Download Types of DR Island Systems - IEEE Standards working groups

IEEE P1547.4 Meeting Notes:
Next Steps
Update Working Group list
Post Meeting Notes, TOC, and extended outline on web page by Feb 18.
Send out email to WG on web postings.
Writing assignments due to Ben Kroposki or Tom Basso by April 29.
New sections to be posted on web by May 6
Possible web meeting in May to discuss inputs
Next Working Group Meeting may be in July/August 2005 (possible - NRECA
Arlington, VA)
Guide Balloted and Approved - December 2007
TOC (2/9/2005)
Introduction (… history of the standard, a description of its purpose,… 1547 series).
Introduction: Reasons for DRIS - reliability; maintenance; economic factors (peak shaving;
deferred T&D; line/voltage support); power quality; power security (backup);
1. Overview
a. scope, purpose
b. use - objectives improved reliability, ease of operations
c. major recommendations
2. References
3. Definitions and Acronyms
4. Electrical System Characteristics
DR Island System Overview (diagrams??) – Ben Kroposki, Sam Ye
Characteristics of loads – Jim Daley
Characteristics of EPS (Local and Area) – Murray Davis
Characteristics of DRs and interconnection systems (M. Davis, R.
Wills, K. Sheldon)
e. Methods of voltage and frequency control
a.
b.
c.
d.
5. Functionality of the DR island system
a.
b.
c.
d.
EPS connected – Doug B
Transition mode – Ron Hartzel, M. Davis
Island mode (details in Section 6) – Rob Wills, Kent Sheldon
Reconnection mode
6. Design and integration of DR island systems
a. Types of Islands – Ben Kroposki, Sam Ye
b. Engineering Considerations (concerns with solutions)
i. Step Loads
c. EPS Planning (short circuit, load flows, evolution of systems over
time) – Dave Costyk
7. Operation of DR island systems
a. Central dispatch vs. distributed vs. autonomous – Dave Costyk
b. Communication and information exchange – Tom Basso
Annex A – Bibliography (R. Wills, CERTS microgrids, CERTS Protection white
paper, NEMA MG 1, EGSA Books??, Color Books (e.g., IEEE gold book reliability), Marine Power System Requirements Std (Yuri/Basso), IEEE Std 666,
Grid Grounding (IEEE Std 80) C62.90.xxx, C62.21 – insulation levels fro
grounding, NFPA 70 (NEC), IEC (JCG DRES; TC64; from Koepfinger)), European
Frame 5 microgrid project, 1547 series, PES microgrid from M. Davis,
Annex B – Example DR Island Applications? (include new diagram of
DR at Substation)
Keywords: microgrid, minigrid,, intentional island, planned island, unplanned island, black start,
seamless transfer, premium power,
February 9, 2005
Section 5 - Functionality of the DR island system
5.a. EPS Connected Mode
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When DR Island System is connected to the EPS then 1547 requirements apply (Can 1547.2
cover this section?)
The DR Island System should recognizing problems on EPS and disconnecting per 1547
Coordination of disconnect criteria with EPS (intentional vs. EPS failure) – DR owner may want to
island system before 1547 requirements. Or Area EPS may want DR to stay on line outside 1547
requirements.
Power import/export control
o economic dispatch (dispatch algorithm may be different from EPS mode to Island mode)
o the setting of this can influence how/when to transition to island mode. (magnitude of this
setting. (Excess power, reserve of power, etc.)
Monitoring – Area EPS may want to know breaker status, DR real and reactive power, what
system is doing prior to island, what potential island is doing
DR Voltage Control
o Passive Control – track system voltage (per IEEE 1547 requirement)
o Active Control – absorb/export VARs (needs utility approval) – this can be beneficial but a
study is needed so that it does not hurt system
Connecting Inverters to Area EPS in voltage source mode instead of current source mode (this
could improve power quality by active harmonic suppression, improve voltage regulation (reduce
sags and swells) and imbalance)
Ancillary Services (contractual agreements with Area EPS)
Voltage Regulation – how to keep voltage on distribution system within limits with DR installed
Aggregation of multiple DR
5.b. Transition Mode from EPS Connected to Island Mode
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Types of Islands [Address for all topologies in figures 1, 2, …?]
o Planned – decision made intentionally
 Utility requested
 DR Owner requested
 End User requested
o Unplanned – loss of utility or Area EPS voltage or frequency out of
tolerance
 Sensing EPS voltage (below ANSI or other agreed-on limits)
 Sensing EPS frequency (below load-shed steps)
 Current magnitude and direction (faults)
 Power magnitude and direction (directional power relay)
 Transfer trip request
 Any other specified condition, e.g. phase shift, impedance change,
harmonic content, parameter rate of change
Identify load requirements during transition
o Load sensitivity to voltage fluctuations (references, examples)
 Few cycles
 Tenths of a second to seconds
 > 10 seconds
o Load sensitivity to frequency fluctuations (references, examples)
o Current inrush requirements (transformer magnetization)
o Power Quality requirements during transition
 Harmonics
 Frequency and voltage response (regulation and recovery)
 Voltage imbalance (magnitude and phase angle) [single phase
loads on island]
 dc injection
 Switching transients
 Flicker
Notes:
Address cold load pickup
Transition time includes detection and response
Initiation Time
Transition types
o Seamless is defined as transition within the voltage and frequency
tolerance of the load
 Within ITIC requirements
 Open transition (power contacts break before make)
 Closed transition (power contacts make before break)
 momentary make-before-break (sources paralleled for a
maximum of 100ms) [usually passive, i.e., does not employ
control of fuel or excitation]
 extended make-before-break
o soft load transfer -usually employs active control of
fuel and excitation
o Temporary load interruption
 Open transition (time-delay neutral, load voltage decay)
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Generation/ Load matching (capacity/load management)
o Increase generation to match load
 Reduce voltage to reduce load
 Add static var compensation to reduce load current
 Add reserve generation
 Change control to load-following
o Decrease load to match generation
 Load disconnect
 Frequency initiated
 Voltage initiated
 Demand initiated (PLC, meter, or other controller)
 Load cycling (air conditioning, water heating)
 Reduce load consumption (dim lights)
 Other load management schemes
DR operation mode (current, voltage, power, VARS)
o Inverter (Current mode to voltage mode)
o Synchronous generator (Controlled to load-following)
o Induction generator (Self-excited or wound-rotor)
o Interaction of mixed generation
o Double fed (synchronous/inverter - wind generators)
o Multiple unit controls
 Master/slave
 Droop/isochronous
5.c. Island Mode
Load Management
 Control scheme should manage:
 Can DR serve all loads?
 Load Shedding
Generation Management
 Level Loading per Isochronous Control
 Economic Dispatch
 Generation reduction due to lack of load
i. Via communications
ii. Via voltage or frequency limits (best linear reduction to preserve stability)
Load Imbalance
 Single phase loads on three phase system
o Line-Line & Line-Neutral
 Split single phase systems
 Single Phase Generation
o Automatic re-allocation
o Increased reliability
o May not be available in distribution
Voltage Imbalance
 Causes circulating currents in three phase systems
Voltage Regulation
 Allow relaxed operational limits outside Ansi C84??/1547
 Allow relaxed trip limits vs. 1547?
o Eg resistive loads would not be damaged
o Look at existing generator specs
o Will be site and load specific
DR Control
 Single-DR Control
o Simple voltage and frequency regulation
o Similar to existing rotating machine and stand-alone inverter control
 Multi-Unit DR Control
o Categories
 All Rotating
 Could have induction machines
 Rotating and Inverter
 Could have induction machines
 All Inverter
 Synchronous Machine Control
o Most multi-unit systems use isochronous control
o Fast PID frequency control with slower load control input
o Droop voltage control with slower reactive power control input
o More common is cross-current var compensation control (more info required
Basler Electric
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o Alternative is droop control on frequency. Can be done without communications,
but frequency will be variable.
Inverter Control Methods
o Several Classes of control – current, voltage, combination
o Can have a mix of both types
 General
 For optimal operation, inverter control and rotating machine
control methods should be compatible (voltage and frequency
controls)
 Murray:
 Current Source
 The output of the inverter is a controlled ac current which is
frequency synchronized with the local EPS.
 Disadvantage is no transient load following
 Normal mode for interconnection
 Need another DR source to regulate voltage and frequency. For
example a battery-inverter system that sets voltage and frequency,
supplies transient loads and absorbs excess generation.
 Voltage Source
 The output of the inverter is a controlled ac voltage which is
frequency synchronized with the local EPS (island or microgrid).
 Probably want to emulate synchronous machine behavior for
voltage control
 Droop is used for load sharing
 Combination Control
 Current control with output voltage “droop”
 Voltage control will transition to current control when max. current
limit is reached (prime-mover, magnetic and thermal limitations)
o Frequency Control
o Possible Schemes:
 Can have a master synch signal but ideally just use the terminal voltage
 Use existing rotating machine (RM) isochronous control and load share
techniques.
 Should control have inertia?
 Isochronous control – local PID control of frequency plus input via
communications: all machines broadcast their load percentage. Each
calculates average total load percent and changes its own generation to
match the average via a slower PID controller.
o Transient Power/Frequency Limiting
o Induction Machine Issues
 Need to supply reactive power for voltage regulation
 Penetration percentage – need enough other generation to regulate
o Stability control issues
Steady-State and Dynamic Stability
o Steady-State
o Dynamic
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Transient Stability
o Step Loads
o Equipment Outages
o Faults
Real Power
Reactive Power
Circulating Current Issues
o Need to investigate further:
o Could be caused by voltage imbalance, var flow, load imbalance
Transient Behavior
o Generation surge rating
o Control Means
Harmonic Loads
Power Quality requirements of loads
 Basic requirements should follow 1741 (5% total THD in SA mode with linear
loads)
 Performance should be comparable to rotating machines
 Allow clipping for transient start.
DR limitations
 Current, voltage, power, VARS
 Fuel/Prime Mover limits
Cold load pickup
 Blackstart typically relates to one generator or a small group – situation where there is no
power.
 Easier to do inside a facility than across several customers
 Full load pickup can be up to 6x normal load
 May require load control and/or the ability to parallel multiple generators before load
connection
 Could have systems that carry through on grid fail, but cannot perform a cold load pickup
 Turbines have little peak capability.
 Recip machines typically will not do more than 100% because of turbocharging even
though generator is capable of 300%. (need to know more of this). Underfreq typically at
58 Hz. Frequency rolloff (Volts per Hz) rolls off output voltage when frequency drops.
 Soft starts on large motors could help
Reliability
 N+1 Load supply
 Distinguish between essential and non-essential loads
 Reliability requirements are different for residential, agricultural, commercial, etc.
Time Control
Correcting time error over 24 hour period so that clocks read correctly
Protection Issues (Fault protection)
 Integration with area EPS protection
 Coordination
 Different Fault Levels
 Fault study analysis needed
o Place faults in different locations assess fault currents
o Fault currents could be in different directions to normal
o Significant difference between utility capability and rot.gen (300% for 10 seconds
– field forcing).
o Distance relays based on impedance could become inaccurate
 Recloser Timing
Interconnection/Isolation/Sectionalizing Switching Device
 Device requirements are in 1547
 Need double voltage rating plus 10%
 Could have an Area EPS fault – need to cope with this fault current which is the sum of
the aggregate generation
 Might have both situations simultaneously
 Check IEEE & UL standards (UL1001)
 May want to allow for lightning strikes in addition – perhaps need disconnects in addition
(compare with air-break switches for transmission).
 Reclosers may not be useable as they are not rated for this use.
Protection against accidental reconnection to EPS
 Need minimum equipment requirements
Monitor DR Island Condition and EPS parameters for Return to Interconnection
Regulations
 Islanding part of the Area EPS
 Likely to have special requirements
5.d. Reconnection of DR Island System to EPS
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Automatic and Manual Reconnect
o Identify transition types (seamless, within CBEMA, momentary make-before-break 100ms
transfer, shutdown)
Monitoring Requirements - Monitor EPS parameters to determine if it OK to reconnect
Reconnection Delay - 1547 requires an adjustable time delay or up to 5 min delay before
reconnection
Synchronization - Synchronize DR Island System to Area EPS
o Switch DR operating mode from voltage to current to reconnect. Some DR cannot
reconnect without shutting down
o A simple method of reconnecting is to shut down island and allow EPS to pick loads.
o DR will need to be able to adjust island frequency to synchronize to EPS
o Discussion on synchronism passive/active
o Establish communications link if sync. Link is very far (1 mile) away.
o Direct wiring to unit (phase and voltage)
o Slow increase of frequency
o As long as you are within 1547 parameters for synchronism then you can reconnect
Load Management – EPS may need to have load management to pick up additional loads after
reconnection
Time correction may be needed
Area EPS Operator role???
Additional Information for Outline
Prime Mover types (wind, PV, diesel, renewable or not)
Interconnection Technology types (sync, induction, inverter)
Critical or non-critical load (Loss of Load risk)
Types of DR Island Systems
 facility microgrid (does not include any part of Area EPS)
 planned island with part of Area EPS
 “larger” island systems (a municipality with a portion of another Area EPS)
Engineering Concerns
Integration issues, e.g., volt regulation – within island as well as across “EPS”; communications (MIC);
load sharing; dispatch within the island; generation shedding; energy storage; seamless transfer vs
shutdown and resync; stability (single and multigens); synchronous, inverter, induction based machines;
grounding and neutrals; power quality (transitions, …); system protection (including surge protection);
response to abnormal conditions; safety of units and … (DR, power lines that would otherwise be
expected to be safe, etc.); unintentional islanding (protection); load profile; load management; load
shedding; power transient; mechanical issues (noise, emissions, fuels; out of scope?); frequency and
voltage control; concerns; metering?; consider each subclause of 1547 wrt this activity; economic
dispatch, e.g., pricing structure, etc.?; generation and system reliability (IEEE gold book); dynamics and
(re)-configurability of Area EPS; interoperability of DR; blackstart; transformers (and other equipment,
e.g., reclosers, fuses, );
Engineering Solutions
Goals/Targets/Requirements
Modeling;
Testing;
Characteristics of the loads;
Characteristics of the DG and/or energy storage units;
Characteristics of the power converter;
Integration and interconnection
Design of Islands
 Configurations and architectures
 Requirements for the DRIS
o Steady state, transient,
 Requirements for DR
 Requirements for Area EPS
 Interconnect (disconnect/reconnect) system (includes dispatch functionality, etc. )
Operations of Islands
Semi-autonomous and autonomous operations;
Operation philosophies;
“Safety”;
Monitoring, information exchange and control