Power Electronic Systems & Chips Lab., NCTU, Taiwan
Regulations and Performance Measures of
Grid Converters
鄒應嶼 教 授
國立交通大學
電機與控制工程研究所
2013年1月1日
電力電子系統與晶片實驗室
Power Electronic Systems & Chips Lab.
交通大學 • 電機與控制工程研究所
1/30
Grid Requirements
 Total Harmonic Distortion (THD) and individual harmonic
current levels
 Power factor (PF)
 Level of injected DC current
 Voltage and frequency range for normal operation
 Detection of islanding operation (islanding or non-islanding
functions)
 Automatic reconnection and synchronizing
 Grounding of the system
2/30
International Standards for Grid Converters
 IEC 60364-7-712:2005. Electrical Installations of Buildings. Part 7:
requirements for special installations or locations. Section 712: Photovoltaic
power supply systems. [1]
 IEEE 1547.1-2005 IEEE Standard Conformance Test Procedures for Equipment
Interconnecting Distributed Resources with Electric Power Systems. [2]
 UL 1741. Standard for Safety Inverters, Converters, Controllers and
Interconnection System Equipment for Use with Distributed Energy Resources.
7th May 1999, updated in 2005.
 IEEE 929-2000. Recommended Practice for Utility Interface of Photovoltaic
(PV) Systems. [3]
 IEC 61727 (1995-06) Photovoltaic Systems – Characteristics of the Utility
Interface. [4]
 DS/EN 61000-3-2 (2001) EMC, Limits for harmonic emissions (equipment input
current up to and including 16 A per phase) [5]
 VDE0126-1-1 (2006) Selbsstattige Schaltschtelle zwischen einer
netzparalellen Eigenerzeugungsanlage und dem offentlichen
Niederspannungsnetz [6]
3/30
International Standards for Grid Converters
[1] Danish Standard Association; "DS/HD 60364-7-712 Electrical installations of buildings – Part 7-712:
Requirements for special installations or locations – Solar photovoltaic (PV) power supply systems"; 2005.
[2] IEEE Std 1547.1-2005. IEEE Standard Conformance Test Procedures for Equipment Interconnecting
Distributed Resources with Electric Power Systems.
[3] IEEE 929-2000. Recommended Practice for Utility Interface of Photovoltaic (PV) Systems.
[4] IEC 61727; "Characteristics of the utility interface for photovoltaic (PV) systems"; International Electrotechnical
Commission, IEC 61727, 2002.
[5] BS EN 61000-3-2. (2001) Electromagnetic Compatibility - Part 3-2: Limits - Limits for harmonic current
emmisions (equipment input current up to and including 16A per phase).
[6] DKE Deutsche Kommission Elektrotechnik Electronik Informationstechnik im DIN un VDE; "Selbsttatige
Freischaltstelle zwischen einer netzparallelen Eigenerzeugungsanlage und dem offentlichen
Niederspannungsnetz"; DIN VDE 0126-1-1, 2006.
REF: David L. King, Sigifredo Gonzalez, Gary M. Galbraith, and William E. Boyson,
Performance Model for Grid-Connected Photovoltaic Inverters, Sandia Report, Sept. 2007.
4/30
Regulations on Inverters for Photovoltaic Applications
 Line Current Harmonics: EN61000-3-2, IEEE std. 1547
 Power Factor: >0.85 (Japan)
 Islanding Protection: Both active and passive methods should be installed
according to the guideline (Japan).
 AC voltage operating range: 100V +20/-20%(Maximum) in case of 100V system, 200V +20/20%(Maximum) in case of 200V system (Japan)
 AC frequency operating range: 50Hz +1,5/-1,5Hz(Maximum), 60Hz +1,8/-1.8Hz(Maximum), Reaction
time: 0,5 to 2 seconds (Japan)
 Reaction Time: AC frequency operating range: <0.2 sec (Austria)
 Limits for DC Injection into AC Grid: < 1% (Japan), 0.5% (USA), 5mA
(UK)
 Limits regarding high-frequency capacitive leakage currents
[1] Utility aspects of grid connected photovoltaic power systems, International energy agency – photovoltaic power
systems programme, IEA PVPS T5-01: 1998, 1998, www.iea-pvps.org.
[2] IEEE Standard for interconnecting distributed resources with electric power systems, IEEE std. 1547, 2003.
[3] Grid-connected photovoltaic power systems: Status of existing guidelines and regulations in selected IEA member
countries, International energy agency – photovoltaic power systems programme, IEA PVPS V-1-03, 1998,
www.iea-pvps.org.
[4] E.D. Spooner and G. Harbidge, "Review of international standards for grid connected photovoltaic systems,"
Renewable Energy vol. 22, pp. 235-239, 2001.
[5] PV System Installation and Grid-Interconnection Guidelines in Selected IEA countries, Task 5, November 2001.5/30
Regulations for Grid-Connected PV Inverters
CE
yes
EMC guideline
EMC 89/336/EEG
Emission
EN 50081-1
Harmonisation
EN 61000-3-2
Immunity
EN 50082-2
LV guideline
LV 73/23/EEC
Safety
EN 60950
6/30
Testing the Inverter
 European Efficiency
 Line Current THD and Power Factor
 Islanding Protection
 MPPT Response Time & Efficiency
 HF Capacitive Leakage Currents
DC
PV
DC
DC
iPV
Grid
SMPS
AC
uPV
iPV,ref
uDC
Microcontroller with PWM and ADC
ugrid
igrid
7/30
Current Harmonics
 Most countries have agreed upon the EN61000-3-2-A standard for current harmonics. However,
Japan and the US demands a current Total Harmonic Distortion (THD) below 5 %, and any
harmonics below 2 % of the fundamental current.
EN 61000-3-2-A harmonic current limits
8/30
Line Current THD of Several PV Inverters
Sunnuy boy
2400
Tauro PRM3
Sun Profi 2400
Ingecon
Sun 2500
Solete 2500
Manufacturer
Nominal Power (W)
Voltage range (VDC)
Efficiency (%)
SMA
1500
150-300
≧93
Enertron
2500
300-250
Max: 94
< 4 with
P0 > 0.5 and
THDv < 2%
Sun Power
1700
252-450
90-94
With P0> 0.15
3.0
Ingeteam
2500
125-450
Max: 94
THD1(%)
Atersa
1900
42-66
Max: 93
89 with P0=0.8
< 3.5 with
P0=0.6 and
THDv < 2%
< 4.0
< 3 with
P0=1
(h2 ) 2  (h3 ) 2    ( hn ) 2
THD 
 100%
h1
Dpto. de Fisica Aplicada II, Universidad de Ma’laga, and Campus de Teatinos, “Analysis of the current total harmonic distortion for
different single-phase inverters for grid-connected pv-systems," Solar Energy Materials & Solar Cells 87, pp. 529–540, 2005.
9/30
Power Factor
 The Power Factor (PF) should be close to unity in order not to generate or consume reactive
power. Denmark requires a PF better than 0.95 for 50% of nominal power.
10/30
Inrush Current
 During fault situations on the medium or high voltage overhead lines, these lines may be
switched out in order to clear the fault. This causes a sudden voltage drop at the grid and hence
the inverter. The inverter must cease to energize the grid if this happens. Disabling the
semiconductors in the output circuit is sufficient. When the voltage restores or the inverter is
connected to the grid for the first time, the current into the inverter must not reach damaging
values.
11/30
Efficiency of Grid Converters
 PV inverters usually have two efficiencies reported by the manufacturer: the highest DCAC conversion efficiency, also called as “Maximum Efficiency”, and a weighted efficiency
dependent on efficiencies at different irradiation levels, called “European efficiency”, based
on the formula below [1]:
European Efficiency is defined as:
 EU  0 .03 5  0 .0610  0 .13 20  0 . 1 30  0 .48 50  0 .2100
CEC (California Energy Commission) Efficiency is defined as:
 EU  0 .00 5  0 .0410  0 .05 20  0 .12 30  0 .2150  0 .53 75  0 .05100
[1] H. Haberlin, Ch. Liebi, and Ch. Beutler; "Inverters for grid connected PV-Systems: Test results of some new inverters and latest
reliability data of the most popular inverters in Switzerland"; in 14th European Photovoltaic Solar Energy Conference, 30 Jun. - 4 Jul.
1997.
[2] H. Haberlin, L. Borgna, M. Kaempfer, and U. Zwahlen; "New tests at grid connected PV inverters: Overview over test results
and measured values of total efficiency"; in 21st European Photovoltaic Solar Energy Conference, 4-8 Sep. 2006
[3] M. Meinhardt; "Improvement of Photovoltaic Inverter Efficiency – Targets, Methods, Limits"; SMA Technologie AG, 2005.
12/30
Efficiency
is(t)
vs(t)
io(t)
Power Supply
vo(t) LOAD
Instantaneous Power = p(t)  v(t)i(t)
Average Power = PAVG
Efficiency ( ) =
1 t0  T
= 
p(t)dt  vAVGiAVG
t
T 0
Po(AVG)
Ps(AVG)
1
=T
1
T

t0  T

t0  T
t0
t0
vo (t)io (t)dt
vs (t)is (t)dt
13/30
European Efficiency – A Weighted Efficiency
84
VIN = 85V
81
Efficiency [%]
78
VIN = 110V
75
VIN = 140V
72
69
66
63
60
0
20
40
60
80
100 105
Output Power [%]
European Efficiency is defined as:
 EU  0 .03 5  0 .0610  0 .13 20  0 . 1 30  0 .48 50  0 .2100
CEC (California Energy Commission) Efficiency is defined as:
 EU  0 .00 5  0 .0410  0 .05 20  0 .12 30  0 .2150  0 .53 75  0 .05100
14/30
Efficiency Measurement of PV Inverters
100
Efficiency, %
95
90
85
80
300 Vdc
75
70
0%
345 Vdc
480 Vdc
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% of Rated Output Power
Inverter performance measurements conducted by a nationally recognized testing
laboratory and documented by the CEC (California Energy Commission).
15/30
Measured Performance 2.5-kW Inverter, 13-Day Period
“Field test” results for a 2.5-kW Solectria PVI2500 inverter recorded during system operation at
Sandia, showing both inverter efficiency and relationship between ac-power and dc-power over an
extended 13-day test period, including both clear and cloudy days.
Galvanic Isolation Requirement for PV Inverters




Germany: Not required for low-voltage grid applications [1].
Spain and Great Britain: Required for all applications [2].
Italy: Required for Power > 20 kW [3]
US: Required Grounding of one of the panel outputs [4] ,
which leaves few alternatives for the use of transformerless
topologies, aside from a few specially developed circuits
[5], [6].
[1] Eigenerzeugungsanlagen am Niederspannungsnetz—Richtlinie für An-schluß und Parallelbetrieb von Eigenerzeugungsanlagen am
Niederspan-nungsnetz (Energy Generation Equipment Connected to the Low Voltage Grid—Guideline for the Connection and
Parallel Operation of Energy Generation Equipment on Low Voltage Grid), 4th ed. Berlin, Germany: Verband der
Elektrizitätswirtschaft VDEW e. V., 2001.
[2] M. Haag, “Auswirkungen neuer modultechniken und marktbeson-derheiten auf die technik von PV-Wechselrichtern,” in Proc.
ETG-Fachtagung Leistungselektronische Systeme für die dezentrale Stromerzeugung. Berlin, Germany: VDE Press, 2008.
[3] DK-5940 Criteri di Allacciamento di Impianti di Produzione alla rete BT di ENEL Distribuzione (Criteria for the Connection of
Generating Appliances on the Low Voltage Grid of the ENEL Distributor), Jun. 2006.
[4] M. W. Earley, J. S. Sargent, J. V. Sheehan, and J. M. Caloggero, National Electrical Code Handbook, 10th ed. Long Beach, CA: Nat.
Fire Protection Assoc., 2005, pp. 1031–1032.
[5] D. Karschny, “Wechselrichter,” German Patent DE19 642 522 C1, Apr. 1998.
[6] D. Schekulin, “Transformerless ac inverter circuit for coupling photovoltaic systems or wind generator systems, especially in the low
17/30
power range, to current networks,” German Patent DE19 732 218 C1, Mar. 1999.
Grounding
 Equipment ground is required in all countries. System ground
is required in some countries for systems with voltages over 50 V
(PV module open circuit voltage) [1]. Equipment ground involves
that all metallic surfaces, etc., are grounded.
 Grounding is necessary when considering maintenance safety,
lightning protection, electromagnetic coupling (EMC) diminishment,
and electromagnetic pulses (EMP) protection.
 Above certain dc voltage level, e.g., 100 V, the DG resource is
required earth-grounded.
 A single-phase inverter with line-to-neutral grid interconnection also
has one terminal to be grounded. In such a case, the DG inverter has
to operate normally under the “dual-grounding” circumstance.
 Dual Grounding: Both the DG resource and the grid converter must
be grounded.
[1] Utility aspects of grid connected photovoltaic power systems, International energy agency – photovoltaic power systems programme,
IEA PVPS T5-01: 1998, 1998, www.iea-pvps.org.
18/30
Limit of Injected DC Current
IEC61727
DC current
injection
< 1% of rated
output current
VDE0126-1-1
IEEE1547
EN61000-3-2
IEEE 929-2000
< 1A
< 0.5% of
rated output
current
< 0.22A
corresponds to
a 50W halfwave rectifier
< 0.5% of rated
output current
Note: The VDE 0126-1-1 standard states, that in the case of a DC current injection
greater than 1 A, disconnection is mandatory in 0.2 s. The other standards do not
mention a requirement for disconnection time.
REF: S. Kjaer, J. Pedersen, and F. Blaabjerg; "A review of single-phase grid connected inverters for photovoltaic modules"; IEEE
Transactions on Industry Applications, vol. 41, no. 5, Sep. 2005, pp. 1292- 1306
19/30
Limits for DC Injection into AC Grid




<0.5% (USA) [1]
< 1% (Japan) [2]
5mA (UK) [3]
1A (Germany) [4]
VPV
PV
Array
Idc may exist due to unbalance!
EMI
Igrid
Filter
[1] IEEE Recomended Practice for Utility Interface of Photovoltaic (PV) Systems, IEEE Std. 929-2000, Apr. 2003.
[2] Japan Ind. Standards Assoc., Technical Guideline for the Grid Interconnection of Dispersed Power Generating Systems, Japan,
2001.
[3] Engineering Recommendation, United Kingdom ER G83/1 Recommendations for the Connection of Small-Scale Embedded
Generations (up to 16 A per phase) in Parallel With Public Low-Voltage Distribution Network, Sep. 2003.
[4] DIN V VDE V 0126-1-1 Automatic Disconnection Device Between a Generator and the Public Low-Voltage Grid. Berlin, Germany:
20/30
VDE Press, 2006, 9 pp.
Leakage Currents to Ground
Photovoltaic
array
Inverter
A
EMC
FILTER
DC
B
EMC
FILTER
AC
Vg
Stray capacitance
Ground
icm
According to the German standard VDE 0126-1-1, there are three different
currents that have to be monitored:
 Ground Fault current, which happens in case of insulation failure when the
current flows through the ground wire;
 Fault current, which represents the sum of the instantaneous values of the
main currents, that in normal conditions leads to zero;
 Leakage Ground currents, which is the result of potential variations of
capacitive coupled parasitic elements;
Switching Noise of Inverter System
 Differential-Mode Noise: reduced by LC-filter
 Common-Mode Noise: its effect depends on parasitic values
22/30
Monitoring of Leakage Current (VDE 0126-1-1)
Leakage current jumps and their corresponding disconnection times for VDE 0126-1-1
Leakage current jump value
Disconnection time
(mA)
(s)
30
0.3
60
0.15
100
0.04
 The monitoring is typically done using a Residual Current Monitoring Unit (RCMU), which
measures the fault and leakage current of the whole system. The standard states that
disconnection from the grid is necessary within 0.3 s in case the leakage current is higher than 300
mA.
 Furthermore, it recommends a table detailing the Root Mean Square (RMS) value of the
fault/leakage current jumps and their respective disconnection times, as detailed in above Table.
23/30
Earthing System for Electric Power Distribution
TN Networks
TN-S Networks
TT Networks
IT Networks
TN-C Networks
TN-C-S Networks
Input Voltage Levels
PV Array Levels for a Given Grid Voltage and Topology Ratio
(1000 W/m2 and 20ºC)
Max.
Grid
Peak
Voltage
Topology
specific
ratio
Min.
MPP
voltage
Max.
MPP
Voltage
Max.
Array
Voltage
Full-Bridge
358
1
376
537
751
Half-Bridge
358
2
751
1073
1503
Type
(100 W/m2 and 50ºC)
Islanding Protection
 Islanding is the continued operation of the inverter when the grid has been removed by
purpose, by accident, or by damage. In other words, the grid has been removed from
the inverter, which then only supplies local loads. The inverter must be able to detect
an islanding situation, and take appropriated measure in order to protect persons
and equipment.
Limits for detection of islanding operation
26/30
Islanding Protection Compliance
Collection of international standards, which the inverter must fulfill.
27/30
Test Plan











Static Power Efficiency
Power Factor
Current Harmonics
MPP Tracking Efficiency.
Standby Losses
Disconnections of AC Power Line
Disconnections of DC Power Line
AC Voltage Limits
Frequency Limits
Response to Abnormal Utility Conditions
Field Test
28/30
Define and Check of Specifications
Interfaces and Parameters
PV
Grid
Specified value
Obtained value
Observed?
Nominal PV module power
160 W
Min. 150 W
(Yes)
Maximal open circuit voltage
50 V
Min. 42 V
(Yes)
Maximum power point range
23 V to 38 V
20 V to 38 V
Yes
Ripple at normal power (LF-amplitude, and
HF peak-peak)
4.1 V / 0.5 V
0.06V to 0.7 V
Yes / No
Maximum short circuit current
8A
Min. 6.4 V
(Yes)
MPP current range
0-7.2 A
Saturates at 5 A
No
Nominal grid voltage
230 V ± 10%
230V±10%
Yes
Nominal grid frequency
49.5 Hz to 50.5 Hz
Not tested for.
TBD
Non islanding operating range, voltage
195 V to 253 V
197 V to 255 V
Yes
Non islanding operating range, frequency
48 Hz to 52 Hz
Not tested for.
TBD
Standby losses
-
0.5 W
-
Current harmonics
EN61000-3-2A
-
Yes
82/308/CDV
-
No
Power factor at 50% of nominal power
0.95
0.98
Yes
Inrush current and voltage
< 13 A, <450 V
0.5 A / 350 V
Yes
29/30
References: Distributed Power Generation
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
A. Timbus, M. Liserre, R. Teodorescu, P. Rodriguez, and F. Blaabjerg, "Evaluation of Current Controllers for Distributed Power
Generation Systems," IEEE Transactions on Power Electronics, vol. 24, no. 3, pp. 654-664, March 2009.
David L. King, Sigifredo Gonzalez, Gary M. Galbraith, and William E. Boyson, Performance Model for Grid-Connected
Photovoltaic Inverters, Sandia Report, Sept. 2007.
A. F. Zobaa and C. Cecati, "A comprehensive review on distributed power generation," International Symposium on Power
Electronics, Electrical Drives, Automation and Motion (SPEEDAM), pp.514-518, 23-26 May 2006.
Blaabjerg, F., Guerrero, J.M., "Smart grid and renewable energy systems", International Conference on Electrical Machines
and Systems (ICEMS), pp. 1–10, 2011.
T. Suntio, J. Puukko, L. Nousiainen, T. Messo, and J. Huusari, "Change of paradigm in power electronic converters used in
renewable energy applications", IEEE 33rd International Telecommunications Energy Conference (INTELEC), pp. 1-9, 2011.
Mohamed, Y.A.-R.I., El-Saadany, E.F., "A Robust Natural-Frame-Based Interfacing Scheme for Grid-Connected Distributed
Generation Inverters", Energy Conversion, IEEE Transactions on, On page(s): 728 - 736 Volume: 26, Issue: 3, Sept. 2011.
Reyes, M., Rodriguez, P., Vazquez, S., Luna, A., Teodorescu, R., Carrasco, J.M., "Enhanced Decoupled Double
Synchronous Reference Frame Current Controller for Unbalanced Grid-Voltage Conditions", IEEE Transactions on Power
Electronics, pp. 3934-3943, vol. 27, no. 9, Sept. 2012.
Qing-Chang Zhong, Hornik, T., "Cascaded Current–Voltage Control to Improve the Power Quality for a Grid-Connected Inverter
With a Local Load", Industrial Electronics, IEEE Transactions on, On page(s): 1344 - 1355 Volume: 60, Issue: 4, April 2013.
A. Kahrobaeian and Mohamed Y.A.-R.I. "Interactive Distributed Generation Interface for Flexible Micro-Grid Operation in Smart
Distribution Systems", IEEE Transactions on Sustainable Energy, pp. 295 – 305, vol. 3, no. 2, April 2012.
30/30
Power Electronic Systems & Chips Lab., NCTU, Taiwan
Smart Power Processing for Energy Saving
Thanks for your kind attention!
Knowledge, Innovation, and Education
電力電子系統與晶片實驗室
Power Electronic Systems & Chips Lab.
交通大學 • 電機與控制工程研究所
31/30
Power Electronic Systems & Chips Lab., NCTU, Taiwan
Any Questions ???
Questions inspire effective learning!
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 記筆記
 問問題
電力電子系統與晶片實驗室
Power Electronic Systems & Chips Lab.
交通大學 • 電機與控制工程研究所
32/30
Power Electronic Systems & Chips Lab., NCTU, Taiwan
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電力電子系統與晶片實驗室
Power Electronic Systems & Chips Lab.
交通大學 • 電機與控制工程研究所
33/30