a semi-modular-based and sic-based smart transformer

Chair of Power ElectronicsChristian-Albrechts-Universität zu KielKaiserstraße 224143 Kiel

A Semi-modular-based and SiC-based Smart Transformer

Prof. Marco Liserre

06.6.2018

Chair of Power Electronics | Marco Liserre | ml@tf.uni-kiel.de 1

Studentische Hilfskräfte (HiWis)

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Chair of Power Electronics at CAU

Prof. Dr.-Ing. Marco Liserre (Lehrstuhlinhaber) Prof. Dr.-Ing. Friedrich W. Fuchs (Pens.) Dr.-Ing. Markus Andresen, Dr.-Ing. Rongwu Zhu, Dr.-Ing. Giovanni De Carne Prof. Costas Vournas, NTUA, Griechland (Lehrauftrag + Gastprofessor), Prof. Hossein Immanini ,

University of Tehran, Iran, Nimrod Vazquez Nava, Instituto Tecnologico de Celaya, Mexico 3 Sekretärinnen + 2 Labortechniker 20 wissenschaftliche Mitarbeiter +

- Associate Prof. at Politecnico di Bari, Italy

- Professor – Reliable Power Electronics at Aalborg University, Denmark

- Professor and Head of Power Electronics Chair at Christian-Albrechts-Universität zu Kiel, September 2013

− Listed in ISI-Thomson report World’s Most Influential Minds

− Active in international scientific organization (IEEE Fellow, journals, Vice-President, conf. organization)

− EU ERC Consolidator Grant (only one in EU in the field of power sys.)

− Created or contributed to the creation of several scientific laboratories

Head of the Chair: Prof. Dr. Ing. Marco Liserre

Chair of Power Electronics at CAU

Senior People of the ChairDr.-Ing. Rongwu Zhu

− PhD in University of Aalborg

− Several Projects in Wind Power System

− 13 Journal articles

Dr.-Ing. Markus Andresen

− PhD from CAU Kiel

− Visiting scholar at University of Wisconsin, Madison (USA), 2017

Dr.-Ing. Giovanni De Carne

− PhD from CAU Kiel

− Visiting scholar at Georgiatech (USA), 2017

Chair of Power Electronics

50 (Year) 2 Mill Euro (Year)

People Funding

Cooperation with20 companies

60 articles every year(20 in journals)

Chair of Power Electronics

Competence in PE Applications

Wide-Band-Gap SemiconductorsElectric Vehicles, Electrical Drives,

Aerospace

Isolated DC/DC-ConverterElectrical Vehicles, Active Grid, Aerospace

Control of Inverters

Industrial Drives, Active Grid, HVDC, Power Quality, Wind Energy, Electrical Vehicle,

Aerospace

Multilevel Modular Converters Wind Energy, Active Grid, HVDC

Lifetime and ReliabilityWind Energy, Industrial Drives, Active Grid,

HVDC, Aerospace

Grid Integration of inverters

in PSCAD in one of the seveninverters

Test of inverter in realistic grid conditions

Features:

RTDS with 2 racks

Power Amplifier voltage or current controlled

7 inverters controlled through Dspace

Thermal Analysis of power converters

Setup for „Thermal Characterization of powerelectronic Converters“ (TC-PEC)

• High speed IR Camera with positioningsystem, AC & DC Voltage Sources, Electronicloads, Oscilloscope, Power Analyzer,Synchronization & Control system

IR-camera with positioning system for junctiontemperature measurement in modular power converters.

Medium-Voltage (MV) Laboratory

Planned Contruction Work in Building (Stand Oktober 2015).

Planned test for the MV Lab

Table of Contents

Smart Transformer in the electric grid Semi-modular topologies Comparison between MMC and CHB Comparison between DAB and QAB Results of the actual prototype Reliability/Maintenance challenge of the Smart Transformer Smart Transformer and Solid State Transformer tailored for the grid

Table of Contents

What is the „Smart“ Transformer?

The Smart Transformer is:– a “power electronics based” transformer– a power system management node– a link to different ac or dc infrastructures– a possible storage-integration technology– a link to other energy sources (gas, heat, hydrogen)– a support for the EV infrastructure

The Smart Transformer relieves thedemand on single renewable sources andincreases the capacity of electrical lines

Impact of the „Smart“ Transformer

Wind/PV systemsHarbours Charging stations Data centers

centralized peak

decentralized peak

massive investments to modernize the electric grid:

- Higher mobility of people- Electric vehicles charging infrastructure

- Renewables Energies- Booming of internet -> large data centres

Smart Infrastructures are also „lighter“ infrastructures

“Power electronics based” transformer in traction application

Traditional solution• LF transformer (16 2/3 Hz) – very bulky and heavy• Low efficiency: 90 ~ 92 %• Around 7tons

Main concern:• Reduce volume and weight • Efficiency improvement

“Power electronics based” transformer in distribution application

Main requirements• Replace the traditional LF distribution

tranformer• HF/MF isolation• Provide additional functionalities

Functionalities• Voltage sag and harmonics

compensation• Load voltage regulation• Disturbance Rejection

• Power Factor Correction• VAR Compensation and Active

filtering• Overload and short-circuit

protection

The Smart Transformer

Smart Transformer in the electric grid

The Smart Transformer features shall be:– LV and MV DC-links available

– Advanced control of all the three-stages

– The system should be able to work even with faulty

modules

– During partial loading conditions it should be able to

fully use its rating for other services

Smart Transformer in the electric grid

• Voltage support (steady state and LVRT)

• Reactive power compensation at HV/MV substation

• Power quality improvements• Islanding control (high DG in LV)

• Integration of EV-charging stations • Integration of storage for dispatching• Reverse Power Flow limitation

Smart Transformer

• Impedance identification• Load identification• Reverse Power Flow limitation• ST overload control• Soft-load reduction• Damping of harmonics and resonances• LV-side power quality

Challenges of the DC-DC Stage

• High voltage Isolation• High Input voltage • High output current• Galvanic Isolation in Medium/High frequency• Power flow control – dc link control• Dc breacker feature (short circuit current

proctection)

DC-DC Stage: The most challenge stage

IsolationEfficiencyCost

Deserves more attention

Implementation: DC-DC Stage

Dual-Active-Bridge (DAB) Series-Resonant Converter (SRC) Multicell converter

•Less number of HF transformer

•Operates similarly to eh DAB converter

•Easy to control (degree of freedom)•Efficiency: ~ 97%

•Open loop operation (no control / less sensors)

•Efficiency: ~ 98%

• Operate at high frequency and high power

• Most challenging converter: high voltage in the MV side and current in the LV side

DC-DC Stage: Implementation Concept

• Low voltage/current rating semiconductors• Scalability in voltage/power• Fault tolerance capability• Reduced dV/dt and dI/dt

• Fewer number of components• High Voltage WBG devices• Simple control/communication system

Non-Modular Vs Modular

Challenges of the DC-DC Stage

• High Voltage Isolation• Bidirectional power flow• Galvanic Isolation in Medium/High frequency• Power flow control – dc link control• Dc breacker feature (short circuit current

proctection)

DC-DC Stage: Building Block Converter

Efficiency

Review on high efficiency dc-dc converter

Relevant converters: Phase-shift Full-Bridge Series-Resonant Converter

Dual-Active-Bridge Multiple-Active-Bridge

Target: Efficiency

Reliability

Accurate losses modeling

Automatic design - (optimum parameter selection)

Wideband gap devices

Fault tolerant topology

Lifetime devices considerations

Series-Resonant Converter

• Wideband-gap devices plays an important role• Design: correct parameters selection

Max Eff = 98.61%Eff (@Pmax) = 98.1%

Overview of basic dc-dc topologiessuitable to be used as a building block ofthe ST dc-dc stage

CAU Kiel dc-dc converter

Influence on efficiency:

Fault Tolerant Series-Resonant Converter

Regulated output voltage

• Wideband-gap devices plays an important role• Design: correct parameters selection

Max Eff = 97.5%

Overview of basic dc-dc topologiessuitable to be used as a building block ofthe ST dc-dc stage

CAU Kiel dc-dc converter

Influence on efficiency:

Quadruple Active Bridge

Highest efficiency of a MAB converter

DC/DC for the Smart Transformer

Dual/Quad Active Bridge Serie Resonant Converter

controlability

Voltage and current sensors

simplicity

LVDC link controlDAB VSI

Dual/Quab Active Bridge Serie Resonant Converter

• CHB controlsthe MVDC linkand, consequenltythe LVDC link

• DAB controls the LVDC link

DC/DC for the Smart Transformer

Electric Car Charging Station

DC distribution for higher efficiency

Load Control to smooth effect of the charging

The needed charging power is increasing and the peak charging power is challenging the electric grid

Problem

Solution

Datacenter

Connectivity among several busses

Higher reliability

In 2016, the average cost of an unplanned outage per minute was nearly $9,000 per incident and the most expensive cost of an unplanned outage was higher than $17,000 per minute. The requested reliability for this application is 99.999%

Problem

Solution

Aerospace

Higher Safety because of more connectivity

Lower Volume and Weight because of less magnetic component

The military standard (MIL-STD-704F) has rigorous requirements on the reliability and uninterrupted operation of the aerospace power supply system. According to NPRD-95, the failure rate of the inverter is 6.7123 per million hours and the failure probability is 0.006699 in 1000 hours.

Problem

Solution

In cooperation with Prof. G. Buticchi, Nottingham electrification center, Ninbo China

Table of Contents

Semi-modular topologies

Modulation level– Cell level– Converter level– System level

Different modular levels can be freely combined

Concept of semi-modular

Modular Architecture:Basic modules are used as building blocks for the entire ST

Basic Module

Semi-Modular Architecture:The building block is composed by several cells and a central (unreplaceable) element. In this case: Multiwinding transformer

Asymmetrical vs. SymmetricalPossible configurations

Generic Asymmetrical

• MV side: 3 cell• LV side: 1 cell

Symmetrical

• MV side: 2 cell• LV side: 2 cell

1. DAB-Based• Standard / Benchmark• 9 MV cells – 9 Units

2. Assymetrical QAB• 9 MV cells – 3 Units• Same voltage – MV side

3. Symetrical QAB – (V)• 10 MV cells – 5 Units• Same voltage – MV side• Less power per unit

4. Symetrical QAB – (P)• 6 MV cells – 6 Units• Same power rating / unit• less MV cells

1. DAB-Based 2. Assymetric QAB 3. Symetric QAB – (V)

4. Symetric QAB – (P)

Table of Contents

Comparison between MMC and CHB

The Comparison is carried out for different blocking voltages and different grid voltages

Optimal design of the CHB+DC/DC

Table of Contents

Comparison between DAB and QAB

Comparative analysis: considering different semiconductor technologies1. Design consideration

• Semiconductors / Capacitors / Heatsink

• Magnetics (wire losses and cost)

• Auxillaries (gate driver, power supply,

communication)

2. Specifications 3. Design algorithm

Comparative analysis – results of performance (losses/kw) and cost1. DAB-Based

• Standard / Benchmark• 9 MV cells – 9 Units

2. Assymetrical QAB• 9 MV cells – 3 Units• Same voltage – MV side

3. Symetrical QAB – (V)• 10 MV cells – 5 Units• Same voltage – MV side

4. Symetrical QAB – (P)• 6 MV cells – 6 Units• Same power rating per unit

But…why QAB and NOT DAB? Around 20% of cost reduction when AQAB

is adopted

But…why QAB and NOT DAB?

• Less semiconductor on the LV side, but with higher current rating.

• Few impact on the cost

Reduced number of:• Auxilar components (GDU, APS and control)• Semiconductors on LV side

Around 20% of cost reduction when AQAB

is adopted

But…why QAB and NOT DAB? • DAB and QAB have similar efficiencies (only 5% of difference in favor of

the QAB)

• SiC offers 10% of losses reduction, but increase the cost in around 40%

Optimal QAB design

Table of Contents

Smart Transformer in the electric grid Semi-modular topologies Comparison between MMC and QAB Comparison between DAB and QAB Results of the actual prototype Reliability/Maintenance challenge of the Smart Transformer Smart Transformer and Solid State Transformer tailored for the grid

Results of the actual prototype

Semi-modular – 3 stage architecture Specification:• Three-phase system• MVAC: 2.6 kVrms (line-to-line)• LVDC: 800 Vdc• Power: 100 kVA (33 kVA x 3)Features:• Power stage: MVAC-MVDC-LVDC

- MV stage: CHB- DC-DC stage: QAB

• Available funcionalities- Bidrectional power flow- VAr and voltage

compensation in both MV/LVAC

- LVDC connectivity<Semi-modular architecture>

Efficiency measurement: QAB and the whole prototype (QAB+CHB)

Same unit circuit, but… NEW configuration

New Topology: interphase use of QAB

Combining them . . .

Power delivered to dc-buses is always balanced

Multi dc-buses easlypossible

Easy maintenance

New Topology: interphase use of QAB

Table of Contents

Lifetime target in various PE applications

Applications Typical design target of LifetimeAircraft 24 years (100,000 hours flight operation)Automotive 15 years (10,000 operating hours, 300,000 km)Industry motor drives 5-20 years (40,000 hours in at full load)Railway 20-30 years (10 hours operation per day)Wind turbines 20 years (18-24 hours operation per day)Photovoltaic plants 20-30 years (12 hours per day)

Applications from which companies participated in the study.

• The Different O&M program

Designed lifetime target for the different applications.Data source: KDEE Kassel, Chair of Power Electronics, Kiel, Investigation of reliability issues in power electronics, ECPE study, 2017.

Solutions for high reliability from survey

Which trends or approaches will improve the system reliability of power electronic converters in the future?

Scale: Not beneficial 1 to very beneficial 6

Please rank the following options to achieve high reliability for power electronic systems

Highest priority 5 points to lowest priority 1 point

Topologies & condition monitoring

Robust components & intelligent control

Data source: KDEE Kassel, Chair of Power Electronics, Kiel, Investigation of reliability issues in power electronics, ECPE study, 2017.

Reliability challenge of modular systems:

• Modular power converters consist of several components, which can potentially fail:

• Capacitors (1 dc-link per H-bridge)• Power semiconductors (8 per H-bridge)• Drivers (1 per transistor)• …

• Modular power converters obtain redundancy on the building block level

• Redistribution of the stress (Power routing)• A failure of a component can be delayed

Principle of Power routing for three building blocks.

Power routing for maintenance schedule

• Components will fail and maintenance will be required

• Power routing can be utilized to control the wear out and schedule maintenance

• Power routing can be used to delay maintenance

Reducing the variance of the time to the failure• Slightly different temperatures of the

devices affect different lifetimes:

• With similar loading, the lifetime will have a high variance

• With power routing the variance of the lifetime is significantly reduced

• The time to a 5% failure probability is increased and mean lifetime is also slightly increased

Improving reliability of More Electric Aircraft with power routing• Reliability is crucial in aircraft applications

• Penetration of onboard power electronics converters is increasing• Thermal parameter variations and cooling system failures may

result in unexpected failures while processing equal power• Lifetime control provides better prognostic maintenance with lower

early failure probability

Unbreakable HEART

Table of Contents

Smart Transformer and Solid State Transformer tailored for the grid

How to rate ST and SST?

Join the PhD Course

13-15 Feb 2019

Half time in Lab !

Acknowledgement

Thank you for the contribution of:

• Prof. Giampaolo Buticchi (University of Nottingham, Ningbo, China)• Dr. Markus Andresen (CAU Kiel)• Levy Costa (ABB Corporate Research Center, Switzerland)• Vivek Raveendran (CAU Kiel)

a semi-modular-based and sic-based smart transformer

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