Rapid EV Chargers: Implementation of a Charger

Rapid EV Chargers: Implementation of a Charger
Rapid EV Chargers: Implementation of a Charger
Ben Jar* 1, Neville Watson2, Allan Miller1
1
Electric Power Engineering Centre (EPECentre), University of Canterbury
2
Department of Electrical and Computer Engineering, University of Canterbury
*Presenting
EEA Conference & Exhibition 2016, 22 - 24 June, Wellington
Abstract
The uptake of electric vehicles in New Zealand is rapidly increasing and there is a desire for
information about charging systems. This information is required by consumers, engineers, and
businesses interested in installing charging infrastructure. This project was completed during
the 2015-2016 summer break and aimed to enhance the University of Canterbury EPECentre’s
knowledge of charging technologies. In addition to gaining a general understanding of charging
technologies, detailed research into rapid DC chargers using the CHAdeMO protocol was
conducted. The project also included the building and testing of an open source 12kW rapid
DC charger using the CHAdeMO protocol. This paper combines the findings of researching
the numerous charging technologies with the practical experience of building the charger.
Although the charger was not tested with a compatible car due to time constraints, it was
successfully built and initial testing was completed. Plans are also underway to conduct more
comprehensive testing on the charger to fully characterise it.
1
1
Introduction
During the university summer break of 2015-2016 a summer scholarship was awarded to the
author to work on an open source rapid electric charger (EV). The primary purpose of this
project was to gain an understanding of rapid EV charging systems; in particular, chargers
using the CHAdeMO protocol. The University of Canterbury wanted to gain further
understanding of the technology used in these chargers for research and teaching purposes. The
eventual aim is to research how to use the chargers to allow bidirectional power flow for
vehicle-to-grid (V2G) applications. A practical component of the project was required with the
build and test of an open source charger.
As of March 31st 2016, there are 1128 light EVs registered in New Zealand with this number
rapidly increasing [1]. As EVs become more mainstream within New Zealand, the demand for
charging technologies will substantially increase. This includes both residential systems and
commercial public chargers. In particular, there will be a demand for rapid charging stations
where consumers will be able to recharge their vehicles to approximately 80% in as little as 30
minutes. This will help reduce ‘range anxiety’ and further encourage consumers to use their
EVs for longer journeys. To encourage the uptake of these technologies, stakeholders including
consumers, investors, engineers, and electricity companies will need reliable information.
Although there is plenty of information available, it is challenging to combine numerous
sources and determine how it relates to the New Zealand market. As part the summer project,
significant research into EV charger technology with an emphasis on CHAdeMO chargers was
completed. This paper combines the research into EV charging technologies with the
experiences of building the open source CHAdeMO charger to provide a source of information
for anyone interested this rapidly changing field.
2
Electric Vehicle Charging Technologies
The field of electric vehicle (EV) charging systems is rapidly evolving with numerous
standards, types, connectors, and terms used to describe chargers. The generic term used to
describe the piece of equipment used to charge an electric vehicle is ‘electric vehicle supply
equipment’ (EVSE). EVSE can be further categorised into three levels that relate to their output
power capabilities [2]. Level 1 and level 2 EVSE both supply alternating current (AC) to an
electric vehicle’s on-board charger and level 3 systems supply direct current (DC) to the EV
[2]. The use of the term ‘charger’ for levels 1 and 2 is misleading, as they are not technically
chargers. They supply AC electricity to the EV where the on-board charger converts the AC to
DC, which charges the batteries [2]. EVSE also provides important safety features for both
users and charging equipment [3].
The battery management system (BMS) is another vital component in an EV charging system.
It is responsible for thermal management, cell balancing, over charge and over discharge
monitoring of the battery pack [4]. An EV battery pack is not made of a single battery; instead,
many individual cells are combined to form a bank [4]. A single cell may only have a small
safe working voltage range and it is important to ensure it stays within this range. This is
particularly important with variants of lithium ion batteries commonly used in EVs. Over
charge and over discharge can result in disastrous consequences including reduced battery life
or total battery failure causing fires [4]. It is the job of the BMS to monitor the battery cells to
2
ensure they all stay within normal operating voltages and temperatures [4]. The BMS also
balances individual cells by redistributing charge from cells of higher electric potential
(voltage) to lower potential cells [4]. BMS’s use numerous techniques to manage the battery
pack and Cao et al. (2008) give an excellent review of such technology [5]. The BMS is also
responsible for the voltage and current requests from the charger [6] . This includes both the
on board charger for levels 1 and 2 or the off board charger for level 3 EVSE. Multiple charging
profiles (constant current, constant voltage etc.) are available to charge a battery; however, this
is outside the scope of this paper.
2.1 Level 1 and 2 Charging
As previously, mentioned, level 1 and 2 chargers provide AC electricity to the EV’s on board
charger. There is communication between the EVSE and the EV to ensure the on board charger
does not draw more current than the EVSE can supply, and to safely protect the user and
equipment [3]. The current limit is dependent on the EVSE level and more importantly, its
electrical supply.
Level 1 chargers are typically inline chargers which are stored with the EV. Their compatibility
with standard household electrical sockets limits the power they can deliver which
consequently increases charging times. This portability, combined with their compatibly,
allows their use as emergency chargers in situations where the EV battery has gone flat. In the
United States, level 1 supplies correspond to a single phase supply of 12A at 110V. This allows
a maximum power transfer to the EV of 1.4 kW. These chargers are slow and it can typically
take 4-11 hours to fully charge an EV [2]. In countries such as New Zealand, where the grid
voltage is 230V single phase, this allows a higher charging power for the same current, which
reduces charging times. Assuming people’s use of their EVs does not drain the battery too
much on a daily basis, a level 1 EVSE can provide adequate charging overnight. Figure 1 shows
an example level 1 EVSE.
Level 2 EVSE aims to improve the power output by using a dedicated ‘box’ permanently
mounted on a wall or other appropriate structure. The permanently mounted box allows for a
dedicated electrical supply of sufficient capacity, enabling a significantly higher power output
compared to level 1. In the United States, the electrical supply to the EVSE is often spilt phase.
This increases the voltage supplied to the EV to 240V, which significantly increases the power
without drawing more current. Level 2 EVSE can provide between 4 and 20 kW depending on
the local supply. This can reduce charging times of an EV to 1-6 hours. Both homes and
dedicated charging facilities (private or public) are common locations for level 2 EVSE. Figure
2 shows an example level 2 EVSE.
3
Figure 1: A level 1 EVSE.1
Figure 2: A level 2 EVSE.2
The standardisation of connectors and protocols for levels 1 and 2 is variable across countries
and manufacturers. In America, the Society of Automotive Engineers’ (SAE) J1772 standard
is used to define the connector and the protocol used for levels 1 and 2 EVSE. Figure 3 shows
an example SAE J1772 charge port. The connector used in Europe for levels 1 and 2 charging
is the IEC 62196-2 or Mennekes connector and is shown in Figure 4. To confuse matters
further, The IEC 62196 standard also defines the J1772 connector as the type 1 connector with
the Mennekes connector defined as type 2. The type of connector does not relate to the EVSE
level. It is important to note that both connectors use the same signalling protocol for
controlling the charging process. Although both connectors are similar, the type 2 connector
has two additional power pins. This is to allow a three phase AC supply to be connected directly
to the EVs on board charger, further reducing charge time. Given J1772 and type 2 connectors
use the same protocols, it is possible to purchase adapters to swap between connector types.
Table 1 lists example manufacturers who use each of the connectors.
1
Retrieved from: http://www.roperld.com/Science/EVChargingSWVA_SWV.htm
Retrieved from: https://www.emotorwerks.com/store-juicebox-ev-charging-stations/202-juicebox-pro-40smart-40-amp-evse-with-24-foot-cable
2
4
Figure 3: J1772 connector and charge port.3
Figure 4: Mennekes Connector. Also known as Type 2
and 62196-2.4
Table 1: Manufacturers who use J1772 and 62196-2
Manufacturer
Nissan
Vehicle
Leaf
Mitsubishi
i-MiEV
BMW
Ford
i3
Focus
Connector
J1772
J1772 (American Models
62196-2 (European Models)
62196-2
J1772
Level 1 and level 2 EVSE with either the J1772 or type 2 connector contain signalling
electronics to improve user safety and protect the infrastructure. Figure 5 contains an example
of the J1772 electronic circuit schematic. One of the key safety features with the signalling
electronics is the prevention of voltage being present at the connector terminals while it is not
correctly mated to the EV [7]. This helps protect the user, by ensuring if they were to touch the
connector pins they would not receive an electric shock. While the connector is connected, the
vehicle is also immobilised to prevent driving while charging [7]. The EVSE also monitors the
potential ground to ensure there is no earth leakage, further reducing electric shock risk [7].
Communications between the EVSE and EV are not bidirectional and are completed using a
modulated 1 kHz square wave [7]. The EVSE generates the square wave and its duty cycle
indicates to the EV the maximum available current. The square wave nominally oscillates
between -12V and +12V, however, this voltage can also be altered to indicate various states.
These states are: not connected; EV connected; EV charge; EV charge ventilation required;
and error [7]. Further information is available on the OpenEVSE website.5
3
Retrieved from: http://www.edn.com/electronics-blogs/automotive-currents/4421241/How-the-J1772charging-standard-for-plug-in-vehicles-works
4
Retrieved from:
http://www.mennekes.de/es/latest0.html?tx_ttnews%5Btt_news%5D=47&cHash=2cbd3681e707bf1d7049
bf520c120e95
5
http://support.openevse.com/support/home
5
Figure 5: Signalling circuit schematic for the J1772 standard.6
2.2 DC Rapid Charging
Level 3 is the highest power level for EV charging systems. DC charging, fast charging or rapid
charging are other common names used to refer to level 3 EVSE. Due to their large power
requirements and significant capital cost, level 3 systems are found only at dedicated charging
facilities [8]. The two major competing standards for level 3 charging are the SAE combined
charging system (CCS) and the Japanese CHAdeMO standard. The third standard is Tesla
Motors’ own Supercharger, which is only compatible with their vehicles. The Tesla
Supercharger (Figure 7) is currently the world’s fastest EV charger with 120kW installations
found around the world [9]. Charging of Tesla vehicles using CHAdeMO infrastructure is also
possible with the addition of an adapter produced by Tesla Motors. Unlike levels 1 and 2 EVSE,
DC electricity is supplied to the EV, bypassing the on board charger. The charger is actually
located off board and is the charging station. In the simplest terms, a level 3 EVSE is a
controllable DC power supply. As with levels 1 and 2 systems, the BMS monitors the battery
to ensure it stays within the safe operating parameter.
Figure 7: A Tesla Motors Supercharger.8
Figure 6: An example of a DC charger.7
6
Retrieved from: https://commons.wikimedia.org/w/index.php?curid=19090771
Retrieved from: https://smartenergyacademy.psu.edu/gridstar/rapid-dc-electric-vehicle-charging
8
Retrieved from: https://chargedevs.com/newswire/teslas-liquid-cooled-supercharger-cable-could-enable-fastercharge-times/
7
6
2.2.1 Combined Charging System (CCS)
CCS, also known colloquially as the combo standard, is an addition to the J1772 standard used
for levels 1 and 2 AC charging. The combo plug uses the existing J1772 connector and adds
two DC power pins to its base. This forms a connector known as a type 1 CCS connector. There
is also a type 2 CCS connector, which is the addition of two DC power pins to the Mennekes
connector used in Europe for AC charging. Figure 8 shows both types of connector and plug.
The communications protocol used for CSS is the HomePlug standard for power line
communications (PLC) [10]. Although HomePlug or PLC is not common for automotive
communications, it is often used in smart grid applications [11]. High power EV chargers will
become a significant load on electrical grids and their compatibility with smart gird protocols
is advantageous. CCS infrastructure is commonly 50kW, however, the standard is likely to
increase in the future [10]. Numerous manufacturers produce charging systems that comply
with the SAE CCS standard.
Figure 8: Combined changing standard connectors and plugs. European version on the left (Type 2) and
American version on the right (Type 1).9
2.2.2 CHAdeMO Protocol
The CHAdeMO association’s name is a contraction of the French term ‘charge de move’, or
“let’s charge and move”, and is short for the Japanese term “let’s have some tea”, indicating
that CHAdeMO intends to provide rapid charging infrastructure so EV owners can recharge
their vehicle in as little time as it takes to have a cup of tea. In general rapid chargers aim to
charge the batteries to 80% capacity as charging times from 80% - 100% increase significantly
due to a decrease in the current the batteries can take. A safety first design has been
CHAdeMO’s strength; with manufacturers required to have their chargers approved and tested
by CHAdeMO before they are allowed to be marketed as official chargers. The CHAdeMO
protocol uses a dedicated connector designed only for DC rapid charging. This enables EV
manufacturers extra flexibility in positioning charge ports on their vehicles. The CHAdeMO
protocol also has the capability of allowing bidirectional power flow or V2G. In some
situations, the term vehicle-to-home (V2H) or vehicle-to-business (V2B) is preferred. This
9
Retrieved from: http://articles.sae.org/11484/
7
feature spawned out of a need for emergency power supplies after the March 2011 earthquake
and subsequent Tsunami in Japan. Currently, very few products on the market utilise these
features. Unsurprisingly, the CHAdeMO protocol is favoured among Japanese manufacturers,
particularly Nissan and Mitsubishi who were part of the initial formation of the association.
This information was sourced from the CHAdeMO Association’s webpage [12].
For a more detail and technical description of the CHAdeMO protocol, please refer to the
appendix.
3
Summer Work
eMotorWerks is a producer and retailer of EVSE based in the United States of America. They
produce a range of products including level 2 EVSE, DC chargers and CHAdeMO controllers.
Certain products within their range also come either as an assembled production unit or as a
kitset for the ‘DIY’ user. On behalf of Northpower, the University of Canterbury purchased the
following from eMotorWerks: an assembled 12kW smart charger, a kitset 12kW smart charger,
a CHAdeMO controller, and a charging cable with CHAdeMO compatible 3D printed
connector. Purchasing of the assembled charger was to assist in the construction of the kit
charger. The open source design of the smart charger was a key reason for choosing
eMotorWerks.
Figure 9: The assembled 12 kW DC charger.
Figure 10: The CHAdeMO Controller.
Figure 11: The 3D printed CHAdeMO connector from eMotorWerks.
8
3.1 Design and Construction
The 12kW smart charger is of a cascaded boost-buck topology. The charger is a standalone
unit that can charge batteries with a range of parameters including voltage and battery capacity.
In the simplest terms, the charger is a controllable DC power supply with both voltage and
current mode control available. It also has functionality to communicate with a BMS to provide
smarter charging protocols for battery packs with larger cell numbers. Furthermore, combining
the smart charger with an eMotorWerks’ CHAdeMO controller will produce a rapid DC EV
charger that uses their version of the CHAdeMO protocol.
Both the first, boost stage and the second, buck stage use insulated-gate bipolar transistors
(IGBTs) as the switching devices. Control for each IGBT is independent from one another,
with a dedicated power factor correction (PFC) chip controlling the first stage and an Arduino
microcontroller controlling the second stage. The PFC control chip uses a fixed PWM
frequency of 22 kHz and maintains a power factor of better than 0.9 at the input. The charger
design allows the user to configure the hardware to be compatible with a range of supply
voltages, and output voltages and currents. The chargers were configured to work with a 3phase 400V (phase-to-phase) input voltage. The DC bus voltage between the stages is also
configurable and was set to 647 Vdc. Selection of this voltage was as per eMotorWerks
recommendation to ensure compatibility with the CHAdeMO controller and New Zealand’s
electrical supply. The Arduino controlled buck stage uses the DC bus voltage to generate the
desired DC output voltage. The charger has the ability to provide either a constant current or a
constant voltage output.
The charger arrived with three printed circuit boards (PCB), two of which required complete
assembly (power and control), and one required configuration and bug fixes (driver). Table 2
contains further information about what each board does and its key components. Although
assembling the boards should have been a straightforward process, poor documentation
considerably slowed it down. In particular, the incomplete and out of date build manual coupled
with out of date schematics and bill of material (BOM) information caused delays while
clarifications were sought from eMotorWerks.
Table 2: Description of each PCB for the charger.
Board
Power
Driver
Control board
Description
This board contains all the power electronics to implement the
boost and buck convertors. Key components include the
electrolytic bulk capacitors, filtering capacitors, IGBTs, hall effect
current sensor, and filtering capacitors.
This board handles producing the signals required to drive the gates
on the IGBT. It also contains the PFC chip used to generate the duty
cycle to control the boost stage.
This board contains the Arduino microcontroller used for both the
user interface control and for controlling the output voltage. Key
components include the microcontroller, display, buttons, and
signal conditioning circuitry.
9
Apart from the three circuit boards, the charger also has the following components: the heat
sink; thermistor; two inductors; a three-phase rectifier; three cooling fans; 12Vdc power
supply; and the metal enclosure. The heat sink is a 10mm thick aluminium plate with 60mm
long fins to keep the IGBTs and three-phase rectifier within their operating temperatures. Bolts
mount the IGBTs and rectifier to the heat sink and a thin layer of thermal paste between the
component and heat sink enhances the thermal conduction between the surfaces. Silicone glued
the thermistor onto the heat sink so the Arduino could monitor the temperature and ensure the
IGBTs and rectifier stayed within operating temperatures; the system can de-rate the power
output in situations where the heat sink temperature increases above a certain threshold. The
inductors used as part of the boost and buck stages of the charger appear to be of a custom
design as they had few manufacturer markings and did not appear to have a datasheet. Bolts
mounted the inductors to the metal enclosure and jumper wires connected them to the power
board. The rectifier is a standard four-diode bridge and worked with a range of inputs including
single phase AC, three phase AC, and DC. Three standard 12Vdc computer fans provid
additional airflow to cool the heat sink and other components, such as the electrolytic
capacitors. The metal enclosure is not a required part, but it certainly made the assembly easier
as it provided mounting points for the fans, and the rest of the components. The control board,
driver board and cooling fans use the 12Vdc power adapter supplied by eMotorWerks. Figure
12 shows the completed charger.
Figure 12: The assembled charger.
Given the dangerous voltages present with the chargers, it was important to ensure user safety.
Unfortunately, the chargers do not use an isolated design. Nor do they have adequate earthing
to comply with the New Zealand wiring regulations (AS/NZS 3000:2007). As such, when
constructing the charger, all exposed metal components (the enclosure, component mounting
bolts, and fan grills) were connected together and connected to the AC supply earth. This
included removing paint from the enclosure to ensure an adequate electrical bond to the
metallic case. A bolt was used as the main earth point as per the New Zealand wiring
regulations.
10
4
Results
The major aims of the project were to gain an understanding of CHAdeMO EV chargers and
associated technologies, and to build and test an open source CHAdeMO EV charger. The
author now has a significant understanding the CHAdeMO protocol, other EV charging
protocols, and the electrical design of various chargers, fulfilling the first aim of the project.
Building and testing of the open source CHAdeMO charger was mostly successful. Assembly
of the kitset charger along with the testing procedures outlined by the manufacturer were
completed. Unfortunately, without access to a compatible EV, with willing owner, such as a
Nissan Leaf, complete testing of the CHAdeMO charger was not possible.
As this project was for a fixed duration (10 weeks), any delays encountered ultimately reduced
the progress towards the end goal. Initially, shipping issues caused the first delays due to the
packages arriving later than expected. As previously mentioned the lack of up-to-date
documentation caused significant delays during the construction phase. Requested support
from eMotorWerks was often a waiting game due to time zone differences and poor support
processes. Other issues encountered included poor manufacturing of both the assembled
charger and other components in the DIY kit. For example, bug fixes on the assembled charger
were not completed. This was contradictory considering the chargers reportedly come tested
from the manufacturer and are ready for use. Further examples of substandard manufacturing
include poor soldering with dry joints and a surface mount capacitor shorted out due to a large
solder blob.
Although the project was frustrating at times, the experience gained was immense. It was a
fantastic opportunity to apply knowledge and skills acquired during the Electrical and
Electronic Engineering Degree. In particular, the author’s understanding of common power
electronic topologies was enhanced and their surface mount soldering techniques also
improved. The project also showed the importance of having correct documentation that is up
to date, correct and easy to understand. The project also allowed the author to gain a significant
understanding of EV charging technologies with a particular emphasis on rapid chargers using
the CHAdeMO protocol.
5
Discussion and Conclusion
Testing of the charger with compatible EVs is the next important step in the project. This
involves taking the equipment up to Northpower and using their EVs as a test platform. The
initial testing will be to ensure the charger can successfully charge an EV using the CHAdeMO
protocol. Once this has been completed, several more specific tests will be conducted. Ideally,
data of the following phenomenon would be useful: charge time; charge currents and voltages
over time (charge profile); AC and DC side power quality; power factor; and CAN bus
communications. This data could be used to gain further understanding of EV chargers and
their impacts on the grid. Furthermore, this information can be used to continue progress on
achieving bidirectional power flow for V2G applications. This is a major goal of the University
of Canterbury and the EPECentre as it creates the opportunity to use EVs as emergency power
supplies.
11
As shown, the field of EV charging technology is currently overwhelmed with numerous
technologies, standards and connectors. It is not as simple as plugging an EV into a universal
charger. It is important for key stakeholders such as engineers to understand this field so they
can determine the correct infrastructure to be installed into New Zealand. Unfortunately, it is
likely commercial charging stations will have to support multiple connectors and protocols for
some time. The battle between standards, particularity in the rapid DC charging area, is set to
continue while various manufacturers support multiple standards. People have compared this
to the videotape battle of VHS vs Betamax.
6
Acknowledgement
The authors acknowledge the funding provided by the Ministry of Business Innovation and
Employment, Transpower, the EEA and the University of Canterbury for the GREEN Grid
project that has enabled this research to be carried out. They also acknowledge and thank
Northpower for the purchase of the materials that enabled this project to be carried out, and
thank Russell Watson for his assistance. They also acknowledge Edsel Villa and Ken Smart
from the University of Canterbury Power Electronics and Machines laboratories for their
assistance.
12
7
Appendix – The CHAdeMO Protocol
On the most basic level, a CHAdeMO charger is simply a controllable DC power source. The
EV being charged requests a current of a certain magnitude or a specific voltage and the charger
supplies this. A typical CHAdeMO charger is therefore likely to have similar major
components. Those components are a rectifier, an isolation transformer, filtering components
(AC and DC side), power factor correction (PFC) components, DC-DC converter, controllers,
and ground fault interrupters [13]. Figure 13 provides an example block diagram [14].
Figure 13: Block diagram of a typical CHAdeMO compatible charger.
The following section has been developed using information from the CHAdeMO
Association’s website [12], and a paper [15] and presentation [14] by Anegawa.
The rectifier converts AC current to DC. Separation of the AC and DC ground with the use of
an isolation transformer significantly improves the safety of the charger by preventing the
injection of high voltage from the AC side into the battery system. The isolation stage is likely
to be at a higher frequency than mains (50Hz or 60Hz) to reduce the cost and size of the
transformer. AC side filtering helps to reduce harmonic distortion ensuring the charger
complies with local regulations for power quality. The DC side filtering suppresses any AC
ripple present within DC current supplied to the EV batteries, helping to reduce battery
degradation. Since these chargers require large currents from the utility it is important to
minimise reactive power and therefore a PFC stage is used. DC-DC conversion generally steps
down the voltage from rectified supply to the level requested by the EV. Numerous topologies
for this converter are available for manufacturers, each with their own benefits and drawbacks.
The use of topologies such as the fly-back converter can also be advantageous as the converter
itself provides galvanic isolation. This can reduce costs by removing the needs for a separate
isolation transformer. A control system is required to regulate the DC voltage and current in
order to charge the batteries safely and efficiently. Ground fault interrupters monitor the
grounds (AC and DC side) for flowing ground current. In the event of detected ground currents,
the charger is to prevent electric shock to the user and/or equipment damage.
As previously mentioned, the CHAdeMO association has adopted a safety first approach. The
connector design and the CHAdeMO communication protocols are evidence of this. Figure 14
shows the connector layout indicating the DC power pins, five analogue pins, and two
controller area network (CAN) bus pins. The analogue pins provide signals used to switch
transistors as part of the analogue communications between the EV and charger. The two CAN
bus pins provide the digital communications between the CV and charger. Figure 15 shows a
flowchart explaining how the CHAdeMO protocol works and how the analogue signals are
used [13].
13
Figure 14: Description of the CHAdeMO connector pinout and schematic.
Figure 15: Flow diagram of the CHAdeMO chagrining protocol.
14
Once the user presses the ‘start charge’ button, the charger supplies 12V through ‘d1’ to the
EV and excites the photocoupler at ‘f’. The EV detects this and transmits charging parameters
(voltage and current limits, and battery capacity) via the CAN bus. The charger checks whether
it is compatible and transmits its maximum voltage and current to the EV though the CAN bus.
Once the EV is satisfied the charger is compatible, it conducts the transistor at ‘k’; this in turn
tells the charger it has permission to enable charging. The charger then locks the connector and
performs insulation and ground tests. This ensures the charger’s connector and cable are in
working order, allowing charging to begin. The charger closes relay ‘d2’, which conducts the
photocoupler at ‘g’ indicating to the EV the preparation procedures are complete and charging
is ready to begin. Since both ‘d1’ and ‘d2’ are now closed, the EV can close its main battery
contactor. This allows direct connection between the charger and EV battery pack for charging.
The EV transmits the required current every 0.1 seconds through the CAN bus and charger
supply this through constant current control. The EV constantly monitors the battery pack
parameters (voltage, current, temperature etc.) and can stop the current four ways should a
problem arise.
1)
2)
3)
4)
Request a zero current through the CAN bus.
Send an error message through the CAN bus.
Turn of the transistor at ‘k’, which removes the charging, enabled signal.
Opening of the EV battery contactor.
The charger is also monitoring its own voltage, current, and temperature for potential problems.
Should a problem be detected, the charger sends the EV and error signal and stops the charging
process. Stopping the charging process from the charger side and be done multiple ways
depending on the charger topology. Examples include [15]:
1) Blocking of the gate drive signal on the switching converter.
2) Open the output contactor.
3) Open a circuit breaker on the input.
Once the charging has been completed the EV transmits a zero current request over the CAN
bus and the charger stops outputting. Once the EV confirms zero current is flowing, the EV
opens the battery contactor. The EV also sends the ‘disable charging’ signal by switching
transistor ‘k’ off. Once the charger has detected zero output current it opens relays ‘d1’ and
‘d2’. The connector is unlocked and the charger procedure is complete.
Although the CAN bus could communicate all the data required for the charger, CHAdeMO
prefers to use a combination of analogue and digital communication. The CHAdeMO
association states this design improves the safety of the charger in three key ways [15]:
1) It prevents the erroneous start of charging due to malfunctions in the digital control
system.
2) It can be confirmed that both control system in the vehicle and the charger are operating
correctly at each step of the operation.
15
3) When the analogue signal is lost, the charging operation will be shut down
immediately. As the result, shutdowns can be achieved faster than transmitting a digital
signal. An important feature of this design is the fail-safe function.
Although the power for the EV battery contactor comes from the charger via ‘d1’ and ‘d2’, the
EV still controls when the contactor is closed. This duel method improves safety by ensuring
that without the connector in place, the EV battery contactor cannot close. This prevents the
possibility of the EV battery bus voltage being present at the charge port terminals when no
connector is present. Before the opening the contactor, the current must first have decreased
significantly to reduce the possibility of the contactor welding shut.
16
8
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
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