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March 2004
DESIGN QUALIFICATION OF INVERTERS FOR GRID-CONNECTED OPERATION OF PHOTOVOLTAIC POWER GENERATORS Dutch Guidelines Edition 2
P.M. Rooij P.J.M. Heskes Members NEC 82
Preface This document has been written as • second edition of ECN’s Dutch Guidelines • to provide input for a new NTA (Netherlands Technical Agreement) and • to provide input to the International Committee TC 82 of the International Electrotechnical Commission (IEC) and CENELEC. At various phases of the editing process this document was presented to members of the Nederlands Elektrotechnisch Comité (NEC 82) and other experts in the field of photovoltaic systems and components. Their comments and suggestions have contributed to this standard for both the structure and the technical contents. NEC82 is the Netherlands National Committee for Solar energy systems of the: International Electrotechnical Commission (IEC) European Committee for Electrotechnical Standardization (CENELEC)
Acknowledgement The authors would like to thank the following persons for their detailed comments which have contributed to the technical contents of this document and the improvement of the text. Wouter Hermelink (NKF Kabel BV, member NEC 82) Henk Oldenkamp (OKE-Services) Hans Welschen (Philips Lighting BV, member NEC 82) Ronald van Zolingen (Shell Solar Energy, chairman NEC 82) Arno van Zwam (Mastervolt BV, member NEC 82) As a result of the intense discussions this document is supported by members of NEC 82, Dutch PV inverter industry and ECN.
Abstract This document lays down requirements for design qualification of inverters for grid-connected operation of photovoltaic power generators with a power up to and including 5kVA for singlephase power conditioners feeding into the utility low-voltage grid. This document is a supplement to the committee draft for vote (CDV) 82/330/CDV of IEC 62093 and specifies those requirements for grid-connected inverters, which are not yet discussed in the CDV. In combination with the CDV this document gives a procedure for design qualification of grid connected PV-inverters and comprises performance, utility interface protection, electromagnetic compatibility (EMC) and field tests. This document can be used by manufacturers in the design process, by testing institutes, for research and development, and by certification bodies.
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How to use this document This document can be used as an integral part of the IEC 62093 for qualifying grid-connected inverters in all their aspects. IEC 62093 specifies qualification procedures, visual inspection, insulation testing and environmental testing. While this document specifies the electrical testing like performance, utility interfaces EMC and field-tests. Also this document can be used as stand-alone document for electrical testing. Chapter 5 gives all the relevant tests to characterise the electrical parameters of the inverter and chapter 6 describes a field test.
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CONTENTS LIST OF TABLES
6
LIST OF FIGURES
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1.
SCOPE
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2.
PROCEDURE FOR DESIGN QUALIFICATION
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3.
DEFINITIONS
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4.
NORMATIVE REFERENCES
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5. 5.1 5.1.1 5.1.2 5.1.3 5.1.4 5.1.5 5.1.6 5.1.7 5.2 5.2.1 5.2.2 5.2.3 5.2.4 5.2.5 5.2.6 5.3 5.4
SPECIFIC FUNCTIONING TEST PROCEDURE – INVERTERS Performance tests Power conversion efficiency (static) European efficiency Power factor Static MPPT efficiency Dynamic MPPT response Stand-by loss at night Electric shock Utility interface tests Over / under voltage protection Over / under frequency protection Islanding Start-up delay Response to utility recovery Direct-current injection EMC Harmonics
12 13 13 13 13 14 14 15 15 16 16 16 17 17 17 18 18 19
6.
FIELD MEASUREMENTS (OUTDOORS)
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APPENDIX A
TEST SET-UP
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APPENDIX B
DEFINITION PV SIMULATOR
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APPENDIX C
DEFINITION GRID SIMULATOR
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APPENDIX D
CALCULATION OF INPUT VOLTAGES
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APPENDIX E
BEST PRACTICE
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APPENDIX F
REPORTING
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LIST OF TABLES Table 5-1 Table 5-2 Table 5-3 Table 5-4
Input voltage test level Specification irradiation Response to Abnormal Voltages Distortion limits
12 14 16 19
LIST OF FIGURES Figure 5-1 Irradiation pattern Figure 6-1 General test set-up for grid-connected inverters Figure 6-2 Test set-up for grid-connected inverters with Power / Spectrum analyser
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1.
SCOPE
This document lays down requirements for the design qualification natural environments of inverters for grid connected photovoltaic (PV) systems with a power up to and including 5kVA for a single phase connection feeding into the utility low-voltage grid, suitable for long-term operation indoor, conditioned or unconditioned; or outdoor in general open-air climates as defined in IEC 60721-2-1, protected or unprotected. In combination with the committee draft for vote (CDV) 82/330/CDV of IEC 62093 this document, Dutch Guidelines Edition 2, gives a procedure for design qualification of grid connected PV-inverters and comprises performance, utility interface protection, electromagnetic compatibility (EMC) and field tests. This document must be seen as a supplement to the committee draft for vote CDV and specifies those requirements for grid-connected inverters, which are not yet discussed herein.
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2.
PROCEDURE FOR DESIGN QUALIFICATION
The procedure for design qualification is laid down in the committee draft for vote (CDV) 82/330/CDV of IEC 62093 in chapter 4, 7 and 8. The “Specific Performance Tests for Components” (paragraph 12.3 of the CDV) is supplemented with the “Specific Functioning Test Procedure – inverters of chapter 5 of this document ”. The test set-up for the specific functioning test procedure – inverters of chapter 5 is described in appendix A. The PV simulator is described in appendix B and the grid simulator in appendix C.
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3.
DEFINITIONS
For the purpose of this document the following definitions apply. Array: A mechanically integrated assembly of modules or panels together with support structure, but exclusive of foundation, tracking apparatus, thermal control and other such components, to form a d.c. power-producing unit. (IEC 61277) Current-voltage characteristic (I = f(V)): The output current of a photovoltaic (PV) generator as a function of output voltage, at a particular temperature and irradiance. (IEC 60904-3) Fill factor (FF): The ratio of maximum power to the product of open-circuit voltage and short-circuit current: FF = Pmax /( Voc Isc ) (IEC 60904-3) Inverter: A device which changes d.c. input into an a.c. output. (IEC 61277) inverter efficiency: The ratio of the useful a.c. electrical output power of the inverter to the d.c. power input. (IEC 61277) Irradiance (G): Radiant power incident upon unit area of surface. (IEC 60904-3) Unit: W⋅m–2 Maximum power (Pmax ): The power at the point on the current-voltage characteristic where the product of current and voltage is a maximum. (IEC 60904-3) Unit: W Module: The smallest complete environmentally protected assembly of interconnected solar cells. (IEC 60904-3; IEC 61277) Open-circuit voltage (Voc ): The voltage across an unloaded (open) photovoltaic (PV) generator at a particular temperature and irradiance. (IEC 60904-3) Unit: V Panel: A group of modules fastened together, pre-assembled and wired, designed to serve as an installable unit in an array and/or subarray. (IEC 61277) Power conditioner: The electrical equipment used to convert electrical power into a form or forms of electrical power suitable for subsequent use. (IEC 61277) Rated output power (Prated): The inverters maximum AC power under continuous operation at nominal voltage of the utility interface, under specified operating conditions. Unit: W NOTE - The Rated output power can be dependent of the DC input voltage.
Short-circuit current (Isc ): The output current of a photovoltaic (PV) generator in the short circuit condition at a particular temperature and irradiance. (IEC 60904-3) Unit: A Voltage temperature coefficient (β): The change of the open circuit voltage of a photovoltaic (PV) device per unit change of cell temperature. (IEC 60904-3) Unit: V⋅°C–1 NOTE – This coefficient varies with irradiance and to a lesser extent with temperature.
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4.
NORMATIVE REFERENCES
The following normative documents contain provisions, which, through reference in this text, constitute provisions of this standard. At the time of publication, the editions indicated were valid. All normative documents are subjected to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. IEC 60364-7-712, Electrical installations of buildings – Part 7: Requirements for special installations or locations – Section 712: Photovoltaic power supply systems IEC 60449, Voltage bands for electrical installations of buildings IEC 60529, Degrees of protection provided by enclosures (IP Code) IEC 60950, Safety of information technology equipment, including electrical business equipment IEC 60721-2-1, Classification of environmental conditions – Part 2: Environmental conditions appearing in nature - Temperature and humidity, Amendment 1 IEC 61683, Photovoltaic systems - Power conditioners - Procedure for measuring efficiency IEC 61727, Characteristics of the utility interface for photovoltaic (pv) systems (under construction, committee Draft for Vote 82/308/CDV) IEC 61836, Solar photovoltaic energy systems – Term and symbols IEC 62093, Balance-of-system components for photovoltaic systems – Design Qualification natural environments (under consideration, Committee Draft 82/311/CD) IEC 62124, Photovoltaic (pv) stand-alone systems – design verification (under consideration, Committee Draft for Vote 82/303/CDV) EN 61000-3-2, Electromagnetic Compatibility – Part 3: Limits – Section 2: Limits for harmonic currents emissions (Equipment input current up to and including 16A per phase) EN 61000-3-3, Electromagnetic Compatibility – Part 3: Limits – Section 3: Limitation of voltage fluctuations and flicker in low-voltage supply systems for equipment with rated current =< 16A EN 61000-4-2, Electromagnetic compatibility (EMC) – Part 4: Testing and measuring techniques – Section 2: Electrostatic discharge requirements EN 61000-4-3, Electromagnetic compatibility (EMC) – Part 4: Testing and measuring techniques – Section 3: Radiated, radio-frequency, electromagnetic field immunity test EN 61000-4-4, Electromagnetic compatibility (EMC) – Part 4: Testing and measuring techniques – Section 4: Electrical fast transient / burst requirements
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EN 61000-4-5, Electromagnetic compatibility (EMC) – Part 4: Testing and measuring techniques – Section 5: Surge immunity tests EN 61000-4-6, Electromagnetic compatibility (EMC) – Part 4: Testing and measuring techniques – Section 6: Immunity to conducted disturbances, induced by radio-frequency fields EN 61000-4-11, Electromagnetic compatibility (EMC) – Part 4: Testing and measuring techniques – Section 11: Voltage dips, short interruptions and voltage variations – immunity tests EN 61000-6-1, Electromagnetic compatibility (EMC) – Part 6-1: Generic standards; Immunity for residential, commercial and light-industrial environments EN 61000-6-3, Electromagnetic compatibility (EMC) – Part 6-3: Generic standards; Emission standard for residential, commercial and light-industrial environments
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5.
SPECIFIC FUNCTIONING TEST PROCEDURE – INVERTERS
Inverters have a variety of input voltage ranges. Inverters suitable for one or two PV panels normally have a small input voltage range. String inverters can have an input voltage range of several hundreds of volts. The behaviour of the inverter under test can be different at minimum and maximum input voltage. Therefore electrical parameters must be measured at different input voltages. The number of different input voltages depends on the input voltage range of the inverter. As guidance the number of voltage ranges and levels of the IEC 61683, Photovoltaic systems – Power conditioners – Procedure for measuring efficiency, is taken. The different input voltages of the IEC 61683 are: minimum input voltage, nominal input voltage and 90% of the inverter’s maximum input voltage. appendix D describes how to calculate these three input voltages. The tests described in chapter 5 must be carried out at the input voltages as specified in Table 5-1. Table 5-1 Input voltage test level Paragraph Functioning Test 5.1.1 Energy efficiency 5.1.2 European efficiency 5.1.3 Power factor 5.1.4 MPPT efficiency 5.1.5 MPPT response time 5.1.6 Stand-by loss 5.1.7 Electric shock 5.2.1 Over/Under voltage 5.2.2 Over/Under frequency 5.2.3 Islanding 5.2.4 Start-up delay 5.2.5 Utility recovery 5.2.6 Direct-current injection 5.3 EMC 5.4 Harmonics 6 Field measurement (outdoors)
Umin X X X X
X
Unom X X X X X X X X X X X X X X X X
90%Umax X X X X
X
All measurements described in chapter 5 shall be carried out at room temperature after the inverter under test is warmed up. An initially warming up phase could exist of 15 to 30 minutes of operation of the inverter at full power. Remark In chapter 5, requirements in Italic refer to the original text of the standard mentioned for the edition as mentioned in chapter 4. If the relevant standard changes due to a new release or the standard mentioned is overruled by a new standard, than the text in Italic and requirements are no longer applicable and shall be replaced by the new text and requirements of the new standard.
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5.1
Performance tests
The procedures and requirements of the sub-clauses of paragraph 5.1 are applicable for single and multi PV-input inverters with one phase output. For multi PV-input inverters the input power must be equally divided over the individual inputs.
5.1.1 Power conversion efficiency (static) Procedure The static power conversion efficiency must be measured in compliance with the procedure for grid-connected inverters described in IEC 61683. The power test levels are: 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115%, and 120% of the rated output power. The power test levels must be measured for all input voltage test levels specified in Table 5-1. The power conversion efficiency must be measured over a period of 60 seconds for each power level. In case the inverter cannot operate at overload conditions, power levels higher than 100%Prated are not applicable for the inverter under test. The power conversion efficiency shall be part of the qualification in order to assess the heat production and the energy yield. Requirements See appendix E
5.1.2 European efficiency Procedure The European efficiency must be calculated for all input voltage test levels specified in Table 5-1. The formula for the European efficiency is specified by: ηEU = (0.03×η5%) + (0.06×η10%) +(0.13×η20%) +(0.1×η30%) +(0.48×η50%) +(0.2×η100%) The efficiency data required for calculating the European efficiency equals the efficiency data of the power conversion efficiency test of paragraph 5.1.1. The index percentage of the efficiency is the power test level percentage. The European efficiency shall be part of the qualification in order to assess the heat production and the energy yield. Requirements See appendix E
5.1.3 Power factor Procedure The power factor must be measured for the power test levels: 50%, 75%, 100% and 120% of the rated output power. The power factor must be measured for all input voltage test levels specified in Table 5-1. The power factor must be measured over a period of 60 seconds for each power level. In case the inverter cannot operate at overload conditions, power levels higher than 100%Prated are not applicable for the inverter under test.
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Requirements The power factor shall comply with the requirements of IEC 61727. The PV system shall have an average lagging power factor greater than 0.9 when the output is greater than 50%Prated. If the inverter is specially designed and produced for application in a specific country then the power factor shall be in accordance with the national standards of the specified country.
5.1.4 Static MPPT efficiency Procedure The static maximum power point tracking (MPPT) efficiency must be measured for the power test levels: 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110% and 120% of the rated output power. The static MPPT efficiency must be measured for all input voltage test levels specified in Table 5-1. The static MPPT efficiency must be measured over a period of 60 seconds for each power level. In case the inverter cannot operate at overload conditions, power levels higher than 100%Prated are not applicable for the inverter under test. The static MPPT efficiency shall be part of the qualification in order to assess the MPPT range. Requirements See appendix E
5.1.5 Dynamic MPPT response Procedure The dynamic mppt response test shall be part of the qualification in order to characterise the tracking behaviour of the inverter under dynamic irradiations. The dynamic MPPT response must be determined for a continuously changing input power corresponding to the irradiation patterns specified in Figure 5-1and Table 5-2, for all input voltage test levels specified in Table 5-1. The DC input power of the inverter must be measured with an oscilloscope after one minute of operation. In three successive cycles per pattern the time must be noted the mpp tracker needs to reach 90% of its final state. Pattern 1 2 3 4 5
GL GH tr [W/m²] [W/m²] [s] 300 800 5 300 800 3 300 800 2 300 800 1 300 800 0.5
tf [s] 5 3 2 1 0.5
Table 5-2 Specification irradiation As a reference the irradiation can be simulated as follows: • G=1000W/m² corresponds to a Pmpp suitable for the rated output power • G is linearly with Pmpp The times tH and tL, see Figure 5-1, are inverter dependent and shall be chosen long enough to stabilise the inverter in its new point of operation due to maximum power point tracking.
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GH
GL
tr
tH
tf
tL
Figure 5-1 Irradiation pattern Requirements See appendix E
5.1.6 Stand-by loss at night Procedure The stand-by loss shall be part of the qualification in order to assess the loss of energy yield due to night consumption when the irradiation level is Gi = 0W/m². Stand-by loss must be measured in compliance with the procedure for grid-connected inverters described in IEC 61683. Stand-by loss, active power drawn from the grid (W) and apparent power (VA), and load current of the inverter must be measured. The measurement starts after the switching to the "night operation" state of the inverter and must be measured over a period of time of 60 seconds. Requirements See appendix E
5.1.7 Electric shock Procedure The discharge of the internal capacitor of the inverter at the grid connection must be measured for all input voltage test levels specified in Table 5-1 when the inverter is first operating at 100%Prated then the grid is disconnected at the voltage maximum of the sinus. Requirements The voltage on the grid connection after disconnection of the grid shall comply with the requirements of IEC 60950. Equipment is considered to comply if any capacitor having a marked or nominal capacitance exceeding 0,1 µF and connected to the external mains circuit has a means of discharge resulting in a time-constant not exceeding: 1 second for pluggable equipment type A - 10 seconds for permanently connected equipment and for pluggable equipment type B During an interval equal to one time-constant the voltage will have decayed to less than 37% of its original value.
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5.2
Utility interface tests
5.2.1 Over / under voltage protection Procedure The under voltage and over voltage levels, with nominal frequency, of the utility interface must be measured at which the inverter ceases to energise the utility line. Also the trip times must be measured. The under voltage and over voltage levels and the trip times must be measured for all input voltage test levels specified in Table 5-1 when the inverter is operating at 50%Prated. Requirements The under voltage and over voltage levels and the corresponding trip times shall be in accordance with IEC 61727, see Table 5-3. As voltages of 135% of the nominal grid voltage and higher are supposed to be destructive for the inverter under test, the maximum voltage may be limited to 120% of the nominal grid voltage. Table 5-3 Response to Abnormal Voltages Voltage (at point of utility connection) V < 50% 50% ≤ V < 85% 85% ≤ V ≤ 110% 110% < V < 135% 135% ≤ V
Maximum Trip Time* 0.1 seconds 2.0 seconds Continuous Operation 2.0 seconds 0.05 seconds
*Trip time refers to the time between the abnormal condition occurring and the inverter ceasing to energize the utility line. There are no requirements for the voltage levels at which the inverter must energise the utility line again after the utility service voltage has recovered to within the specified ranges If the inverter is specially designed and produced for application in a specific country then the under voltage levels, over voltage levels, the corresponding trip times and the behaviour at recovery shall be in accordance with the national standards of the specified country.
5.2.2 Over / under frequency protection Procedure The under frequency and over frequency levels of the utility interface must be measured at which the inverter ceases to energise the utility line. Also the trip times must be measured. The under frequency and over frequency levels and the trip times must be measured for all input voltage test levels specified in Table 5-1 when the inverter is operating at 50%Prated for both the minimum and the maximum voltage level of the utility interface where the inverter can operate continuously. Requirements The under frequency and over frequency levels and the corresponding trip times shall be in accordance with IEC 61727. When the utility frequency is outside the range of +/- 1 Hz the inverter should cease to energise the utility line within 0.2 seconds.
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There are no requirements for the frequency levels at which the inverter must energise the utility line again after the utility service frequency has recovered to within the specified ranges If the inverter is specially designed and produced for application in a specific country then the under frequency levels, over frequency levels, the corresponding trip times and the behaviour at recovery shall be in accordance with the national standards of the specified country.
5.2.3 Islanding Procedure No special procedure is prescribed for measuring islanding protection. An inverter that complies to the tests and requirements of paragraphs 5.2.1 and 5.2.2 is considered to be sufficiently protected against islanding. Requirements The islanding protection shall be in accordance with IEC 61727. A PV system that ceases to energise the utility line in case of a voltage and frequency situation outside of the ranges stated in IEC 61727 within the timeframes set in the IEC 61727 is considered to be sufficiently protected against islanding.
5.2.4 Start-up delay Procedure The start-up delay must be measured for a power test level of 50% of the rated output power. The start-up delay must be measured for all input voltage test levels specified in Table 5-1. Starting with a disconnected inverter, the inverter is connected to the grid and energised. Then the solar input is connected and energised. The start-up delay is the time between the moment of energising both the solar input and the grid connection and the moment the inverter is starting to energise the utility line. Requirements Start-up delay is a normal operating action due to installing the inverter to the grid or due to wake-up of the inverter in the morning where the utility interface supplies a continues grid voltage and frequency in-range with the conditions for normal operation. Therefore there is no relation with utility recovery according to IEC 61727. The start-up delay shall be in accordance with national standards.
5.2.5 Response to utility recovery Procedure The response to utility recovery must be measured for a power test level of 50% of the rated output power. The response to utility recovery must be measured for all input voltage test levels specified in Table 5-1. Following an out-of-rang condition that has caused the photovoltaic system to cease energising, the system shall respond to recovery of the utility service voltage and frequency within the specified ranges with a delay before starting to energise the utility line. Requirements The response to utility recovery shall be in accordance with IEC 61727. Following an out-of-range utility condition that has caused the photovoltaic system to cease energising, the photovoltaic system shall not energise the utility line for 3 minutes after the utility service voltage and frequency have recovered to within the specified ranges.
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If the inverter is specially designed and produced for application in a specific country then the response to utility recovery shall be in accordance with the national standards of the specified country.
5.2.6 Direct-current injection Procedure The direct-current injection into the utility line must be measured for two power test levels of the rated output power. One power test at 95% of the highest power level where the inverter operates in the maximum power point. A second power test level where the inverter operates outside the maximum power point at maximum power (output power limitation). The directcurrent injection must be measured for all input voltage test levels specified in Table 5-1. Requirements The direct-current injection shall be in accordance with IEC 61727. The PV system shall not inject dc current greater than 1% of the rated inverter output current into the utility ac interface.
5.3
EMC
Procedure The electromagnetic compatibility (EMC) must be tested. In the EMC tests, emission and immunity, the repercussion of the inverter to the grid and the surrounding area are measured. The measurements are based upon the requirements stated in EN 61000-6-1 and EN 61000-6-3 both for residential, commercial and light industry applications. Requirements The inverter must satisfy the requirements of the following standards: Emission • Emission • Harmonic distortion • Flicker
EN 61000-6-3 *) EN 61000-3-2 EN 61000-3-3
Immunity • Immunity • Electrostatic discharge • Radiated immunity • Electric fast transient • Surge • Conducted immunity • Voltage dips
EN 61000-6-1 EN 61000-4-2 EN 61000-4-3 EN 61000-4-4 EN 61000-4-5 EN 61000-4-6 EN 61000-4-11
*)
For PV-systems with very short DC-lines, like modules with integrated inverters, conducted emission measurement on the DC-lines may not be obliged, however the module area could work as an antenna. In this case a measurement of the radiated field between 150 kHz and 30 MHz is recommended.
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5.4
Harmonics
Additionally to the requirements of paragraph 5.3 EMC the inverter must satisfy the requirements of IEC 61727 too. Procedure The harmonic current emission injected into the utility interface must be measured while the inverter is operating at 100%Prated. Voltage harmonics of the utility interface shall be in accordance with appendix C. The harmonic currents must be measured for all input voltage test levels specified in Table 5-1. Requirements The harmonic current emission shall be in compliance with IEC 61727. Even harmonics shall be less than 25% of the next higher odd harmonics listed in the IEC 61727. Total harmonic distortion shall be less than 5% at the rated inverter output. Each individual harmonic shall be limited to the percentage listed in Table 5-4 Even harmonics in these ranges shall be less than 25% of the odd harmonics listed. Table 5-4 Distortion limits Odd harmonics 3rd through 9th 11th through 15th 17th through 21st 23rd through 33rd
Distortion limit Less than 4.0% Less than 2.0% Less than 1.5% Less than 0.6%
NOTE: A procedure for determining the effect of harmonic current emission of an inverter as a response on harmonic voltage pollution of the grid is under consideration.
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6.
FIELD MEASUREMENTS (OUTDOORS)
Outdoors measurements are necessary to assess the maximum power point tracker performance of the inverter. Outdoor measurements have the advantage that the actual maximum power point tracker behaviour can be observed with a real PV array, so that potentially unrealistic interactions between maximum power point tracker and solar simulator can be avoided. Procedure Operate the inverter in a PV system with a real PV panel or PV array and a real utility power line. There shall be fault protection according to clause 712.413 of IEC 60364-7-712. The PV panel or PV array shall be able to continuously supply the DC power sufficiently for the inverters rated output power, at a maximum irradiance of 1000W/m². The field measurements must be carried out for all input voltage test levels specified in Table 5-1. At a minimum of four irradiance levels (preferably 100W/m², 200W/m², 600W/m² and 1000W/m²) data of Udc, Idc and G must be acquired with a sample rate of 1000Hz. Three plots must be made of the tracking behaviour of the inverter at the given irradiance levels. • The first plot must show the irradiance G and the DC power Pdc versus time. This plot shows the power deviation as a result of the search algorithm of the MPP tracker. • The second plot must show the DC voltage versus time. A voltage swing with a frequency of twice the grid frequency can possibly be seen. • The third plot must show the DC power Pdc versus the DC voltage Udc. This plot is a part of the IV curve of the PV panel or PV array and shows if the maximum power point tracker finds the maximum power point. Requirements The inverter shall not show abnormal operation.
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APPENDIX A
TEST SET-UP
The test-up is defined in Figure 6-1 and Figure 6-2 of this appendix. Two test set-ups have been defined. Test set-up according to Figure 6-1 is applicable for basic measuring instruments. Test set-up according to Figure 6-2 makes use of an intelligent measuring device such as a power / spectrum analyser. The test set-up describes the place of the measuring instruments or devices for each solar input and for the grid connection for single input or multi input PV inverters with a 1-phase output. The test set-up is in accordance with test set-up of IEC 61683 for utility-interactive type power conditioners.
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A1 PV Simulator
W2
W1 V1
Inverter under test
A2
PF
V2
F
R*
Grid Simulator
Figure 6-1 General test set-up for grid-connected inverters
A1 A2 W1 W2 R*
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DC ammeter AC ammeter DC wattmeter AC wattmeter Resistive load (optional, see appendix C)
V1 V2 PF F
DC voltmeter AC voltmeter power factor meter frequency meter
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S1 PV Simulator
S2 U1
Inverter under test
U2
R*
Grid Simulator
Power / Spectrum Analyser Figure 6-2 Test set-up for grid-connected inverters with Power / Spectrum analyser
S1 S2 R*
DC current shunt AC current shunt Resistive load (optional, see appendix C)
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U1 U2
DC voltage probe AC voltage probe
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APPENDIX B
DEFINITION PV SIMULATOR
The PV simulator is a manually adjustable or computer driven power supply. The DC output follows the IV-characteristic of a normal PV-array. The IV-curve can be obtained by a data table, analogue or numerical computation. The PV simulator shall have sufficient speed in relation to the dynamic behaviour of the inverter, such as the ripple due to the grid frequency in case of a 1-phase inverter and the inverters MPPT-algorithm. The PV simulator shall not interfere with the switching behaviour of the inverter. The IV curve shall be described by three variables: Isc = Short-circuit current Voc = Open Circuit voltage (no load voltage) FF = Fill factor (sharpness of the curve) The fill factor shall be between 0.70 and 0.75 in case of simulating c-Si PV-modules, in case of simulating a-Si PV-modules the fill factor shall be between 0.60 and 0.65. The formulas for Isc=f(G) and Voc=f(G) for both c-Si and a-Si PV-modules are defined in the draft standard of IEC62124 as: Translation factors
Isc , 2 = Isc ,1 ⋅ [1 + α ⋅ (T 2 − T 1)] ⋅
G2 G1
and
G2 Voc , 2 = Voc ,1 ⋅ 1 + a ⋅ ln + b ⋅ (T 2 − T 1) G1 Module parameters α : temperature coefficient of Isc b : temperature coefficient of Voc a : dimensionless radiation factor of Voc
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(default = 0.0005 /°C) (default = -0.004 /°C) (default = 0.06)
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APPENDIX C
DEFINITION GRID SIMULATOR
The grid simulator is a manually adjustable or computer driven power supply with an AC output, 1 phase, able to sink and source power. When the output of the grid simulator cannot sink all the power or when the output of the grid simulator can only source power, a resistive load of sufficient power can be placed in parallel with the grid simulator. Due to internal resistance, external wiring and (current) measuring devices the output voltage may drop or rise. The voltage at the grid connection of the inverter shall be within 1% of the adjusted output voltage of the grid simulator. The harmonic ratios of the test voltage shall not exceed the following values with the EUT connected as in normal operation: 0.9 % for harmonic of order 3; 0.4 % for harmonic of order 5; 0.3 % for harmonic of order 7; 0.2 % for harmonic of order 9; 0.2 % for even harmonics of order from 2 to 10; 0.1 % for harmonics of order 11 to 40. (The harmonics and percentages are in accordance with IEC 61000-3-2) The grid simulator must be able to sink DC currents produced by the inverter.
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APPENDIX D
CALCULATION OF INPUT VOLTAGES
The input voltages Umin, Unom and 90%Umax are defined as the simulated PV array that gives the corresponding voltage, according to the manufacturers specification, in the maximum power point of the IV-curve when the inverter is operating at the specified power. The specified power can be voltage dependent. The inverter may not show a current limiting, voltage limiting or power limiting behaviour. By specifying a simulated PV array the input voltage and input current of the inverter changes as a result of irradiance and mppt behaviour. The dependency of Isc=f(G) and Voc=f(G) for both cSi and a-Si PV-modules is defined in appendix B. As a reference the input voltages can be calculated as follows: 90%Umax is the simulated PV array that gives an Umpp , at the rated output power (Prated), equal to 90% of the maximum of the mpp voltage range specified by the manufacturer of the inverter. If the corresponding Uoc should exceed the absolute maximum voltage of the inverter then the Umpp must be adjusted to such a value that Umpp corresponds to Uoc=Uoc max. Unom is the simulated PV array that gives an Umpp , at the rated output power (Prated), equal to the nominal input voltage (Umpp) of the inverter. If the manufacturer does not specify a nominal value then an average value can be calculated. Umin is the simulated PV array that gives an Umpp equal to 120% of the minimum of the mpp voltage range specified by the manufacturer of the inverter. The value of 120% allows the inverter to operate at low power levels while the input voltage is still higher than the minimum Umpp specified by the manufacturer. Due to a possible limitation of the input current the rated output power at Umin can be less than the rated output power for Unom or 90%Umax. Note: For inverters with a small input voltage range the nominal input voltage can be about equal or even more than 90% of the inverter’s maximum input voltage. If the calculated input voltages lead to unpractical or illogical values, alternatives must be chosen in consultation with the designer or manufacturer of the inverter.
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APPENDIX E
BEST PRACTICE
Not all the tests of chapter 5 have requirements according to an international standard or a national standard. For those tests a best practice is defined. This best practice reflects a performance level that is achievable to day. It is not a mandatory requirement. Due to an optimization of the price/performance ratio other performance levels are acceptable. As standards omit, it is not up to a test institute to approve or disapprove the inverter under test. Power conversion efficiency (static) For today's inverters, power conversion efficiency higher than 90% for power levels higher than 20%Prated is achievable. European efficiency For today's inverters a European efficiency higher than 91% is achievable. Static MPPT efficiency For today's inverters, static MPPT efficiency higher than 97% for power levels between 10%Prated and 95%Prated is achievable. Dynamic MPPT response The inverter must continue its normal operation during and after the test. The fastest pattern that passes the test will be noted. Stand-by loss at night The stand-by loss must comply with the specifications according to the manufacturer.
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APPENDIX F
REPORTING
All test results must be reported. Aspects to discuss in the report are: General: • Test set-up • Used equipment • Specification of IV-curves • Specification of the grid Tests • • • • •
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Measuring data Data according to specification of the manufacturer Selection of standard Data according to standards Data according to best practice
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