IEC TS 62933-2-2:2022

Electrical energy storage (EES) systems - Part 2-2: Unit parameters and testing methods - Application and performance testing

IEC TS 62933-2-2:2022(E) defines testing methods and duty cycles to validate the EES system’s technical specification for the manufacturers, designers, operators, utilities and owners of the EES systems which evaluate the performance of the EES systems for various applications. The following items are covered in this document. The energy storage devices and technologies are outside the scope of this document:
application;
performance testing methods;
duty cycles for specific application.

General Information

• Status: Published
• Publication Date: 25-Apr-2022
• ICS: 13.020.30 - Environmental impact assessment
• Technical Committee: TC 120 - Electrical Energy Storage (EES) systems
• Drafting Committee: WG 2 - TC 120/WG 2
• Current Stage: PPUB - Publication issued
• Start Date: 26-Apr-2022
• Completion Date: 31-May-2022

Overview

IEC TS 62933-2-2:2022 is a Technical Specification from IEC TC 120 that defines unit parameters, testing methods, duty cycles and application performance tests for electrical energy storage (EES) systems. Edition 1.0 (2022‑04) provides standardized procedures to validate an EES system’s technical specifications and operational performance across a range of grid and power‑management applications. Note: specific energy storage devices and technologies (cell/chemistry details) are explicitly outside the scope.

Key Topics

• Application classification and duty cycles: Defined duty cycles for Class A/B/C applications, including frequency control, PV/wind fluctuation reduction, reactive‑power/voltage control, voltage sag mitigation, peak shaving, renewable firming, islanded grid operation and back‑up power tests.
• Parameter testing methods: Procedures to measure:
  • Actual energy capacity
  • Roundtrip efficiency (including duty‑cycle roundtrip efficiency)
  • Step response time and ramp rate
  • Auxiliary power consumption
  • Self‑discharge
  • State of charge (SOC) determination
  • Reference signal tracking
• Duty‑cycle performance tests: Standardized profiles and numerical data (normative Annex A) for representative 24‑hour and other test durations to assess application‑level behavior.
• Test planning and items: Tabled lists of required test items per application to help manufacturers and testers prepare consistent validation procedures.

Applications and Practical Value

Who uses this standard:

• Manufacturers - validate product claims (capacity, efficiency, response) against recognized duty cycles.
• System designers and integrators - size and select EES systems for specified grid services.
• Utilities and grid operators - evaluate performance for frequency control, renewable firming and grid support services.
• Project owners/operators - verify contractual performance, optimize operation strategies and inform lifecycle forecasting.

Practical uses:

• Consistent lab and field test methodologies for procurement and acceptance testing.
• Comparative benchmarking across EES products and suppliers.
• Informing control strategy design (SOC windows, ramp limits, response times) for targeted applications such as frequency response, peak shaving and PV/wind smoothing.
• Supporting performance guarantees, warranty claims and regulatory compliance checks.

Related standards

• Other parts of the IEC 62933 series on Electrical Energy Storage (EES) systems (see IEC catalogue for the complete list).
• General IEC publications and normative references cited within IEC TS 62933‑2‑2 for test instrumentation and measurement best practices.

Keywords: IEC TS 62933-2-2, electrical energy storage, EES systems, duty cycles, performance testing, roundtrip efficiency, frequency control, peak shaving, renewable firming, SOC, IEC.

Standards Content (Sample)

IEC TS 62933-2-2 ®
Edition 1.0 2022-04
TECHNICAL
SPECIFICATION
colour
inside
Electrical energy storage (EES) systems –
Part 2-2: Unit parameters and testing methods – Application and performance
testing
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IEC TS 62933-2-2 ®
Edition 1.0 2022-04
TECHNICAL
SPECIFICATION
colour
inside
Electrical energy storage (EES) systems –

Part 2-2: Unit parameters and testing methods – Application and performance

testing
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 13.020.30 ISBN 978-2-8322-1104-1

– 2 – IEC TS 62933-2-2:2022 © IEC 2022
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms, definitions and abbreviated terms . 8
3.1 Terms and definitions . 8
3.2 Abbreviated terms . 9
4 Application of EES system . 9
4.1 General . 9
4.2 Class A applications . 9
4.2.1 Frequency control . 9
4.2.2 Primary/secondary/tertiary frequency control . 9
4.2.3 Fluctuation reduction of PV and wind farms . 10
4.2.4 Reactive-power voltage control . 10
4.2.5 Voltage sag mitigation . 10
4.3 Class B applications . 10
4.3.1 Peak shaving . 10
4.3.2 Renewable firming . 10
4.3.3 Islanded grid . 11
4.4 Class C applications . 11
5 Parameter testing methods for application . 11
5.1 Parameter tests . 11
5.1.1 General . 11
5.1.2 Actual energy capacity . 11
5.1.3 Roundtrip efficiency . 11
5.1.4 Step response time and ramp rate . 12
5.1.5 Auxiliary power consumption . 12
5.1.6 Self-discharge . 12
5.1.7 SOC . 12
5.2 Duty cycle performance tests . 12
5.2.1 General . 12
5.2.2 Duty cycle roundtrip efficiency . 12
5.2.3 Reference signal tracking . 12
5.3 Test items for each application . 14
6 Duty cycle for specific applications . 15
6.1 General . 15
6.2 Frequency control . 15
6.2.1 Frequency control duty cycle . 15
6.2.2 Primary/secondary/tertiary frequency control duty cycle . 16
6.2.3 Deviation control of frequency . 18
6.3 Fluctuation reduction of PV and wind farm . 20
6.4 Reactive-power voltage control . 22
6.5 Voltage sag mitigation . 23
6.6 Peak shaving . 26
6.6.1 “One charge-one discharge” mode . 26
6.6.2 “Two charges-two discharges” mode . 28

6.7 Renewable firming . 29
6.8 Islanded grid . 30
6.9 Back-up power . 32
6.9.1 General . 32
6.9.2 Grid outage test . 32
6.9.3 Step load test . 32
6.9.4 Unbalanced load test . 33
6.9.5 Function test . 33
6.9.6 Grid recovery test . 33
Annex A (normative)  Numerical data for duty cycle . 34
Bibliography . 66

Figure 1 – Frequency control duty cycle . 16
Figure 2 – Primary frequency control signal – 24 h duty cycle with 30 s discharge
every half hour shown over a) 24 h and b) 2 h . 17
Figure 3 – Secondary frequency control signal – 24 h duty cycle with 20 min discharge
every hour shown over a) 24 h and b) 3 h . 18
Figure 4 – Example of droop active power frequency control with a dead band . 19
Figure 5 – Duty cycle of fluctuation reduction of PV (photovoltaic energy systems) . 20
Figure 6 – Duty cycle of fluctuation reduction of wind farm . 21
Figure 7 – Duty cycle of fluctuation reduction of wind farm (low standard deviation) . 21
Figure 8 – Duty cycle of fluctuation reduction of wind farm (average standard
deviation) . 22
Figure 9 – Duty cycle of fluctuation reduction of wind farm (high standard deviation) . 22
Figure 10 – Reactive-power voltage control test profile . 23
Figure 11 – Voltage sag mitigation test profile (test level: 80 %) . 24
Figure 12 – Voltage sag mitigation test profile (test level: 70 %) . 25
Figure 13 – Voltage sag mitigation test profile (test level: 40 %) . 25
Figure 14 – Voltage sag mitigation test profile (test level: 0 %) . 26
Figure 15 – Duty cycle for peak shaving application of “one charge-one discharge”
mode . 28
Figure 16 – Duty cycle for peak shaving of “two charges-two discharges” mode . 29
Figure 17 – Duty cycle for renewable firming mode . 30
Figure 18 – Duty cycle for fluctuation reduction of renewable energy sources (power)
and frequency control . 31
Figure 19 – Duty cycle for fluctuation reduction of renewable energy sources (power)
without frequency control . 31
Figure 20 – Duty cycle without fluctuation reduction of renewable energy sources
(power) or frequency control . 32

Table 1 – Test items for each application . 15
Table 2 – Reactive-power voltage control test profile . 23
Table A.1 – Numerical data of Figure 1 (duty cycle of frequency control ) . 35
Table A.2 – Numerical data of Figure 5 (duty cycle of fluctuation reduction of PV
(photovoltaic energy systems) ) . 40
Table A.3 – Numerical data of Figure 7 (duty cycle of fluctuation reduction of wind
farm (low standard deviation)) . 44

– 4 – IEC TS 62933-2-2:2022 © IEC 2022
Table A.4 – Numerical data of Figure 8 (duty cycle of fluctuation reduction of wind
farm (average standard deviation)) . 45
Table A.5 – Numerical data of Figure 9 (duty cycle of fluctuation reduction of wind

farm (high standard deviation)) . 46
Table A.6 – Numerical data of Figure 17 (duty cycle for renewable firming mode) . 47
Table A.7 – Numerical data of Figure 18 (duty cycle for fluctuation reduction of
renewable energy sources (power) and frequency control) . 51
Table A.8 – Numerical data of Figure 19 (duty cycle for fluctuation reduction of
renewable energy sources (power) without frequency control) . 56
Table A.9 – Numerical data of Figure 20 (duty cycle without fluctuation reduction of
renewable energy sources (power) or frequency control) . 61

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL ENERGY STORAGE (EES) SYSTEMS –

Part 2-2: Unit parameters and testing methods –
Application and performance testing

FOREWORD
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rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 62933-2-2 has been prepared by IEC technical committee TC 120: Electrical Energy
Storage (EES) Systems. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
120/249/DTS 120/264A/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.

– 6 – IEC TS 62933-2-2:2022 © IEC 2022
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 62933 series, published under the general title Electrical energy
storage (EES) systems, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under 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.
•
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•
INTRODUCTION
Considering the wide variety of applications of EES systems, it is becoming important to define
the typical application of each EES system depending on its purpose and control types, and
also important to define the corresponding performance testing methods and procedures of the
EES system.
IEC 62933-2-1 describes the general specification of unit parameters and testing methods for
EES systems, in which details of duty cycles for typical grid applications and the associated
performance metrics and testing methods are not covered.
This part of IEC 62933 focuses on developing generic duty cycles for applications, identifying
relevant performance metrics and developing performance testing methods and procedures for
EES systems.
– 8 – IEC TS 62933-2-2:2022 © IEC 2022
ELECTRICAL ENERGY STORAGE (EES) SYSTEMS –

Part 2-2: Unit parameters and testing methods –
Application and performance testing

1 Scope
This part of IEC 62933 defines testing methods and duty cycles to validate the EES system’s
technical specification for the manufacturers, designers, operators, utilities and owners of the
EES systems which evaluate the performance of the EES systems for various applications. The
following items are covered in this document. The energy storage devices and technologies are
outside the scope of this document:
– application;
– performance testing methods;
– duty cycles for specific application.
This document will be used as a reference when selecting testing items and their corresponding
evaluation methods.
This document considers applications such as:
• frequency control;
• primary/secondary/tertiary frequency control;
• fluctuation reduction of PV and wind farm;
• reactive-power voltage control;
• power quality events mitigation;
• peak shaving;
• renewable firming;
• back-up power;
• islanded grid.
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 62933-1, Electrical energy storage (EES) systems – Part 1: Vocabulary
IEC 62933-2-1, Electrical energy storage (EES) systems – Part 2: Unit parameters and testing
methods – General specification
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 62933-1 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
3.2 Abbreviated terms
EES: Electrical energy storage
EESS SOC: State of charge of EES system
POC: Point of connection
UPS: Uninterruptable power systems
4 Application of EES system
4.1 General
The applications of EES systems differ according to their purposes. The applications of EES
systems are classified into three classes:
a) class A applications: short duration/power intensive applications (with a duty cycle of less
than 1 h);
b) class B applications: long duration/energy intensive applications (with a duty cycle of more
than 1 h), and
c) class C applications: back-up applications.
IEC 62933-2-1 provides classification details. The typical application of each class will be
described hereinafter.
4.2 Class A applications
4.2.1 Frequency control
EES systems provide a grid frequency control function to increase the frequency by discharging
and to reduce the frequency by charging. The system frequency will be controlled within a
predetermined bandwidth. The control subsystem in the EES system continuously measures
the frequency and then sends a control signal to the power conversion subsystem to increase
or decrease the amount of active power injected into the grid or the amount of load on the grid.
4.2.2 Primary/secondary/tertiary frequency control
In this application, there is a sudden loss of generation which leads to be made up through a
discharge from the EES system. In the case of a sudden loss of load in the grid, energy is
charged into the EES.
Generally, the definition of each control is based on the control order and control time period.
The following are example cases for reference.
Primary frequency control comes first and usually it is automatically initiated. It is activated
within a few seconds and lasts up to a few minutes.
Primary frequency control is followed by secondary frequency control if necessary and is
initiated automatically or manually. It should have an activation time typically between 30 s and
up to15 min.
Tertiary frequency control is used to resolve any additional imbalance that exists after the
primary and secondary frequency control has been carried out. It should have an activation time
typically between 15 min and several hours.

– 10 – IEC TS 62933-2-2:2022 © IEC 2022
The activation time period of these controls is usually set in the grid code of each country or
region.
4.2.3 Fluctuation reduction of PV and wind farms
An EES system is used to reduce the rapid fluctuations of the power output from PV and wind
farms. The purpose of fluctuation reduction of the power output from PV and wind farms is to
help to meet the ramp rate requirements. This action will mitigate frequency variation and
stability issues at both feeder and transmission levels particularly with high penetration PV and
wind farm scenarios.
At the feeder level, fluctuation reduction of PV and wind farm is implemented to mitigate voltage
flicker and voltage deviations from desired bands. At the transmission level, PV and wind farm
variability can require an additional operating reserve to be set aside. This can cause traditional
power generation facilities to be cycled on/off more often than desirable.
The method by which the EES system can provide reduction of PV and wind farm output power
power at appropriate times as determined by
fluctuation is to absorb or supply active/reactive
a control system resulting in a less variable composite power signal at the feeder and/or
transmission level.
4.2.4 Reactive-power voltage control
The reactive-power voltage control application addresses the fluctuations in the grid voltage by
providing reactive power support. EES systems inject reactive power as the grid voltage dips
and absorb reactive power as the grid voltage increases.
4.2.5 Voltage sag mitigation
The sag or interruption in voltage potentially causes power disturbances that negatively impact
power quality. EES systems mitigate voltage sags by discharging real power for up to a few
tens of seconds. The application of an EES system to improve power quality does not require
the EES system to provide enough energy for customers to ride through sag or interruption.
NOTE An event duration of more than 1 min is considered as outage mitigation.
4.3 Class B applications
4.3.1 Peak shaving
The EES system discharges stored energy into the grid upon an excess or peak of demand or
absorbs excess energy, available in the grid, for storage. With this balancing a time shift
between power generation and electricity usage is achieved.
Examples of this application include energy time shift of conventional/wind/solar/base load-
generation, and include transmission/distribution grid congestion relief.
4.3.2 Renewable firming
Renewable firming is the use of an EES system to provide energy to supplement renewable
power generation such that their combination produces steady power output over a desired time
window. More precisely, the purpose of renewable firming is to provide energy (or conversely,
to absorb energy) when renewable generation falls below some threshold (or conversely,
exceeds this threshold).
This service is performed to provide steady power output over a desired time window, usually
a period of multiple hours. Typically, the threshold is based upon the forecasted nominal
renewable power generation over the desired time window. Thus, the EES system is
compensating for the forecast uncertainty in actual renewable generation during that time
window.
The method by which the EES system performs this service is described as follows. The EES
system discharges power during periods for which renewable generation falls short of the
threshold and absorbs power when renewable generation exceeds this threshold.
4.3.3 Islanded grid
The EES supports in islanded grids their multiple loads, distributed energy generation and
storage resources. In such a service the EES system provides energy to the load of the islanded
grid. The EES system converter typically operates in the voltage/frequency mode to control the
islanded grid.
The EES systems supply the islanded grid for a limited time when the power supply from the
other grid is interrupted for some reason.
4.4 Class C applications
EES systems used as back-up power are independent sources of electrical power that support
critical loads on loss of normal power supply. Back-up power systems are, for example, installed
to protect life and property from the consequences of loss of primary electric power supply.
Uninterruptable power systems (UPS) are out of the scope in this application.
5 Parameter testing methods for application
5.1 Parameter tests
5.1.1 General
Parameter tests shall be conducted for all EES systems regardless of intended application(s)
in accordance with Clause 5, and the results shall be used to determine EES system
performance that can be subsequently used as a baseline to assess any changes in the
condition of the EES system and performance over time and use. Parameter tests shall be
conducted to determine baseline performance of the EES system prior to duty cycle testing.
5.1.2 Actual energy capacity
The actual energy capacity of the EES system shall be tested at rated power, and at short
duration input power or at additional power values different from rated power if such parameters
are required.
The energy capacity shall be evaluated as the product of the rated output power and the output
duration time. The values of the output power from the EES system shall be obtained at the
point of connection (POC) by placing calibrated power meters at the POC and auxiliary feed
points (in case of auxiliaries fed from a substation).
The actual energy capacity is defined in IEC 62933-1. Also, the actual energy capacity test shall
be performed in accordance with the test methods defined in IEC 62933-2-1.
5.1.3 Roundtrip efficiency
The roundtrip efficiency test shall be conducted to determine the amount of energy output that
the EES system can deliver, relative to the amount of energy input into the EES system during
the preceding charge and discharge.
The roundtrip efficiency test shall be performed in accordance with the test methods defined in
IEC 62933-2-1.
– 12 – IEC TS 62933-2-2:2022 © IEC 2022
5.1.4 Step response time and ramp rate
The step response time of the EES system is the duration of the time interval between the
instant when the set point value is received at the EES system and the instant when the active
power at the POC starts to stay within ±2 % of deviation from the set point. The ramp rate of
the EES system is the average rate of active power variation per unit time.
The response time and ramp rate of the EES system shall be performed in accordance with the
test methods defined in IEC 62933-2-1.
5.1.5 Auxiliary power consumption
The auxiliary power consumption shall be measured with the ESS system connected to the POC.
The auxiliary power consumption of the EES system shall be tested in accordance with the test
methods defined in IEC 62933-2-1.
5.1.6 Self-discharge
The self-discharge of the EES system is the energy loss of the EES system in the stopped state
during the standard measurement time. The self-discharge of the EES system shall be tested
in accordance with the test methods defined in IEC 62933-2-1.
5.1.7 SOC
The state of charge (SOC) of the EES system (EESS SOC) is the ratio between the available
energy from the EES system and the actual energy capacity, expressed as a percentage. The
available energy is defined in IEC 62933-1.
The testing methods of available energy are defined in IEC 62933-2-1.
5.2 Duty cycle performance tests
5.2.1 General
Duty cycle performance tests shall be conducted for each intended application of an EES
system using the duty cycles as defined in Clause 6.
5.2.2 Duty cycle roundtrip efficiency
The duty cycle roundtrip efficiency is used in the determination of the performance of the EES
system for each application duty cycles defined in Clause 6.
The duty cycle roundtrip efficiency of the EES system shall be tested in accordance with the
test methods defined in IEC 62933-2-1.
5.2.3 Reference signal tracking
The ability of the EES system to respond to a signal for the duration of the duty cycle for each
intended application of the EES system reflects the ability of the EES system to track the signal.
The tests of the ability should be conducted by Formula (1) to Formula (4) below separately for
each intended application of the EES system while applying the duty cycle relevant to each
intended application of the EES system. The procedures of the tests are as follows.
The ability should be defined and determined by the manufacturer of the EES system in
accordance with the provisions of Clause 6. The signal should be changed in accordance with
the duty cycle(s) for each intended application of the EES system.

The manufacturer of the EES system should also determine and report separately the total
percentage tracking and the times when the EES system stops tracking and restarts tracking
as an indication of whether the EES system is capable of tracking high peaks and/or high energy
half-cycles.
The manufacturer should also determine whether the EES system can go through the required
duration of the duty cycle without reaching the lower or upper EESS SOC limits. This should be
performed during the application of the relevant duty cycle as described in Clause 6, and any
time during that period when the EES system indicates an ability or inability to follow the signal
should be reported.
An inability for the power signal to follow the signal shall be considered a situation where the
EES system cannot deliver or absorb the required signal power during the duration when the
signal is to be changed.
For the energy signal, an inability to follow the signal shall be considered a situation where the
EES system cannot deliver or absorb the required energy signal during the duration when the
energy signal remains positive or negative, respectively. Simulations of the signal can be
applied for the testing.
NOTE There are some cases where the inability of the EES system to follow the signal is not caused by the EES
system performance itself but by the external conditions such as energy capacity specified under some restrictions
or changing of the SOC limits set-points by the external control system.
The ability of the EES system to respond to a signal should be measured during the duty cycle
roundtrip efficiency test. The residual sum of squares or the sum of the square of errors between
the power signal (P ) and the power delivered or absorbed by the EES system (P ) should
signal eess
be calculated in accordance with Formula (1) and used to estimate the inability of the EES
system to track the signal.
PP-
∑( )
signal eess
(1)
APT =
N
where
APT is the ability of the power signal tracking,
P is the power signal,
signal
P is the EES system power (watts), and
eess
N is the number of data during one duty cycle.
The measurements should be taken at every point in time that the EES system receives a
change in the power signal. The sum of the absolute magnitudes of the difference between the
power signal and EES system power should be calculated in accordance with Formula (2).
PP-
∑ signal eess
(2)
APTA =
N
where
APTA is the ability of power signal tracking in absolute.
The sum of the absolute magnitudes of the difference between the signal energy and EES
system energy should be calculated in accordance with Formula (3) and reported by the
manufacturer of the EES system to account for the inability of the EES system to follow the
signal due to the EES system reaching the EESS SOC limits provided in the manufacturer’s
specifications and operating instructions.

– 14 – IEC TS 62933-2-2:2022 © IEC 2022
E - E
∑ signal eess
(3)
AETA =
N
where
AETA is the ability of energy signal tracking in absolute,
is the signal energy for a half-cycle, with the half-cycle being the signal of the same sign
E
signal
(positive or negative),
E is the energy supplied to or absorbed by the EES system for each half-cycle, and
eess
N is the number of data during one duty cycle.
The total time when the EES system cannot follow the power signal and the percentage tracked
where (P – P ) / P is less than 0,02 should be determined in accordance with
signal eess signal
Formula (4). However, the value of 0,02 should be determined by negotiation with the user of
the EES system.
When | P – P ) / P | is less than a certain value, the EES system should be
signal eess signal
considered to track the signal. The percentage of time the signal is tracked during the duration
of the duty cycle for the application(s) of the EES system should be determined in accordance
with Formula (4)
time signal is tracked (h)
PST = × 100
(4)
duration of the duty cycle (h)
where
PST is the percentage of signal tracking.
5.3 Test items for each application
The parameter test and duty cycle performance test items that are required for each application
are shown in Table 1. If the EES system has implemented the functionality of multiple
applications, all the tests corresponding to each application shall be performed.

Table 1 – Test items for each application
Test items Frequency Primary/ Fluctuation Reactive- Power Peak Renewable Islanded
control secondary/ reduction power quality shaving s firming grid
tertiary of PV and voltage events
frequency wind farm control mitigation
control
Actual
energy √ √ √ √ √ √ √ √
capacity
Roundtrip
√ √ √ √ √ √ √ √
efficiency
Step
response
√ √ √ √ √ √ √ √
time and
ramp rate
Auxiliary
power √ √ √ √ √ √ √ √
consumption
Self-
√ √ √ √ √ √ √ √
discharge
SOC √ √ √ √ √ √ √ √
Duty cycle
roundtrip √ √ √ √ √ √ √
efficiency
Reference
signal √ √ √ √ √ √ √
tracking
6 Duty cycle for specific applications
6.1 General
The duty cycle patterns described in Clause 6 should be considered to apply for specific
applications. Otherwise the duty cycle pattern shall be specified the by the user and system
supplier. In either case, it shall be agreed between user and system supplier.
6.2 Frequency control
6.2.1 Frequency control duty cycle
The duty cycle presented in Figure 1 should be applied in determining the performance of an
EES system for a frequency control application.
The duty cycle in Figure 1 is shown as power normalized with respect to the rated power of the
EES system over a 24 h time period, where positive represents a discharge from the EES
system and negative represents a charge into the EES system as a function of time in hours.
The initial EESS SOC should be set according to the manufacturer’s specifications and
operating instructions. At the end of the application of the duty cycle in conducting the testing
under 5.2, the EES system should be brought back to its initial EESS SOC.

– 16 – IEC TS 62933-2-2:2022 © IEC 2022

Figure 1 – Frequency control duty cycle
Peak power (1,0 p.u.) should be determined and applied for Figure 1 testing considering the
intended control value for ΔF under the concept of Figure 4.
The test pattern is based on actual field conditions in North American power grids and can be
adapted to local operating conditions as needed.
The test evaluation is for one duty cycle. It does not mean to ensure the operation for multiple
duty cycles. If the number or pattern of charging processes affects battery performance in a
long period of time, the number should be subject to the manufacturer's individual specification
or the pattern should be agreed between the user and manufacturer for the EES system to
perform with the expected performance throughout the life of the battery.
Test conditions such as use of constant-current/constant-voltage supply, maximum
current/voltage, or temperature range should be specified prior to testing based on the battery
technology and the manufacturer's individual specification.
6.2.2 Primary/secondary/tertiary frequency control duty cycle
The duty cycles in Figure 2a) and b) should be applied in determining the performance of an
EES system in a frequency control application. The duty cycles shown in Figure 2a) and b)
cover a primary frequency control situation during a sudden loss of generation.
This duty cycle corresponds to an EES system discharge for 30 s at 1 min peak power rating,
a rest for 29 min, and then repeats this same pattern of use over a period of 24 h or to a point
in time when when the EESS SOC reaches to the lowest limit. Figure 2a) shows the entire duty
cycle over 24 h, while Figure 2b) shows the magnified portion of the duty cycle in order to
provide detail on the discharge characteristics.
The duty cycles in Figure 3a) and b) cover a secondary frequency control situation where the
duty cycle duration is such that energy is withdrawn or absorbed under the appropriate peak
power of the EES system rating.
This duty cycle corresponds to a continuous 20 min EES system discharge, a rest for 40 min,
and then repeats this same pattern of use over a period of 24 h or to a point in time when the
EESS SOC reaches the lowest limit.

While the captions to Figure 2 and Figure 3 only mention discharge, the duty cycles represented
in these figures apply to both discharge (sudden loss of generation) and charge (sudden loss
of load). The initial EESS SOC should be set at maximum EESS SOC for sudden loss of
generation and at minimum EESS SOC for sudden loss of load.
At the end of the application of each duty cycle, the EES system should be brought back to its
initial EESS SOC by charging (for a sudden loss of generation) or discharging (for a sudden
loss of load) at rated power before the application of another duty cycle.
When necessary, tertiary frequency control should be applied with an activation period from
15 min to hours over a period of 24 h, or to a point in time when the EESS SOC reaches the
lowest limit.
Peak power (1,0 p.u.) should be determined and applied to Figure 2 and Figure 3 testing
considering the intended control value for Δf under the concept of Figure 4.
The test conditions such as the use of constant-current/constant-voltage supply, maximum
current/voltage, or temperature range should be specified prior to testing based on the battery
technology and the manufacturer's individual specification.

a)
b)
Figure 2 – Primary frequency control signal – 24 h duty cycle with 30 s
discharge every half hour shown over a) 24 h and b) 2 h
...