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Grid requirements to connect DPGS based on RES
Grid requirements to connect DPGS
based on RES
Marco Liserre
[email protected]
Marco Liserre
[email protected]
Grid requirements to connect DPGS based on RES
Introduction

Grid requirements for DPGS are stringent and subject to changes

They are different for different renewable energy sources

IEEE made an attempt, with IEEE 1547 series, to have a common
approach for all DPGS below 10 MW

In fact power level is maybe more important than source type

Grid operators consider low power DPGS as a kind of “disturbance” or
“negative” load

Higher power DPGS are starting to be consider a resource for grid
stability
Marco Liserre
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Grid requirements to connect DPGS based on RES
Introduction

Safety issues are also important due to the higher penetration of DPGS
at low voltage level

Power quality and EMC are stringent too

In the following the grid requirements are reviewed with focus on:



Photovoltaic systems
Wind systems
However considerations on the influence of the power level will be
made
Marco Liserre
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Grid requirements to connect DPGS based on RES
Photovoltaic systems
Marco Liserre
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Grid requirements to connect DPGS based on RES
Outline
 International Regulations
 Public Voltage Quality
 Response to abnormal grid conditions
 Power Quality
 Anti-islanding requirements
 References
 Conclusion
Marco Liserre
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Grid requirements to connect DPGS based on RES
International Regulations
Grid connection requirements

IEEE 1547-2003 Standard for Interconnecting Distributed Resources with Electric Power Systems

IEEE 1547.1- 2005 Standard for Conformance Tests Procedures for Equipment Interconnecting Distributed Resources
with Electric Power Systems

IEEE 929-2000, Recommended Practice for Utility Interface of Photovoltaic (PV) Systems – incorporated in IEEE 1547

UL 1741, Standard for Inverters, Converters, and Controllers for Use in Independent Power Systems - elaborated by
Underwriters Laboratories Inc. – compatibilzed with IEEE 1547

IEC61727 [6] Photovoltaic (PV) systems - Characteristics of the utility interface - December 2004

IEC 62116 Ed.1 2005: Testing procedure of islanding prevention measures for utility interactive photovoltaic inverter
(describes the tests for IEC 61727) – approved in 2007

VDE0126-1-1 2006 Automatic disconnection device between a generator and the public low-voltage grid” – Safety
issues- applied on German Market
EMC

IEC 61000-3-2, Ed. 3.0 – “Electromagnetic compatibility (EMC) –Part 3-2: Limits –Limits for harmonic current emissions
(equipment input current ≤16 A per phase)”, ISBN 2-8318-8353-9, November 2005

EN 61000-3-3, Ed. 1.2 —“Electromagnetic compatibility (EMC) –Part 3-3: Limits – Limitation of voltage changes,
voltage fluctuations and flicker in public low-voltage supply systems, for equipment with rated current ≤16 A per phase
and not subject to conditional connection”, ISBN 2-8318-8209-5, November 2005

IEC 61000-3-12, Ed. 1 – “Electromagnetic compatibility (EMC) –Part 3-12:Limits – Limits for harmonic currents
produced by equipment connected to public low-voltage systems with input current >16 A and ≤75 A per phase” ,
November 2004

IEC 61000-3-11, Ed. 1 —“ Electromagnetic compatibility (EMC) – Part 3-11: Limits – Limitation of voltage changes,
voltage fluctuations and flicker in public low-voltage supply systems – Equipment with rated current ≤75 A and subject to
conditional connection” , August 2000Standard EN 50160 – “Voltage Characteristics of Public Distribution System”,
CENELEC: European Committee for Electrotechnical Standardization, Brussels, Belgium, November 1999
Utility Voltage Quality

Standard EN 50160 – “Voltage Characteristics of Public Distribution System”, CENELEC: European Committee for
Electrotechnical Standardization, Brussels, Belgium, November 1999 .
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Grid requirements to connect DPGS based on RES
Public Voltage Quality – EN 50160
 voltage unbalance for three phase inverters. Max unbalance is 3%
 voltage amplitude variations: max +/-10%
 frequency variations: max +/-1%
 voltage dips: duration < 1 sec, deep < 60%
 voltage harmonic levels. Max voltage THD is 8%
Odd harmonics
Not multiple of 3
Order
h
Marco Liserre
Even harmonics
Multiple of 3
Relative
(%)
voltage
Order
h
Relative
(%)
voltage
Order
h
Relative
(%)
voltage
5
6
3
5
2
2
7
5
9
1.5
4
1
11
3.5
15
0.5
6..24
0.5
13
3
21
0.5
17
2
19
1.5
23
1.5
25
1.5
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Grid requirements to connect DPGS based on RES
Response to abnormal grid conditions
 Voltage deviations
IEEE 1547
IEC61727
VDE0126-1-1
Voltage range (%)
Disconnection
time (s)
Voltage range (%)
Disconnection
time (s)
Voltage range (%)
Disconnection
time (s)
V < 50
0.16
V < 50
0.10
110 ≤ V < 85
0.2
50 ≤ V < 88
2.00
50 ≤ V < 85
2.00
110 < V < 120
1.00
110 < V < 135
2.00
V ≥ 120
0.16
V ≥ 135
0.05
Obs. The purpose of the allowed time delay is to ride through short-term disturbances to avoid excessive
nuisance tripping
IEEE 1547
 Frequency
deviations
IEC61727
VDE0126-1-1
Frequency
range (Hz)
Disconnecti
on time (s)
Frequency
range (Hz)
Disconnecti
on time (s)
Frequency
range (Hz)
Disconnecti
on time (s)
59.3 < f <
60.5*
0.16
fn-1 < f <
fn+1
0.2
47.5 < f <
50.2
0.2
Obs. The VDE0126-1-1 allow much lower frequency limit and thus frequency adaptive synchronization
is required.
 Reconnection after
trip
IEEE 1547
IEC61727
VDE0126-1-1
88 < V < 110 [%]
AND
59.3 < f < 60.5 [Hz]
85 < V < 110 [%]
AND
fn-1 < f < fn+1 [Hz]
AND
Min. delay of 3 minutes
N/A
Obs. The time delay in IEC61727 is an extra measure to ensure resynchronization before reconnection in
order to avoid possible damage
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Grid requirements to connect DPGS based on RES
 DC Current
Injection
Power Quality
IEEE 1574
IEC61727
VDE0126-1-1
Idc < 0.5 [%]
of the rated RMS current
Idc < 1 [%]
of the rated RMS current
Idc < 1A
Max Trip Time 0.2 s
Obs. For IEEE 1574 and IEC61727 the dc component of the current should be measured by using harmonic
analysis (FFT) and there is no maximum trip time condition
IEEE 1547 and IEC 61727
 Current
harmonics
Individual harmonic
order (odd)*
h < 11
11 ≤ h < 17
17 ≤ h < 23
23 ≤ h < 35
35 ≤ h
Total harmonic
distortion
THD (%)
(%)
4.0
2.0
1.5
0.6
0.3
5.0
Obs. The test voltage for IEEE1574/IEC61727 should be produced by an electronic power source with a
voltage THD < 2.5% (typically ideal sources)
Odd harmonics
Order h
if IEC 61727 is not considered, the practice is
that the harmonic limits are set by the IEC
61000-3-2 for class A equipments
Current (A)
Even harmonics
Order h
Current (A)
3
2.30
2
1.08
5
1.14
4
0.43
7
0.77
6
0.30
9
0.40
8 ≤ h ≤ 40
0.23 x 8/h
11
0.33
13
0.21
13 ≤ h ≤ 39
0.15 x 15/h
Obs. The current limits in IEC61000-3-2 are given in amperes and are in general higher than the ones in
IEC61727. For equipments with a higher current than 16 A but lower than 75A another similar standard
IEEE 61000 3-12 applies
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Grid requirements to connect DPGS based on RES
Power Quality
Average Power Factor
 Only in IEC61727 it is stated that the PV inverter shall have an average lagging
power factor greater than 0,9 when the output is greater than 50%. Most PV
inverters designed for utility-interconnected service operate close to unity power
factor.
 In IEEE1574 as this a general standard that should allow also distributed
generation of reactive power there is no requirement for the power factor
 No power factor requirements are mentioned in VDE0126-1-1
Obs. Usually the power factor requirement for PV inverters should be interpreted
now as a requirement to operate at quasi-unity power factor without the possibility
of regulating the voltage by exchanging reactive power with the grid. For high
power PV installations connected directly to the distribution level local grid
requirements apply as they may participate in the grid control. For low power
installations it is also expected that in the near future the utilities will allow them
to exchange reactive power but new regulations are still expected.
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Grid requirements to connect DPGS based on RES
Anti-islanding Requirements
What is Islanding?
Islanding for grid connected PV systems takes place when the PV inverter
does not disconnect very short time after the grid is tripped, i.e. it is continuing
to operate with local load. In the typical case of residential electrical system
co-supplied by a roof-top PV system, the grid disconnection can occur as a
result of a local equipment failure detected by the ground fault protection, or
of an intentional disconnection of the line for servicing. In both situations if
the PV inverter does not disconnect the following consequences can occur:
Retripping the line or connected equipment damaging due to of out-ofphase closure
 Safety hazard for utility line workers that assume de-energized lines
during islanding
In order to avoid these serious consequences safety measures called antiislanding (AI) requirements have been issued and embodied in standards
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Grid requirements to connect DPGS based on RES
Anti-islanding Requirements – IEEE 1574
In IEEE 1574 the requirement is that after an unintentional islanding where the distributed
resources (DR) continues to energize a portion of the power system (island) through the PCC,
the DR shall detect the islanding and cease to energize the area within 2 seconds.
S3
S1
Simulated
Area EPS
RLC
Load
S2
EUT
NOTES
1 – Switch S1 may be replaced with individual switches on each of the RLC load components
2 – Unless the EUT has a unity output p.f., the receiver power component of the EUT is considered
to be a part of the islanding load circuit in the figure.

V2
R 
P


V2

L 
2 f PQ f


PQ f
C 
2 f V 2


Adjustable RLC load should be connected in parallel between the PV inverter and the grid. The resonant
LC circuit should be adjusted to resonate at the rated grid frequency and to have a quality factor of 1 or in
other words the reactive power generated by [VAR] should equal the reactive power absorbed by [VAR]
and should equal the power dissipated in [W]
The parameters of the RLC load should be fine tuned until the grid current through S3 should be lower
than 2% of the rated value on a steady-state base. In this balanced condition, the S3 should be open and the
time before disconnection should be measured and should be lower than 2 seconds.
The UL 1741 standard in US has been harmonized with the anti-islanding requirements stated in IEEE
1547
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Grid requirements to connect DPGS based on RES
Anti-islanding Requirements – IEC62116
In IEC 62116-2006 similar AI requirements as the IEEE1547 is proposed. The test can also be
utilized by other inverter interconnected DER. In the normative reference IEC 61727-2004 the
ratings of the system valid in this standard has a rating of 10 kVA or less, the standard is though
subject to revision. The test circuit is the same as in the IEEE1547.1 test power balance is required
before the island detection test. The requirement for passing the test contains more test cases but
the conditions for confirming island detection do not have a significant deviation compared to the
IEEE1547.1 test.
The inverter is tested at three levels of output power (A 100-105%, B 50-66% and C 25-33% of
inverters output power). Case A is tested under maximum allowable inverter input power, case C at
minimum allowable inverter output power if > 33 %.
The voltage at the input of the inverter also has specific conditions. All conditions are to be tested
at no deviation in real and reactive load power consumption then for condition A in a step of 5%
both real and reactive power iterated deviation from -10% to 10% from operating output power of
inverter.
Condition B and C are evaluated by deviate the reactive load in an interval of ±5 % in a step of 1
% of inverter output power.
The maximum trip time is the same as in IEEE 1547.1 standards 2 s.
In IEC61727, there is no specific description of the anti-islanding requirements. Instead reference
to IEC62116 is done.
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Grid requirements to connect DPGS based on RES
Anti-islanding Requirements – VDE-0126-1-1
The VDE0126-1-1 allows the compliance with one of the following anti-islanding methods:
A.
Impedance measurement
S
~
B.
semiconductor
switch
DC-AC Inverter
Pgrid
R1
L1
L1
R2
L2
L2
Grid
R3
C1
Disconnection detection with RLC resonant load
The test circuit is the same of the one reported in IEEE1547.1 and the test conditions are that the
RLC resonant circuit parameters should be calculated for a quality factor bigger than 2
With balanced power the inverter should disconnect after the disconnection of S2 in maximum 5
seconds for the following power levels: 25%, 50% and 100%.
For three-phase PV inverters a passive anti-islanding method is accepted by monitoring all three
phases voltage with respect to the neutral. This method is conditioned by having individual current
control in each of the three phases.
Finding a software based anti-islanding method has been a very challenging task resulting in a
large number of research work and publications.
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Grid requirements to connect DPGS based on RES
Conclusions
An overview of the most relevant standards related to the grid connection requirements of PV
inverters is given.
High efforts are done by the international standard bodies in order to “harmonize” the grid
requirements for PV inverters worldwide.
The IEEE1574 standard has done a big step in the direction of issuing a standard that includes grid
requirements not only for PV inverters but for all distributed resources under 10 MVA.
Underwriters Laboratories in US has revised this year the UL 1471 by accepting the grid
requirements of IEEE1574 and also IEC62116 was revised to harmonize with the requirements of
IEEE1574 in the anti-islanding requirements.
Even the very specific German standard VDE0126-1-1 was revised in 2006 where the grid
impedance measurement has become optional and an alternative requirement very similar to
IEEE1574 was included. All these positive actions needs to be followed by adoption in different
countries that still use their own local regulations.
Marco Liserre
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Grid requirements to connect DPGS based on RES
References
[1]
Dugan, R.C.; Key, T.S.; Ball, G.J., "Distributed resources standards," Industry Applications Magazine, IEEE , vol.12, no.1, pp. 27-34, Jan.-Feb. 2006
[2]
IEEE Std 929-2000 – “IEEE Recommended Practice for Utility Interface of Photovoltaic (PV) Systems,", ISBN 0-7381-1934-2 SH94811, April 2000.
[3]
UL standard 1741, “Inverters, Converters, and controllers for Use in Independent Power Systems”, Underwriters Laboratories Inc. US, 2001
[4]
IEEE Std 1547-2003 – “Standard for Interconnecting Distributed Resources with Electric Power Systems," ISBN 0-7381-3720-0 SH95144, IEEE, June
2003
[5]
IEEE Std 1547.1-2005 – “Standard Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems”
ISBN 0-7381-4736-2 SH95346, IEEE, July 2005
[6]
IEC 61727 Ed.2 – “Photovoltaic (PV) Systems - Characteristics of the Utility Interface”, December, 2004
[7]
IEC 62116 CDV Ed. 1 – “Test procedure of islanding prevention measures for utility-interconnected photovoltaic inverters”, IEC 82/402/CD:2005
[8]
VDE V 0126-1-1 “Automatic disconnection device between a generator and the public low-voltage grid”,VDE Verlag, Doc nr. 0126003, 2006
[9]
IEC 61000-3-2, Ed. 3.0 – “Electromagnetic compatibility (EMC) –Part 3-2: Limits –Limits for harmonic current emissions (equipment input current ≤16
A per phase)”, ISBN 2-8318-8353-9, November 2005
[10] EN 61000-3-3, Ed. 1.2 —“Electromagnetic compatibility (EMC) –Part 3-3: Limits – Limitation of voltage changes, voltage fluctuations and flicker in
public low-voltage supply systems, for equipment with rated current ≤16 A per phase and not subject to conditional connection”, ISBN 2-8318-8209-5,
November 2005
[11] Standard EN 50160 – “Voltage Characteristics of Public Distribution System”, CENELEC: European Committee for Electrotechnical Standardization,
Brussels, Belgium, November 1999 .
[12] IEC 61000-3-12, Ed. 1 – “Electromagnetic compatibility (EMC) –Part 3-12:Limits – Limits for harmonic currents produced by equipment connected to
public low-voltage systems with input current >16 A and ≤75 A per phase” , November 2004
[13] IEC 61000-3-11, Ed. 1 —“ Electromagnetic compatibility (EMC) – Part 3-11: Limits – Limitation of voltage changes, voltage fluctuations and flicker in
public low-voltage supply systems – Equipment with rated current ≤75 A and subject to conditional connection” , August 2000
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Grid requirements to connect DPGS based on RES
Wind systems
Marco Liserre
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Grid requirements to connect DPGS based on RES
Outline
 Grid codes, description and purpose
 Transmission system operator demands
 Active power control, frequency control
 Reactive power control, voltage control
 Ride-Through Capabilities
 Conclusion
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Grid requirements to connect DPGS based on RES
Grid Codes description and purpose
Operate a wind farm/wind turbine like a power station/plant
Grid Code: Technical document containing the rules governing the
operation, maintenance, & development of the system defined at
the Point of Common Coupling – PCC (not turbine specific)
Steady state
Frequency /Power control
Low/high frequency support
Voltage support/reactive power compensation
Power Quality, flicker, harmonics
Transient /dynamic state
Fault ride through, to stay connected during low voltage on the grid
Ramp rate
Communication /power dispatch
Reliable communication
Wind forecasting
Participate power market
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Grid requirements to connect DPGS based on RES
Recent Grid Codes
Europe: The grid codes of Europe are affected by the fact that the grid has
traditionally been strong and stable – but the fact that the wind power penetration
has been increasing - LVRT (Low Voltage Ride Through) has entered the scene
and most grid codes at least specifies LVRT requirements as defined by the
German E.ON. In Spain, Scotland and Ireland the grid codes exceeds the
“standard” requirements.
Australia & New Zealand: Are characterised by a weak and unstable grid with
frequency variations from -10 % to +6 % (in extreme) and -6 % to +4 % (more
common). Voltage control and site dependent requirements are standard
North America: Characterised by a large number of “smaller” power systems
requiring local control capabilities such as voltage control. The PF range is more
standardised as 0.9c to 0.9i.
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Grid requirements to connect DPGS based on RES
Grid Codes Trends
Voltage control: Future demands is going towards operation in a voltage set point
control mode; with a continuously-variable, continuously-acting, closed loop
control voltage regulation system, acting like a synchronous generator, where
reactive power changes are based on measured voltage.
Power control: The trend in power control is fast ramp rates – both up and down,
in order to support the frequency of the grid. The latest comments for GB grid
codes for power recovery after grid faults states power restoration of 90 % within
1 s. Further frequency control is required in some countries, both under frequency
and over frequency support.
Plant control: Having wind power plants tending the capabilities of primary
control units, traditional power system control features are indisputable. As the
need for more dynamical response will increase, the needs for fast and reliable
control-infrastructure between the turbines in a park facility are increasing.
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Grid requirements to connect DPGS based on RES
Grid Codes Trends
Low voltage ride-through: Is becoming standard for all grid codes! In addition
to symmetrical faults, which are three-phased, new trend setting grid
requirements will be covering single and two-phase faults ride-through capability.
Voltage support during grid disturbances is becoming a common requirement. An
increase in the low voltage duration is foreseen – today GB codes mention 3 min.
at 85 % voltage.
Simulation models: Validated park control models with full disclosure are
already defined for various grid code drafts. Park simulation models are an
integrated part of the tender phase in more and more projects. Most connection
agreements are decided on background of simulation studies. Also nonconfidential block diagrams are required, mainly Australia and New Zeeland, but
US are also requiring open-source models. PSCAD, DigSilent and PSS/E are
preferred tools.
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Grid requirements to connect DPGS based on RES
Different National Grid Codes
[AESO] Canada
Wind Power Facility - Technical Requirements (Draft proposal)
[CER] Ireland
Wind farm Transmission Grid Code Provisions - A Direction by the
Commission for Energy Regulation
[Eltra] Denmark
Vindmølleparker tilsluttet net med spændinger over 100 kV
[E.ON] Netz Germany
Netzanschlussregeln- Hoch- und Höchstspannung
[ESB] National Grid Ireland
[REE] Spain
Wind Code Changes - Distribution Code Modification Proposal Form
Operation procedures for the electrical system. PO 12.1, 12.2 and 12.3
[NECA] Australia
National Electricity Code - Version 1.0 Amendment 8.6
[NGC] National Grid
The Grid Code - Issue 2, revision 16
[Vattenfall] Germany
Netzanschluss- und Netznutzungsregeln der Vattenfall Europe
Transmission GmbH
[VDN] Germany
Transmission Code 2003- Netz- und Systemregeln der deutschen
Übertragungsnetzbetreiber
[Western Power] Australia
Technical Code Version 1
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Grid requirements to connect DPGS based on RES
Voltage and Frequency limits
Eltra – Denmark.
Voltages and frequencies used for design of a wind turbine with voltages below
100 kV
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Grid requirements to connect DPGS based on RES
Voltage and Frequency limits
E-On – Germany.
Voltage and frequency range for generating units in the E-On grid.
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Grid requirements to connect DPGS based on RES
Voltage and Frequency limits
Great Britain
Voltages and frequencies in GB grid
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Grid requirements to connect DPGS based on RES
Transmission System Operator demands
Primary control:
Maintain the balance between generation and demand in the network using
turbine speed regulators
Automatic control to stabilize the grid frequency in seconds
Secondary control:
Secure import/export balancing with neighbouring areas with reserve generating
capacities. Control within minutes
In case of a steady major deviation in the control area, to restore the frequency
and to free capacity for the primary control
Can be manual or automatic
Tertiary control:
As automatic or manual change in the working points of generators in order to
restore adequate secondary control reserve at the right time
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Grid requirements to connect DPGS based on RES
NORDEL
Transmission System Operator demands
UCTE
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Grid requirements to connect DPGS based on RES
Transmission System Operator demands
UCTE:
Primary control
Insensitive dead band 10 mHz
Frequency deviation of 200 mHz it must be possible to activate
the total primary control power range required by the power
plant in 30 sec and to supply it for at least 15 min.
Primary control must be again available after 15 min of activation.
Dispatch 2-8% of rated capacity for primary frequency control.
Secondary control
It restores the frequency to its rated value and releases engaged
primary reserves
Start within 30 sec. Fully activated within 15 min.
N-1 network security
Ability to re-establish supply after black out
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Grid requirements to connect DPGS based on RES
Transmission System Operator demands
NORDEL:

Decoupling of power plants
Lowering
generation
Emergency power by HVDC
connections
Frequency control/primary control
The reserve is activated
Emergency power by
HVDC connections
Load shedding,
diconnection of
connection lines
Marco Liserre
Disconnection of
large combined
power plants

Primary control
 0 MW in frequency
control reserve
(50,1-49,9 Hz)
 192 MW in
momentarily
disturbance reserve
(49,9-49,5 Hz) 50%
(5sek),100 % (30
sek), HVDC
emergency power,
 Re-established
within 15 min.
Secondary control
 Fast reserve 600 MW
within 15 min
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Grid requirements to connect DPGS based on RES
Transmission System Operator demands
Power control
 Production
 Reduction
limit control both on transmission and distribution
below 20% of maximum power in less than 2s on transmission level
 Automatic
power control after faults up to full power reduction or increase within
30s on transmission level
 Distribution
level decrease and increase in power from 10-100% of rated power
per minute
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Grid requirements to connect DPGS based on RES
Regulation functions for active power
System protection
Protection function that shall be able to perform
automatic down-regulation of the power production to
an acceptable level for electrical network. In order to
avoid system collapse it should act fast.
Frequency control
Frequency control
All production units shall contribute to the
frequency control. Automatic control of power
production based on frequency measurement to reestablish the rated frequency.
Stop control
Wind farm shall keep the production
on the actual level even if it is an
increase in the wind speed
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Grid requirements to connect DPGS based on RES
Regulation functions for active power
Balance control
The power production shall be adjusted downwards
or upwards in steps at constant levels.
Production rate
Sets how fast the power production can be
adjusted upwards or downwards
Absolute production limit
Limit the maximum production level in the PCC in
order to avoid the overloading of the system.
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Grid requirements to connect DPGS based on RES
Regulation functions for active power
Delta control
The wind farm shall operate with a certain
constant reserve capacity in relation to its
momentary possible power production capacity.
Horns Reef
offshore windfarm
10*8*2MW=160MW:
Operates with 10% Delta
Control
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Grid requirements to connect DPGS based on RES
Regulation functions for active power
Horns Reef
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Grid requirements to connect DPGS based on RES
Frequency control
Eltra – Denmark
Requirements for wind turbines connected to grids with voltages below 100 kV
fd-=48.70
fd+=51.30
fn=49.85
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fu=50.15
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Grid requirements to connect DPGS based on RES
Frequency control
E-On: power reduction at over frequencies
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Grid requirements to connect DPGS based on RES
Frequency control
Ireland: Frequency control characteristic
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Grid requirements to connect DPGS based on RES
Reactive power control
Eltra – Denmark
The reactive power flow between the wind turbine including the transformer
and the electrical network must be calculated as an average value over 5 min
within the control band
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Grid requirements to connect DPGS based on RES
Reactive power control
E-On – Germany
Every generating units shall provide in the connection point the range
of reactive power provision shown in the figure without limiting
delivered active power
Type of regulation
• Power factor
• Mvar regulation
• Voltage
regulation
Marco Liserre
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Grid requirements to connect DPGS based on RES
Reactive power control
Great Britain
Every generating unit other than synchronous one with a completion
date after 1 January 2006 should be able to support an active reactive
power flow shown in the figure.
Marco Liserre
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Grid requirements to connect DPGS based on RES
Voltage quality
Eltra – Denmark.
Requirements for wind turbines to grids with voltages below 100 kV
Marco Liserre
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Grid requirements to connect DPGS based on RES
Ride-through capability
Eltra – Denmark.
Requirements for wind turbines to grids with voltages below 100 kV
The wind turbine shall be disconnected from the electrical grid
according to the figure.
Under some special situations a WT shall not be disconnected from the
electrical network
Marco Liserre
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Grid requirements to connect DPGS based on RES
Eltra – Denmark
Ride-through capability
Requirements for wind turbines to grids with voltages below 100 kV

The wind turbine shall stay connected in the
following cases.
 3-phase
short-circuit for 100 msec;
 2-phase
short-circuit with or without ground
for 100 msec followed after 300-500 msec
by a new short-circuit of 100 msec duration.

Sequences in which WT should keep connected:
 At
least two 2-phases short-circuits within 2
min interval;
 At
least two 3-phases short-circuit within 2
min interval.

Energy reserve to remain connected when:
 At
least six 2-phases short-circuits with 5
min interval;
 At
least six 3-phases short-circuit with 5
min interval.
Marco Liserre
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Grid requirements to connect DPGS based on RES
Ride-through capability
E-On - Germany

Three-phase short-circuits or fault related symmetrical voltage dips must not lead to instability above
the red line

Between lines red and blue:

All generating plants should experience the fault without disconnection from the grid. If, due to
the grid connection concept, a generating plant cannot fulfill this requirement, it is permitted
with agreement from E-On to shift the limit line while at the same time reducing the
resynchronisation time and ensuring a minimum reactive power injection during the fault

If, when experiencing the fault, the individual generators becomes unstable or the generator
protection responds, a brief disconnection of the generating plant from the grid is allowed by
agreement with E-On. At the start of a brief disconnection resynchronisation of the generating
plant shall take place within 2 seconds at the latest. The active power infeed must be increased
to the original value with a gradient of at least 10% of the rated generator power per second.
The highest
value of the 3phase line-toline grid
voltage is
considered in
this figure
Marco Liserre
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Grid requirements to connect DPGS based on RES
Ride-through capability
E-On - Germany

The generating plants shall support the grid voltage with additional reactive
current during a voltage dip.

The voltage control shall act within 20 msec after fault recognition.

The generator unit shall provide a reactive current on the low voltage side of
the transformer equal to at least 2% from the rated current for each percent of
the voltage dip.

If necessary the generating unit shall be able to provide full rated reactive
current.
Marco Liserre
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Grid requirements to connect DPGS based on RES
REE – Spain
Marco Liserre
Ride-through capability

The wind turbines shall remain connected during three-phase, twophase or single-phase to ground faults with a voltage profile as shown
in this figure.

In the case of isolated two-phase faults the valley of the voltage
profile is set to 60%.
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Grid requirements to connect DPGS based on RES
Ride-through capability
REE – Spain.

No active/reactive power will be consumed at the PCC neither during the fault
period nor during the grid voltage recovery period after the fault clearance.

The wind turbine should inject maximum reactive current both during the fault
and after the fault is cleared and the grid voltage is in the recovering process
with maximum delay of 150ms.
Marco Liserre
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Grid requirements to connect DPGS based on RES
Ride-through capability
Comparison of different national voltage profiles for fault
ride-through capability
Marco Liserre
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Grid requirements to connect DPGS based on RES
Resume of several national grid codes
Marco Liserre
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Grid requirements to connect DPGS based on RES
Conclusions




Few European countries have dedicated grid codes for interconnection
requirements of RES and in most of the cases these requirements reflects the
penetration of renewable sources into the electrical network.
Many different grid codes around the world focusing on:
 Frequency /Power control
 Voltage support/reactive power compensation
 Power Quality, flicker, harmonics
 Fault ride through
All considered grid codes requires fault ride-through capabilities. Voltage profiles
are given by the depth and the clearance time of the voltage dip. In some of the
grid codes the calculation of the voltage during all types of unsymmetrical faults
is very well defined e.g Ireland, while others does not define clearly this
procedure.
On the other hand Germany and Spain requires grid support during faults by
reactive current injection up to 100% from the rated current. This demand is
relative difficult to meet by some type of wind turbines.
Marco Liserre
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Grid requirements to connect DPGS based on RES
References
1.
S. Heier, Grid Integration of Wind Energy Conversion Systems. John Wiley & Sons, 1998.
2.
T. Ackermann, Wind Power in Power Systems. John Wiley & Sons, Ltd., 2005, iSBN: 0-470-85508-8.
3.
L. H. Hansen, L. Helle, F. Blaabjerg, E. Ritchie, S. Munk-Nielsen, H. Bindner, P. Sørensen and B. Bak-Jensen,
“Conceptual survey of Generators and Power Electronics for Wind Turbines” Risø National Laboratory, December 2001,
106 p., ISBN 87-550-2745-8 http://www.risoe.dk/rispubl/VEA/ris-r-1205.htm
4.
IEEE15471, “IEEE standard for interconnecting distributed resources with electric power systems,” July 2003.
5.
Eltra and Elkraft, “Wind turbines connected to grids with voltage below 100 kV,” http://www.eltra.dk, 2004.
6.
E.ON-Netz, “Grid code – high and extra high voltage,” E.ON Netz GmbH, Tech. Rep., 2003. [Online]. Available:
http://www.eon-netz.com/EONNETZ eng.jsp
7.
S. M. Bolik, “Grid requirements challenges for wind turbines” Fourth International Workshop on Large Scale Integration
of Wind Power and Transmission Networks for Offshore Wind Farms, Oct. 2003.
8.
Geza Joos, “Review of grid codes” First International Conference on the integration of RE and DER, 1-3 december,
Brussel, Belgium. http://cetc-varennes.nrcan.gc.ca/fichier.php/38852/2004-153e.pdf
9.
P.B. Eriksen, T. Ackermann, H. Abildgaard, P. Smith, W. Winter, J.R. Garcia,
“System operation with high wind penetration” IEEE Power and Energy Magazine,
Vol. 3, No. 6, Nov.-Dec. 2005 pp. 65 - 74
10. I. Erlich, U. Bachmann, ”Grid Code Requirements Concerning Connection and Operation of Wind Turbines in Germany”
IEEE Power Engineering Society General Meeting, June 12-16, 2005 pp. 2230 - 2234
Marco Liserre
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Grid requirements to connect DPGS based on RES
Conclusions: the role of the grid converter

Grid requirements constraints on the grid converter:

Harmonic limits -> hardware (dc voltage rating) and control

Dc current and leakage current -> hardware (converter structure,
transformer, filter) and control (modulation)

Islanding detection -> control

Operation within a frequency range -> control (PLL)

Operation under over/voltage condition -> hardware (dc voltage and
semiconductor rating)

Reactive power injection (set/point, voltage control or power factor
control) -> hardware (dc voltage rating, filter design) and control

Frequency control -> control (PLL)

Fault Ride-through capability -> hardware (semiconductor rating) and
control (estimation and control of inverse sequence)
Marco Liserre
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Grid requirements to connect DPGS based on RES
Acknowledgment
Part of the material is or was included in the present and/or past editions of the
“Industrial/Ph.D. Course in Power Electronics for Renewable Energy Systems –
in theory and practice”
Speakers: R. Teodorescu, P. Rodriguez, M. Liserre, J. M. Guerrero,
Place: Aalborg University, Denmark
The course is held twice (May and November) every year
Marco Liserre
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