Transcript ppt - Arizona Solar Center

Inverters for
PhotoVoltaic Systems
© AH, ARJ 2002
Evolution & Applications of
Inverters
Square Wave:
– mechanical switching
– now extinct
Modified Square-Wave
Modified Sine Wave (mid-70’s):
– low cost, high reliability, easy service.
– Control Average Voltage.
– not good for some TV’s, ballasts, laser printers,
energized coils/transformers.
Sine Wave Inverters
Sine wave: Series I and II (early-90’s):
– higher cost, added features & complexity
– handle surge currents, >2:1
– 1st line tie capability, higher efficiency, less
heat, increased size/weight
Added Features
• Battery Charging
– full-bridge rectifier
– 3-stage advantages
• Power Management
– Relays for generator starting, exercise, charge timing,
selling power back to utility
– voltage-driven, or clock-driven
• Temperature Management
– Heat sinking, variable-speed fan control, high
efficiency is your friend
High Frequency Switching
Sine Wave Inverters
• Light-weight and with a very high quality
sine-wave.
• Early units did not have the surge capability
of the SW inverters.
Line-Tie Inverters
• Sine wave inverters dedicated or modifies
to feed power back to the Utility Line.
• Stringent safety requirements to protect the
inverter and utility.
• High efficiency, relatively low cost.
Inverter Classifications
• Uninterruptable Power/Stand-Alone: Battery powered;
independent of electric utility; can often charge batteries
with AC hybrid source.
• Utility-Interactive or Grid-Connected: Must detect the
waveform and consume power (nighttime) from the
electric utility to function; synchronizes voltage, frequency
and phase with utility; controls the PV array directly.
• Stand-Alone with Utility-Interactive : Can operate in
conjunction with utility but provide power independently if
power fails.
Inverter Comparison
Stand-alone
Utility-interactive
• Inverter creates voltage
waveform.
• Load current may distort
waveform or shift phase.
• Grid creates voltage
waveform - inverter
unlikely to distort.
• Inverter behaves like
negative load, feeding
current back into grid.
• Loads respond to grid
voltage, not inverter
current.
– Motor current lags voltage
– Computers demand current
at voltage waveform peaks
Inverter Comparison con’t.
Stand-alone
Utility-interactive
• Inverter has no control
over battery charging via
PV, wind, hydro, etc.
• Amount of energy
extracted from PV array is
a function of battery
voltage .
• Maximum Power Point
Tracking (MPPT)
eliminates separate
controller & extracts max
power from PV array at
temperature.
Codes for Inverters
UL 1741 and IEEE 929-2000:
• Avoid “islanding” when utility-interactive:
inverter powering loads on disconnected section
of grid.
• Avoid dumping power into a short.
• Inverter to restart 5 min. after grid specifications
restored (voltage and frequency).
Utility Defined Distributed Generation
Separate, Emergency or
Standby Generation“Non-parallel System”
• No possibility of electrical
connection.
• “Break before make”
transfer switch required
for main service box.
• Or move critical loads
onto separate service box.
Interconnected Generation
- “Parallel System”
• Connected to electrical bus
common with utility.
• “Visible open” disconnect
switch required, protective
relaying, metering, etc.
• Agreements with utility.
Selection Tree
Power Requirement
Less than 10kW
More than 10kW
(Residential / Small Commercial
120 / 240 VAC 80A max.)
(Commercial
3 phase, 480 / 208 VAC)
Residential / Small Commercial
Power /Use / Cost Requirement
Sine Wave
Modified Sine Wave
Residential / Small Commercial
Sine Wave
Grid-Tie
Standalone
Residential / Small Commercial
Grid-Tie
PV
Sunny Boy
Hybrid
ST/XR
SW
Sunny Boy
• High Voltage / high
efficiency.
• Can be used in 3phase circuits.
• Available as 1.8kW
and 2.5kW.
Components
Xantrex SunTie XR
• 48VDC Line Tie Inverter
• Built-in system display
• Optional Remote Display
• 1kW, 1.5kW, 2kW & 2.5kW
• Early ST inverters had problems which
seem to have been solved in the XR series
SW Series Inverter
• Xantrex /Trace SW Inverter /
Battery Charger. Can be used
stand-alone or Grid-Tied (with
interface)
• This is the workhorse inverter for
many standalone systems.
• Available in 4kW and 5.5kW
• Inverters can be combined to
provide 240VAC, or stacked in
parallel to increase power.
Residential / Small Commercial
Standalone
Charger
SW
AEI
MM-5000
No Charger
Exeltech
Prosine
Exeltech
• Innovative design that
provides redundancy and
upgrade capabilities by
adding modules.
• No Battery charging
capability.
• Very high quality sine
wave.
ProSine Series
• Small, light inverters,
often used in the RVs
and boats.
Residential / Small Commercial
Modified Sine Wave
DR
Heart
Rail Mount
UX
etc.
DR Series Inverter
• Modified Square
Wave.
• High Reliability.
• Relatively Cheap.
Commercial
Power
PV
Xantrex
PV Series
Hybrid
AES
Advanced Energy Systems
Australia
PV Series Inverter
• High Voltage High
Power PV only Inverter.
• Available from 10kW –
225kW.
• Requires additional
transformer if not behind
a Utility fence.
AES Hybrid Installation
Decision Tree