IntroductionSummary of Hardware Status and Needs of PV InvertersHardware StatusStatus of Power Semiconductor DevicesStatus of PV InvertersTechnologies for Enhancing ReliabilityHard-switching TechnologySoft-switching TechnologyHard Versus Soft SwitchingDigital Signal Processing (DSP) Control MethodsUniversal Software ModulesReusing Software DesignsModular SoftwareMade-to-order Power ElectronicsStatus and Need for Corporate Plans and InfrastructureDeveloping a New ProductThe Need for Systems EngineeringPresent Manufacturing Barriers to 10-Year LifetimeInflexible Design Leads to Low Volume, Small ManufacturersInadequate Corporate StructureMinimal Staff with Inadequate TimeShortage of Sophisticated Test and Assembly EquipmentMinimal Pre-field TestingSome Manufacturing IssuesPurchasingAssemblyQuality ControlInspectionFailure ReportingTrend IdentificationField ReturnsTrainingPersonnel RotationTestingHighly Accelerated Life Testing and ScreeningCircuit Level TestFinal Assembly Level TestBurn-InBeta TestingDesign for ManufacturabilityEngineering ChangesWork InstructionsSummaryGlossarySAND2002-1085 Unlimited Release Printed April 2002 Status and Needs of Power Electronics for Photovoltaic Inverters: Summary Document Rick West and Konrad Mauch Xantrex Power Engineering Burnaby, BC, Canada V5A 4B5 Yu Chin Qin Millenium Technologies Troy, Michigan 48098 Ned Mohan University of Minnesota Minneapolis, MN 55455 Russell Bonn Photovoltaic Systems Sandia National Laboratories P. O. Box 5800 Albuquerque, NM 87185-0753 ABSTRACT Photovoltaic inverters are the most mature of any DER inverter, and their mean time to first failure (MTFF) is about five years. This is an unacceptable MTFF and will inhibit the rapid expansion of PV. With all DER technologies, (solar, wind, fuel cells, and microturbines) the inverter is still an immature product that will result in reliability problems in fielded systems. The increasing need for all of these technologies to have a reliable inverter provides a unique opportunity to address these needs with focused R&D development projects. The requirements for these inverters are so similar that modular designs with universal features are obviously the best solution for a 'next generation' inverter. A 'next generation' inverter will have improved performance, higher reliability, and improved profitability. Sandia National Laboratories has estimated that the development of a 'next generation' inverter could require approximately 20 man-years of work over an 18- to 24-month time frame, and that a government-industry partnership will greatly improve the chances of success.Table of Contents 1 Introduction ............................................................................................................................. 4 2 Summary of Hardware Status and Needs of PV Inverters.................................................. 7 2.1 Hardware Status.................................................................................................................7 2.1.1 Status of Power Semiconductor Devices................................................................... 7 2.1.2 Status of PV Inverters ................................................................................................ 8 2.2 Technologies for Enhancing Reliability .............................................................................. 9 2.2.1 Hard-switching Technology ....................................................................................... 9 2.2.2 Soft-switching Technology....................................................................................... 10 2.2.3 Hard Versus Soft Switching ..................................................................................... 12 2.2.4 Digital Signal Processing (DSP) Control Methods................................................... 13 2.2.5 Universal Software Modules .................................................................................... 15 2.2.6 Made-to-order Power Electronics ............................................................................ 16 3 Status and Need for Corporate Plans and Infrastructure ................................................. 19 3.1 Developing a New Product............................................................................................... 19 3.2 The Need for Systems Engineering ................................................................................. 20 3.3 Present Manufacturing Barriers to 10-Year Lifetime ........................................................ 21 3.3.1 Inflexible Design Leads to Low Volume, Small Manufacturers................................ 21 3.3.2 Inadequate Corporate Structure .............................................................................. 21 3.3.3 Minimal Staff with Inadequate Time......................................................................... 22 3.3.4 Shortage of Sophisticated Test and Assembly Equipment...................................... 22 3.3.5 Minimal Pre-field Testing ......................................................................................... 22 3.4 Some Manufacturing Issues............................................................................................. 23 3.4.1 Purchasing ............................................................................................................... 23 3.4.2 Assembly ................................................................................................................. 23 3.4.3 Quality Control ......................................................................................................... 23 3.4.4 Inspection................................................................................................................. 24 3.4.5 Failure Reporting ..................................................................................................... 24 3.4.6 Trend Identification .................................................................................................. 24 3.4.7 Field Returns............................................................................................................ 25 3.4.8 Training .................................................................................................................... 25 3.4.9 Personnel Rotation
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