IEC 62891:2020

Maximum power point tracking efficiency of grid connected photovoltaic inverters

IEC 62891:2020 provides a procedure for the measurement of the efficiency of the maximum power point tracking (MPPT) of inverters used in grid-connected photovoltaic (PV) systems. Both the static and dynamic MPPT efficiency are considered. Based on the static MPPT efficiency calculated in this document and steady state conversion efficiency determined in IEC 61683 the overall efficiency can be calculated. The dynamic MPPT efficiency is indicated separately.

General Information

• Status: Published
• Publication Date: 14-Jul-2020
• ICS: 27.160 - Solar energy engineering
• Technical Committee: TC 82 - Solar photovoltaic energy systems
• Drafting Committee: WG 6 - TC 82/WG 6
• Current Stage: PPUB - Publication issued
• Start Date: 15-Jul-2020
• Completion Date: 03-Jul-2020

Overview

IEC 62891:2020 specifies a standardized procedure for measuring the maximum power point tracking (MPPT) efficiency of inverters used in grid‑connected photovoltaic (PV) systems. The standard covers both static MPPT efficiency (steady-state ability to find the MPP) and dynamic MPPT efficiency (response to irradiance fluctuations). Based on the static MPPT efficiency calculated per IEC 62891 and the steady‑state conversion efficiency measured according to IEC 61683, an overall inverter efficiency can be derived. Dynamic MPPT performance is reported separately.

Keywords: IEC 62891, MPPT efficiency, grid‑connected photovoltaic inverters, static MPPT efficiency, dynamic MPPT efficiency, PV inverter testing.

Key topics and technical requirements

• Scope and applicability
  • Procedure applies to grid‑connected PV inverters and may also be used for devices with MPPT (e.g., charge controllers, optimizers).
• Measurement methodology
  • Defines test set‑up, measured and calculated quantities, and clear procedures for static and dynamic MPPT tests.
  • Static MPPT tests assess accuracy across representative operating points; dynamic tests use defined irradiance/voltage/time profiles to evaluate tracking under transient conditions.
• Test apparatus requirements (Annex A)
  • Requirements for PV generator simulators, AC supplies, transient stability, dynamic characteristics and calibration/uncertainty are specified.
• Dynamic test profiles (Annex B)
  • Standardized test sequences and ramp profiles for realistic irradiance fluctuations and start/stop behavior.
• PV generator models (Annex C)
  • Reference current–voltage (I/V) and power characteristics for different PV technologies to ensure repeatable tests.
• Efficiency weighting and normalization (Annexes D & E)
  • Weighting factors for regional efficiency metrics (e.g., European, CEC) and procedures to express efficiencies normalized to rated AC power.
• Reporting
  • Static MPPT efficiency is combined with IEC 61683 conversion efficiency for an overall figure; dynamic MPPT efficiency is reported separately.

Practical applications and users

• Manufacturers - optimize MPPT algorithms, validate product performance and support datasheet claims.
• Test laboratories & certification bodies - perform repeatable MPPT efficiency measurements for conformity, performance labeling and certification.
• System designers & integrators - estimate real energy yield, inform inverter selection for sites with variable irradiance.
• Researchers & consultants - compare MPPT strategies and quantify transient tracking losses for modelling and optimisation.
• Regulators & procurement - set test-based performance requirements for incentive programs or procurement specifications.

Practical benefits include consistent, repeatable measurements for product comparison, improved accuracy in energy-yield estimation, and better understanding of transient losses due to MPPT behavior.

Related standards

• IEC 61683 - Procedure for measuring steady‑state conversion efficiency of power conditioners (used together to compute overall efficiency).
• IEC TS 61836 - PV terms and definitions.
• EN 50160 - Voltage characteristics of electricity supplied by public distribution networks.

Keywords (SEO): PV inverter testing, MPPT performance testing, photovoltaic standards, IEC 62891:2020, inverter efficiency measurement.

Standards Content (Sample)

IEC 62891 ®
Edition 1.0 2020-07
INTERNATIONAL
STANDARD
colour
inside
Maximum power point tracking efficiency of grid connected photovoltaic
inverters
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IEC 62891 ®
Edition 1.0 2020-07
INTERNATIONAL
STANDARD
colour
inside
Maximum power point tracking efficiency of grid connected photovoltaic

inverters
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-8470-4

– 2 – IEC 62891:2020 © IEC 2020
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
3.1 Inverter input (PV generator) . 6
3.2 Inverter output (grid) . 7
3.3 Measured quantities . 7
3.4 Calculated quantities . 8
4 MPPT efficiencies . 9
4.1 General description . 9
4.2 Test set-up . 10
4.3 Static MPPT efficiency . 11
4.3.1 Test conditions . 11
4.3.2 Measurement procedure . 12
4.3.3 Evaluation – Calculation of static MPPT efficiency . 13
4.4 Test conditions for dynamic MPPT efficiency . 13
4.4.1 Dynamic MPPT efficiency . 13
4.4.2 Measurement procedure . 14
4.4.3 Evaluation – Calculation of the dynamic MPPT efficiency . 14
5 Calculation of the overall efficiency . 15
Annex A (normative) Requirements on the measuring apparatus . 16
A.1 PV generator simulator . 16
A.1.1 General . 16
A.1.2 Requirements on the static characteristic . 16
A.1.3 Requirement on the transient stability . 17
A.1.4 Requirements on the dynamic characteristic . 17
A.1.5 Requirements on electrical characteristic . 17
A.1.6 Calibration – Uncertainty . 17
A.2 AC power supply . 17
Annex B (normative) Test conditions for dynamic MPPT efficiency . 18
B.1 Test profiles . 18
B.2 Test sequence with ramps 10 % – 50 % G (See Table B.1) . 20
STC
B.3 Test sequence with ramps 30 % – 100 % G (See Table B.2) . 21
STC
B.4 Start-up and shut-down test with slow ramps (See Table B.3 and Figure B.3) . 21
B.5 Total test duration . 22
Annex C (normative) Models of current/voltage characteristic of PV generator . 23
C.1 PV generator model for MPPT performance tests . 23
C.2 Alternative PV generator model for MPPT performance tests . 27
Annex D (normative) Efficiency weighting factors . 29
D.1 European efficiency . 29
D.2 CEC efficiency . 29
Annex E (normative) Specification of the static MPPT and conversion efficiency in
terms of normalised rated AC power . 30
E.1 General . 30
E.2 Re-normalisation of output power P to the rated output power P . 30
AC AC,r
E.3 Representation of the conversion efficiency in terms of normalised rated
output power . 30
E.4 Interpolation on normative nodes . 31
E.5 Result . 33
Bibliography . 34

Figure 1 – Example test set-up for MPPT efficiency measurements . 11
Figure B.1 – Test sequence for fluctuations between small and medium irradiation
intensities . 18
Figure B.2 – Test sequence for fluctuations between medium and high irradiation
intensities . 19
Figure B.3 – Test sequence for the start-up and shut-down test of grid connected
inverters . 22
Figure C.1 – Irradiation-dependent V-I- and V-P characteristic of a c-Si PV generator . 25
Figure C.2 – Irradiation-dependent V-I- and V-P characteristic of a thin-film PV
generator . 26

Table 1 – Test specifications for static MPPT efficiency . 12
Table A.1 – General requirements on the simulated I/V characteristic of the PV
generator . 16
Table B.1 – Dynamic MPPT-Test 10 %  50 % G (valid for the evaluation of
STC
η ) . 20
MPPTdyn
Table B.2 – Dynamic MPPT-Test 30 %  100 % G (valid for the evaluation of
STC
) . 21
η
MPPTdyn
Table B.3 – Dynamic MPPT- Slow Ramp 1 %  10 % G (valid for the evaluation of
STC
η ) . 21
MPPTdyn
Table C.1 – Technology-dependent parameters . 24
Table C.2 – MPP-values obtained with the cSi PV model . 25
Table C.3 – MPP-values obtained with the TF-PV mode . 27
Table D.1 – Weighting factors and partial MPP power levels for the calculation of the
European efficiency . 29
Table D.2 – Weighting factors and partial MPP power levels for the calculation of the
CEC efficiency (California Energy Commission) . 29
Table E.1 – Measured quantities at the conversion efficiency test . 30
Table E.2 – Conversion efficiency in term of rated AC power . 31
Table E.3 – Allowed limits for the nodes of the normalised AC power . 31
Table E.4 – Sought values by means of interpolation . 32
Table E.5 – Interpolated conversion efficiencies . 33

– 4 – IEC 62891:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MAXIMUM POWER POINT TRACKING EFFICIENCY
OF GRID CONNECTED PHOTOVOLTAIC INVERTERS

FOREWORD
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International Standard IEC 62891 has been prepared by IEC technical committee 82: Solar
photovoltaic energy systems.
The text of this standard is based on the following documents:
FDIS Report on voting
82/1723/FDIS 82/1736/RVD
Full information on the voting for the approval of this standard can be found in the report on
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– 6 – IEC 62891:2020 © IEC 2020
MAXIMUM POWER POINT TRACKING EFFICIENCY
OF GRID CONNECTED PHOTOVOLTAIC INVERTERS

1 Scope
This document provides a procedure for the measurement of the efficiency of the maximum
power point tracking (MPPT) of inverters used in grid-connected photovoltaic (PV) systems.
Both the static and dynamic MPPT efficiency are considered. Based on the static MPPT
efficiency calculated in this document and steady state conversion efficiency determined in
IEC 61683 the overall efficiency can be calculated.
The dynamic MPPT efficiency is indicated separately.
NOTE This document addresses PV inverters connected to an AC grid. However, this procedure may also be
used for other power conversion devices with MPPT functionality used in PV systems, such as charge controllers
or optimizers.
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 61683, Photovoltaic systems – Power conditioners – Procedure for measuring efficiency
IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols
EN 50160, Voltage characteristics of electricity supplied by public distribution networks
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TS 61836 apply, as
well as the following:
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
3.1 Inverter input (PV generator)
3.1.1
maximum input voltage
V
DCmax
allowed maximum voltage at the inverter input
Note 1 to entry: Exceeding of V may destroy the equipment under test.
DCmax
3.1.2
minimum input voltage
V
DCmin
minimum input voltage for the inverter to energize the utility grid, independent of mode of
operation
3.1.3
rated input voltage
V
DC,r
input voltage specified by the manufacturer, to which other data sheet information refers
3.1.4
maximum MPP voltage
V
MPPmax
maximum voltage at which the inverter can convert its rated power under MPPT conditions
3.1.5
minimum MPP voltage
V
MPPmin
minimum voltage at which the inverter can convert its rated power under MPPT conditions
Note 1 to entry: The actual minimum MPP voltage may depend on the grid voltage level.
3.1.6
rated input power
P
DC,r
rated input power of the inverter, which can be converted under continuous operating
conditions
3.1.7
maximum input current
I
DC,max
maximum input current of the inverter under continuous operating conditions
Note 1 to entry: At inverters with several independent inputs, this value may depend on the chosen input
configuration.
3.2 Inverter output (grid)
3.2.1
rated grid voltage
V
AC,r
utility grid voltage to which other data sheet information refers
3.2.2
rated power
P
AC,r
active power the inverter can deliver in continuous operation
3.3 Measured quantities
3.3.1
PV simulator MPP-Power
P
MPP, PVS
MPP power provided by the PV simulator
3.3.2
input power
P
DC
measured input power of the device under test

– 8 – IEC 62891:2020 © IEC 2020
3.3.3
PV simulator MPP voltage
V
MPP, PVS
MPP voltage provided by the PV simulator
3.3.4
input voltage
V
DC
measured input voltage of the device under test
3.3.5
PV simulator MPP current
I
MPP, PVS
MPP current provided by the PV simulator
3.3.6
input current
I
DC
measured input current of the device under test
3.3.7
output power
P
AC
measured AC output power of the device under test
3.3.8
output voltage
V
AC
measured AC voltage
3.3.9
output current
I
AC
measured AC output current of the device under test
3.4 Calculated quantities
3.4.1
MPPT efficiency, energetic
η
MPPT
ratio of the energy drawn by the device under test within a defined measuring period T to the
M
energy provided theoretically by the PV simulator at the maximum power point (MPP):
T
M
p ( t )⋅dt
DC
∫
η = (1)
MPPT
T
M
p ( t )⋅ dt
MPP
∫
where
P (t) is the instantaneous value of the power drawn by the device under test;
DC
P (t) is the instantaneous value of the MPP power provided theoretically by the PV
MPP
simulator.
3.4.2
conversion efficiency, energetic
η
conv
.ratio of the energy delivered by the device under test at the AC terminal within a defined
measuring period T to the energy accepted by the device under test at the DC terminal:
M
T
M
p ()t ⋅dt
AC
∫
η = (2)
conv
T
M
p ()t ⋅dt
DC
∫
where
P (t) is the instantaneous value of the delivered power at the AC terminal of the device
AC
under test;
P (t) is the instantaneous value of the accepted power at the DC terminal of the device
DC
under test.
3.4.3
overall efficiency, energetic
η
t
ratio of the energy delivered by the device under test at the AC terminals within a defined
measuring period T to the energy provided theoretically by the PV simulator:
M
T
M
pt()⋅dt
AC
∫
η = respectively ηη ⋅η (3)
t t conv MPPT
T
M
pt()⋅dt
MPP
∫
3.5
photovoltaic array simulator
current source emulating the static and dynamic behaviour of a PV array, in particular the
current-voltage characteristic (see IEC TS 61836).
Note 1 to entry: The requirements are outlined in Clause A.1.
4 MPPT efficiencies
4.1 General description
The MPPT efficiency describes the accuracy of an inverter to set its operating conditions to
match the maximum power point on the characteristic curve of a PV generator. The overall
MPPT efficiency is divided into static and dynamic efficiency components.
Because inverters with poor MPPT performance operate at a DC input voltage that is different
from MPP voltage, and static power conversion efficiency depends on DC input voltage, the
measurements of static MPPT efficiency and static power conversion efficiency according to
4.3 shall be performed simultaneously.
a) Static MPPT efficiency
=
– 10 – IEC 62891:2020 © IEC 2020
The static MPPT efficiency is determined by means of measurement as follows:
η VI⋅⋅ ΔT (4)
MPPTstat ∑ DC,iiDC,
PT⋅
MPP,PVS M
i
where
V is the sampled value of the inverter’s input voltage;
DC,i
I is the sampled value of the inverter’s input current;
DC,i
is the overall measuring period;
T
M
ΔT is the period between two subsequent sample values.
The static MPPT efficiency describes the accuracy of an inverter to regulate on the maximum
power point on a given static characteristic curve of a PV generator.
V and I shall be sampled at the same time.
DC,i DC,i
b) Dynamic MPPT efficiency
Variations of the irradiation intensity and the resulting transition of the inverter to the new
operation point are not considered with the static MPPT efficiency. For the evaluation of this
transient characteristic the dynamic MPPT efficiency is specified. The dynamic MPPT
efficiency is defined as:
η VI⋅⋅ ΔT (5)
MPPTdyn ∑ DC,i DC,i i
PT⋅ Δ
∑ MPP,PVS,j j
i
j
where
ΔT is the period in which the power P is provided;
j MPP,PVS,j
ΔT is the period in which the power V and I are sampled.
i DC,i DC,i
4.2 Test set-up
The generic test set-up for single phase grid connected inverters is depicted in Figure 1. The
diagram can also be considered as a single-phase representation of a test-circuit for multi
phase inverters.
=
=
Key
EUT Equipment under test (inverter);
I DC current meter;
DC
V DC voltage meter;
DC
P DC power meter;
DC
V AC voltage meter;
AC
P AC power meter.
AC
Figure 1 – Example test set-up for MPPT efficiency measurements
The DC source connected to the PV input of the inverter shall be a PV simulator in
accordance to the specifications in Clause A.1.
The AC supply of the inverter shall be in accordance to the specifications in Clause A.2.
For the conversion efficiency, the DC and AC voltages shall be measured as close as
possible to the inverter terminals. For MPPT efficiency, the DC voltage shall be measured as
close as possible to the PV simulator. For combined conversion and MPPT efficiency
measurements, two voltage measurements will be required at the output of the PVS and the
DC input of the EUT, in order to avoid measurement errors resulting from the voltage drop
between the PVS and the EUT.
4.3 Static MPPT efficiency
4.3.1 Test conditions
The measurement of the conversion and static MPPT efficiency shall be performed
simultaneously with test specifications as defined in Table 1.
For test devices with several independent MPPT input terminals, the measurements shall be
performed for all input configurations as intended by the manufacturer. Unless otherwise
provided by the manufacturer, the total power shall be split equally on the individual input
terminals.
– 12 – IEC 62891:2020 © IEC 2020
Table 1 – Test specifications for static MPPT efficiency
MPP voltage of the Simulated I/V MPP power of the simulated I/V characteristic normalised
d f
simulated I/V characteristic to rated DC power , P /P
MPP,PVS DC,r
characteristic (see Annex C)
0,05 0,10 0,20 0,25 0,30 0,50 0,75 1,00
of the PV generator
V or c-Si
MPPmax
a,c
(0,8 · V )
DCmax
e
V c-Si
DC,r
V c-Si
MPPmin
b
V or TF
MPPmax
a,c
(0,7 · V )
DCmax
b
V TF
DC,r
b
V TF
MPPmin
The MPP voltages at the different test conditions (V , V , V ) shall be kept constant during the test
MPPmax DC,r MPPmin
for each power level.
a
The lower of the two values shall be used. The specified MPP voltages ensure that the correct MPPT
operation is not affected by reaching voltage limits.
b
For devices under test that are not intended for the operation with thin-film technologies, these measuring
points can be omitted.
c
For other cell technologies the value V = n·V shall be set accordingly.
MPPmax DCmax
d
In order to specify the static MPPT efficiency in terms of normalised rated AC power, the procedure in
Annex E shall be used.
e
If this value is not specified by the manufacturer, V = (V + V )/2 shall be used.
DC,r MPPmax MPPmin
f
If this value is not specified by the manufacturer, it can be defined as P = P / η , in which η is
DC,r AC,r conv,r conv,r
the conversion efficiency at rated DC voltage. If the rated conversion efficiency is not specified, it shall be
measured.
The measurement shall be performed at nominal grid voltage V in order to avoid any
AC,r
impact of the grid voltage level on the measurement results. Deviations shall be documented
in the measurement report.
The measurement should be performed at an ambient temperature of 25 °C ± 5 °C. Other
ambient temperatures can be mutually agreed. The actual ambient temperature shall be
specified in the test report.
4.3.2 Measurement procedure
For each of the above specified test conditions a corresponding I/V characteristic has to be
defined which shall be emulated by means of the PV simulator.
NOTE The requirements on the accuracy of the defined characteristic are outlined in Annex C.
After commissioning the device under test the stabilization of the MPP tracking shall be
awaited firstly.
Given the multitude of various MPPT methods and their parameters, a specific waiting period
is not defined in this standard. The stabilization time depends on the characteristics of the
device under test and shall be set accordingly in each case. The stabilization time shall be
documented in the test report. If a stabilisation of the MPPT can’t be observed due to the
behaviour of the device under test, a latency of at least 5 min is defined.
The measuring time for each test condition as specified in Table 1 amounts to 10 min. For the
first power level of each MPP voltage setting, the stabilisation of the MPPT-tracker has to be
awaited. If a stabilisation cannot be observed a stabilisation time of at least 5 min is defined.
...