Utility-interconnected photovoltaic inverters - Test procedure for under voltage ride-through measurements

IEC TS 62910:2020 is available as IEC TS 62910:2020 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.
IEC TS 62910:2020 provides a test procedure for evaluating the performance of Under Voltage Ride-Through (UVRT) functions in inverters used in utility-interconnected Photovoltaic (PV) systems. This document is most applicable to large systems where PV inverters are connected to utility high voltage (HV) distribution systems. However, the applicable procedures may also be used for low voltage (LV) installations in locations where evolving UVRT requirements include such installations, e.g. single-phase or 3-phase systems. The assessed UVRT performance is valid only for the specific configuration and operational mode of the inverter under test. Separate assessment is required for the inverter in other factory or user-settable configurations, as these may cause the inverter UVRT response to behave differently. This second edition cancels and replaces the first edition issued in 2015 and constitutes a technical revision.

General Information

Status
Published
Publication Date
23-Jul-2020
Current Stage
PPUB - Publication issued
Completion Date
24-Jul-2020
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IEC TS 62910
Edition 2.0 2020-07
TECHNICAL
SPECIFICATION
colour
inside
Utility-interconnected photovoltaic inverters – Test procedure for under voltage
ride-through measurements
IEC TS 62910:2020-07(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TS 62910
Edition 2.0 2020-07
TECHNICAL
SPECIFICATION
colour
inside
Utility-interconnected photovoltaic inverters – Test procedure for under voltage
ride-through measurements
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-8383-7

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TS 62910:2020 © IEC 2020
CONTENTS

FOREWORD ........................................................................................................................... 4

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms, definitions, symbols and abbreviated terms .......................................................... 7

3.1 Terms, definitions and symbols ............................................................................... 7

3.2 Abbreviated terms ................................................................................................... 9

4 Test circuit and equipment ............................................................................................. 10

4.1 General ................................................................................................................. 10

4.2 Test circuit ............................................................................................................ 10

4.3 Test equipment ..................................................................................................... 10

4.3.1 Measuring instruments................................................................................... 10

4.3.2 DC source ..................................................................................................... 11

4.3.3 Short-circuit emulator .................................................................................... 11

4.3.4 Converter based grid simulator ...................................................................... 14

5 Test ............................................................................................................................... 14

5.1 Test protocol ......................................................................................................... 14

5.2 Test curve ............................................................................................................. 16

5.3 Test procedure ...................................................................................................... 17

5.3.1 Pre-test ......................................................................................................... 17

5.3.2 No-load test ................................................................................................... 17

5.3.3 Tolerance ...................................................................................................... 17

5.3.4 Load test ....................................................................................................... 17

6 Assessment criteria ....................................................................................................... 18

Annex A (informative) Circuit faults and voltage drops ......................................................... 19

A.1 Fault types ............................................................................................................ 19

A.2 Voltage drops ....................................................................................................... 21

A.2.1 General ......................................................................................................... 21

A.2.2 Three-phase short-circuit fault ....................................................................... 22

A.2.3 Two-phase short-circuit fault with ground ....................................................... 22

A.2.4 Two-phase short-circuit fault without ground .................................................. 23

A.2.5 Single-phase short-circuit fault with ground ................................................... 24

Annex B (informative) Determination of critical performance values in UVRT testing ............ 26

B.1 General ................................................................................................................. 26

B.2 Drop depth ratio .................................................................................................... 26

B.3 Ride-through time ................................................................................................. 26

B.4 Reactive current.................................................................................................... 26

B.5 Active power ......................................................................................................... 27

Annex C (informative) Requirements of the UVRT curve ...................................................... 28

C.1 General ................................................................................................................. 28

C.2 UVRT curve .......................................................................................................... 28

C.3 Test points ............................................................................................................ 28

Bibliography .......................................................................................................................... 29

Figure 1 – Testing circuit diagram ......................................................................................... 10

Figure 2 – Short-circuit emulator ........................................................................................... 12

---------------------- Page: 4 ----------------------
IEC TS 62910:2020 © IEC 2020 – 3 –

Figure 3 – Converter device example .................................................................................... 14

Figure 4 – UVRT curve example ........................................................................................... 16

Figure 5 – Tolerance of voltage drop..................................................................................... 17

Figure A.1 – Grid fault diagram ............................................................................................. 21

Figure A.2 – Diagram of voltage vector for three-phase short-circuit fault ............................. 22

Figure A.3 – Diagram of voltage vector of two-phase (BC) short-circuit fault with

ground .................................................................................................................................. 23

Figure A.4 – Diagram of voltage vector of two-phase (BC) short-circuit fault ......................... 24

Figure A.5 – Diagram of voltage vector of single-phase (A) short-circuit fault with

ground .................................................................................................................................. 25

Figure B.1 – Determination of reactive current output ........................................................... 27

Figure B.2 – Determination of active power recovery ............................................................ 27

Figure C.1 – The typical curve of UVRT ................................................................................ 28

Table 1 – Accuracy of measurements ................................................................................... 11

Table 2 – Fault type and switch status .................................................................................. 13

Table 3 – Test specification for UVRT (Indicative) ................................................................. 15

Table A.1 – Short-circuit paths for different fault types .......................................................... 19

Table A.2 – Amplitude and phase changes in three-phase short-circuit fault ......................... 22

Table A.3 – Amplitude and phase changes in two-phase (BC) ............................................... 23

Table A.4 – Amplitude and phase changes in two-phase (BC) short-circuit fault .................... 24

Table A.5 – Amplitude and phase changes in single-phase (A) ............................................. 25

---------------------- Page: 5 ----------------------
– 4 – IEC TS 62910:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
UTILITY-INTERCONNECTED PHOTOVOLTAIC INVERTERS –
TEST PROCEDURE FOR UNDER VOLTAGE
RIDE-THROUGH MEASUREMENTS
FOREWORD

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The main task of IEC technical committees is to prepare International Standards. In

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• the subject is still under technical development or where, for any other reason, there is the

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Technical Specifications are subject to review within three years of publication to decide

whether they can be transformed into International Standards.

IEC TS 62910, which is a technical specification, has been prepared by IEC technical

committee 82: Solar photovoltaic energy systems.
---------------------- Page: 6 ----------------------
IEC TS 62910:2020 © IEC 2020 – 5 –

This second edition cancels and replaces the first edition issued in 2015, and constitutes a

technical revision.

It remains a TS because it is limited to providing recommended practices for UVRT testing in

the context of non-uniform grid-codes lacking international consensus, and the rapid

development of test technology in recent years.
The main technical changes with regard to the previous edition are as follows:
Clause Previous edition Present edition

the voltage support of EUT in accordance with the K-factor is to be supplied by the EUT

the voltage drops. The K-factor is to be manufacturer meeting additional requirements

3.1.12

specified by the EUT manufacturer imposed by national standards and/or local codes

Back to Back circuit Back to Back circuit
A A
B B
Figure 2
C C
Grid Grid
(optional) (optional)

The test circuit essentially comprises a voltage The test circuit essentially comprises a voltage

4.3.4 source with a low internal resistance combined source with a low internal resistance combined

with broadband amplifiers...... optionally with broadband amplifiers......

d The test should be carried out under specified d The test should be carried out under specified

K-factor provided by manufacture meeting
K-factor provided by local manufacture.
Table 3
additional requirements imposed by national
standards and/or local codes.
1,2
1,2
1,1
1,1
LVRT curve
LVRT curve
Keep connecting to the grid
Keep connecting to the grid 1,0
1,0
highest point
0,9
0,9
inflection point
0,8 inflection point 0,8
0,7 inflection point 0,7 inflection point
0,6 0,6
0,5 0,5
May cut off from the grid May cut off from the grid
Figure 4
0,4 0,4
0,3 inflection point 0,3 inflection point
0,2
0,2
Lowest point
Lowest point
0,1
0,1
t0 t1 t2 t3 4 t
t t t t 4
0 1 2 3
Time (s)
Time (s)

NOTE The example shows two types of points The example shows three types of points on the

on the UVRT curve: the lowest point and the UVRT curve: the highest point, the lowest point

5.2

inflection point. Tests must be carried out at and the inflection point. Tests shall be carried out

both types of points at above types of points.

Prior to the fault simulation tests, the EUT Prior to the fault simulation tests, the EUT should

should run in normal operating mode. The run in normal operating mode. The selected

5.3.1 selected UVRT curve should be used to identify UVRT curve should be used to identify voltage

voltage drop points, including the lowest point drop points, including the highest point, the

and the inflection point, ...... lowest point and the inflection point, ......
Voltage of PCC ( p.u. )
Voltage of PCC
( p.u. )
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– 6 – IEC TS 62910:2020 © IEC 2020
The text of this Technical Specificationis based on the following documents:
Draft TS Report on voting
82/1607/DTS 82/1640A/RVDTS

Full information on the voting for the approval of this Technical Specification can be found in

the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates

that it contains colours which are considered to be useful for the correct

understanding of its contents. Users should therefore print this document using a

colour printer.
---------------------- Page: 8 ----------------------
IEC TS 62910:2020 © IEC 2020 – 7 –
UTILITY-INTERCONNECTED PHOTOVOLTAIC INVERTERS –
TEST PROCEDURE FOR UNDER VOLTAGE
RIDE-THROUGH MEASUREMENTS
1 Scope

This document provides a test procedure for evaluating the performance of Under Voltage

Ride-Through (UVRT) functions in inverters used in utility-interconnected Photovoltaic (PV)

systems.

This document is most applicable to large systems where PV inverters are connected to utility

high voltage (HV) distribution systems. However, the applicable procedures may also be used

for low voltage (LV) installations in locations where evolving UVRT requirements include such

installations, e.g. single-phase or 3-phase systems.

The assessed UVRT performance is valid only for the specific configuration and operational

mode of the inverter under test. Separate assessment is required for the inverter in other

factory or user-settable configurations, as these may cause the inverter UVRT response to

behave differently.

The measurement procedures are designed to be as non-site-specific as possible, so that

UVRT characteristics measured at one test site, for example, can also be considered valid at

other sites.

This document is for testing of PV inverters, though it contains information that may also be

useful for testing of a complete PV power plant consisting of multiple inverters connected at a

single point to the utility grid. It further provides a basis for utility-interconnected PV inverter

numerical simulation and model validation.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their

content constitutes requirements of this document. For dated references, only the edition

cited applies. For undated references, the latest edition of the referenced document (including

any amendments) applies.
IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms, definitions and symbols

For the purposes of this document, the terms and definitions in IEC TS 61836 and the

following apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
---------------------- Page: 9 ----------------------
– 8 – IEC TS 62910:2020 © IEC 2020
3.1.1
drop depth

magnitude of voltage drop during a fault or simulated fault, as a percentage of the nominal

supply voltage
3.1.2
double drop

sudden decline of the nominal voltage to a value below 90 % of the voltage of point of

common coupling (PCC), followed after a short time by a voltage recovery, which happens

twice

Note 1 to entry: Voltage changes which do not reduce the voltage to below 90 % of the voltage of PCC are not

considered to be voltage drops.
3.1.3
equipment under test
EUT

equipment on which these tests are performed and refers to the utility-interconnected PV

inverter. During test period, EUT is connected with PV simulator instead of real PV modules

on the direct current (DC) side, while alternating current (AC) side is connected with grid

3.1.4
output reactive current of EUT
3.1.5
under voltage ride through
UVRT

capability of an inverter to continue generating power to connected loads during a limited

duration loss or drop of grid voltage
3.1.6
maximum power point tracking
MPPT
control strategy of operation at maximum power point or nearby
3.1.7
EUT
access point of the EUT during the test
3.1.8
rated power of EUT
3.1.9
point of common coupling
PCC

point of a power supply network, electrically nearest to a particular load, at which other loads

are, or may be, connected

Note 1 to entry: These loads can be either devices, equipment or system, or distinct customer’s installations.

Note 2 to entry: In some applications, the term “point of common coupling” is restricted to public networks.

[SOURCE: IEC 60050-161:1990, 161-07-15]
---------------------- Page: 10 ----------------------
IEC TS 62910:2020 © IEC 2020 – 9 –
3.1.10
proportionality constant K
K-factor

the K-factor is to be supplied by the EUT manufacturer meeting additional requirements

imposed by national standards and/or local codes
3.1.11
PV array simulator
simulator that has I-V characteristics equivalent to a PV array
3.1.12
EUT
apparent short-circuit power at N
EUT
S = I × U , I refer to short-circuit current at N during the no-load test
EUT sc N sc EUT
3.1.13
single drop

sudden decline of the nominal voltage to a value below 90 % of the voltage of PCC, followed

after a short time by a voltage recovery, which happens once

Note 1 to entry: Voltage changes which do not reduce the voltage to below 90 % of the voltage of PCC are not

considered to be voltage drops.
3.1.14
grid
grid short-circuit impedance value of the main point (MP) 1 (see Figure 1)
3.1.15
impedance value between the fault point and PCC
3.1.16
impedance value between the fault point and EUT
3.2 Abbreviated terms
AC alternating current
A/D analog to digital
DC direct current
EUT equipment under test
HV high voltage
LV low voltage
MV middle voltage
PV photovoltaic
RMS root mean square
UVRT under voltage ride through
---------------------- Page: 11 ----------------------
– 10 – IEC TS 62910:2020 © IEC 2020
4 Test circuit and equipment
4.1 General

The circuits and equipment described in this clause are developed to allow tests that simulate

the full range of anticipated grid faults, including:
• Single phase to ground fault (any phase).
• Two phase isolated fault, between any two phases.
• Two phase grounded fault, involving any two phases.
• Three phase short-circuit fault.

A full discussion of these faults and the resulting impact on voltage magnitude and phase

angles is included in Annex A.

The short circuit emulator and grid simulator described in 4.3.3 and 4.3.4 are informative

examples and are not intended to restrict design flexibility. Other designs may be used to

achieve equivalent test functionality.
4.2 Test circuit

The UVRT test circuit includes a DC source, the EUT, a grid fault simulator and the grid. A PV

simulator (or PV array) provides input energy for the EUT. The output of the EUT is connected

to the grid via a grid fault simulator, as shown in Figure 1.

NOTE MP1 is the measurement point between the grid and the grid fault simulator; MP2 is the measurement point

at the high voltage side of the transformer; MP3 is the measurement point at the low voltage side of the

transformer.
Figure 1 – Testing circuit diagram
4.3 Test equipment
4.3.1 Measuring instruments

Waveforms shall be measured by a device with memory function, for example, a storage or

digital oscilloscope, or a high speed data acquisition device. Accuracy of the oscilloscope or

data acquisition system should be at least 0,2 % of full scale. The analogue to A/D of the

measurement device shall have at least 12 bit resolution (in order to maintain the required

measurement accuracy).

Voltage transformers and current transformers are the required sensors for measurement.

The accuracy of the transducers should be 0,5 % of full scale or better. It is necessary to

select the transducer measuring range depending on the normal value of the signal to be

measured. The selected measuring range shall not exceed 150 % of the normal value of the

measured signal. The transducer accuracy requirements are shown in Table 1.
---------------------- Page: 12 ----------------------
IEC TS 62910:2020 © IEC 2020 – 11 –
Table 1 – Accuracy of measurements
Measurement device Accuracy
Data acquisition device 0,2 % full scale
Voltage transformer 0,5 % full scale
Current transformer 0,5 % full scale
4.3.2 DC source

A PV array, PV array simulator or controlled DC source with PV characteristics may be used

as the DC power source to supply input energy for the UVRT test. As the EUT input source,

the DC power source shall be capable of supplying the EUT maximum input power and other

power levels during the test, at minimum and maximum input operating voltages of the EUT.

The PV simulator should emulate the current/voltage characteristic of the PV module or PV

array for which the EUT is designed. The response time of a PV simulator should not be

longer than the MPP tracking response time of EUT.

For a EUT under test without galvanic isolation between the DC side and AC side, the output

of the PV simulator shall not be earthed.

The equivalent capacitance between the output of the PV simulator and earth should be as

low as possible in order to minimize the impact on the EUT.

A PV array used as the EUT input source shall be capable of matching the EUT input power

levels specified by the test conditions. It is necessary to select a period of time in which the

solar irradiance is stable and does not vary more than 5 % during the test.
4.3.3 Short-circuit emulator

As part of the grid simulator device, the short-circuit emulator is used to create the voltage

drops due to short-circuits between the two or three phases, or between one or two phases to

ground, via the impedance network Z and Z as shown in the test device layout in Figure 2.

1 2
---------------------- Page: 13 ----------------------
– 12 – IEC TS 62910:2020 © IEC 2020
Figure 2 – Short-circuit emulator

The impedance Z is used to limit the effect of the short circuit on the utility service that

powers the test circuit. The sizing of Z shall therefore account for all test sequences to be

performed and limit the short-circuit current taken from the grid to values that do not cause an

excessive reduction of the grid voltage. Considering an acceptable voltage reduction of at

most 5 % when performing the test, the minimum value of Z shall be at least 20 × Z ,

1 Grid

where Z is the grid short-circuit impedance measured at the test circuit connection point.

Grid

To ensure that the test is realistic, however, the apparent short-circuit power (S ) available

EUT

at the EUT connection node N should be at least equal to 3×Pn, where Pn is the rated

EUT

power of the EUT (minimum value S > 3 × Pn, recommended 5 × Pn < S < 6 × Pn). This

EUT EUT
means during the shor
...

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