Energy Source Diversification

1
Energy Source Diversification

• Patrick Chapman
• Asst. Professor
• UIUC
• Sponsored by National Science Foundation

2
What is a diversified energy source?

• gt 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
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
Research Areas

• Circuit topologies
• Energy source allocation (static control)
• Dynamic control
• Simulation
• Experimentation

5
Conceptual Diagram

• Source-to-load conversions
• Source-to-source conversions
• Load-to-source conversions

6
Selected Applications

• Classic two-input Uninterruptable Power Supply

7
Solar/Battery

• Provide average AC power from solar only

8
Solar/Battery Flexible Bus Voltage

• Allows more flexibility in battery management

9
Fuel Cell / Battery

• Provides dynamic capability to fuel cell system

10
Three-Source Systems

• AC Line, Fuel Cell, Battery
• (plus capacitor)

11
Multiplicity of Same Source

• Unbalanced sources, alternative locations

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
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
Standard DC Link

• Essentially rectifier-inverter circuit
• only we attach different sources and loads

15
DC Link with Phase Leg Approach

• Model after standard bridge inverters, active
  rectifiers
• requires inductive load/source impedance (not
  shown)

16
AC Link

• Use transformer, coupled inductors
• isolation possible
• less scalable

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 doesnt have to)

18
Matsuos Circuit

• An AC link topology
• Used in
• solar/battery
• wind/solar/utility
• Shown experimentally
• Dynamic Analysis

19
Caricchis 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
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
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
Multiple-Input Buck

• Standard buck with parallel inputs
• Originally shown by Rodriguez, et al, with only
  two inputs
• shown with solar/battery

23
New, Recent Work at UIUC

• Multiple-input buck-boost (MIBB)

24
MIBB Characteristics

• Buck and boost operation
• Similar, but simpler, than Matsuos 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
Cousins of the MIBB

• Multiple-input flyback
• add isolation, turns ratio

26
Multiple-Input, Multiple-Output

• Flyback with multiple, isolated outputs

27
Multiple Output, Some Isolated
28
With a bidirectional load/source

• Battery load/source concept

29
MIBB with Multiplicity of Sources

• Battery balancer
• (other, probably better balancers exist)

30
Steady-State Analysis

• Many switching strategies possible
• first attempts involve simple common-edge,
  constant frequency, approach

31
Steady-State Analysis, contd

• Begin with basic MIBB, continuous mode
• The instantaneous inductor voltage
• Setting the average to zero, solving for Vout

32
Effective Duty Cycle

• The effective duty cycle is the time a switch
  conducts nonzero current
• Can be shown

33
Two-Input Case

• V1 gt V2, D1 gt D2
• normal buck-boost, single input
• V1 gt V2, D2 gt D1

34
Selecting Duty Cycles

• Given prescribed
• Power, Pi, for each source
• Output Voltage, Vout
• Input Voltages, Vi

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
Correcting for Nonideal

• Simple switch-drop model
• More complicated models possible
• Feedback to cancel nonidealities

37
Experimental Continuous Mode

• Vary one duty cycle of three
• Hold all other constant, constant R load

38
Discontinuous Mode

• Inductor current is zero for some portion of each
  cycle

39
Average Output Voltage

• Energy balance
• Output Voltage
• similar to standard buck-boost

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
Experimental, Discontinuous

• Vary one duty cycle, hold others constant

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
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