ISO 24352:2023
(Main)Technical requirements for small unmanned aircraft electric energy systems
Technical requirements for small unmanned aircraft electric energy systems
This document provides technical requirements and test methods for small unmanned aircraft electric energy systems (EESs). This document applies to the EES of small unmanned aircrafts (UAs) with the maximum take-off mass (MTOM) less than 25 kg corresponding to unmanned aircraft systems (UASs) at level I, II, III and IV as graded in ISO 21895:2020, and with secondary lithium batteries. This document can apply to new type of batteries to be used in the UA electric energy system in the future.
Exigences techniques relatives aux systèmes d'énergie électrique pour petits aéronefs sans pilote
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 24352
First edition
2023-05
Technical requirements for small
unmanned aircraft electric energy
systems
Exigences techniques relatives aux systèmes d'énergie électrique pour
petits aéronefs sans pilote
Reference number
ISO 24352:2023(E)
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ISO 24352:2023(E)
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© ISO 2023
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ISO 24352:2023(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 System requirements .2
5.1 General . 2
5.2 Performance . 4
5.2.1 Output control . 4
5.2.2 Actuation time . 5
5.2.3 Shutdown time . 5
5.2.4 Rated output power . 5
5.2.5 Discharge capacity . 5
5.2.6 Cycle life . 7
5.2.7 Operational cycle life . 7
5.2.8 Recoverable hovering capacity after high temperature storage . 8
5.3 Information and alert . 8
5.3.1 Requirements . 8
5.3.2 Test method and acceptance criteria . 9
5.4 Energy management and electrical protection functions . 9
5.4.1 Charge state of charge (SOC) calculation . 9
5.4.2 Discharge SOC calculation . 9
5.4.3 Over voltage protection . 10
5.4.4 Under voltage protection . 11
5.4.5 Over temperature protection . 11
5.4.6 Over current protection .12
5.4.7 Overload protection.12
5.4.8 Short-circuit protection . 13
5.5 Structure . 13
5.5.1 Requirements .13
5.5.2 Test method and acceptance criteria . 13
5.6 Electrical shock . 13
5.6.1 Requirements .13
5.6.2 Test method and acceptance criteria . 13
5.7 Connector(s) . 13
5.7.1 Requirements .13
5.7.2 Test method and acceptance criteria . 14
5.8 Enclosure protection requirements . 14
5.9 Environmental adaptability . 14
5.9.1 High temperature and humidity storage . 14
5.9.2 Temperature shock . 14
5.9.3 Low pressure .15
5.9.4 Salt spray .15
5.9.5 Drop test .15
5.9.6 Vibration test . 16
6 Test environment .17
6.1 Normal test atmospheric conditions. 17
6.2 Charging method . 17
6.3 Discharging method. 17
7 Identification, packaging, transportation and storage .18
7.1 Identification . 18
7.2 Packaging, transport and storage . 18
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ISO 24352:2023(E)
Bibliography .19
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ISO 24352:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
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expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,
Subcommittee SC 16, Unmanned aircraft systems.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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INTERNATIONAL STANDARD ISO 24352:2023(E)
Technical requirements for small unmanned aircraft
electric energy systems
1 Scope
This document provides technical requirements and test methods for small unmanned aircraft electric
energy systems (EESs).
This document applies to the EES of small unmanned aircrafts (UAs) with the maximum take-off mass
(MTOM) less than 25 kg corresponding to unmanned aircraft systems (UASs) at level I, II, III and IV as
graded in ISO 21895:2020, and with secondary lithium batteries. This document can apply to new type
of batteries to be used in the UA electric energy system in the future.
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.
ISO 21384-2, Unmanned aircraft systems — Part 2: UAS components
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 60950, Information technology equipment - Safety
IEC 62281:2019, Safety of primary and secondary lithium cells and batteries during transport
United Nations Manual of Tests and Criteria, Seventh revised edition, Section 38.3: Lithium Batteries (2019)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
electric energy system
EES
software and hardware system that provides the energy required for the unmanned aircraft, and
distributes, controls, detects and estimates the energy
3.2
secondary lithium battery
rechargeable unit which incorporates secondary lithium cells (3.3) electrically connected in series and/
or parallel with or without monitoring and protection circuitry for charging and discharging
Note 1 to entry: It may incorporate adequate housing and a terminal arrangement and may have electronic
control devices.
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ISO 24352:2023(E)
3.3
secondary lithium cell
basic functional electrochemical unit where electrical energy is derived from the reversible oxidation/
reduction reaction of lithium between the negative electrode and the positive electrode
Note 1 to entry: The cell typically has an electrolyte that consists of a lithium salt and organic solvent compound
in liquid, gel or solid form and has a metal or a laminate film casing. It is not ready for use in an application
because it is not yet fitted with its final housing, terminal arrangement and electronic control device.
3.4
reference test current
I
t
current that can be used to discharge a battery with the rated capacity in one hour
Note 1 to entry: The rated capacity (C , expressed in A·h) is the quantity of electricity which the battery can
2
deliver when discharged at the reference test current of 0,5 I (expressed in A) to a specified final voltage, after
t
charging, storing and discharging under specified conditions.
3.5
state of charge
SOC
ratio of the electric energy system (EES) (3.1) current capacity to the full-charge capacity
4 Abbreviated terms
AFE analogue front end
FCS flight control system
LED light-emitting diode
MCU microcontroller unit
MTOM maximum take-off mass
RPS remote pilot station
SOH state of health
SOP state of power
UA unmanned aircraft
UAS unmanned aircraft system
UFM unmanned aircraft flight manual
5 System requirements
5.1 General
The functions of the electric energy system (EES) shall include energy supply, signal measurement
and analysis, energy estimation, system protection, energy management, control and distribution, as a
minimum.
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ISO 24352:2023(E)
A typical schematic diagram of the EES is shown in Figure 1. The overall workflow and related functions
are as follows:
a) The temperature, battery voltages and current through battery are detected by the AFE and
transferred to the gauge and the MCU.
b) The gauge processes the signals and calculates the remaining energy amount in the battery, and
sends signals to MCU.
c) MCU manages and controls the battery output based on the signals from the gauge, AFE and the
algorithm stored in the MCU. The MCU limits the current when it is higher than expected and
cuts off the charging process when the voltage is over the protection voltage. It controls also the
distribution of energy and power when the temperature is higher than the protection temperature
that affects the battery performance, reliability and safety.
d) Connectors between the EES and the UA send an indication of battery status to the FCS of the UA.
The UA flight control system controls the flight to protect the battery and itself.
e) The interface includes buttons and visual indicators (e.g. LEDs) to turn on/off the battery and check
the remaining energy.
f) When the EES temperature is abnormal (too high or low), the information is sent to the FCS and
then a message is sent to the RPS to notify the remote pilot. The flight control of the UA limits the
flight attitude or even make the UA to automatically return home for safety reason.
Figure 1 — Typical schematic diagram of electric energy system (EES)
As a minimum, design and installation requirements for the EES shall include:
— It shall be able to provide the necessary voltage and current required by the motor(s) and electrical
equipment throughout the operational envelope.
— It shall include electrical protections.
— The electrical connection shall be guaranteed.
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ISO 24352:2023(E)
— The electrical components shall be designed to accommodate the expected electrical loads.
— It shall be designed to accommodate the risk from the expected operational environments.
— It shall be designed to minimize the risk of electrical shock.
— It shall be able to transmit necessary information and alerts to the UA.
Table 1 is the checklist of the EES requirements, test methods and acceptance criteria.
Table 1 — Checklist of the EES requirements, test methods and acceptance criteria
Test methods and ac-
Requirements Category Items Requirements
ceptance criteria
Output control - -
Actuation time 5.2.2.1 5.2.2.2
Shutdown time 5.2.3.1 5.2.3.2
Rated output power 5.2.4.1 5.2.4.2
Performance
Discharge capacity 5.2.5.1 5.2.5.2
Cycle life 5.2.6.1 5.2.6.2
Operational cycle life 5.2.7.1 5.2.7.2
Recoverable hovering capacity after
5.2.8.1 5.2.8.2
high temperature storage
Information and alert 5.3.1 5.3.2
Charge state of charge calculation 5.4.1.1 5.4.1.2
Discharge SOC calculation 5.4.2.1 5.4.2.2
Over voltage protection 5.4.3.1 5.4.3.2
Under voltage protection 5.4.4.1 5.4.4.2
Energy management and electric
protection functions
Over temperature protection 5.4.5.1 5.4.5.2
Over Current Protection 5.4.6.1 5.4.6.2
Overload protection 5.4.7.1 5.4.7.2
Short-circuit Protection 5.4.8.1 5.4.8.2
Structure 5.5.1 5.5.2
Electrical shock 5.6.1 5.6.2
Connector(s) 5.7.1 5.7.2
Enclosure protection 5.8 5.8
High temperature and humidity stor-
5.9.1.1 5.9.1.2
age
Temperature shock 5.9.2.1 5.9.2.2
Low pressure 5.9.3 5.9.3
Environmental adaptability
Salt spray 5.9.4.1 5.9.4.2
Drop test 5.9.5.1 5.9.5.2
Vibration test 5.9.6.1 5.9.6.2
5.2 Performance
5.2.1 Output control
In startup mode, the EES shall be working and providing power to the UA. In shutdown mode, the EES
shall not provide power.
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ISO 24352:2023(E)
5.2.2 Actuation time
5.2.2.1 Requirements
The EES manufacturer shall ensure that the total time to reach the rated power shall meet the UA
manufacturer’s specification. The recommended actuation time should be less than 60 s.
5.2.2.2 Test method and acceptance criteria
The test shall be conducted in the normal test atmospheric conditions as specified in 6.1. The duration
from issuing the startup command to the EES starting to generate output shall be recorded.
The test shall be passed if the actuation time is less than 60 s.
5.2.3 Shutdown time
5.2.3.1 Requirements
The shutdown time of EES shall be designed to meet the UA manufacturer’s specification. The
recommended shutdown time should be less than 2 min.
5.2.3.2 Test method and acceptance criteria
As the EES works on rated power condition, the duration between receiving the power off command
and entering power off status shall be recorded.
The test shall be passed if the shutdown time is less than 2 min.
5.2.4 Rated output power
5.2.4.1 Requirements
The EES shall be continuously outputting the rated output power during the operation time declared by
the UA manufacturer.
5.2.4.2 Test method and acceptance criteria
The test shall be conducted in the normal test atmospheric conditions as shown in 6.1.
The fully charged EES with the new battery(s) shall run at the rated output power after startup. The
EES voltage shall be recorded once per second during the whole operation time declared by the UA
manufacturer. The voltage during the whole testing process shall not be below the discharging final
voltage declared by the UA manufacturer.
The test shall be passed if the operation time is higher than the UA manufacturer specified.
5.2.5 Discharge capacity
5.2.5.1 Requirements
Nominal capacity shall be included in the specification and be either tested using charge/discharge
current at the reference test current of 0,5 I or stated by the UA manufacturer.
t
When the unmanned aircraft is hovering, the discharge capacity shall not be less than 90 % of the
nominal capacity.
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ISO 24352:2023(E)
5.2.5.2 Test method and acceptance criteria
Charging-discharging devices dedicated by the UA manufacturer should be used to make a loop for
the EES and keep the current in the loop constant. The discharging time shall be recorded until the
voltage of the positive/negative electrodes reaches the discharging final voltage specified by the UA
manufacturer, and the corresponding discharge capacity is the initial discharge capacity of the EES.
a) Testing of nominal discharge capacity and high-rate discharge capacity at room temperature shall
include the following steps.
1) Charge the EES according to the methods in 6.2 within the normal conditions in 6.1.
2) At a temperature of 23 °C ± 3 °C, discharge the EES at a current of 0,5 I until it reaches the
t
specified discharging final voltage. Calculate the discharge capacity (A·h).
3) Repeat steps 1) and 2) at least twice. Record the corresponding discharge capacity and take the
average value as the EES nominal discharge capacity at room temperature.
4) Repeat steps 1) to 3) and discharge the EES using nI current (n = 0,5, 1, …, n , where n is
t max max
the maximum discharging rate used in the UA). Record the discharging current and discharging
time.
5) Calculate the current average discharge capacity (A·h) and the ratio to the nominal capacity.
b) Testing of the high-rate discharge capacity in the low temperature shall include the following steps.
1) Charge the EES according to the methods in 6.2.
2) Put the EES for 4 h in the lowest operational environment temperature designed for the battery
installed in the EES or 0 °C (if not specified).
3) Discharge the EES at a current of nI (n = 0,5, 1, …, n , where n is the maximum discharging
t max max
rate used in the UA) until it reaches the specified discharging final voltage.
4) Repeat steps 1) to 3) at least twice. Record the corresponding discharging current and
discharging time.
5) Calculate the average discharge capacity (A·h) in the low temperature and the ratio to the
nominal capacity.
c) Testing of the high-rate discharge capacity in the high temperature shall include the following
steps.
1) Charge the EES according to the methods in 6.2.
2) Put the EES for 4 h in the highest operational environment temperature designed for the
battery installed in the EES or 45 °C (if not specified).
3) Discharge the EES at a current of nI (n = 0,5, 1, …, n , where n is the maximum discharging
t max max
rate used in the UA) until it reaches the specified discharging final voltage.
4) Repeat steps 1) to 3) at least twice. Record the corresponding discharging current and
discharging time.
5) Calculate the average discharge capacity (A·h) in the high temperature and the ratio to the
nominal capacity.
The test shall be passed if the discharge capacity is not less than 90 % of the nominal capacity.
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ISO 24352:2023(E)
5.2.6 Cycle life
5.2.6.1 Requirements
The cycle life of EES with the battery installed shall be specified and tested in the normal test
atmospheric conditions.
After testing, the actual charge and discharge cycle number shall be greater than the cycle life specified
by the UA manufacturer.
5.2.6.2 Test method and acceptance criteria
The EES shall be tested with the new battery(ies) in an environment with temperature at (23 ± 3) °C.
The dedicated charging-discharging devices shall be used. When the capacity is below 80 % of its initial
capacity or below the usable capacity specified by the manufacturer, it indicates the end of life of the
EES.
The test shall include the following steps.
a) Charge the EES according to the methods in 6.2.
b) Rest the EES for a minimum of 30 min or the manufacturer specified resting duration, whichever is
longer.
c) Discharge the EES at the average hovering current or the cycling current claimed in the
specifications until it reaches the specified discharging final voltage.
d) Rest the EES for a minimum of 30 min or the manufacturer specified resting duration, whichever is
longer.
e) Repeat steps a) to d) until the discharge capacity is below 80 % of the initial capacity or the
specified usable capacity. The cycling numbers are considered as the charge/discharge cycle life of
the EES.
The test shall be passed if the discharge capacity is not below 80 % of the initial capacity or the specified
usable capacity under the cycle number specified by the UA manufacturer.
5.2.7 Operational cycle life
5.2.7.1 Requirements
The operational cycle life of EES shall be specified in the typical operational condition defined by the
UA manufacturer and thus tested to ensure that the EES meets the specified operational cycle life.
After testing, the number of working state cycle shall not be less than the cycle life specified by the UA
manufacturer.
5.2.7.2 Test method and acceptance criteria
In order to simulate the EES actual operating state in the UA, the typical operational condition shall be
defined by the UA manufacturer. If not, the test conditions in 6.1 are recommended.
The EES shall be tested with the new battery(ies) with dedicated charging-discharging devices.
When the capacity is below 80 % of its initial capacity or below the usable capacity specified by the
manufacturer, it indicates the end of life of the EES.
The test shall include the following steps.
a) Charge the EES according to the methods in 6.2.
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ISO 24352:2023(E)
b) Rest the EES for a minimum of 30 min or the manufacturer specified resting duration, whichever is
longer.
c) Pulse discharge according to electrical loads characteristics of the UA typical mission profile until
it reaches the specified discharging final voltage. Record the discharge capacity.
d) Rest the EES for a minimum of 30 min or the manufacturer specified resting duration, whichever is
longer.
e) Repeat steps a) to d) until the discharge capacity is below 80 % of the initial capacity or the
specified usable capacity. The cycling numbers are considered as the operational charge/discharge
cycle life.
The test shall be passed if the discharge capacity is not below 80 % of the initial capacity or the specified
usable capacity under the cycle number specified by the UA manufacturer.
5.2.8 Recoverable hovering capacity after high temperature storage
5.2
...
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