Distribution Grids with LectureTitle · Dual Active Bridge DC -DC Converter Medium-Voltage High-Power DC-DC Converter P = 7 MW, VDC = 5 kV ±10 % Si-Steel 180 µm lamination Efficiency

April 20, 2018

Lecture TitleDistribution Grids with DC Technology

Univ.-Prof. Dr.ir. Dr. h.c. Rik W. De Doncker,Director FEN Research Campus

2

Background: Energy market mechanisms that enabled more decentralized power production

Market changes that were introduced stepwise (EU):

1. Market liberalization allowed decentralized power generation, creating prosumers, typically small scale power generation (CHP) and REN sources (mostly volatile sources, such as PV and wind)

2. CO2 certificates

3. Unbundling of power generation and grid operation

4. Unbundling of TSO and DSO

Challenge:

Need to find technical solutions that are socially and economically viable within these new markets and regulations

3

Global installed capacity of wind

487 GWpeak installed capacity by the end of 2016 – assuming 50% DFG, this translates in approximately 750 GVA of power electronic converters

Multi-megawatt power electronic converters are becoming a mass product. During the past 25 years a major cost reduction of voltage source inverters took place; from 500 €/kVA down to 25 €/kVA

4

Global installed capacity of PV is accelerating

• 285 GWpeak of PV installed by 2016

• About 315 GVA of PV (string and central) inverters are installed by 2016

• LCE of PV in some countries is lower than that of wind or coal power plants

Source: PowerWeb

487 GW instead of 497 GW

5

Price of silicon cells and power electronics inter-twined?

Silicon is made of SiO2 (i.e. sand, an abundant material) and energyEnergy is produced by PVPV energy is controlled and converted by power electronics made of silicon

6

Electrical Grids for a CO2 Neutral Electrical Energy Supply SystemSector coupling to provide massive energy storage

7

Electrical Grids for a CO2 Neutral Electrical Energy Supply SystemAbout 1/3 in HV, 1/3 in MV, 1/3 in Low-Voltage Distribution Grid

Interesting observation:The transmission grid requires just minimal extension with HVDC. ETG Task Force expects less cost for DC integration in infrastructure.The MV distribution grid will become bottleneck.

8

The “1/3 rule” already applies to the German installed capacities

Future grids cannot ignore the energy feed-in in medium- and low-voltage distribution grids and must become interconnected

Offshore-wind parks

Large solar andwind parks

Industrial powerplants

Central power stations

40,7 GW Solar andwind parks

Municipal powerplants

4,5 GW

23,2 GW PV-systems in localDistribution gridsLocal distribution

grids

-

Bi-directional, interconnected grid structure

High voltagefrom 100 kV

Medium voltage

Low voltage

Conventional power sources Renewable power sources

Daten: Bundesnetzagentur - Daten und Informationen zum EEG (31.12.2015) , Kraftwerksliste und Zahlen (10.06.2016, Status 2015)(5 GW not associated)

Intelligent MVDC Interconnected SubstationsDual-Active Bridge as modular PEBBFurther development with ARCPZVS extension with tap changerMultiport converter as power router

10

Urban Regional, Flexible MVDC Distribution Grid linked to HVDC Cellular „Underlay“ structure

© R.W. De Doncker, J. von Bloh

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Intelligent MVDC Interconnected Substations

AixControl XRS7070

Physiology

DC-DC converterLandscape architecture

Research grid

Medium-frequency transformer

12

Dual Active Bridge DC-DC ConverterMedium-Voltage High-Power DC-DC Converter

P = 7 MW, VDC = 5 kV ±10 % Si-Steel 180 µm lamination Efficiency up to 99.2 % @1 kHz Ultimately air-cooled devices are an option DC substation at 1/3 weight of 50 Hz

transformer

R. Lenke, „A Contribution to the Design of Isolated DC-DC Converters for Utility Applications“, Diss. RWTH Aachen University, E.ON ERC, 2012N. Soltau, „High-power medium-voltage DC-DC converters : design, control and demonstration”, Diss., RWTH Aachen University, E.ON ERC, 2017

DAB uses ABB IGCT Stacks

13



transformer


R. Lenke, „A Contribution to the Design of Isolated DC-DC Converters for Utility Applications“, Diss. RWTH Aachen University, E.ON ERC, 2012N. Soltau, „High-power medium-voltage DC-DC converters : design, control and demonstration”, Diss., RWTH Aachen University, E.ON ERC, 2017

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transformer

power

5 MW DAB DC-DC Converter


15



transformer

power



Vin

Vout

jXI

I

ϕ

P ≈ sin ϕVin Vout

X

16



transformer

power



Vout/Vin

ϕ in deg

1.0

1.5

0.5

Soft switching area

17

Medium-Voltage High-Power DC-DC ConverterDual-Active Bridge as a universal PEBB

Three-Phase Dual-Active Bridge (DAB)

− High efficiency (99%)− Medium-frequency ac-link− Modular approach- PEBB− Scalable in power and voltage− Buck-Boost operation− Short circuit proof− Primary and secondary side can be

connected in series or parallel− Can be built with redundancy

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Dual Active Bridge DC-DC ConverterFurther Development with ARCP

Operation Principle of the Dual-Active Bridge with Auxiliary-Resonant Commutated Pole

Main goal is to guarantee a zero-voltage condition at the main converter legs

N. Soltau, J. Lange, M. Stieneker, H. Stagge and R. W. De Doncker, "Ensuring soft-switching operation of a three-phase dual-active bridge DC-DC converter applying an auxiliary resonant-commutated pole," 2014 16th European Conference on Power Electronics and Applications, 2014, pp. 1-10. doi: 10.1109/EPE.2014.6910857

J. Voss, B. Bagaber and R. W. De Doncker, "Full soft-switching capability of the dual-active bridge by using the auxiliary-resonant commutated-pole technique," 2017 IEEE 8th International Symposium on Power Electronics for Distributed Generation Systems (PEDG), 2017, pp. 1-8. doi: 10.1109/PEDG.2017.7972487

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Dual Active Bridge DC-DC ConverterFurther Development with ARCP

Characterization of Four-Quadrant Switches for ARCP

Tested up to 2kV - Extrapolated Losses @ 5 kV

Thyristor with SiC 3.41 kW

IGBT 10.19 kW

IGBT with SiC 3.37 kW

IGCT with SiC 3.76 kW

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Dual Active Bridge DC-DC Converter with Tap ChangerZero Voltage Switching Extension

Tap changer extends the zero-voltage switching− The DAB with tap changer can be modulated completely in ZVS if at low load the

triangular modulation strategy is used Trade-off between reduction of losses and number of taps

V1 = 50 V

V2

in V

ϕ in deg ϕ in deg ϕ in deg

V2

in V

V2

in V

Tr = 5 Tr = 3, 5, 7 Tr = 2 to 8

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Dual Active Bridge DC-DC Converter with Tap ChangerPrototype DAB with Tap Changer

LV-H-bridge 4

LV-H-bridge 3

LV-H-bridge 2

LV-H-bridge 1Transformer

HV-H-bridge

LV H-bridges Transformer Tap changer HV H-bridge

S. Taraborrelli, R. Spenke and R. W. De Doncker, "Bidirectional dual active bridge converter using a tap changer for extended voltage ranges," 2016 18th European Conference on Power Electronics and Applications (EPE'16 ECCE Europe), Karlsruhe, 2016, pp. 1-10, doi: 10.1109/EPE.2016.7695668

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Modulation Schemes to Extend Soft-Switching RangeAsymmetrical Duty-Cycle Control

Injection of common-mode voltage into the transformer neutral point

Zero-current switching is achieved inextended operation range by three modulation modes

aS

New modulation waveforms Original soft-switching range Extended soft-switching range

Hauke van Hoek, “Design and operation considerations of three-phase dual active bridge converters for low-power applications with wide voltage ranges,” PhD Thesis, RWTH Aachen University, DOI: 10.18154/RWTH-2017-02955J. Hu, N. Soltau and R. W. De Doncker, "Asymmetrical duty-cycle control of three-phase dual-active bridge converter for soft-switching range extension," 2016 IEEE Energy Conversion Congress and Exposition (ECCE), Milwaukee, WI, 2016, pp. 1-8., doi: 10.1109/ECCE.2016.7854888

http://dx.doi.org/10.18154/RWTH-2017-02955

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Modulation Schemes to Extend Soft-Switching RangeAsymmetrical Duty-Cycle Control

• J. Hu, N. Soltau and R. W. De Doncker, "Asymmetrical duty-cycle control of three-phase dual-active bridge converter for soft-switching range extension,"2016 IEEE Energy Conversion Congress and Exposition (ECCE), Milwaukee, WI, 2016, pp. 1-8.

• Jingxin Hu, Zhiqing Yang, N. Soltau and R. W. De Doncker, "A duty-cycle control method to ensure soft-switching operation of a high-power three-phase dual-active bridge converter, " 2017 IEEE 3rd International Future Energy Electronics Conference and ECCE Asia (IFEEC 2017 - ECCE Asia),Kaohsiung, 2017, pp. 866-871.

Efficiency for various voltage ratios and power levels

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Multiport DC-DC Converters as Power Router

Fully bidirectional power flow between different loads/grids, i.e., no intermediate (high voltage) stage is required to exchange power between loads/grids of different or equal voltage levels

Low component count (each load/grid requires only one power electronic port)

High utilization of components

Arbitrary number of loads/grids can be operated in island mode

Highly efficient and flexible way for interconnecting dc grids/loads

identical power stages

Using multi-port dc-dc converter

Using separate dc-dc converters

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Three-Phase Triple-Active Bridge DC-DC Converter

M. Neubert, A. Gorodnichev, J. Gottschlich and R. W. De Doncker, "Performance analysis of a triple-active bridge converter for interconnection of future dc-grids," 2016 IEEE Energy Conversion Congress and Exposition (ECCE), Milwaukee, WI, 2016, pp. 1-8., doi: 10.1109/ECCE.2016.7855337

150 kW, 20 kHz 5 kV, 760 V and 380 V 10 kV SiC MOSFETs10 kV SiC MOSFETs and gate drivers

of medium-voltage port

Protection Strategies and ControlUnderlay gridsProtection in meshed DC gridsConverter control methodsHardware-in-the-Loop enabling real-time control evaluation

27

Classical Distribution Grids are radialIntegration of decentralized supplies. renewables, storage and e-Mobility is difficult

MV MV

LVLVLVLV

HV

25% 25% 25% 25%

50% 50%

=~3~

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Classical Distribution Grids are radial and massively oversizedIntegration of decentralized supplies. renewables, storage and e-Mobility is difficult

HV

25% 25% 25%

100 %

25% 25% 25%

MV MV

LVLVLVLV

25%

=~3~

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Hybrid Approach to Maximize Capacity of Distribution Grids Integration of e-Mobility, PV, Wind, Storage … by MVDC-Backbone

3~= =

3~= =MVDC

MVDC

3xFCS

HV

= == = = == = = == = = =

3xFCS= =

25%

25%

25%

100% 100%

25%50 %50 %

MV MV

MVDC

LVLVLVLV

30

= =N x (F)CS

= == = = =

Hybrid Approach to Maximize Capacity of Distribution GridsIntegration of e-Mobility, PV, Wind, Storage … by MVDC-Backbone

3~= =

3~= =MVDC

MVDC

HV

= = = == = = =N x (F)CS

25%

25%

25%

100% 100%

25%50 %50 %

MV MV

MVDC

LVLVLVLV

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Possible MVDC Grid StructureDual-Active Bridge and Multiport Converter

Galvanically isolated sub-grid structures− Multi-/ Three-Port DC-DC converter− Galvanic isolation− Connection of three different voltage levels possible

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Fault in Meshed DC GridsFault Isolation With DC Circuit Breaker

Normal operation

DC substationDC substationDC circuit breaker DC circuit breaker

DC substation

DC circuit breaker

33



DC substation

DC circuit breaker

Normal operation - fault occurs

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DC substation

DC circuit breaker

Normal operation - fault occurs Clearing and isolation of the fault with DC Circuit Breakers Non affected part of three-port converter continued operation

35

Fault in Meshed DC GridFault Isolation with DC Disconnects

Normal Operation

Picture: Siemens, Sicat 8WL6134 DC disconnector, 3 kV

DC substationDC substation

DC substation

36


Fault occurs



DC substation

37


Fault occurs Fault extinction via DC-DC converters (short interruption in power supply)



DC substation

38


Fault occurs Fault extinction via DC-DC converters (short interruption in power supply) Isolation of fault with disconnectors Non affected part of three-port converter can continue operation



DC substation

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DC-SwitchingState of the Art

Products are available for low voltage applications, ex. Traction applications (high speed mechanical circuit breakers)

Wide variety of designs proposed in research, hybrid, snubbered mechanical, active current injection, and solid-state circuit breakers topologies

Prototypes developed by different manufacturer (ex. Mitsubishi, ABB), ultra fast mechanical circuit breaker is a key component

Project Goal− Design of a circuit breaker in MVDC systems

[GEI12] GE Industrial Systems, “Gerapid High Speed DC Breaker Application Guide”, Plainville, USA (2012)[TOK15] S. Tokoyoda, K. Tahata, K. Kamei, K. Kikuchi, D. Yoshida, S. Oukaili*, R. Yamamoto, H. Ito. “DC circuit breakers for HVDC grid applications HVDC and Power Electronics technology and developments”. In: Across Borders – HVDC Systems and Market Integration International Symposium Cigre, Lund (2015), pp. 135–143.[DER14] Jürgen Häfner and Björn Jacobson. “Proactive Hybrid HVDC Breakers - A key innovation for reliable HVDC grids”. In: The electric power system of the future -Integrating supergrids and microgrids International Symposium Cigre, Bolonia (2011), pp. 264–273.

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DC – SwitchingCircuit Breaker Concepts of Interest

Hybrid Circuit Breaker− Circuit breaker opens upon fault current detection− current commutate through a PE-device

commutation path, low voltage drop develops over the mech. circuit breaker

− Active turn-off PE devices interrupt the current when arc extinguishes

Snubbered Mechanical Circuit Breaker (SMCB)

− Circuit breaker opens upon fault current detection− Capacitors limits the voltage over circuit breaker

during opening− Thyristors turn off at zero current detection to

eliminate oscillations with the network

Hybrid circuit breaker

CSnubber

Snubbered Mechanical Circuit Breaker

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Hybrid DC BreakerDevelopment of a new Power Electronic Device

Device− Consists of a GTO-wafer, a diode

stack, and a gate MOSFET− For a successful commutation

and turn-off, the condition to be satisfied is

𝑉𝑉pn + 𝑉𝑉Diode > 𝑉𝑉MOSFET− Work in progress: Proof of

concept and package design and construction (presspack)

Driver − Develop a driver based on similar

thyristor based power electronic devices

− Building prototype II after defining and solving issues of prototype I

42

Dynamic Control of Dual Active Bridge DC-DC ConverterMedium-Voltage High-Power DC-DC Converter

DAB is a third order system (C - L- C) Oscillates when disturbances occur Active damping or predictive control is

needed to prevent instabilities

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Dynamic Behavior at Abrupt Change of Load Angle φ

Step change of φ leads to asymmetric phase currents

Oscillations of the dc current can be observed

Oscillations decay exponentially with time constant:

τ = Ls / Rwith R being the winding resistance of the transformer. Strong oscillations with highly

efficient converters (low R) featuring an increased dynamic voltage range (high Ls)

Limited bandwidth of current control

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Abrupt Change of Load Angle φ

Phase currents and dc current Phase currents in the αβ plane

45

Predictive Instantaneous Current Control

Edges of the hexagon are proportional to load angle Introduction of pre-calculated intermediate steps in the load angle force the

current to settle on the intended trajectory, within half the switching period

46

Load Angle Change with the Instantaneous Current Control

Phase currents and dc current Phase currents in the αβ plane

47

Real-Time Control Evaluation

Replacement of bulky expensive hardware with real-time model

Extensive testing of control− Interfaces− Control Algorithm− Platform / Processor Hardware

Real-Time Controller

MeasurementsADC

PWM Signals

Real-Time Simulator

Code model

C++ user-definedstate-machine and control

Converter Hardware

F. Adler, A. Benigni, H. Stagge, A. Monti and R. W. De Doncker, "A new versatile hardware platform for digital real-time simulation: Verification and evaluation," 2012 IEEE 13th Workshop on Control and Modeling for Power Electronics (COMPEL), Kyoto, 2012, pp. 1-8., doi: 10.1109/COMPEL.2012.6251742A Benigni, F Adler, A Monti, R De Doncker “Real Time Simulation of large Wind Farms”, E.ON ERC Series, Volume 6, Issue 3, July 2014, ISSN:1868-7415

48

Real-Time SimulationSetup

Roadmap development of DC ConvertersCost developmentImpact of New Materials – Increased power density

50

Price development for transformer can change the AC-paradigm

Metal prices (Cu, Al , Si-Fe) for transformers at LMEx are increasing on long term Prices of power electronic systems are continuously dropping

− Increasing production quantities, new semiconductor generations and materials− Higher operating frequency and voltage levels During last 25 years a reduction of specific cost for frequency inverters

from 500 €/kVA to 25 €/kVA, 5 €/kVA expected in 2020

Milestone: In 2013 a frequency inverter was no longer more expensive(20 k€/MVA) than a 50 Hz transformer

Price transformer (€/MVA)Prices converter (€/kVA)

Thou

send

€/M

VA

51

Technology Drivers Price Development of Power Electronics

• Specific cost for EV inverters− 1995: $50/kVA1

− 2015: $5/kVA2

− 2020 R&D target: $3.3/kVA

1 Source: Data provided by R. De Doncker2 Source: U.S. Department of Energy, Vehicle Technologies Office

3

4

5

6

7

8

2010 2012 2014 2016 2018 2020

cost

in $

/kW

year

52

Technology Drivers Price Development of Power Electronics

• DC-DC converter cost− Comprises two inverters and HF transformer− 2020 R&D target: $7.7/kW− Cost reduction using soft-switching and Wide

Bandgap Devices

1 Source: Data provided by R. De Doncker2 Source: U.S. Department of Energy, Vehicle Technologies Office

• Specific cost for EV inverters− 1995: $50/kVA1

− 2015: $5/kVA2

− 2020 R&D target: $3.3/kVA

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HI-LEVELDemonstrator next generation, low-cost EV inverters

• Project goal− Novel compact concept for reliable

electronics for drives of electric vehicles• Technology

− Drive converter based on high-current PCBs

− Embedding of power electronic devices into the PSB

• Demonstrator− 3-phase inverter− 50 kW, battery voltage 170-320 V,

phase current up to 320 A (short time)Turn-off transient

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Wide Bandgap and Si-Superjunction Converters

• SiC HV Battery DC-DC converter − fsw = 150 kHz− Pmax = 126 kW (3*42 kW)− Vbatt = 300…500 V − Vdc-link = Vbatt…800 V

• SiC Traction Inverter− fsw,max = 100 kHz− Pmax = 160 kW− Vin = 800 V

• GaN MHz DC-DC Converter− fsw = 30,3 MHz− Pmax = 150 W− Vin= 200 V− Vout= 40 V

• GaN Bidirectional Charger− fsw = 300 - 500 kHz− Pmax = 3.7 kW− Vgrid = 230 V − Vbattery = 250…400 V

• Superjunction LV Battery DC-DC Converter− fsw = 100 kHz− Pmax = 3 kW− Vbatt= 10…16 V− Vdc-link= 170…380 V

55

05

101520253035

2010 2012 2014 2016 2018 2020kW

/ l

0

5

10

15

20

25

2010 2012 2014 2016 2018 2020

kW /

kg

Power Density Development of DC-DC Converters

2012• fsw = 16 kHz• Si-Module• classic cooler and inductances

2016• fsw = 150 kHz• SiC-Module• classic cooler

and inductances

2018• fsw = 400 kHz• discrete SiC devices• 3D-printed cooler

and inductor bobbin

April 20, 2018

Lecture TitleDistribution Grids with DC Technology

Univ.-Prof. Dr.ir. Dr. h.c. Rik W. De Doncker,Director FEN Research Campus

57

Future Vision: City of Geilenkirchen

280 ha(160 ha GI)

60-100 MWp≅ 4-7 Mio. €/a*)

*) 900 h/a, 7,5 ct/kWh

Fast-charging

Elimination110 kV

Load balancingsubstations

Documents

Distribution Grids with LectureTitle · Dual Active Bridge DC -DC Converter Medium-Voltage High-Power DC-DC Converter P = 7 MW, VDC = 5 kV ±10 % Si-Steel 180 µm lamination Efficiency