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Chair of Power Electronics Christian-Albrechts-Universität zu Kiel Kaiserstraße 2 24143 Kiel Reliability Enhancement of Modular Power Converters by Uneven Loading of Cells Marco Liserre

Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

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Page 1: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

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

Reliability Enhancement of Modular Power Converters by Uneven Loading

of CellsMarco Liserre

Page 2: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 1

- 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, conferences 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

− Grid-connected converters (15 years) and reliability (last 5 years)

Chair of Power Electronics

Head of the Chair

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Chair of Power Electronics | Marco Liserre| [email protected] slide 2

Chair of Power Electronics

50 people

9 Mill Euro (3.5 Year)

Participating in the two major German initiatives regarding “Energiewende” Power Electronics Laboratory

Medium Voltage Laboratory under construction

Several industrial Partners

Several research Partners

Page 4: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 3

Reliability Enhancement by Uneven Loading of Cells

Page 5: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 4

Outline

Design of power electronics systems for Reliability

Modular Power Converters

The technological challenges of the DC/DC converter

Power Routing of Modular Power Converters

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Chair of Power Electronics | Marco Liserre| [email protected] slide 5

Design of power electronics systems for Reliability

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Chair of Power Electronics | Marco Liserre| [email protected] slide 6

Typical 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.

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Chair of Power Electronics | Marco Liserre| [email protected] slide 7

Field Experience of Wind Turbines

Contribution of subsystems and assemblies to the overall failure rate of wind turbines.

Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011.

Failure of power electronic systems in wind/PV application

5 Years of Field Experience of a 3.5 MW PV Plant

Data source: Moore, L. M. and H. N. Post, "Five years of operating experience at a large, utility-scale photovoltaic generating plant," Progress in Photovoltaics: Research and Applications 16(3): 249-259, 2008

Unscheduled maintenance events by subsystem.

(ACD: AC Disconnects, DAS: Data Acquisition Systems)

Page 9: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 8

Critical stressors for power electronic converters by application field. The bars show the deviation around

the mean value for each stressor and application. Scale: (1 not critical, 6 very critical).

Stressors identified in the survey

Temperature is still considered the most

critical stressor

Page 10: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 9

An example of major wear-out failures in IGBT module

Break down of a typical IGBT module.

Stress: Thermal cyclingStrength: Cycles to failureFailures: Dislocation of joints Symptom: Increase of Vce, thermal impedance, etc.

Bond wire lift-off

Soldering cracks

Page 11: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 10

Control for reliability

Page 12: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 11

Control for reliability

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Chair of Power Electronics | Marco Liserre| [email protected] slide 12

Modular Power Converters

Page 14: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 13

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

Page 15: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 14

Modularity

• Scalability of voltage and power rating• Reduced dv/dt and/or di/dt• Fault tolerance capacibility

Advantages of modular system

• Number of components – cost and reliabilityimpact• Number of series semiconductors

Disadvantages of modular system

Page 16: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 15

Implementation: AC-DC Stage

Neutral Point Clamped (NPC)

•Availability of the MVDC-link

•Reliable and well known topology

• It is not modular

Cascaded H-Bridge (CHB) Modular Multilevel Converter (MMC)

•Low frequency operation

• MVDC-Link•Complex control system

•Low frequency operation

•simple to be controlled

• Isolated dc sources

•No MVDC-link

Page 17: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 16

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

.

Page 18: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 17

Implementation: DC-AC Stage

T-Type Full-Bridge

• It is possible to have several feeders• Four wires topology• NPC topology allows the use of 600V IGBT, while the FB topology must use 1200V IGBT• In FB topology, the fourth leg can be combined to the splited dc-link, to improve the dc-link utilization.

Neutral Point Clamped (NPC)

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Chair of Power Electronics | Marco Liserre| [email protected] slide 18

Smart Transformer Architectures Classifications

• 1st Stage - Medium Voltage (MV):• Cascaded H-Bridge (CHB)• Modular Multilevel Converter (MMC)

• 2nd Stage - Isolated DC-DC:• Modular

• Dual-Active-Bridge (DAB)• Series-Resonant Converter (SRC)

• Semi-Modular• Quadruple-Active-Bridge (QAB)

• 3rd Stage - Low Voltage (LV) :• Voltage source inverter• NPC• T-type

Power Converter Topologies

Page 20: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 19

The technological challenges of the DC/DC converter

Page 21: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 20

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

Page 22: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 27

Target: Efficiency

Reliability

Accurate losses modeling

Automatic design - (optimum parameter selection)

Wideband gap devices

Fault tolerant topology

Lifetime devices considerations

Series-Resonant Converter

Page 23: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 28

• 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:

Series-Resonant Converter

Page 24: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 29

• Extension of the DAB with 2 additonal ports

• Operation is similar to DAB

• Phase shift modulation for power transfer

• Power transfer between all ports possible:

Quadrupole Active Bridge

Page 25: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 30

• Phase shift affects power transfer between bridges

• Demonstration for:

• Phase shift modulation affects additional reactive

currents -> additional losses

Schematic voltages and currents for the QAB.

Quadrupole Active Bridge

Page 26: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 32

Quadrupole Active Bridge

Input voltage (MV side): 1.8 kVVoltage of the MV cells: 600 VOutput voltage (LV side): 700 VPower: 10 kW

Efficiency 97.5 %SiC-based

Page 27: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 33

• 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

(SiC)

Highest efficiency of a MAB converter

Page 28: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 34

DAB or QAB ?

Page 29: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 35

Power routing of Modular Power Converters

Page 30: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 36

Power routing concept

Improve the efficiency: activate/de-activate parallel power paths to work on the maximum efficiency point, mainly in lightpower.Only the components in the activated power paths are stressed, while the power quality is affected

On/off control for parallel power converters (State of the art)

Page 31: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 37

Power routing concept

Control the lifetime: Identify aged IGBTs and reduce the power processed by them, until the repair or replacement of themodule. Consequently, optimize remaining useful lifetime and efficiency

Power routing for parallel power converters (Innovation)

Page 32: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 38

Power routing concept

State of the art: activation/deactivation of modules for efficiency improvement Negative impact on power quality Changes thermal stress distribution Results in unequal aging

Power Routing Maximization of the time to next maintenance Delay the processed power dependent failures

Modular ST composed of cells with different aging

Page 33: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 39

Reliability and cell loading

Impact of Power Routing on Reliability

3 cell system with one cell approaching end of life

Aging indication (e.g. collector emitter voltage measurement) shows condition of each building block

Changing power changes remaining useful lifetime for all building blocks

Page 34: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 40

Reliability and Cell Loading

Relation between thermal swing and cycles to failure

The effect of unbalanced loading on the power cycling capability of the system

The simplified relation betweenpower imbalance and lifetime.

System design for maximum ΔT = 60 K , Tj,max = 90 °C for Ta = 30 °C.

Example: unbalanced

loading with 30% : 70% results in a

significantly different number of cycles to failure

Effect of thermal design on lifetime

Page 35: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 44

Power Routing in cascaded H-bridges

Series connected building blocks can share the power unequally:

Unequal power Pa ,Pb and Pc is processed

Different stress is affected for the devices connected to the cells

The concept requires a sufficient margin of Vgrid/Vdc

The potential of the algorithm is mission profile dependent

Concept of (multi-frequency) power routing for a seven level CHB-converter

Page 36: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 45

Power Routing in cascaded H-bridges

Extending the power routing capability with multiple frequencies (using the 3rd harmonic):

Demonstration of the multi-frequency power routing.Capability for unloading series connected cells in a modular power converter using the 3rd harmonic with Vgrid/VDC = 0.8.

Page 37: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 46

Power Routing in cascaded H-bridges

Experimental demonstration of the

multi-frequency power routing concept.

Control diagram for the implementation of the power routing.

Extending the power routing capability with multiple frequencies (using the 3rd harmonic):

Page 38: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 47

Power Routing in cascaded H-bridges

Control variables of the power routing for series-

connected building blocks.

Demonstration of the concept for a highly varying mission profile with the resulting junction temperatures and accumulated damage for the power semiconductors in the cells.

Page 39: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 49

Power Routing in dc/dc converters

Control variables of the single QAB for power routing in the isolation stage.

Extending the power routing capability with multiple frequencies (using the 3rd harmonic):

Virtual resistors can be used to control the current in each port of the QAB.

Page 40: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 50

Power Routing in dc/dc converters

Demonstration of the Power routing:

One LV-side H-bridge has a significantly higher age than the others

The power is unequally distributed to unload the H-bridge

A Power cycle is also unequally shared by the redundant paths, reducing the stress for the aged parts

Page 41: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 51

Power Routing in parallel converters

Case study of 3 parallel converters with unequal accumulated damage

Similar thermal characteristics for each converter assumed

Without power routing, converters reach end of life at different times

The remaining useful lifetime and the efficiency can be controlled

LV-side of the ST consisting of 3 parallel 2 level converters.

Two level voltage source converter with neural wire.

Page 42: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 52

Power Routing – Analytical Validation

Case study of 3 parallel converters with unequal accumulated damage

By changing the power distribution, the damage can be equalized

As a result, the remaining lifetime is equal and the time to the next failure can be maximized

Case study on the impact of power routing (PR) on the estimated lifetime of the system

0 50 100 150 200 2500

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

months

Cum

ulta

ive

dam

age

Without PR(Conv 1)Without PR(Conv 2)Without PR(Conv 3)With PR(Conv 1)With PR(Conv 2)With PR(Conv 3)

Page 43: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 53

Power Routing in parallel converters

Case study of 3 parallel converters with unequal accumulated damage

Similar thermal characteristics for each converter assumed

Without power routing, converters reach end of life at different times

The remaining useful lifetime and the efficiency can be controlled

Demonstration of the power routing by varying the power distribution.

Page 44: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 55

Power Routing in parallel converters

Demonstration of the power routing by varying the power distribution.

Case study of 3 parallel converters with unequal accumulated damage

Efficiency impact of different power distribution is studied

Highest efficiency is achieved for balanced loading

Efficiency decreases for higher power imbalance

Page 45: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 56

Power Routing in parallel converters

Control variables of the power routing for parallel-connected building blocks.

Demonstration of the concept for a highly varying mission profile with the resulting junction temperatures and accumulated damage for the power semiconductors in the cells.

Page 46: Reliability Enhancement of Modular Power Converters by ......Data source: Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011. Failure

Chair of Power Electronics | Marco Liserre| [email protected] slide 57

Summary

Power routing for modular power converters has been introduced with the target to equalize the useful remaining lifetime in the system

The concept has been presented for different topologies consisting of parallel and series connected building blocks

The potential of the concept is dependent on the mission profile and the system design

The extension of the time to the next failure has been demonstrated analytically

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Chair of Power Electronics | Marco Liserre| [email protected] slide 58

Join the PhD Course

21-23 Feb 2018

Half time in Lab !