1. Advance Power Electronic Converters for Renewable Energy Systems Dr. Prasad. N. Enjeti Texas A&M University

2. Outline of Presentation 1 Introduction to Texas A&M 2 3 4 Advance Power Electronic Converters for Renewable Energy Systems Challenges & Opportunities Conclusions 3. Texas A&M University 2014/7/8 4 College Station 4. Established in 1876 as the first public college in the state. Home of Texas A&M is ranked nationally among the top 10 Academic year 2013 enrollment is over 55,000 students studying for degrees in 10 academic colleges. Also starting in 2003 we have opened a 2nd branch campus (TAMU-Q) in Doha, Qatar Texas A&M University 5. 6 PhD/TTF ; we graduate 40-PhD + 110-MS / Year IEEE Fellows: 28; NAE: 3; Number of PhD graduates placed in academia: 125 (total) 6. TAMU - Electrical & Computer Engineering 7. More than 10,000 students applied to the Look College in 2012 for the 1,600 slots TAMU enrollment for Fall 2012 was 11,281 total students (8,397 undergraduate; 1,375 master's; 1,509 doctoral) Anticipated annual growth of: 6.5% UG ; 15% M.S. (both online and on-campus) 5% Ph.D The Texas Workforce Commission is projecting a 19 percent growth in engineering jobs in the next 12 years. This equates to more than 43,000 jobs. This projection mirrors a recent call by the President's Council of Advisors on STEM for the nation to increase the number of STEM graduates to one million in the next 10 years. http://engineering.tamu.edu/25by25 8. Transformative Power Electronics Technologies For Renewables and Smart Grid Power Conversion Options for large Wind Energy Systems Medium Frequency AC Collection Grid for Large Scale Solar PV Plants Medium Frequency Transformer Isolation for Grid Connected Renewables / Data Centers Smart PV Panels Direct Power Converter Fuel Cells Dr. Prasad Enjeti, ECE Dept, TAMU 9. Dr. Prasad Enjeti: enjeti@tamu.edu Power Electronics & Power Quality Laboratory Facilities State of the art Laboratory 54 kVA, 480V, 50/60 Hz Programmable AC Power Source 10 kVA, 208V, 400Hz / 20kW Motor / Gen test stands DSP control development platforms for Converters 3kW and 15kW solar panel installations on the roof 10W to 3kW Fuel Cell power systems test bed High current DC power supplies / programmable loads / Frequency response analyzer High temperature power electronics test bed Advance simulation laboratory with hardware in the loop capability 10. 11 PV at Texas A&M 11. The grid of today 12. The grid of the future: is it a Smart Grid? 13. Power Electronics Main Enabling Technology 14. The grid of the future? 15. 16 16. Current Installed Wind Power in US Texas is nearly of the total 17. Current Installed Wind Power in US 18. China Installed Wind Capacity China became the largest wind energy provider worldwide, with the installed wind power capacity reaching 41.8 GW at the end of 2010. China has identified Wind Power as a key growth component of the country's economy. With its large land mass and long coastline, China has exceptional wind resources. Researchers from Tsinghua University have found that China could meet all of their electricity demands from wind power through 2030 China has now become the worlds largest producer of wind energy equipment, and components made in China are now starting to not only satisfy domestic demand, but also meet international needs. Two Chinese companies, Sinovel and Goldwind, were already among the worlds top five turbine manufacturers in 2009 Other Asian countries with new capacity additions in 2010 include Japan (221 MW, for a total of 2.3 GW), South Korea (31 MW for a total of 379 MW) and Taiwan (83 MW for a total of 519 MW). 19. Wind Power Systems in India 20. India Installed Wind Capacity India is third - behind China and the USA in terms of new installed capacity during 2010 at 2,139 MW, taking total capacity up to 13.1 GW 21. Conventional Wind Power System Transformer size / weight / cost is an issue Utility transformer is sometimes located on the top of the tower. Large size adds to the cost of the structure 22. New Architectures for Large Scale Wind Power Systems 23. 24 Modulated with a MF square wave (switching frequency fsw) AC-AC converter modulates the line frequency (fs) sine wave into fsw fs Hz and higher frequency components No line frequency components in the transformer voltage Proposed Medium Frequency (MF) Isolation Transformer 24. 25 Modular Concept High frequency ac link primary converter secondary converter Load . . Vp Vs primary converter primary converter High Voltage 4 kV to 15 kV 120 V/240 V 60 Hz 25. 26 The AC-AC converter has 2 fictitious converter sections- one to rectify the input voltage and another to convert the pulsating DC to medium frequency AC A 1-phase diode rectifier or PWM rectifier can do rectifier operation and an IGBT full bridge can do inverter operation Bidirectional AC-AC Converter 26. 27 Unidirectional AC-AC Converter For unidirectional power flow one can replace 4 IGBTs with 4 diodes as shown The resulting converter is simple and is suitable for unidirectional power flow at unity displacement power factor 27. 28 JFE Steel Corporation recently introduced JNEX Super Core steel with 6.5% Silicon (more Si than conventional steel) Reduced acoustic noise and low core loss for medium frequencies around 3kHz, due to low magnetostriction Generates lesser heat and provides higher design induction Core Material: JNEX 6.5% Silicon Steel Core Ref: http://www.jfe-steel.co.jp/en/products/electrical/supercore/index.html 28. 2014/7/8 30 Medium Voltage WTG-BESS Interface Converter Topology With MF Isolation Transformer; no fixed DC bus on utility side 3-Port Network. 29. 2014/7/8 31 Direct AC-AC Wind Power Conversion Concept Interleaved direct Matrix Converter based topology MFT with No DC-link / Energy Storage in any part of the converter 30. Advance Wind Power Conversion Concepts Offshore Wind Farms + udc - udc = 0-66kV 35k V 33kV 150k 35kV DC Collection ~ ~ = = 35kV 150k 33kV AC Collection ~ ~ == 0-690V 690V 33kV AC WT losses Cable losses Cable losses DC WT losses 3% 2.5% 1% 1.3% 0.4% 2% 1.2% AC collection (todays solution) Total losses ~10% ~ = 1% 1.2% 1.2% 1% 1.2% Total losses ~7% DC collection (future solution) 31. Conventional Approach For: DC - Collection Grid Advantages: Well understood and proven topology Relatively simpler construction and operation Disadvantages Bulky DC link, output L-C filter components Full power 60Hz isolation transformer to generate MVDC 32. TAMU Rectifier is an isolated AC-DC converter that converts the WTG AC (~3.3kV) to nearly +/- 20kV DC The isolated rectifier can be constructed in uni-directional or bi- directional configuration 2014/7/8 34 Advance Wind Power Conversion Concepts Offshore Wind Farms DC Collection Grid 33. Medium Frequency Transformer Isolation Approach # 1 Advantages: Standard NPC power module on input side Resonant switching in MF link Disadvantages Resonant capacitor rating Multiple converter modules necessary at the output to be connected in series to achieve +/- 20kV 34. Topology TAMU Approach Advantages: Boost PFC emulates resistive load and also functions as the main power control block. Input current is nearly sinusoidal Extensive use of diodes to increase reliability No series resonant capacitors in the power flow path. Disadvantages: Unidirectional power flow 35. WTG Simulation Setup Parameters Values Generator Voltage 3 kVrms(LL) to 0.75 kVrms(LL) Generator Impedance 4 mH (1.0 p.u. per phase), 10mOhms Generator Frequency 60 Hz to 15 Hz Inverter Frequency 600 Hz XFMR Frequency 600 Hz XFMR Turns Ratio 1 : 6 Boost PFC Frequency 720 Hz (*Selected to reduce resonances) Boost PFC Inductance 20 mH (~ 0.1 p.u. of MVDC w.r.to 60 Hz) Boost PFC Capacitor Two 2 mF capacitors in series per phase Input filter Capacitor 10 uF Input Power 8 MVA maximum Output Voltage +/- 20 kV Number of IGCTs (5.5kV) 12 (primary) + 18 (secondary) Number of Diodes (5.5kV) 12 (primary) + 54 (secondary) 36. WTG Simulation Results 100% WTG power & 15 m/s wind speed 37. New Architectures for Large Scale PV Power Systems 38. Introduction Growth was driven primarily by the utility solar market, which installed 873 MW in Q1 2014, up from 322 MW in Q1 2013[*]. During 2014, the pre-contracted utility scale PV capacity reached 4 times the operation[*]. Solar on a Mountain View, CA home. Photo: SunPower Solar Panels in Walmart Puerto Rico. Photo: Walmart U.S. Quarterly PV Installations by Market Segment[*] U.S. Utility PV Pipeline 2014 [*] [*] U.S. SOLAR MARKET INSIGHT REPORT | Q1 2014 | EXECUTIVE SUMMARY 39. Utility Scale Installations 40. 42 Transformational PV Science and Technology Next Generation Photovoltaics DOE estimates that a $1/W installed photovoltaic (PV) solar energy system equivalent to 56 per kilowatt hour (kWh) would make solar energy competitive with the wholesale rate of electricity without additional subsidies Achieving $1/W installed systems by 2020 represents a significantly more challenging goal than current Business As Usual projections of reaching $2.20/W for utility scale systems by 2016 41. DC Collection Grid 42. 1-phase or 3-phase output Most common of power electronics used PV modules wired in series up to 1000V of open-circuit Multiple strings within the array in parallel DC Collection Grid Note: MPPT is implemented at the central inverter 43. Conventional Utility Scale PV Installations Series-parallel combination of PV panels 1 MW each 480 V 13 kV Y - Y - Y - 1 2 10 10 MW to utility First Solar Inc First Solar Inc First Solar Inc MPPT DC-DC MPPT DC-DC MPPT DC-DC DC-AC Inverter DC-AC Inverter DC-AC Inverter 44. 2014/7/8 46 Advance Solar Power Conversion Concepts MW scale plant divided into zones Each zones DC output converted into medium frequency AC MFT has three secondary windings (one for each phase) Partial shading: Zonal power balancer controls inductor current to be difference between array currents within that zone 45. 2014/7/8 47 Vector Diagrams for Multilevel Inverter Grid Interconnect Powers in an AC system, real and reactive, through a transmission line 21sin SX P 2V1V 21cos 2 SXSX Q 2V1V1V Multilevel output voltage vector is sum of individual cells output voltage vectors Is 180 Vs 0 VL= IsXs 270 V1 1 V2 2 Vn n VAO n21AO VVVV A system with n cascaded inverters has an output voltage n i i 1 VAOV 46. 48 Vector Diagrams for Multilevel Inverter Grid Interconnect (continued) Is 180 Vs 0 VL= IsXs 270 V1 1 V2 2 Vn n VAO n21AO VVVV Power flow in multilevel inverter n i iPtotalP 1 Power flow in each inverter happens between inverter output voltage vector and resultant voltage vector of all other voltages ii SX ji iP n ij j sin 1 VSVV iicos SX ji SX i iQ n ij 1j 2 VSVV V sin SXtotalP SVAOV Real and reactive power flows fairly decoupled. Real power is function of power angle i Reactive power is function of voltage magnitude Vi 47. 49 Vector Diagrams for Multilevel Inverter Grid Interconnect (continued) When insolation is different among zones (m out of n reduced insolation) Output voltage vectors of m inverters reduce in magnitude n-m inverters experience higher than before magnitudes of output vectors Is -(180-) Vs 0 V1 1 Vm m Vm+1 m+1 Vn n VAO,1 VL = jXs .Is -(180-) n21AO VVVV Output vectors of inverters controlled such that Resultant vector satisfies system phase voltage requirement System power factor maintained at unity *APEC 2012 Paper: A new multilevel converter for MW solar pv utility integration. 48. AC Collection Grid Eggebek PV farm North Germany on the Danish border[*]. Largest PV farm in Germany at 2011, total area is 1.3 milionm2[**]. Construction cost 130milion euro[*]. 80 MW of peak electrical power. 371,000 PV modules[**]. 5061 Inverters(15 kW each)[**]. Location of Eggebek Solar Park[*] [*] Wikipedia, Online: http://en.wikipedia.org/wiki/Eggebek_Solar_Park, access on May 29th 2014 [**] Danfoss, Optimized system layout-80 MW Facility in Eggebek, Germany realized with Danfoss TLX Pro Series string inverter concept. 49. Sector 7 Solar Field 480Vrms 60 Hz Frequency 480V/20kV Layout of Eggebek Solar Park[*] Sector 1 Sector 2 Eggebek PV farmAC-CollectionGrid 50. Eggebek PV farm a transformer with high turns ratio is essential 480V to 20kV series connected PV panel string voltage needs to be less than 1000V (DC) to prevent electrostatic discharge and to maintain safety The AC collection grid voltage cannot be greater than 480V (AC) which results in high amperage and contributes to significant cabling cost/weight and losses Solar Field 480Vrms 60 Hz Frequency 480V/20kV Layout of Eggebek Solar Park[*] Drawback 51. 13kV Medium Voltage 60Hz Utility Grid 35kV 60Hz Utility grid 3 Phase to 3 Phase Cycloconverter Medium Frequency Transformer (400Hz to 5kHz) 480Vrms Medium Frequency (400 Hz to 5kHz) Standard 3 Phase P WM Inverter with MP PT 3 Phase LC Filter Boost DC/DC + - PWM Inverter Three Phase Filter CableLength=787ft Solar Field #1 Solar Field #2 Solar Field #3 Proposed Medium Frequency AC Collection grid 52. Proposed Medium Frequency AC Collection grid 13kV Medium Voltage 60Hz Utility Grid 35kV 60Hz Utility grid 3 Phase to 3 Phase Cycloconverter Medium Frequency Transformer (400Hz to 5kHz) 480Vrms Medium Frequency (400 Hz to 5kHz) Standard 3 Phase PWM Inverter with MPPT 3 Phase LC Filter Boost DC/DC + - PWM Inverter Three Phase Filter CableLength=787ft Solar Field #1 Solar Field #2 Solar Field #3 Three phase cycloconverter SiC based SCR Naturally and forced commutation Cables Medium Frequency transformer Delta/Open star Secondary series connected to build the MV Three phase inverters SiC based IGBT Each process 10kW(480V/10 00Hz) Ten connected in parallel Three phase LC filters tuned at 1000Hz 53. Advantage of the proposed architecture The MF transformer isolates the PV and the distribution grid. Modular structure that Increase the system expansion ability Facilitate independent operation of PV field with MPPT Decrease cost and reduce mean time to repair The cascaded MF transformers structure will Decrease the voltage stress on three phase VSI Decrease the transformer turns ratios Increased overall efficiency of the collection grid since the AC collection grid is at higher voltage. Decreased output filter size will due to MF in the collection grid. Decreased Cable and transformer size in the collection system. Small MF transformer/package requirement. Eliminates the bulky line frequency transformer Reduces site preparation (elimination of concrete pads / access rods) and allow more room for PV arrays. Proposed Medium Frequency AC Collection grid 54. Direct AC PV Panel In smart PV module, groups of cells called pixels within a PV module are power conditioned by dedicated low power integrated dc-dc converters. The output of these converters are series connected and fed into H- bridge inverter modules to produce 120V/240V AC voltage. Analysis Control Design Results 9/46 55. Advantages of Direct AC PV Panel The power electronic circuitry along with MPPT algorithm associated with each pixel can be combined within a monolithic IC. The approach enables easy integration of PV modules to suite an end user application. It has the potential to incorporate intelligence to communicate important date to the user and manage information interchange between the panels. The entire system operates optimally when installed on curved surfaces such as in BIPV systems Since MPPT is now optimized at a sub-module level, the overall energy harvesting efficacy is greater. Analysis Control Design Results 10/46 56. System Architecture Each subsection consists of 5 pixel-flyback converters connected in series to an inverter. The inverters are then connected in series to form a four phase cascaded inverter. The multi level cascaded inverter is centrally grounded to provide split phase 120V/ 240V AC voltage Analysis Control Design Results 14/46 57. Control of Smart PV Module The functional overview of each controller is listed below: Implementation of MPPT algorithm at the DC stage Control of auto-connected flyback converters Feed forward control of inverter modules for dc link voltage ripple rejection Analysis Control Design Results 15/46 58. Control of DC-DC Converter The MPPT algorithm generates the reference pixel voltage, Vref for a particular insolation The control input of the converter, duty cycle, d is generated using a PI controller to make the pixel voltage follow the desired reference, Vref Analysis Control Design Results 17/46 59. Design of Smart PV Module Maximum Power 235W Type of Cell Monocrystalline Silicon Cell Configuration 60 in series Open Circuit Voltage 37.0V Maximum Power Voltage 30.0V Short Circuit Current 8.6A Maximum Power Current 7.84A Specifications for Sharps NU-Q235F2 PV module Maximum Power 11.75W Number of cells/ pixel 3 in series Maximum Power Voltage 1.5V Maximum Power Current 7.84A Flyback switching frequency 200kHz Inverter switching frequency 20kHz Inverter operating frequency 60Hz DC link voltage ripple 20% DC link voltage 85-100V Output voltage of flyback 20V Specifications for 3 cell/pixel configuration Smart PV Module system specifications 1. Voltage gain of flyback converter For N2/N1: 16/1 D: 0.435 2. Magnetizing inductance of flyback : 7.35 uH 3. Output capacitor of flyback :1.05 uF 4. DC link capacitor :45uF 5. Output filter inductor :16 mH Analysis Control Design Results 30/46 60. Experimental Results Hardware Prototype for one pixel-converter Flyback converter with control circuitry Analysis Control Design Results PV pixel formed by series connection of 3 cells 37/46 61. New Data Center Power Systems Architecture 62. Low Voltage Data Center 480V - 63. Data Center Current 480V System 64. Best practice for data centers power optimization are 1. Measure Power Usage Effectiveness(PUE) 2. Manage air flow 3. Adjust thermostat 4. Utilize Free cooling 5. Optimize Power distribution These techniques optimized the existing power network structure from 2.0 to 1.12 Total Facility EnergyPUE = IT equipment Energy Power Usage Effectiveness (PUE) 65. Facility Overhead Energy - Transformer losses - Low voltage Cable losses - Medium voltage cables losses - Computer Room Air conditioning cooling - Energy consumption for supporting infra structure (e.g. lighting, office space ..etc.) Any Decrease in the Facility Overhead Energy will Decrease the PUE Total Facility EnergyPUE = IT equipment Energy IT equipment Energy+Facility Overhead Energy= IT equipment Energy Power Usage Effectiveness (PUE) 66. Medium Voltage Systems 67. Medium Voltage Systems 68. Medium Voltage Switch Gear 69. Data Center Distribution Systems - Options Conventional LV 480V, 60 Hz System LV 480V system High current switch board & duct work adds to higher cost & increased losses Conventional UPS & Gen set MV 4160V system Low current switch board & duct work results in lower cost & lower losses 4160V UPS & 4160V Gen set Proposed MV 4160V, 60 Hz System (35kV, 60Hz) (480V) (600V) (Servers) (480V, 60Hz) (480V) (35kV, 60Hz) (4160V) (600V) (Servers) (4160V, 60Hz) (4160V) (480V) 70. Data Center Distribution Systems Proposed MV Medium Frequency Transformer Option Compared to conventional 60Hz architecture MV MFT approach Has the following advantages: Higher efficiency / lower losses Significant reduction in size/weight & floor space An integrated UPS to supply critical loads (35kV, 60Hz)(4160V, 60Hz) Medium Frequency Core (4160V, 60Hz) Main SWBD AC-ACAC-AC AC-DCAC-DC (4160V, MF) LV BatteryEssential Loads (208V/480V, 60Hz) Critical Loads / Server Power 71. Medium Voltage Medium Frequency Transformer / Battery Backup System for Data Centers 3-Phase Medium Frequency Transformer n Iin_a Isec_A A B C Vsec,A Vpri,phA2 VcVa Vb N 4160V/60Hz Medium Voltage Utility Grid 3-Phase Input Filter Iin_a_filtered 1-Phase Boost PFC LPFC Vsec,ph Vdc Vdc,A Vdc,B Vdc,C Critical Load/ Server Power Boost PFC Boost PFC Boost PFC LT 3-phase PWM Rectifier S3 S4 S2 S5 S6 CR UPSBattery VBatM1 LR S1 AC-AC Converter Vpri,phVC1 Vdc 72. Medium Voltage Medium Frequency Transformer / for Data Centers 73. Data Center Distribution Systems Proposed MV Medium Frequency Transformer Option (35kV, 60Hz)(4160V, 60Hz) Medium Frequency Core (4160V, 60Hz) Main SWBD AC-ACAC-AC AC-DCAC-DC (4160V, MF) LV BatteryEssential Loads (208V/480V, 60Hz) Critical Loads / Server Power Medium Frequency Transformer with Integrated UPS 98% efficient Critical Power Loss < 5% Grid to Rack With Substantial Savings in Space/Weight Medium Frequency Transformer for Essential Loads 99% efficient 74. Advantages of the Proposed MV Medium Frequency Transformer Option Eliminate 80% of PVC and copper content in data center electrical distribution Make electrical equipment rooms significantly smaller and require less building structure Help bring the total power loss between utility grid and power racks < 5% 75. Multi-Port Converter for Smart Grid 76. Multi-Port Converter for Smart Grid 77. 81 Multi-Port Converter Two DC Sources Independent Operation 78. Multi-Port Converter Four DC Sources Independent Operation 79. Thank You Power Electronics is one of the Chief Enabling Technology for Smart Grid