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Chair of Power ElectronicsChristian-Albrechts-Universität zu KielKaiserstraße 224143 Kiel
Reliability Enhancement of Modular Power Converters by Uneven Loading
of CellsMarco Liserre
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
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
Chair of Power Electronics | Marco Liserre| [email protected] slide 3
Reliability Enhancement by Uneven Loading of Cells
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
Chair of Power Electronics | Marco Liserre| [email protected] slide 5
Design of power electronics systems for Reliability
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.
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)
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
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
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
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
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
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
.
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)
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
Chair of Power Electronics | Marco Liserre| [email protected] slide 19
The technological challenges of the DC/DC converter
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
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
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
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
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
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
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
Chair of Power Electronics | Marco Liserre| [email protected] slide 35
Power routing of Modular Power Converters
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)
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)
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
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
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
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
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.
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):
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.
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.
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
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.
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
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Without PR(Conv 1)Without PR(Conv 2)Without PR(Conv 3)With PR(Conv 1)With PR(Conv 2)With PR(Conv 3)
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.
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
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.
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
Chair of Power Electronics | Marco Liserre| [email protected] slide 58
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