At the just-concluded third session of the 13th National People’s Congress, Premier Li Keqiang of the State Council proposed in the government work report to focus on supporting the “two new and one heavy” construction that not only promotes consumption and benefits the people’s livelihood, but also adjusts the structure and increases stamina, charging piles and 5G applications, etc. These key infrastructure construction projects are regarded as key industrial layouts to strengthen the construction of new infrastructure, develop a new generation of information networks, stimulate new consumer demand, and facilitate industrial upgrading. The government work report sounded the rallying call for the rapid and high-quality development of the charging pile industry, and added strong momentum to achieving the planning goal of “car piles follow, intelligent and efficient” charging infrastructure system.
According to the statistics of the China Charging Alliance, as of the end of 2019, the total number of charging piles in the country was 1.219 million, and the vehicle-to-pillar ratio was only 3.1:1. The charging infrastructure is still the main short board of the new energy vehicle industry chain. “In the new infrastructure plan at the beginning of the year and the latest government work report of the two sessions, the construction of charging piles is particularly regarded as one of the key elements to help industrial upgrading. With the active industrial deployment of the government and society, the completion of charging pile infrastructure is expected to be completely complete. Addressing the ‘range anxiety’ that severely constrains the electric vehicle market,” said Songgang Zhang, Marketing Manager of Analog Devices’ Industrial and Energy Division, at a recent event. As a company that provides the most extensive solutions for electric vehicle battery system management, ADI also provides industry-leading solutions for major functional modules such as charging pile power metering, DC conversion modules, and charging controllers.
Songgang Zhang, Marketing Manager, Industrial and Energy Division, Analog Devices
New infrastructure accelerates the popularization of electric vehicles, and high-power charging piles relieve key constraints
The “2019 Beijing New Energy Vehicle Charging Behavior Report” shows that the average charging capacity of a single user is 22.15kWh, the charging time of a single charging using a public fast charging pile is 1.32 hours, and the charging time of a public slow charging pile is 5.09 hours (excluding queuing time). It is worth noting that according to the statistics of the qualification certificate, the electric charge of newly added pure electric vehicles in my country has increased from 22.2kWh in January 2015 to 48.3kWh in January 2020, and 22.15kWh can only supplement 50% of pure electric passenger vehicles. -80% of the electricity, the construction of high-power DC charging piles is imperative. “If a pure electric vehicle wants to unlock the ‘quick blood recovery’ skill like a fuel vehicle, it must use a higher-power charging pile. However, the problems brought about by the increase in power are the increase in the size of the charging pile and thermal management. It is necessary to take into account the charging. Pile size, efficiency and power, and improving the switching frequency of power devices are very critical.” Zhang Songgang pointed out.
The advancement of semiconductor technology has allowed the switching frequency of power MOSFET devices to be rapidly and effectively increased. IGBT has increased from about 20k in the past to 40k to 50k now, while gallium nitride (GaN) and silicon carbide (SIC) MOSFET devices can achieve higher switching frequencies . “The drive method is the key to achieving the switching frequency that these switching devices can support, and the switching frequency determines the optimal balance between system design cost, size and efficiency. Higher switching frequencies are increasingly demanding gate drivers. , the transmission delay, dead time, common mode transient immunity (CMTI) and other indicators of the gate driver used play a key role in improving the power and efficiency of the charging pile.” Zhang Songgang said.
Unlock high-power DC chargerElectrical, isolated gate drivers are key
To operate a MOSFET/IGBT, a voltage is usually applied to the gate, and a dedicated driver is used to apply the voltage and drive current to the gate of the power device. Zhang Songgang pointed out: “The isolation performance, common-mode transient immunity, total propagation delay and other indicators of the isolated gate driver will determine the overall power, efficiency and system size of the DC module, and the correct selection of such solutions is critical.” Compared with traditional optical isolation based gate drivers, the iCoupler isolated gate drivers from ADI offer good gate drive characteristics and isolation performance.
According to Zhang Songgang’s analysis, the traditional optical coupling isolation method has a long transmission delay (150-200 nanoseconds), while the iCoupler isolated gate driver has a transmission delay of about 50-60 nanoseconds, which greatly reduces the transmission delay. , and the transmission delay consistency is better, and lower transmission delay and delay consistency play an important role in improving the switching frequency and efficiency. In addition, the dead time of the isolated gate driver is also one of the key characteristics, and the lower dead time of the iCoupler isolated gate driver will effectively reduce losses. For large-scale deployment of charging piles, even a few tenths of a percent efficiency improvement has great economic and social benefits.
Songgang Zhang took ADI’s latest ADuM4136 as an example to analyze the characteristics of the iCoupler isolated gate driver: it can achieve a common mode transient immunity (CMTI) of 150kV/µs, drive SiC MOSFETs at a switching frequency of hundreds of kHz; plus desaturation With fast fault management features such as protection, designers can properly drive single or parallel SiC MOSFETs up to 1200V. “The inherent advantages of iCoupler’s magnetic isolation make these features significantly better than opto-isolated gate drivers, which can ensure that the charger can achieve ultra-high power density in the power converter without sacrificing efficiency.” Zhang Songgang pointed out.
In addition, good isolation performance is also critical in terms of functional safety and user life and property safety. The “2019 New Energy Vehicle Consumption Market Research Report” disclosed that 20.65% of public charging piles failed. In addition, CCTV once reported that among the 10 batches of charging pile products of 9 companies, 7 batches did not meet the requirements of the national standard. Therefore, the isolation function of the isolated gate driver in the functional circuit of the charger is very critical, to realize the electrical separation between the functional circuits in the charging module, so that there is no direct conduction path between them, thereby improving the safety performance.
Destruction tests have proven that the iCoupler isolated gate driver does not affect isolation withstand performance in the worst case.
Dr. Bernhard Strzalkowski, ADI’s expert in power management/digital power/iCoupler applications, has written that in highly reliable, high-performance applications, isolated gate drivers need to ensure that the isolation barrier is intact under all conditions, due to the extremely high power density. Therefore, when making the driver chip, it is necessary to ensure that the electrical isolation can be maintained even if the chip itself fails. To this end, he conducted a special destructive test test: that is, in the worst case, when the high-power MOSFET/IGBT fails, the capacitor bank of several thousand μF of the inverter will discharge rapidly, and the released current will cause the MOSFET/IGBT Damage, package explosion, plasma discharge to the environment, and a portion of the current entering the gate drive circuit can cause electrical overload. The test results proved that in the worst case, when high power is applied to the output chip, small area damage occurs near the output pins of the driver, and this test does not affect the withstand performance of the isolation.
The trend of high-power popularization under the new infrastructure outlet, how to “enable” the charging pile?
Not long ago, the State Grid Marketing Department issued the 2020 smart electricity professional work points, which clarified the State Grid’s development plan for charging facilities in 2020, and mentioned a number of energy storage-related tasks, including closely tracking distributed photovoltaics, storage Energy policy, technology, industrial development, research on the impact on the power grid and load balancing of electric vehicles, customer-side energy storage, distributed power generation, etc. Not long ago, the Xinjiang Autonomous Region Development and Reform Commission issued a similar statement in the “Notice on Accelerating the Construction of Charging Infrastructure Complexes”, encouraging investment units to invest in charging pile facilities + distributed energy + energy storage projects + commercial complexes.
In fact, the high-power and widespread deployment of charging piles is an inevitable trend, but it also poses challenges to related infrastructure construction – how to meet the peak load requirements of charging stations cost-effectively? For example, if a charging station with 20 charging piles needs to meet the all-weather charging state, the local charging peak power that the grid needs to provide exceeds 1 MW. Such high peak load power could cause the grid to collapse at multiple points, or require huge investments to improve transmission lines and centralized power plants to substantially increase baseload capacity. “Increasing the energy storage system can use this reserve energy to increase the charging load capacity of electric vehicles. The energy storage system can keep the power grid stable by adjusting the power peak, or provide charging power in the event of a power outage.” Zhang Songgang gave such a solution. ideas.
Schematic diagram of power conversion system configuration of future electric vehicle charging station
In addition to alleviating the pressure on the power grid from peak charging, the energy storage system can also achieve environmental protection and consumption reduction goals with the help of supporting renewable energy. Big “just need”. This is also in line with the trend of global vehicle-to-network interaction (V2G). For example, Tesla has prepared two-way charging technology for Model 3 and Model Y. State Grid is also gradually promoting V2G projects to explore market-oriented operations with reasonable costs and high business efficiency. new mode. The North China branch of State Grid Corporation of China officially incorporated the vehicle-to-network interaction (V2G) charging pile resources into the North China Electric Power Peak Shaving Auxiliary Service Market for the first time not long ago and officially settled. “Like V2G, the layout of the energy storage system + the power supply side of the power grid should be the future development trend, and this type of application is still in the market exploration stage.” Zhang Songgang said.
In order to meet the challenges faced by the future DC fast charging infrastructure, an optimized high-power DC charging system and a power supply side with large load capacity are the keys. As a high-performance analog technology provider, ADI provides highly competitive high-quality solutions for reliable metering, monitoring and control in power applications. Its leading battery management system (BMS) solutions, DCDC power management, high Reliable isolation technology, system-level mixed-signal conversion, and entire signal and power chain products optimized for EV chargers are expected to be key boosters in this new infrastructure boom. “There are many more areas of these systems that need to be focused on, including everything from current metering to fault protection devices, from gas detection to functional safety that are extremely important, and Analog Devices is actively developing all of these subsystems to ensure that our customers can Efficient and robust solutions are obtained in all links of energy conversion, measurement, connection, protection and drive.” Zhang Songgang said.