1. Energy Source Diversification Patrick Chapman Asst. Professor UIUC Sponsored by: National Science Foundation Grainger Center for Electric Machinery and Electromechanics

2. What is a diversified energy source? • > 1 energy source • Power flow both to and from some sources • “Source” may be energy storage • Overall ability of multiple sources exceeds the ability of one alone • reliability • environmental responsibility • adaptability • interchangeability Grainger Center for Electric Machinery and Electromechanics

3. Motivation • Incorporate more ‘preferred’ energy sources • wind • solar • fuel cell • Conversion methods that adapt to various sources and loads • address wide market with single product • Take advantage of deregulation laws Grainger Center for Electric Machinery and Electromechanics

4. Research Areas • Circuit topologies • Energy source allocation (static control) • Dynamic control • Simulation • Experimentation Grainger Center for Electric Machinery and Electromechanics

5. Conceptual Diagram • Source-to-load conversions • Source-to-source conversions • Load-to-source conversions Grainger Center for Electric Machinery and Electromechanics

6. Selected Applications • Classic two-input: Uninterruptable Power Supply Grainger Center for Electric Machinery and Electromechanics

7. Solar/Battery • Provide average AC power from solar only Grainger Center for Electric Machinery and Electromechanics

8. Solar/Battery; Flexible Bus Voltage • Allows more flexibility in battery management Grainger Center for Electric Machinery and Electromechanics

9. Fuel Cell / Battery • Provides dynamic capability to fuel cell system Grainger Center for Electric Machinery and Electromechanics

10. Three-Source Systems • AC Line, Fuel Cell, Battery • (plus capacitor) Grainger Center for Electric Machinery and Electromechanics

11. Multiplicity of Same Source • Unbalanced sources, alternative locations Grainger Center for Electric Machinery and Electromechanics

12. Restricted Switch Types • More general switch schematic symbols • Forward-conducting, bidirectional-blocking (FCBB): • GTO, some cases SCR, MOSFET-diode, IGBT-diode, MCT,RB-IGBT (new) Grainger Center for Electric Machinery and Electromechanics

13. Circuit Topologies • Straightforward approaches • “n” sources, “n” converters (or similar) • dc link • ac link • New topologies • “n” sources, “1” converter (with “n” inputs) • embed sources in the converter Grainger Center for Electric Machinery and Electromechanics

14. Standard DC Link • Essentially rectifier-inverter circuit • only we attach different sources and loads Grainger Center for Electric Machinery and Electromechanics

15. DC Link with ‘Phase Leg’ Approach • Model after standard bridge inverters, active rectifiers • requires inductive load/source impedance (not shown) Grainger Center for Electric Machinery and Electromechanics

16. AC Link • Use transformer, coupled inductors • isolation possible • less scalable Grainger Center for Electric Machinery and Electromechanics

17. Prior Work • First ‘multiple-input’ converter from Matsuo, et al, c. 1990 • ‘Multiple input’ can be interpreted more broadly • e.g. three-phase rectifier has three inputs • Here, consider the narrow interpretation • three inputs could handle three different sources (but doesn’t have to) Grainger Center for Electric Machinery and Electromechanics

18. Matsuo’s Circuit • An AC link topology • Used in • solar/battery • wind/solar/utility • Shown experimentally • Dynamic Analysis Grainger Center for Electric Machinery and Electromechanics

19. Caricchi’s circuit • Caricchi, et al, developed DC link version, c. 2001 • Shown in • hybrid automobile • wind/solar/utility • Can be used with fewer switches • depends on directionality of sources, loads • Boost only from source to cap. • Buck only from cap. to load Grainger Center for Electric Machinery and Electromechanics

20. DC Link Circuit • Uses one inductor for each load, source • or requires load, source to have inductive series impedance • Essentially the standard phase legs we know well, applied to multi-source • Uses capacitive energy storage • could be battery instead, but high voltage Grainger Center for Electric Machinery and Electromechanics

21. Buck-Derived Two-Input • Ordinary buck topology • diode cathode goes to a second source, not ground • Sebastian, et al, showed high efficiency attainable • diversification not studied. Grainger Center for Electric Machinery and Electromechanics

22. Multiple-Input Buck • Standard buck with parallel inputs • Originally shown by Rodriguez, et al, with only two inputs • shown with solar/battery Grainger Center for Electric Machinery and Electromechanics

23. New, Recent Work at UIUC • Multiple-input buck-boost (MIBB) Grainger Center for Electric Machinery and Electromechanics

24. MIBB Characteristics • Buck and boost operation • Similar, but simpler, than Matsuo’s approach • Scalable to n inputs • Can regulate output voltage with an prescribed power flow from each input (in theory) • Probably has some niche in energy source diversification field • In base form, only accommodates unidirectional source/load • can modify a bit to get bidirectional Grainger Center for Electric Machinery and Electromechanics

25. Cousins of the MIBB • Multiple-input flyback • add isolation, turns ratio Grainger Center for Electric Machinery and Electromechanics

26. Multiple-Input, Multiple-Output • Flyback with multiple, isolated outputs Grainger Center for Electric Machinery and Electromechanics

27. Multiple Output, Some Isolated Grainger Center for Electric Machinery and Electromechanics

28. With a bidirectional load/source • Battery load/source concept Grainger Center for Electric Machinery and Electromechanics

29. MIBB with Multiplicity of Sources • Battery balancer • (other, probably better balancers exist…) Grainger Center for Electric Machinery and Electromechanics

30. Steady-State Analysis • Many switching strategies possible • first attempts involve simple common-edge, constant frequency, approach Grainger Center for Electric Machinery and Electromechanics

31. Steady-State Analysis, cont’d • Begin with basic MIBB, continuous mode • The instantaneous inductor voltage • Setting the average to zero, solving for Vout: Grainger Center for Electric Machinery and Electromechanics

32. Effective Duty Cycle • The effective duty cycle is the time a switch conducts nonzero current • Can be shown: Grainger Center for Electric Machinery and Electromechanics

33. Two-Input Case • V1 > V2, D1 > D2 • normal buck-boost, single input • V1 > V2, D2 > D1 Grainger Center for Electric Machinery and Electromechanics

34. Selecting Duty Cycles • Given prescribed: • Power, Pi, for each source • Output Voltage, Vout • Input Voltages, Vi Grainger Center for Electric Machinery and Electromechanics

35. Plausibility of Duty Cycles • Sum of all effective duty cycles less than one? • YES, since: • May be issues with extreme duty cycles • same for all converters Grainger Center for Electric Machinery and Electromechanics

36. Correcting for Nonideal • Simple switch-drop model • More complicated models possible • Feedback to cancel nonidealities Grainger Center for Electric Machinery and Electromechanics

37. Experimental Continuous Mode • Vary one duty cycle of three • Hold all other constant, constant R load Grainger Center for Electric Machinery and Electromechanics

38. Discontinuous Mode • Inductor current is zero for some portion of each cycle Grainger Center for Electric Machinery and Electromechanics

39. Average Output Voltage • Energy balance • Output Voltage • similar to standard buck-boost Grainger Center for Electric Machinery and Electromechanics

40. Characteristics of Discontinuous Mode • Very sensitive to parameters • feedback a must • Improve accuracy by including • switch drop model • core loss model • taken from Micrometals data sheets • iterative procedure with switch-drop model as starting point Grainger Center for Electric Machinery and Electromechanics

41. Experimental, Discontinuous • Vary one duty cycle, hold others constant Grainger Center for Electric Machinery and Electromechanics

42. Other Work at UIUC • Multiple-input flyback • currently being investigated • successful simulation, analysis • Multiple-input boost • n boost converters with common output capacitor • power from unlike solar array sources • simulation, design stage Grainger Center for Electric Machinery and Electromechanics

43. Work to be Done • Dynamic analysis • Dynamic control • case-by-case? • Static control • power management • case-by-case • Evaluation of topologies • Interchangeable sources • Topology restructuring Grainger Center for Electric Machinery and Electromechanics