1. February 2, 2004Grainger Center for Electric Machinery and Electromechanics 1 Energy Source Diversification Patrick Chapman Asst. Professor UIUC Sponsored by: National Science Foundation

2. 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

3. 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

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

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

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

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

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

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

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

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

12. 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)

13. 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

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

15. 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)

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

17. 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)

18. 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

19. 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

20. 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

21. 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.

22. 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

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

24. 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

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

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

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

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

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

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

31. 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 V out :

32. 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:

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

34. Grainger Center for Electric Machinery and Electromechanics 34 Selecting Duty Cycles Given prescribed: – Power, P i, for each source – Output Voltage, V out – Input Voltages, V i

35. 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

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

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

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

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

40. 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

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

42. 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

43. 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