IEC TR 62933-2-200:2021

Electrical energy storage (EES) systems - Part 2-200: Unit parameters and testing methods - Case study of electrical energy storage (EES) systems located in EV charging station with PV

IEC TR 62933-2-200:2021(E) presents a case study of electrical energy storage (EES) systems located in electric vehicle (EV) charging stations with photovoltaic (PV) power generation (PV-EES-EV charging stations) with a voltage level of 20 kV and below. EES systems are highlighted in this document because they are a desired option to make the charging stations (especially the high-power fast charging stations) grid-friendly, improve the self-consumption of clean energy generation, and increase the revenue of stations. In this application, EES systems show excellent performance by running in a variety of available operating modes, such as peak shaving, power smoothing, load tracing, time-of-use (TOU) price arbitrage, and ancillary services. The general duty cycle is recommended based on the summary of the operation characteristics of the EES systems.

General Information

• Status: Published
• Publication Date: 02-Sep-2021
• ICS: 13.020.30 - Environmental impact assessment
• ICS: 27.160 - Solar energy engineering
• ICS: 43.120 - Electric road vehicles
• Technical Committee: TC 120 - Electrical Energy Storage (EES) systems
• Drafting Committee: WG 2 - TC 120/WG 2
• Current Stage: PPUB - Publication issued
• Start Date: 03-Sep-2021
• Completion Date: 01-Oct-2021

Overview - IEC TR 62933-2-200:2021 (EES systems in PV + EV charging stations)

IEC TR 62933-2-200:2021 is a Technical Report from the International Electrotechnical Commission that presents case studies, unit parameters and testing-method guidance for electrical energy storage (EES) systems co-located with photovoltaic (PV) generation at electric vehicle (EV) charging stations (PV‑EES‑EV). The report focuses on installations at distribution voltage levels (20 kV and below) and explains how EES can make high‑power fast‑charging sites more grid‑friendly, increase PV self‑consumption and improve station revenues.

Key topics and technical requirements

The report covers practical technical topics and recommended procedures, including:

• Unit parameters and testing methods for EES devices intended for PV‑integrated charging stations.
• System topologies and case projects for both common DC bus and common AC bus architectures.
• Operation modes and control strategies: peak shaving, power smoothing, load tracing, time‑of‑use (TOU) price arbitrage, ancillary services and demand response.
• Duty cycle analysis and recommended general duty cycles derived from operational data and mode summaries.
• Communication architecture and system control requirements to support coordinated PV, EES and EV charging operation.
• Informative figures and tables showing EV/PV profiles, operating power examples, daily energy flows, and time‑division of operation modes.

The TR provides case studies (commercial and business scenarios) with operation data analysis and simulated operating profiles rather than prescriptive product specifications.

Practical applications - who should use this standard

IEC TR 62933-2-200 is valuable for:

• System integrators and designers planning PV+EES solutions for EV charging stations.
• EV charging station operators and site owners evaluating business cases and operation strategies (TOU arbitrage, peak shaving).
• EES and PV manufacturers developing units and validating testing methods for charging‑station integration.
• Testing laboratories and certification bodies seeking duty‑cycle and test scenarios relevant to PV‑EES‑EV use cases.
• Utilities and grid operators assessing grid impacts, ancillary service participation and interoperability needs.

Using the TR helps stakeholders optimize EES sizing, control logic and testing to improve self‑consumption, reduce peak demand charges, and enable grid services.

Related standards and further reading

• Part of the broader IEC 62933 family addressing electrical energy storage systems. Users should consult other IEC publications for normative requirements, safety, and grid‑connection standards when implementing PV‑EES‑EV projects.

Standards Content (Sample)

IEC TR 62933-2-200 ®
Edition 1.0 2021-09
TECHNICAL
REPORT
colour
inside
Electrical energy storage (EES) systems –
Part 2-200: Unit parameters and testing methods – Case study of electrical
energy storage (EES) systems located in EV charging station with PV
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IEC TR 62933-2-200 ®
Edition 1.0 2021-09
TECHNICAL
REPORT
colour
inside
Electrical energy storage (EES) systems –

Part 2-200: Unit parameters and testing methods – Case study of electrical

energy storage (EES) systems located in EV charging station with PV

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 13.020.30; 27.160; 43.120 ISBN 978-2-8322-1021-0

– 2 – IEC TR 62933-2-200:2021 © IEC 2021
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms . 7
4 Overview of EES systems located in EV charging stations with PV power
generation . 8
4.1 General . 8
4.2 Application scenarios . 8
4.3 System communication architecture . 9
4.4 Duty cycle analysis . 10
5 Project of commercial PV-EES-EV charging station based on common DC bus . 11
5.1 Case project overview . 11
5.2 System operation and control . 12
5.2.1 Operation data analysis . 12
5.2.2 Operation mode analysis . 13
5.3 Summary . 15
6 Project of commercial PV-EES-EV charging station based on common AC bus . 17
6.1 Case project overview . 17
6.2 System operation and control . 18
6.2.1 Operation data analysis . 18
6.2.2 Operation mode analysis . 19
6.3 Summary . 21
7 Project of business PV-EES-EV charging station based on common DC bus . 23
7.1 Case project overview . 23
7.2 System operation and control . 24
7.2.1 Operation data analysis . 24
7.2.2 Operation mode analysis . 25
7.3 Summary . 27
8 Project of business PV-EES-EV charging station based on common AC bus . 29
8.1 Case project overview . 29
8.2 System operation and control . 29
8.2.1 Operation data analysis . 29
8.2.2 Operation mode analysis . 30
8.3 Summary . 33
9 Recommendation for operation modes of EES systems located in EV charging
station with PV panels . 34
Annex A (informative) Duty cycles of the EES systems located in EV charging station
with PV . 36
A.1 General . 36
A.2 Project of commercial PV-EES-EV charging station based on common DC
bus . 36
A.3 Project of commercial PV-EES-EV charging station based on common AC
bus . 38
A.4 Project of business PV-EES-EV charging station based on common DC bus . 45
Bibliography . 47

Figure 1 – Example of communication system architecture of PV-EES-EV charging
station . 10
Figure 2 – System structure of case commercial PV-EES-EV charging station based on

common DC bus . 11
Figure 3 – EV load and PV power for the case of a commercial charging station based
on common DC bus . 12
Figure 4 – TOU and charging service prices for the case of a commercial charging
station based on common DC bus . 12
Figure 5 – Operating power in low- and medium-price periods in the case of a

commercial charging station based on common DC bus . 14
Figure 6 – Operating power in high-price periods in the case of commercial charging
station based on common DC bus . 15
Figure 7 – EES system duty cycle in the case of a commercial charging station based
on common DC bus . 15
Figure 8 – Daily electricity flow for the case of a commercial charging station based on

common DC bus . 17
Figure 9 – System structure for the case of a commercial PV-EES-EV charging station
based on common AC bus . 18
Figure 10 – EV load and PV power for the case of a commercial charging station based
on common AC bus . 19
Figure 11 – Operating power in power smoothing mode for the case of a commercial

charging station based on common AC bus. 19
Figure 12 – Operating power in peak shaving mode for the case of a commercial
charging station based on common AC bus. 20
Figure 13 – Operating power in the TOU price arbitrage mode for the case of a
commercial charging station based on common AC bus . 21
Figure 14 – EES duty cycle for the case of a commercial charging station based on

common AC bus . 22
Figure 15 – Daily electricity flow of for the case of a commercial charging station based
on common AC bus . 22
Figure 16 – System structure for the case of a business PV-EES-EV charging station
based on common DC bus . 23
Figure 17 – PV power, EV load and output power for the case of a business charging

station based on common DC bus . 24
Figure 18 – TOU and charging service prices for the case of a business charging
station based on common DC bus . 24
Figure 19 – Operating power in equivalent load tracing mode for the case of a
business charging station based on common DC bus . 25
Figure 20 – Operating power in TOU price arbitrage mode for the case of a business

charging station based on common DC bus . 26
Figure 21 – Operating power in demand response mode for the case of a business
charging station based on common DC bus . 27
Figure 22 – Operating power involved in TOU arbitrage and demand response for the
case of a business charging station based on common DC bus . 27
Figure 23 – EES duty cycle for the case of a business charging station based on

common DC bus . 28
Figure 24 – Daily electricity flow for the case of a business charging station based on
common DC bus . 28
Figure 25 – System structure for the case of a business PV-EES-EV charging station
based on common AC bus . 29

– 4 – IEC TR 62933-2-200:2021 © IEC 2021
Figure 26 – EV load and PV power for the case of a business charging station based
on common AC bus . 30
Figure 27 – Simulation results for operation strategy 1 for the case of a business

charging station based on common AC bus. 31
Figure 28 – Simulation results for operation strategy 2 for the case of a business
charging station based on common AC bus. 31
Figure 29 – Simulation results for operation strategy 3 for the case of a business
charging station based on common AC bus. 33
Figure 30 – Three operation strategies and resultant operation modes of the EES

system for the case of a business charging station based on common AC bus . 33

Table 1 – Time division of EES system’s operation modes in the case of a commercial
charging station based on common DC bus . 16
Table 2 – Time division of the EES system’s operation modes for the case of a
commercial charging station based on common AC bus . 21
Table 3 – Time division of EES operation modes for the case of a business charging
station based on common AC bus . 34
Table 4 – Recommended operation modes of the EES system in various installation
scenarios of a PV-EES-EV charging station . 35
Table A.1 – Charging-discharging power of EES system for the case of a commercial
charging station based on common DC bus (per-unit value) . 36
Table A.2 – Charging-discharging power of EES system for the case of a commercial
charging station based on common AC bus (per-unit value) . 38
Table A.3 – Charging-discharging power of EES system for the case of a business
charging station based on common DC (per-unit value) . 45

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

Part 2-200: Unit parameters and testing methods –
Case study of electrical energy storage (EES) systems
located in EV charging station with PV

FOREWORD
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rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 62933-2-200 has been prepared by IEC technical committee TC 120: Electrical Energy
Storage (EES) Systems. It is a Technical Report.
The text of this Technical Report is based on the following documents:
Draft Report on voting
120/231/DTR 120/238/RVDTR
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 Report is English.

– 6 – IEC TR 62933-2-200:2021 © IEC 2021
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
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ELECTRICAL ENERGY STORAGE (EES) SYSTEMS –

Part 2-200: Unit parameters and testing methods –
Case study of electrical energy storage (EES) systems
located in EV charging station with PV

1 Scope
This part of IEC 62933, which is a Technical Report, presents a case study of electrical energy
storage (EES) systems located in electric vehicle (EV) charging stations with photovoltaic (PV)
power generation (PV-EES-EV charging stations) with a voltage level of 20 kV and below. EES
systems are highlighted in this document because they are a desired option to make the
charging stations (especially the high-power fast charging stations) grid-friendly, improve the
self-consumption of clean energy generation, and increase the revenue of stations. In this
application, EES systems show excellent performance by running in a variety of available
operating modes, such as peak shaving, power smoothing, load tracing, time-of-use (TOU) price
arbitrage, and ancillary services. The general duty cycle is recommended based on the
summary of the operation characteristics of the EES systems.
This document includes the following elements:
– overview of general PV-EES-EV charging stations;
– operational analysis of EES systems in typical project cases;
– summary and recommendation of EES systems’ operation modes.
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
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
AC Alternating current
BAMS Battery array management system
BCMU Battery cluster measurement unit
BMU Battery measurement unit
– 8 – IEC TR 62933-2-200:2021 © IEC 2021
CAN Controller area network
DC Direct current
EES Electrical energy storage
EMS Energy management system
EV Electric vehicle
EVSE Electric vehicle supply equipment
PCS Power conversion system
POC Point of connection
PV Photovoltaic
SOC State of charge
TOU Time-of-use
V2G Vehicle-to-grid
4 Overview of EES systems located in EV charging stations with PV power
generation
4.1 General
The growing problems of climate change and environmental degradation on a global scale are
the great challenges faced by people all over the world. Electric vehicles (EVs), which help
reduce dependence on fossil fuels, are the key to advancing energy transition in the
transportation sector. The convenience of charging has always been an important factor that
affects whether consumers consider electric vehicles as an option. In recent years, EV charging
infrastructures, especially the commercial charging stations and the business charging stations,
have achieved rapid growth.
The integration of renewable power generation in the charging stations is conducive to further
improving the use of clean energy while reducing the energy cost of the charging stations.
Limited by the size of the site, PV power generation is often the primary choice for the charging
stations. PV panels can be deployed on the roof of the station or integrated on the top of the
charging infrastructure according to local conditions, which show significant advantages over
wind turbines. However, both PV power and EV charging load are highly uncertain, and the
charging demand of EV users during peak hours sometimes has a huge impact on the stable
operation of the external power grid. EES systems can smooth the charging load of EV users
and promote the local consumption of PV power generation. As for the operation of the charging
station, EES systems can delay the expansion of the transformer at the charging station due to
the rapidly increasing load, achieve peak-valley arbitrage according to TOU prices, and even
assist the charging station to participate in ancillary service of the power grid.
The integration of PV and EES systems is the development trend of the EV charging stations.
Many countries in the world, such as China, the United States, Germany, the United Kingdom,
and Australia, have deployed the projects of EV charging stations integrated with PV and EES
systems.
4.2 Application scenarios
Some PV-EES-EV charging stations are designed to operate off-grid, where the PV system
provides the initial energy and the EES system serves as the storage place for electricity and
timely power EVs. The entire station does not exchange energy with the external grid. At a
charging station that operates in this mode, the capacity of EES systems is the key parameter
that directly determines how many EVs can continue to serve.
Compared with the off-grid ones, the more common operation modes of charging stations are
based on grid-connected operation. In this case, the charging needs of EV owners are always
met even if the installed capacity of the EES system and PV is not sufficient. These kinds of

charging facilities are widely deployed in residents’ homes, parking lots, highway service areas
and other places with high traffic flow.
In the grid-connected charging stations, EES systems can operate in a variety of modes, such
as load tracing, peak shaving, power smoothing, TOU price arbitrage, and ancillary service,
rather than simply balancing PV generation and charging load as in off-grid settings.
After investigating a large number of charging stations around the world, four typical application
scenarios for the grid-connected PV-EES-EV charging stations from the perspective of electrical
structure were found, namely commercial charging stations with common direct current (DC)
bus, commercial charging stations with common alternating current (AC) bus, business charging
stations with common DC bus, and business charging stations with common AC bus.
The main purpose of commercial charging stations is to provide charging services for general
EV users and obtain economic revenues. In general, the commercial charging station is an
independent interest subject and can be seen as a general load from the grid point of view due
to the forbidden power feedback to the external grid in most cases. In this document, two
practical cases are discussed in Clause 5 and Clause 6, respectively. In Clause 5, a DC
common bus based PV-EES-EV charging station is introduced. The EES system in this station
plays the role of load tracing and TOU price arbitrage. Alternatively, the PV-EES-EV charging
station in Clause 6 is an AC common bus based station, and the EES system of this station
mainly operates in power smoothing, peak shaving and TOU price arbitrage mode.
Business charging stations generally refer to charging stations built alongside commercial malls,
office buildings, communities, campuses, which can not only provide services for EVs, but also
power the surrounding load. In Clause 7, a common DC bus based PV-EES-EV charging station
is analysed, where the EES system plays a comprehensive role in load tracing, TOU price
arbitrage, and demand response. The entire charging station also undertakes the task of
supplying power to a nearby shopping mall in the price peak time periods. At last, in Clause 8
a common AC bus based business charging project sponsored by the U.S. Department of
Energy is introduced and the operation modes of one of the charging stations in this project are
elaborated.
4.3 System communication architecture
Figure 1 shows a typical architecture of the communication system of a grid-connected EV
charging station integrated with the PV and EES system in China. The battery energy
management system is divided into three levels, namely the battery array management system
(BAMS), battery cluster measurement unit (BCMU), and battery measurement unit (BMU). The
controller area network (CAN) is used for information exchange between the upper and the
lower management systems/measurement units. Only the highest level of BAMS communicates
with the power conversion system (PCS) via RS 485. PV panels are linked to the PV controller
through the convergence box. For unification, all components in the EV charging system
communicate through CAN. The PV controller, battery PCS, and electric vehicle supply
equipment (EVSE) are connected to the charging station’s energy management system (station-
EMS). The station-EMS responds to the commands of the external distribution network
according to IEC 60870-5-104.
– 10 – IEC TR 62933-2-200:2021 © IEC 2021

Figure 1 – Example of communication system architecture
of PV-EES-EV charging station
Note that the above communication structure and protocols in Figure 1 are only intended as a
typical demonstration for the cases practically adopted in China. In fact, some other open and
interoperable protocols are also available. For example, IEC 61851 (all parts), ISO 15118 (all
parts), CHAdeMO 2.0, and IEEE 2030.5 can be used as alternative protocols between EV and
EVSE. In terms of the communication between the station-EMS and EV system, battery system,
and PV system, IEC 61850 (all parts) is a good option to provide a higher level of security
against unauthorized commands or interception of data.
4.4 Duty cycle analysis
A duty cycle is a charge/discharge profile that represents the demands placed on an EES
system by a specific application. The duty cycle for the EES system in the EV charging station
with PV panels will take into account how an EES system operates in a set cycle to make the
charging station operate more efficiently.
Because the charging load of the charging station and PV power generation is random, and
there are peak and valley periods, it is necessary to provide a 24 h duty cycle for the operation
of the EES system to better provide energy for the charging station.
The following procedure is generally used to configure the duty cycle of an EES system in PV-
EES-EV charging stations.
• Step 1: The charging stations are classified according to the collected data, which include
PV data, EES system data, point of connection (POC) data, and load data.
• Step 2: The PV, EES system, POC, and load data are processed separately, which mainly
includes filling in the missing data and making the sampling intervals of the four types of
data the same.
• Step 3: The operation modes of the EES system in PV-EES-EV charging stations are
analysed, and the corresponding operation curve is extracted according to different
operation modes. Different methods are used for different operating modes to calculate their
respective EES system operating curves.

• Step 4: The 24 h working curves under each operation mode are synthesized, and the typical
duty cycle of the EES system is extracted.
5 Project of commercial PV-EES-EV charging station based on common DC
bus
5.1 Case project overview
The electricity both generated by PV panels and required by EVs is in the form of direct current,
and so are batteries. In order to reduce energy loss, many charging stations are deployed as
DC systems. One of the typical representatives is the PV-EES-EV charging station. Figure 2
shows the electrical structure of a commercial PV-EES-EV charging station located in China.

Figure 2 – System structure for the case of a commercial PV-EES-EV
charging station based on common DC bus
This project is equipped with a DC bus to connect major in-station equipment, including 30 kW
PV panels, 500 kW/500 kWh EES system and 6 DC fast charging piles. The maximum power of
each pile can reach 120 kW. The charging station is connected to the AC bus with an AC/DC
converter, through which it can purchase electricity from the external grid. However, the
charging station is not allowed to inject power to the external power grid. In other words, the
station is just a general load from the power grid view.
The main purpose for installing an EES system in this station is to meet the demand for fast
charging and provide quality service without increasing the load demand on the external power
grid of the charging station. If an EES system is not deployed, the service limit of the charging
station is 250 kW based on the capacity of the AC/DC grid-connected converter in the case
where the PV power output is zero. With the help of the EES system, the charging station can
meet the charging demand up to 750 kW. In practice, the maximum power of the EES system
is set to 250 kW (50 % of maximum output rating) under normal operating conditions to extend
the service life of the batteries. In an emergency situation when the charging load exceeds the
total power supply capacity of PV panels, EES, and the external grid, the EES system is allowed
to run in the range of 250 kW to 500 kW.

– 12 – IEC TR 62933-2-200:2021 © IEC 2021
5.2 System operation and control
5.2.1 Operation data analysis
The historical data of power generation and consumption on a typical day are illustrated in
Figure 3. PV panels generate electricity mainly between 7:00 and 18:00. EV charging service
is available 24 h a day. Figure 4 shows the TOU price and EV charging service tariffs for that
day.
Figure 3 – EV load and PV power for the case of a commercial
charging station based on common DC bus

Figure 4 – TOU and charging service prices for the case of a commercial
charging station based on common DC bus

5.2.2 Operation mode analysis
5.2.2.1 General
The EES system is able to absorb electricity from the external power grid during the low-price
periods and release it when the price rises. Due to the fact that the EV charging load is unknown
(this station is not equipped with a charging load prediction system); the reserve energy in the
EES system has to be relatively large to avoid such a case as the state of charge (SOC) of EES
falling below the allowable lowest when many cars are coming to charge at the same time. In
this project, the minimal state of charge (SOC) of the EES system is set to 32 % for an
unexpected charging situation. When the peak-price periods come, it is ensured that enough
electricity (95 % of the rated capacity of EES system in this project) is already stored in the
batteries.
The EES system in this charging station plays the role of equivalent charging load tracing and
TOU price arbitrage. Equivalent load is the difference between the EV charging load and PV
power. In the low-price and medium-price periods, the charging load demand of electric vehicles
is mainly satisfied by the external power grid, and the EES system is expected to supplement
the stored electricity while the charging demand exceeds the sum of the capacity of the AC/DC
grid-connected converter and the PV power. In the high-price periods, the EES system focuses
on tracking the equivalent EV charging load. When the EES power is insufficient, the extra EV
charging load is provided by the external power grid.
5.2.2.2 TOU price arbitrage mode
The TOU price arbitrage mode is mainly concentrated in low- and medium-price periods, i.e.,
0:00 to 8:00, 11:00 to 18:00, and 21:00 to 24:00 (Figure 4). The equivalent load equals the EV
charging load minus the PV output. The battery power is positive in the discharging mode and
negative in the charging mode. The grid power is positive when the charging station gets power
from the external power grid.
During these periods, the EES system is basically in the charging mode due to the relatively
low price, and the external grid satisfies the equivalent EV charging load. When the equivalent
load is below 250 kW, it is completely satisfied by the external power grid. At the same time, if
the SOC of the EES system has not reached 95 %, it is in charging mode. The charging power
of the EES system equals 250 kW (the capacity limit of the AC/DC grid-connected converter)
minus the equivalent load. However, when the equivalent load demand exceeds 250 kW, for
example, from 2:30 to 2:45 in Figure 5a), or from 14:05 to 14:45 in Figure 5b), the excess EV
charging load is supplied by the EES system. In this case, the EES system is in discharging
mode.
Note that the EES system is in the standby mode from 21:00 to 22:00 (as shown in Figure 5c)),
in which the EES system does not charge and only discharges when the EV load exceeds the
limit of 250 kW. The reason is that it achieves more cost savings to delay the charging behaviour
of the EES system to a later low-price period (from 22:00 to 6:00 of the next day) than to charge
during the medium-price period (from 21:00 to 22:00). However, during other medium-price
periods, for example from 11:00 to 18:00, the EES system needs to charge in preparation for
discharging at the later high-price period of the day.

– 14 – IEC TR 62933-2-200:2021 © IEC 2021

a) Operating power from 0:00 to 8:00 b) Operating power from 11:00 to 18:00

c) Operating power from 21:00 to 24:00
Figure 5 – Operating power in low- and medium-price periods
for the case of a commercial charging station based on common DC bus
5.2.2.3 Equivalent load tracing mode
In high-price periods the EES system operates in the equivalent load tracing mode, as shown
in Figure 6. Figure 6a) shows the operation power from 8:00 to 11:00, and Figure 6b) shows
the operation power from 18:00 to 21:00. The EV charging load is first supplied by the EES
system. In order to extend the service life of batteries, the discharging power of the EES system
is limited to 250 kW. The part of the charging demand that exceeds this value is provided by
the external grid, as shown in Figure 6a), for example between 9:20 and 9:50. If the charging
load is large and exceeds 500 kW, then the EES system will supply the excess during the time
period (this situation did not happen in this case). What needs to be pointed out is that when
the SOC of the EES system reaches the lower limit of 32 %, the EES system stops discharging
and the equivalent load is satisfied by the external power grid, for example between 10:25 and
11:00.
a) Operating power from 8:00 to 11:00 b) Operating power from 18:00 to 21:00
Figure 6 – Operating power in high-price periods for the case
of a commercial charging station based on common DC bus
5.3 Summary
The resultant EES system duty cycle is the synthesis of the curves for each of the above two
modes, as shown in Figure 7. It can be seen that the peak charging load is shaved due to the
capacity constraint from the grid-connected converter. The EES system in the station satisfies
the excess charging demand. In general, it can be seen that the EES system has gone through
two big charging and discharging processes in the duty cycle of one day in Figure 7b). The time
division of the EES system’s duty cycle is tabulated in Table 1.

a) Comprehensive power b) SOC of the EES system
Figure 7 – EES system duty cycle for the case of a commercial
charging station based on common DC bus

– 16 – IEC TR 62933-2-200:2021 © IEC 2021
Table 1 – Time division of EES system’s operation modes in the case
of a commercial charging station based on common DC bus
Modes Periods Target Remarks
The EES system is in charging mode until
SOC reaches the upper limit of 95 % to
0:00~8:00
– When the equivalent load is
prepare for discharging in the morning peak
above the external grid input
period.
limit of 250 kW, the EES system
The EES system is in charging mode until
is discharged to the excess
SOC reaches the upper limit of 95 % to
load.
11:00~18:00
prepare for discharging in the evening peak
TOU price
– When the SOC of the EES
period.
arbitrage
system reaches 95 %, the
The EES system is in standby mode to wait
charging mode is stopped.
21:00~22:00
for charging in the low price period.
– The maximum charging power of
The EES system is in charging mode until
the EES system is set as
SOC reaches the upper limit of 95 % to
250 kW.
22:00~24:00
prepare for discharging in the morning peak
period.
– The maximum discharging
power of the EES system is set
8:00~11:00
at 250 kW. When the equivalent
load is above 250 kW, the
Equivalent
The EES system is in discharging mode to
excess load is satisfied by the
load
trace the equivalent load.
external power grid.
tracing
– When the SOC of the EES
18:00~21:00
system reaches 32 %, the
discharging mode is stopped.
In this practical project, the EES system is programmed to charge up to 95 % to prepare for the
discharge during the high-price periods. If load forecasting is employed, the level of recharge
will be optimized. For example, the SOC of the EES drops to 35 % after 21:00, but it is still
above the set minimum threshold of 32 %. In other words, if the charging load for the rest of
the day is known in advance, the EES system would not have to be charged to 95 % during the
middle-price periods.
Figure 8 shows the daily electricity flow of the charging station (the value at the t time point
means the total electricity from the t time point to the t+1 time point). The left axis shows the
flow electricity of the power grid, PV and EV load for each hour. The right axis shows the stored
electricity in the EES system. It can be seen that the utilization rate of the charging piles (the
ratio of the charging power to the maximum power of charging piles) is considerable, reaching
an average of 20 %/h. However, the PV capacity equipped with this charging station is relatively
inadequate at only 30 kW. Better economic benefits are expected if more PV panels are
installed.
Figu
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