International Trends in Fast Charging Standards

　　In March 2010, Japan established the "CHAdeMO" Electric Vehicle Fast Charger Association; in May this year, eight major automakers including General Motors and Volkswagen jointly issued a statement that they would jointly promote the "Combo" fast charging system.

　　Although my country's electric vehicles have been in development for many years, the Chinese characteristic of "construction before standards" has made the electric vehicle market and charging construction face embarrassment. Compared with developed countries such as Europe, the United States and Japan, China's role in the international standards stage has not been taken seriously.

　　1. Let’s start with “A cup of tea is enough”

　　"CHAdeMO" is an organization that aims to promote the international standardization of electric vehicle fast chargers. The Japanese word "茶でも" is pronounced "CHAdeMO", which means "a cup of tea is enough" in Chinese, implying that the time required for fast charging of electric vehicles can be achieved with just a cup of tea.

　　1. Power and time settings

　　Increasing the charging output power can shorten the charging time, thus improving the convenience of charging. CHAdeMO's research results show that 10 minutes for an electric vehicle to travel 50-60 km best meets the actual needs of users, and is also the most economical (charger cost) and practical (time consumption).

▲Charger parameter settings

　　Excessive power will lead to increased investment in charging infrastructure; high-power charging equipment has more stringent requirements for safety design. As can be seen from the yellow curve and the second ordinate in the figure, the cost of the charger will increase exponentially if the charging time is shortened and the charging power is increased. After the charging power is greater than 50kW, the impact on shortening the charging time is not obvious. According to actual operation and statistical data analysis, it is most reasonable to set the power consumption of electric vehicles to 7km/kWh. If this is used as a basis to determine that charging for 10 minutes can travel 50-60km as the design goal, the output power of the fast charger is exactly 40-50kW.

　　2. Measures to prevent battery aging

　　The technical focus of fast charging is how to avoid battery aging caused by fast charging. The main reason for the reduction of battery capacity is the influence and control of high temperature and overvoltage. High voltage and high temperature can easily damage the battery plate and cause the capacity to drop rapidly. Therefore, electric vehicles must be equipped with battery management devices to meet the control requirements of voltage, temperature, etc. for lithium-ion batteries during use.

　　Since battery performance will change due to material properties and operating conditions, if the charger is simulated to a standard, the only way to avoid battery aging is to determine the charging current based on the worst operating environment and the worst battery. In this way, the purpose of fast charging cannot be achieved. Even if battery performance is improved in the future, fast charging will still be difficult to achieve. The on-board battery is monitored and managed by the battery management system for temperature, which can automatically control the charging current within the range that meets the battery temperature requirements, so that the problem of overtemperature can be avoided.

　　The fast charging method adopted by CHAdeMO is shown in the figure. The current is controlled by the CAN bus signal of the car. That is, while monitoring the battery status, the current value required for charging is calculated in real time, and a notification is sent to the charger through the communication line; the fast charger receives the current command from the car in time and provides current according to the specified value.

▲CHAdeMO fast charging system

　　The battery management system monitors the battery status and controls the current in real time, fully realizing all the functions required for fast and safe charging, ensuring that charging is not limited by the universality of the battery. Even if battery performance improves in the future, the charging infrastructure will not be eliminated due to battery upgrades.

　　3. Connectors and interfaces

　　As a public facility for fast charging, standardization is needed to achieve universal chargers for electric vehicles. In addition to communication protocols, connectors and interfaces must be included in the scope of standardization. Since safety design must be based on maximum voltage and maximum current, connectors must have sufficient safety factors to deal with potential risks.

CHAdeMO Connector and Interface Circuit

　　In addition to the data control line, the CHAdeMO method also uses the CAN bus as a communication interface. Due to its superior noise resistance, high error detection capability, high communication stability and reliability, it is widely used as a distributed network technology for vehicle controllers. When fast charging uses CAN technology, the gateway is separated from other vehicle devices for safety reasons, allowing ECU and charger control unit to achieve one-to-one communication.

　　4. Fast charging circuit design

　　The power supply system and the battery system are separated by an isolation transformer to prevent the voltage of the power supply system from increasing to the battery system due to a single fault. In addition, not only is an improvement circuit to improve efficiency, but an AC filter to eliminate the influence of high-order harmonics is also installed.

　　In terms of the battery system, in order to prevent adverse effects on lithium-ion batteries, a filter that can eliminate ripple voltage noise is designed at the outlet. In order to detect whether there is leakage in the car during charging, a ground detector is specially installed at the source of the charger circuit. This makes the diameter of the fuse between the charger and the vehicle thinner. In the event of leakage, the safety concerns of thinner fuses can be reduced. In fact, the fuse that achieves protection through current bypass cannot play its due role, but the ground detector can eliminate risks and improve the safety performance of the charger.

▲CHAdeMO fast charging circuit design

　　5. Fast charging process

　　(1) Charging preparation

　　Press the "Start" button of the fast charger to start the charging process. The charger turns off the "d1" protection, and the 12 V voltage on the charger side supplies power to the vehicle through analog pin 2, triggering the "f" photocoupler at the same time. The vehicle recognizes that the charging operation has officially begun, and the battery's maximum voltage, battery capacity and other parameters are communicated to the charger via CAN.

▲CHAdeMO fast charging process

　　After receiving the information, the charger confirms that the vehicle is a vehicle that can be powered by itself, and then sends its own maximum voltage, maximum output current and other data to the vehicle side through CAN. After receiving the signal, the vehicle confirms that it matches itself and transmits the charging instruction to analog pin 4 through the "k" transistor. After receiving the instruction, the charger locks the connector and briefly pressurizes the outlet circuit to test whether there are any abnormalities in the outlet circuit including the connector interface in terms of short circuit and ground wire. Each charging is carried out according to this method to confirm the insulation test to prevent accidents such as short circuit caused by aging of the connector cable. After the insulation test is completed, the information that the charger is fully prepared is conveyed to the vehicle through analog pin 10 by turning off "d2". The vehicle is identified based on the "g" photocoupler and is ready for charging. It is feasible to perform all preparation actions through CAN communication. The above charging preparation procedure only takes a few seconds.

　　(2) Power on

　　The vehicle turns off the EV contactor configured on the inlet side of the battery system. The vehicle monitors the battery system, determines the maximum current that can be charged, and sends the parameter value to the charger via CAN at 0.1s intervals. The charger supplies a current consistent with the parameter value based on steady-state current control. During this period, the vehicle also monitors the on-board battery status and supply current. If an abnormality is detected, charging will be stopped in one of the following 4 ways: ① Send an output current "zero" indication to the charger based on CAN communication; ② Send an output "error" indication to the charger based on CAN communication; ③ Cut off "k" and send a charging prohibition analog signal to the charger; ④ Open the EV contactor to disconnect the input current.

　　The charger also monitors the current, voltage and temperature of each circuit, and sends an "error" signal via CAN to stop the power supply when the limit value is exceeded. In addition, a function is designed to automatically stop the power supply if the charging time exceeds the expected time. Of course, you can also manually press the "stop" button to end the charging.

　　(3) End charging

　　When charging is finished, the vehicle sends a zero current indication signal through CAN communication. After the charging current returns to zero, the EV contactor is opened, the "k" transistor is cut off, and an analog stop signal is sent to the charger. After confirming that the output current is zero, the "d1" and "d2" relay protections are opened. The protection function of the "d2" relay is mainly to provide a 12 volt power supply to the solenoid of the EV contactor.

　　The EV contactor switch is operated by the EV contactor control relay protection switch according to the vehicle's judgment. The solenoid power of the EV contactor is provided by the charger to avoid the EV contactor from being shut down by mistake due to misoperation on the vehicle side. When the connector is not inserted, the risk of the EV contactor being shut down by mistake is reduced because the solenoid is not conductive, which can prevent the battery voltage at the socket from exceeding 300 volts.

　　Even though the ground wire is thin, it is safe because a ground wire detector is set. If the ground wire is broken, the "f", "g", and "j" photocoupler signals will disappear at the same time, immediately causing a chain reaction of charger output stopping and EV contactor opening. This shows that the connector pin layout and the overall safety design of the charging system are closely linked.

　　After charging stops, the voltage of the outlet circuit is confirmed to drop below 20 volts, and the connector gate is opened, thus completing the entire series of charging procedures.

　　2. International Standardization Trends of Fast Charging

　　When promoting and popularizing fast chargers as public infrastructure, a unified interface is required, and infrastructure that can charge different types of vehicles must be provided. It is necessary to unify the physical interface with the connector and the aforementioned communication protocol software interface.

　　Technical standards are a powerful weapon to seize the technological high ground, and have become a battleground for countries around the world, especially industrialized countries. Of course, the battle over standards will never last forever. If all countries adopt their own standards, automobile imports and exports will be embarrassed. Advanced technology, high cost-effectiveness, safety, convenience, speed and system stability are all the goals pursued by standards. In the future, fast chargers will surely achieve unified international standards.

　　1. Japanese JARI Draft

　　In the late 1990s, the Japanese charger standard was planned and formulated by the former Japan Electric Vehicle Association (now the Japan Automobile Research Institute). Today, physical interfaces such as the CHArge de Move connector all use this specification.

　　Regarding the communication protocol, while taking into account the design guidelines of different chargers, Tokyo Electric Power Company, automobile companies, power equipment manufacturers, etc., based on the old specifications, added some content: (1) Data communication of vehicle and charger specification information and vehicle current command values, including the start, charging, and stop of charging. Both parties notify each other of their respective situations and ensure safe charging through control procedures. (2) Correct operation procedures are specified for different types of EVs to be correctly connected to fast chargers. In order to ensure that charging can start and end safely, both the charger and the vehicle must perform various confirmation and verification operations each time charging. If the operation of either party lasts longer than the set time, the control program will not be established or charging may not be possible. (3) In the new specifications, the waiting time and implementation matters of all steps in the start and stop of charging are clearly defined. By clearly defining abnormal situations, safe charging operation can be achieved under all operating conditions.

　　Japan has adopted the CHArge de Move method for all fast chargers and corresponding electric vehicles, which has in fact become the industry standard. It is expected that in the future, it will enter a stage of technical improvement and promotion policies for wider popularization. As a group for popularization activities, the "CHArge de Move Agreement" was established in March 2010. As of May this year, more than 430 automobile and charger manufacturers, including world-renowned automobile manufacturers Toyota and Nissan, have joined as members. At present, a large number of automobile companies and charger manufacturers have adopted the CHA de MO protocol. This fast charger has been installed and put into use in markets such as Europe and the United States. In Japan, 1,154 fast chargers installed according to the CHAdeMO standard are in use.

　　The maximum power of CHAdeMO charger is 62.5kW. The JARI draft has been submitted to SEA and IEC for standard review. Based on this draft, many countries have proposed amendments to connectors and functional expansion. CHAdeMO members are working together, improving technology, and solving difficulties to achieve close cooperation with related companies and groups beyond their respective fields and interests, so that fast charging technology can become an international standard.

　　2. Discussion on SAE in the United States

　　Tesla Motors launched an electric car equipped with a large-capacity battery, and then began to discuss the specifications for fast charging. At the beginning, the majority of SAE members believed that it would be appropriate to set the battery capacity at around 50kWh and the output of fast charging at 200kW. However, some people pointed out that in order to achieve such a large capacity, large cables and connectors would be required, which would be inconvenient for ordinary users, especially the elderly and women, to operate.

　　In addition, during the stage of improving infrastructure, there are problems such as excessive system load and the need to strengthen distribution line equipment. It is generally believed that the 50kW power standard proposed by Japan fully considers the balance between charging time, equipment scale and cost, and has certain scientific rationality.

　　Previously, automobile companies led by GM and Ford proposed a combined connector that integrates the connectors for AC normal charging and DC fast charging. GM and Ford are latecomers in the use of DC fast charging, but in order to use it in plug-in hybrid vehicles in the future, they proposed to control the body opening to a minimum. On the other hand, if the combined connector is too large, it will reduce the convenience of operation; in terms of safety such as the locking mechanism, if it is too complicated, it will also cause problems of poor practicality.

　　3. Discussion on European IEC

　　The group called e-Mobility project, which is centered around Daimler, Renault, and RWE, proposed to install AC three-phase 400V wires on the charger and attach authentication and billing devices. The main reason is that the utilization rate of chargers installed on the roadside is very high, and due to the EU's electricity liberalization order, electricity retail is relatively free. By making the charger a common infrastructure, anyone can use it by adding user authentication and settlement roaming functions. The group also proposed a plan to use PLC as a system communication method, but no consensus was reached on high-speed and low-speed selection and the scope of standardization. The AC charging method is still under discussion through IEC 61851-22. In addition to YAZAKI (SAE J1772), the European schemes of MENNEKES and SCAME have been proposed in IEC. e-Mobility supports the charging scheme MENNEKES with a maximum of 44kW. In response, the group led by Electricité de France proposed the SCAME scheme to prevent sidewall flooding by using a smaller capacity. As a result, the European Commission ordered CEN-CENELEC to formulate standard specifications, which shifted the direction of discussion. DC charging established IEC61851-23 in July 2010, and discussions began with Japan's proposal as the center.

　　Last year, Ford, GM, Volkswagen, Audi, BMW, Daimler and Porsche proposed a DC combo fast joint charging standard system, and now Chrysler has joined them. In the future, all electric vehicles of the above automakers will use the same standard charging interface. The promotion of the combined charging system, which is compatible with four DC and AC charging modes, is intended to compete with Nissan, the leader in pure electric vehicles, at the industry standard level.

　　4. New trends in China

　　At the end of 2010, the National Technical Committee for Automotive Standardization took the lead in drafting three series of recommended national standards, including "Connection Devices for Conductive Charging of Electric Vehicles", which were reviewed and approved in January 2012.

　　Albrecht Pfeiffer, project manager of new energy vehicle charging system of BMW Group, believes that there are 11 obvious differences between China's AC charging standards and international standards, 3 of which have safety risks. China has not yet defined the PWM (pulse width modulation) duty cycle. The description of PWM duty cycle has been deleted in the GB/T20234.2-2011 standard that has been issued. The latest version of the GB/T18487.1 standard should include the PWM duty cycle without the description of PWM. The coexistence of different duty cycles will create safety risks. If there is no PWM indication point for high-level communication, DC charging and existing Combo cannot be combined.

　　Faced with the situation of numerous disorderly small-scale car factories in China and foreign manufacturers starting mass production, the government has been committed to ending the chaos of independent charging standards, but it will take some time for the national electric vehicle charging standards to be unified. Cities such as Shenzhen, Hefei, and Chongqing have each formulated their own "local policies" for electric vehicle charging standards.

　　In fact, most of my country's electric vehicle standards are formulated with reference to relevant foreign standards and international standards. Product technology, level, quality, research and development, innovation and other aspects cannot be compared with those of developed countries with developed automobile industries and multinational parts companies. Therefore, even if the government promulgates national electric vehicle standards, it is difficult to defend China's voice in the International Organization for Standardization in actual operation.