power electronics for wind energy applications

7/29/2019 Power Electronics for Wind Energy Applications

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By

Dennis Woodford, P.Eng.

IEEE Life Fellow

[email protected]

17 September, 2012


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The earliest windturbine generatorsapplied inductiongenerators (one or twospeed)

They required a largeshort circuit ratio,

above 7 to operateeffectively

No power electronics

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US patent 5,083,039

granted January 21,1992 to Richardsonand Erdman andassigned to U.S.

Windpower, Inc. Applied power

electronics in a DFIGconfiguration

Ended up beingowned by GE

Expired Feb 1, 2011

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GE DFIG Wind Turbine GeneratorsCourtesy of GE


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The European and AsianManufacturers of WindTurbine Generators coulduse power electronicsthat applied with ACvoltage control

However, they could not

sell them in NorthAmerica. No AC voltagecontrol allowed

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Vestas DFIG Wind Turbine

Generator in Denmark


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Short circuit ratio less than 7 possible depending on

SVC or STATCOM used


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Requires short circuit ratio of 2.5 (2.0 minimum)


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Minimum short circuit ratio < 2 theoretically possible


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Numerous complex powerelectronic devices: Wind farms,HVDC/VSC, PV Inverters...

Weak systems, low ESCR, reduced

system inertia Increased loads, need for RAS

schemes

Series capacitors, SVCs and

STATCOMs (instead of newtransmission lines)

Doing more with what you got

New research required for

simulation tools!

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There is a possibility ofSub-synchronous controlinstability (SSCI)

What is SSCI?

Interactions between apower electroniccontroller (such as a wind

turbine generator, DClink, VSC, etc) and aseries compensatedsystem

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Typical series compensation(Courtesy of ABB)


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Wind projects in Texas

Radial 345 kV lines

ERCOT CREZ system expansion

345 kV series compensated lines

PacifiCorp Gateway system expansion

500 kV lines, series capacitors, SVCs Alberta southern system expansion

230 kV lines, series capacitors, SVCs

Proposed 500 kV project in PacifiCorp

UK large scale transmission expansion

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Example Series Compensated Feeder


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Current

Voltage

DFIG wind turbines are more prone to SSCI than Full Converter


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Changes to wind interconnection standards

Requirements to study SSCI

Series capacitor safe turbines Obtain Supplier Guarantee

Development of a wind/series capacitor benchmark system

Possible solutions Higher voltage lines, TCSC (thyristor controlled series capacitors),

operating restrictions, selective bypassing, HVDC ...

Sub-synchronous blocking filter across a series capacitorsegment - expensive

Wind turbine modeling Detailed EMT models (using real controller code)

System models and model development methods

Confidentiality concerns

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Blocking filter in parallel with series capacitor

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Transient Stability ToolsPSS/E or PSLF models are required ininterconnection studies in North America

Used for system impact and facilities studiesNot able to reproduce resonant conditions inthe electrical system and not sufficient forSSCI interaction studies

Control models may not be detailed enough


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EMT (electro-magnetic transients) Models:PSCAD or EMTP

Necessary for SSR studies and control interaction studies

Include IGBT firing, harmonics, high speed controls,Multi-level Modular Converters (MMC), etc...

Often use actual code from the hardware -

confidentiality concerns

EMT studies are often not performed or needed in manyinstallations


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Wind farms with Types 3 & 4 wind

turbines are virtually Constant Power Consider South East Colorado:


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PSS/E studies showed a certain maximum power

flow Kansas to Colorado EMT studies indicated a lower max power flow


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The first DC feeder for awind farm is the 400 MWBorWin Alpha project inthe North Sea by ABB

Other DC feeder projects

are in construction by ABBand Siemens

Courtesy of ABB


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Line commutated HVDC (LCC) thyristorrectifiers require AC short circuit capacity to

operate

Basic Type 3 and Type 4 wind turbinegenerators also require AC short circuitcapacity to operate

So, is an LCC rectifier realistic for a feederfor wind farms?


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Synchronous condenser and/or generator

required at the rectifier to create the necessaryshort circuit capacityAn LCC feeder may have a minimum power

capability impacting wind farm stand-by energy


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A voltage sourced converter (VSC) for a

rectifier can generate adequate and effectiveshort circuit capacity with fixed AC busbarfrequency and steady voltage allowing most

types of wind turbine generators to operate


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A voltage sourced converter (VSC) feeder

requires a DC Chopper to protect against DCOvervoltage


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AC cable Molokai to Lanai

One Optionwith VSCs


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DC grid with Multi terminalVSC

Multi terminal VSC modelsnot available in TS programs

Develop EMT models ofonshore VSC converters, DCcables, offshore convertersand turbines (PSCAD)

Use real controls from VSCand wind turbine Suppliers

Interfacing with the EasternInterconnection (PJM) - PSSE

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B4-55 HVDC Connection of Offshore WindPower Plants

B4.56 Guidelines for the Preparation ofConnection Agreements for HVDC GridsB4-57 Development of VSC Models for HVDCGridsB4-58 Devices for Load Flow Control and Direct

Voltage Control in a Meshed HVDC GridB4-59 Control and Protection of HVDC GridsB4-60 Designing HVDC Grids for Optimal

Reliability and Availability Performance

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Parallel Processing of EMT Simulations

Break the EMT simulation into several cases and runthem in parallel talking to each other

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Hybrid Simulations

EMT and Transient Stability simulations are run inparallel, talking to each other

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power electronics for wind energy applications

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