200V
System Power 183kW
System Power (peak) for 300s >234kW
Current per Battery (continuous) 220A
Current per Battery (peak) for 300s 280A
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Working Insulation Voltage 4.2kV
Impulse Withstand Voltage P-S 18kV
Efficiency > 95%
Ambient Temperature 75°C
Cooling Medium Temperature 60°C
Maximum Dimensions 750x360x200 mm
Maximum Weight 25 kg
Chosen topology and optimization procedure
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Modular Dual Active Bridge (DAB) converter Simplified flow chart of theoptimization procedure
• Pre-selected technologies– Transformer with integrated cooling
• Foil windings• Ferrite core• Water cooling
– Semiconductors• SiC MOSFETs
TRANSFORMER MODELING
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Transformer losses
• Winding losses– High frequency effects
• Skin effect losses• Proximity effect losses
– Optimum foil thickness• Analytical model available in literature1
• Core losses– Steinmetz equation
• Steinmetz parameters 𝑘𝑘,𝛼𝛼 and 𝛽𝛽– Extracted from data sheet– Valid only in a limited 𝐵𝐵-, 𝑓𝑓- and Temp. Range
• Can be used for sinusoidal flux waveforms• DC bias/offset is not considered
– Improved Generalized Steinmetz Equation (iGSE)• Can be used for arbitrary flux waveforms• Relaxation losses missing• DC bias/offset is not considered
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[1] W. G. Hurley et. al, Optimizing the AC Resistance ofMultilayer Transformer Windings with Arbitrary CurrentWaveforms, IEEE Trans. on Power Electronics, 2000.
Assumption:1D – H-field
Transformer leakage inductance calculation
• Winding height smaller than window height
𝐿𝐿𝜎𝜎 = 𝜇𝜇0𝑁𝑁𝑃𝑃2𝜋𝜋𝐷𝐷𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑤𝑤𝐿𝐿
ℎ𝑊𝑊𝑘𝑘𝜎𝜎
𝑤𝑤𝐿𝐿 =𝑑𝑑𝑃𝑃 + 𝑑𝑑𝑆𝑆
3 + 𝑑𝑑𝐿𝐿
𝐷𝐷𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 = 𝐷𝐷 + 𝑑𝑑𝑃𝑃 + 𝑑𝑑𝑆𝑆 + 𝑑𝑑𝐿𝐿 −𝑑𝑑𝑆𝑆 − 𝑑𝑑𝑃𝑃
2𝑑𝑑𝑃𝑃 + 𝑑𝑑𝑆𝑆 + 4𝑑𝑑𝐿𝐿𝑑𝑑𝑃𝑃 + 𝑑𝑑𝑆𝑆 + 3𝑑𝑑𝐿𝐿
𝐷𝐷 = 2𝑏𝑏𝑐𝑐 + 𝑑𝑑𝑃𝑃 𝑑𝑑𝑐𝑐 + 𝑑𝑑𝑃𝑃
𝜋𝜋
– Rogowski correction factor2
𝑘𝑘𝜎𝜎 ≈ 1 −𝑑𝑑𝑃𝑃 + 𝑑𝑑𝑆𝑆 + 𝑑𝑑𝐿𝐿
ℎ𝑊𝑊– Different primary and secondary winding heights
ℎ𝑊𝑊 = ℎ𝑐𝑐𝑐𝑐𝑃𝑃ℎ𝑐𝑐𝑐𝑐𝑆𝑆
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(width of the reducedleakage channel)
(equivalent inner diameterof the internal winding)
(mean diameter of thereduced leakage channel)
[2] V. V. Kantor, Methods of Calculating LeakageInductance of Transformer Windings, Elektrotehnika, 2009.
Transformer thermal modeling
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• Types of heat transfer– Conduction
• Usually independent of temperature• Important: Precise material thermal data• Difficulty: Interfaces between materials
– Convection• Conduction + fluid flow• Dependent on temperature• Abundance of analytical and empirical
formulas available in literature
– Radiation• Usually negligible compared to
conduction/convection• Difficult to model – nonlinear / line of sight
𝑅𝑅𝑡𝑡𝑡 =Δ𝑇𝑇𝑃𝑃 =
𝑙𝑙𝜆𝜆𝐴𝐴
𝑅𝑅𝑡𝑡𝑡 =Δ𝑇𝑇𝑃𝑃 =
𝑙𝑙ℎ𝐴𝐴
𝑃𝑃 = 𝜀𝜀𝐴𝐴𝜎𝜎 𝑇𝑇𝑏𝑏4 − 𝑇𝑇𝑚𝑚4
𝑞𝑞 =𝑃𝑃𝐴𝐴
Transformer thermal modeling
• Channel thermal model𝑅𝑅𝑡𝑡𝑡,𝑟𝑟 =
𝑎𝑎𝑤𝑤𝑙𝑙𝜆𝜆𝐻𝐻𝑆𝑆
𝑅𝑅𝑡𝑡𝑡,𝑑𝑑 =1
ℎ𝑙𝑙𝜋𝜋𝑑𝑑with
ℎ =𝑁𝑁𝑢𝑢𝜆𝜆𝑓𝑓𝑓𝑓𝑢𝑢𝑓𝑓𝑓𝑓
𝑑𝑑- heat transfer coefficient
𝑁𝑁𝑐𝑐 - Nusselt number𝜆𝜆𝐻𝐻𝑆𝑆 - thermal conductivity of heat sink material
𝑑𝑑 ≈ 2 ⁄𝐴𝐴 𝜋𝜋 𝑚𝑚 – channel hydraulic diameter of cross-sectional area 𝐴𝐴• Nusselt number is a function of
– Average ducted fluid velocity– Duct geometry– Fluid Prandtl number (𝑷𝑷𝒓𝒓)– Analytical models available in literature3
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[3] Y. S. Muzychka, Generalized models for laminardeveloping flows in heat sinks and heat exchangers, HeatTransfer Engineering, 2013.
Transformer thermal modeling
• Channel thermal model𝑅𝑅𝑡𝑡𝑡,𝑟𝑟 =
𝑎𝑎𝑤𝑤𝑙𝑙𝜆𝜆𝐻𝐻𝑆𝑆
𝑅𝑅𝑡𝑡𝑡,𝑑𝑑 =1
ℎ𝑙𝑙𝜋𝜋𝑑𝑑with
ℎ =𝑁𝑁𝑢𝑢𝜆𝜆𝑓𝑓𝑓𝑓𝑢𝑢𝑓𝑓𝑓𝑓
𝑑𝑑- heat transfer coefficient
𝑁𝑁𝑐𝑐 - Nusselt number𝜆𝜆𝐻𝐻𝑆𝑆 - thermal conductivity of heat sink material
𝑑𝑑 ≈ 2 ⁄𝐴𝐴 𝜋𝜋 𝑚𝑚 – channel hydraulic diameter of cross-sectional area 𝐴𝐴• Nusselt number is a function of
– Average ducted fluid velocity– Duct geometry– Fluid Prandtl number (𝑷𝑷𝒓𝒓)– Analytical models available in literature3
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[3] Y. S. Muzychka, Generalized models for laminardeveloping flows in heat sinks and heat exchangers, HeatTransfer Engineering, 2013.
Transformer thermal modeling
• Water flow in structures with multiple parallel channels∆𝑝𝑝𝑡𝑡𝑡𝑡𝑡𝑡 = ∆𝑝𝑝1= ∆𝑝𝑝2= ⋯ = ∆𝑝𝑝𝑖𝑖 - pressure loss 𝑃𝑃𝑎𝑎�̇�𝑉 = �̇�𝑉1 + �̇�𝑉2 + ⋯+ �̇�𝑉𝑖𝑖 - flow rates ⁄𝑚𝑚3 𝑠𝑠
• Darcy-Weisbach equation for pressure loss in parallel channels
∆𝑝𝑝 = �̇�𝑉2
∑ ⁄𝐾𝐾𝑓𝑓 𝑓𝑓𝑓𝑓2 ; �̇�𝑉 = 𝑉𝑉 � 𝐴𝐴 ; 𝐾𝐾𝑖𝑖 = 𝜋𝜋2�𝑑𝑑𝑓𝑓
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8�𝜌𝜌�𝑙𝑙𝑓𝑓
𝑉𝑉 ⁄𝑚𝑚 𝑠𝑠 – fluid velocity𝑓𝑓 – channel friction factor𝜌𝜌 ⁄𝑘𝑘𝑘𝑘 𝑚𝑚3 – fluid density
• Channel friction factor– Different formulas for laminar and turbulent flow
• Functions of Reynolds number• In turbulent flow channel roughness plays a role
– Reynolds number is a function of fluid velocity• Iterative solving necessary• Few iterations sufficient
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Transformer thermal modeling
• Thermal model of the chosen transformer structure
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OPTIMIZATION AND DESIGN
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Chosen topology and optimization results
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Custom cores (Ferrite N97) Standard cores (Ferrite N97)
Modular Dual Active Bridge (DAB) converter Simplified flow chart of theoptimization procedure
System layout and specifications
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• Single module specifications– Nominal battery side voltage: 700 V– Nominal DC link side voltage: 700 V– Nominal power: 38.5 kW– Peak continuous power: 50 kW– Switching frequency: 35 kHz– Efficiency: 98.5%– Dimensions: 360x195x118 mm– Power density: 6 kW/dm3
– Weight: 18 kg
Mechanical layout of the system
SYSTEM CONTROL DESIGN
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System control design
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• Control parameter optimization
System control design
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• Module control overview
System control design
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• Generalized PWM generator with voltage second balancing4
𝑝𝑝1,1 𝑛𝑛 = 𝜙𝜙2𝑥𝑥 + 𝛿𝛿𝑥𝑥 𝑛𝑛 − 1
𝑝𝑝1,2 𝑛𝑛 = 𝜙𝜙2𝑥𝑥 + 𝛿𝛿𝑥𝑥 𝑛𝑛 − 1 + 𝑇𝑇𝐼𝐼
𝑝𝑝1,3 𝑛𝑛 = 𝜙𝜙2𝑥𝑥 + 𝛿𝛿𝑥𝑥 𝑛𝑛 +𝑇𝑇𝑆𝑆2
𝑝𝑝1,4 𝑛𝑛 = 𝜙𝜙2𝑥𝑥 + 𝛿𝛿𝑥𝑥 𝑛𝑛 +𝑇𝑇𝑆𝑆2
+ 𝑇𝑇𝐼𝐼
𝑝𝑝3,1 𝑛𝑛 = 𝜙𝜙2𝑥𝑥 − 𝛿𝛿𝑥𝑥 𝑛𝑛 + 𝑇𝑇𝑆𝑆 − 𝑇𝑇𝐼𝐼
𝑝𝑝2,1 𝑛𝑛 = 𝜙𝜙2𝑥𝑥 − 𝛿𝛿𝑥𝑥 𝑛𝑛 − 1 +𝑇𝑇𝑆𝑆2− 𝑇𝑇𝐼𝐼
𝑝𝑝2,2 𝑛𝑛 = 𝜙𝜙2𝑥𝑥 − 𝛿𝛿𝑥𝑥 𝑛𝑛 − 1 +𝑇𝑇𝑆𝑆2
𝑝𝑝3,1 𝑛𝑛 = 𝜙𝜙2𝑥𝑥 − 𝛿𝛿𝑥𝑥 𝑛𝑛 + 𝑇𝑇𝑆𝑆
[4] M. Stojadinović et al, Generalized PWM generator withtransformer flux balancing for Dual Active Bridge converter, EPE ECCEEurope, 2017.
Generalized PWM generator with voltage second balancing
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• Properties of the proposed PWM generator:– Seamless transition between different modulation schemes– Allows for flux balancing– No overshoot in the transformer current
SIMULATION & MEASUREMENT RESULTS
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• Temperature distribution in transformer and cooling structure– Same material parameters in
FEM and analytical– Same losses used– Water temperature 𝟐𝟐𝟐𝟐℃– Input flow 𝟖𝟖 ⁄l 𝐦𝐦𝐦𝐦𝐦𝐦
• Velocity profile of the cooling structure
3D-FEM simulation results
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𝑻𝑻𝑪𝑪𝑪𝑪 𝑻𝑻𝑪𝑪𝟐𝟐 𝑻𝑻𝑪𝑪𝑪𝑪 𝑻𝑻𝑨𝑨𝑨𝑨𝑨𝑨 𝑻𝑻𝑾𝑾𝑾𝑾 𝑻𝑻𝑷𝑷𝑷𝑷𝑷𝑷 𝑻𝑻𝑾𝑾𝑾𝑾 𝑻𝑻𝑻𝑻𝑷𝑷𝑾𝑾3D FEM 70℃ 40℃ 29℃ 71℃ 78℃ 77℃ 81℃ 43℃
Analytical 72℃ 42℃ 28℃ 68℃ 83℃ 80℃ 88℃ 66℃
FEM Analytical
Fluid velocity 0.115 ⁄m s 0.116 ⁄m s
Fluid velocity in transformer channels
3D-FEM simulation results
• Eddy current distribution in the bottom part of the cooling structure
– Aluminium bar has better thermal behaviour(part of the structure)
– Thickness not limited– Can be placed only on lower side
for easy manufacturability• Influence on the field (non-symmetrical)• Can lead to even higher losses in windings
• Calculated induced losses (FEM)– Whole transformer structure taken into
account
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with Al bar
Peak current density 𝐽𝐽𝑚𝑚 = 1.3 × 108 ⁄𝐴𝐴 𝑚𝑚2
with Al-Ni bar
Peak current density 𝐽𝐽𝑚𝑚 = 4 × 107 ⁄𝐴𝐴 𝑚𝑚2
Al bar AlNi bar
Induced losses 75W 36W
Measurement results
• Transformer leakage inductance test– Transformer in short circuit connection– Power choke test at 400V– Current ramped up to 65A
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3D FEM Analytical
Leakage inductance 26.2𝜇𝜇𝜇𝜇 26.5𝜇𝜇𝜇𝜇
Measurement setup
Measurement results
• Hydraulic measurements– Simplified pressure drop relation
∆𝑝𝑝 = 𝜁𝜁𝜌𝜌2�̇�𝑉2
𝐴𝐴𝑐𝑐2~𝑘𝑘𝑉𝑉2
𝜁𝜁 – coefficient of fluid resistance𝜌𝜌 – density of the fluid�̇�𝑉 – fluid flow𝐴𝐴𝑐𝑐 – water channel cross section
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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 220
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
measured points 25°Cinterpolated curve 25°Cmeasured points 60°Cinterpolated curve 60°C
Characteristic curve for 25°C & 60°C
flow [dm3/min]
pres
sure
dro
p [m
bar]
Measurement setup
Measurement results
• Dielectric withstand test:– Partial discharge measurement between
transformer primary and secondary– High voltage 50Hz source in a Faraday cage
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PD measurement resultsMeasurement block diagram
• Single Active Bridge (start-up) mode of the converter– DC link side switches are blocked
• Dual active bridge mode in open loop
Open loop tests
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Measurement setup
Voltage second balancing
Closed loop tests
• Current control– Full power reversal 700V / 60A
41
Measurement setup
Dual active bridge thermal test (700V / 60A)
• @ 90mins, water flow changed from 8 l/min to 15 l/min• Internal temperature on the outer surface of the secondary winding:
– 83°C @ 8 l/min– 78°C @ 15 l/min
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𝑻𝑻𝑪𝑪𝑪𝑪 𝑻𝑻𝑪𝑪𝟐𝟐 𝑻𝑻𝑪𝑪𝑪𝑪 𝑻𝑻𝑨𝑨𝑨𝑨𝑨𝑨 𝑻𝑻𝑾𝑾𝑾𝑾 𝑻𝑻𝑷𝑷𝑷𝑷𝑷𝑷 𝑻𝑻𝑾𝑾𝑾𝑾 𝑻𝑻𝑻𝑻𝑷𝑷𝑾𝑾
3D FEM 70℃ 40℃ 29℃ 71℃ 78℃ 77℃ 81℃ 43℃
Analytical 72℃ 42℃ 28℃ 68℃ 83℃ 80℃ 88℃ 66℃
Measurement - 63℃ 27℃ - - - 83℃ 66℃
Comparison of calculated andmeasured temperaturesInlet flow 8 ⁄l min
STANDARDIZATION & MODULARITY
Building block
43
State of the art VS applications
44
LRV
Mass Transit(Metros)
Main Line(Commuter,Regional, …)
Locomotives
Diesel
Fuel Cell
Battery
Supercaps
Characteristics
1500V-1800V 10’000kWh (1000litres) 600kW
100V-600V 530kWh (1000litres) 200-400kW
500V-900V 24.5kWh-75kWh 100-200kW
500V-900V 2kWh 600kW
Requirements
100kW 750V Line
200kW 750V Line
200kW 1500V-2000V
200kW 3kV Line
Building block
45
Electrical and Performance dataPower Flow Bidirectional
Isolation Galvanic isolation
Power 50kW
Voltage 500-900V
Max. Current 70A
Cont. Current 55A
Efficiency > 98%
Mechanical dataDimensions 360x195x118 mm
Weight 18 kg
Main cooling medium Water/Glycol
Secondary cooling medium Forced air
Max. Temperature of water/glycol cooling 60°C
Max temperature of cooling air 75°C
Vin
Ip
VoutVp Vs
Is
MF Transformer
1U
1V
2U
2V
Building block
Metro Application example
46
TractionConverter
Motors
EnergyStorage 1
EnergyStorage 2
EnergyStorage n
Mass Transit(Metros)
200kW 750V Line
Vin
Ip
VoutVp Vs
Is
MF Transformer
1U
1V
2U
2V
Building block
Main Line Application example
47
TractionConverter
Motors
EnergyStorage 1
EnergyStorage 2
EnergyStorage n
Main Line(Commuter,Regional, …)
200kW 1500V-2000V
Vin
Ip
VoutVp Vs
Is
MF Transformer
1U
1V
2U
2V
Building block
Locomotive Application example
48
TractionConverter
Motors
EnergyStorage 1
EnergyStorage 2
EnergyStorage n
Locomotives 200kW 3kV Line
Vin
Ip
VoutVp Vs
Is
MF Transformer
1U
1V
2U
2V
Building block
TALENT 3 BEMU DC/DC
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Summary
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50 % of German railway network is not electrified
53 % shorter than 40 km
Replace diesel trains by BEMUs on non- or partly-electrified regional railway lines
Operating with battery power and recharge under catenary
Market Product & Technology Talent 3 as base product
PRIMOVE battery technology to be adapted to mainline application
MITRAC Solutions
battery operation of up to 40 km
120 km/h (same as DMU) on non-el. lines
EMU BEMU Diesel Diesel Hybrid Fuel Cell
Energy cons. 39 % 45 % 79 % 67 % 100 %
Energy Price 40 % 40 % 32 % 32 % 100 %
Energy costs 15,2 % 17,3 % 39,4 % 33,3 % 100%
CO2 equivalent 8,6 % 9,7 % 100 % 85,2 % 31,4 %
Performance requirements
51
DC/DC VS MF DC/DC
52
QUESTIONS
53