Reliability Enhancement of Modular Power Converters by Uneven Loading of Cells Marco Liserre Chair of Power Electronics Christian-Albrechts-Universität zu Kiel Kaiserstraße 2 24143 Kiel
Chair of Power Electronics Head of the Chair - 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 Marco Liserre ml@tf.uni-kiel.de slide 1
Chair of Power Electronics Participating in the two major German initiatives regarding Energiewende Power Electronics Laboratory Medium Voltage Laboratory under construction Several industrial Partners Several research Partners 50 people 9 Mill Euro (3.5 Year) Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 2
Reliability Enhancement by Uneven Loading of Cells Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 3
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 ml@tf.uni-kiel.de slide 4
Design of power electronics systems for Reliability Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 5
Typical lifetime target in various PE applications Applications Aircraft Automotive Industry motor drives Railway Wind turbines Photovoltaic plants The Different O&M program Typical design target of Lifetime 24 years (100,000 hours flight operation) 15 years (10,000 operating hours, 300,000 km) 5-20 years (40,000 hours in at full load) 20-30 years (10 hours operation per day) 20 years (18-24 hours operation per day) 20-30 years (12 hours per day) Applications from which companies participated in the study. 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 ml@tf.uni-kiel.de slide 6
Failure of power electronic systems in wind/pv application Field Experience of Wind Turbines 5 Years of Field Experience of a 3.5 MW PV Plant Contribution of subsystems and assemblies to the overall failure rate of wind turbines. Unscheduled maintenance events by subsystem. (ACD: AC Disconnects, DAS: Data Acquisition Systems) Data source: Reliawind, Report on Wind Turbine Reliability Profiles Field Data Reliability Analysis, 2011. 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 Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 7
Stressors identified in the survey Temperature is still considered the most critical stressor 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). Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 8
An example of major wear-out failures in IGBT module Bond wire lift-off Break down of a typical IGBT module. Stress: Thermal cycling Strength: Cycles to failure Failures: Dislocation of joints Symptom: Increase of Vce, thermal impedance, etc. Soldering cracks Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 9
Control for reliability Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 10
Control for reliability Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 11
Modular Power Converters Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 12
DC-DC Stage: Implementation Concept Non-Modular Vs Modular Fewer number of components High Voltage WBG devices Simple control/communication system Low voltage/current rating semiconductors Scalability in voltage/power Fault tolerance capability Reduced dv/dt and di/dt Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 13
Modularity Advantages of modular system Scalability of voltage and power rating Reduced dv/dt and/or di/dt Fault tolerance capacibility Disadvantages of modular system Number of components cost and reliability impact Number of series semiconductors Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 14
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) Low frequency operation simple to be controlled Isolated dc sources No MVDClink Modular Multilevel Converter (MMC) Low frequency operation MVDC-Link Complex control system Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 15
Implementation: DC-DC Stage Operate at high frequency and high power Most challenging converter: high voltage in the MV side and current in the LV side. 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% Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 16
Implementation: DC-AC Stage 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) T-Type Full-Bridge Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 17
Power Converter Topologies 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 Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 18
The technological challenges of the DC/DC converter Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 19
Challenges of the DC-DC Stage DC-DC Stage: Building Block Converter 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) Efficiency Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 20
Series-Resonant Converter Target: Efficiency Reliability Accurate losses modeling Automatic design - (optimum parameter selection) Wideband gap devices Fault tolerant topology Lifetime devices considerations Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 27
Series-Resonant Converter Overview of basic dc-dc topologies suitable to be used as a building block of the ST dc-dc stage Influence on efficiency: Wideband-gap devices plays an important role Design: correct parameters selection CAU Kiel dc-dc converter Max Eff = 98.61% Eff (@P max ) = 98.1% Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 28
Quadrupole Active Bridge 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: Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 29
Quadrupole Active Bridge 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. Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 30
Quadrupole Active Bridge SiC-based Input voltage (MV side): 1.8 kv Voltage of the MV cells: 600 V Output voltage (LV side): 700 V Power: 10 kw Efficiency 97.5 % Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 32
Quadruple Active Bridge Overview of basic dc-dc topologies suitable to be used as a building block of the ST dc-dc stage Influence on efficiency: Wideband-gap devices plays an important role Design: correct parameters selection CAU Kiel dc-dc converter Max Eff = 97.5% (SiC) Highest efficiency of a MAB converter Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 33
DAB or QAB? Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 34
Power routing of Modular Power Converters Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 35
Power routing concept On/off control for parallel power converters (State of the art) Improve the efficiency: activate/de-activate parallel power paths to work on the maximum efficiency point, mainly in light power. Only the components in the activated power paths are stressed, while the power quality is affected Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 36
Power routing concept Power routing for parallel power converters (Innovation) Control the lifetime: Identify aged IGBTs and reduce the power processed by them, until the repair or replacement of the module. Consequently, optimize remaining useful lifetime and efficiency Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 37
Power routing concept Modular ST composed of cells with different aging 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 Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 38
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 ml@tf.uni-kiel.de slide 39
Reliability and Cell Loading Effect of thermal design on lifetime Example: unbalanced loading with 30% : 70% results in a significantly different number of cycles to failure Relation between thermal swing and cycles to failure The effect of unbalanced loading on the power cycling capability of the system The simplified relation between power imbalance and lifetime. System design for maximum ΔT = 60 K, T j,max = 90 C for T a = 30 C. Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 40
Power Routing in cascaded H-bridges Series connected building blocks can share the power unequally: Unequal power P a,p b and P c is processed Different stress is affected for the devices connected to the cells The concept requires a sufficient margin of V grid /V dc 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 ml@tf.uni-kiel.de slide 44
Power Routing in cascaded H-bridges Extending the power routing capability with multiple frequencies (using the 3 rd harmonic): Capability for unloading series connected cells in a modular Demonstration of the multi-frequency power routing. power converter using the 3 rd harmonic with V grid /V DC = 0.8. Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 45
Power Routing in cascaded H-bridges Extending the power routing capability with multiple frequencies (using the 3 rd harmonic): Experimental demonstration of the multi-frequency power routing concept. Control diagram for the implementation of the power routing. Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 46
Power Routing in cascaded H-bridges Control variables of the power routing for seriesconnected 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 ml@tf.uni-kiel.de slide 47
Power Routing in dc/dc converters Extending the power routing capability with multiple frequencies (using the 3 rd harmonic): Virtual resistors can be used to control the current in each port of the QAB. Control variables of the single QAB for power routing in the isolation stage. Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 49
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 ml@tf.uni-kiel.de slide 50
Power Routing in parallel converters Case study of 3 parallel converters with unequal accumulated damage Similar thermal characteristics for each converter assumed Two level voltage source converter with neural wire. 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 Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de parallel 2 level converters. slide 51
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 Cumultaive damage 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 Without PR(Conv 1) Without PR(Conv 2) Without PR(Conv 3) With PR(Conv 1) With PR(Conv 2) With PR(Conv 3) 0 0 50 100 150 200 250 months Case study on the impact of power routing (PR) on the estimated lifetime of the system Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 52
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 ml@tf.uni-kiel.de slide 53
Power Routing in parallel converters 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 Demonstration of the power routing by varying the power distribution. Chair of Power Electronics Marco Liserre ml@tf.uni-kiel.de slide 55
Power Routing in parallel converters Control variables of the power routing for parallelconnected 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 ml@tf.uni-kiel.de slide 56
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 ml@tf.uni-kiel.de slide 57
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