Separated DC fast charger in China
In the "two new and one heavy" construction, Separated DC fast charger and 5G applications and other key infrastructure construction projects are used as a key industry layout to strengthen new infrastructure construction, develop a new generation of information networks, stimulate new consumer demand, and promote industrial upgrading. The government work report has sounded the rallying call for the rapid and high-quality development of the charging pile industry, and added strong momentum to achieve the planning goal of a charging infrastructure system of "car piles follow by, smart and efficient".
Charging infrastructure is still the main shortcoming of the new energy automobile industry chain. In the new infrastructure plan at the beginning of the year and the new government work report of the two sessions, the construction of Separated DC fast charger was specifically regarded as one of the key contents to promote industrial upgrading. With the active industrial deployment of the government and society, the complete infrastructure of Separated DC fast charger is expected to completely solve the ‘mileage anxiety’ that has severely restricted the electric vehicle market.
As an enterprise that provides a wide range of solutions for the management of electric vehicle battery systems, ADI also provides industry-leading solutions for major functional modules such as charging pile power metering, DC conversion modules, and charging controllers.
New infrastructure accelerates the popularization of electric vehicles, and high-power Separated DC fast charger relieve key constraints
The "2019 Beijing New Energy Vehicle Charging Behavior Report" shows that the average user charging capacity per transaction is 22.15kWh, the single charging time using public fast Separated DC fast charger is 1.32 hours, and the public slow charging pile charging time is 5.09 hours (not including queue time). It is worth noting that according to the statistics of certification data, my country’s newly-added pure electric vehicles have increased the amount of electricity per vehicle from 22.2kWh in January 2015 to 48.3kWh in January 2020. 22.15kWh can only supplement 50% of pure electric passenger vehicles. -80% of the electricity, the construction of high-power DC Separated DC fast charger is imperative. If pure electric vehicles want to unlock the ‘quick blood return’ skills like fuel vehicles, they must use more powerful Separated DC fast charger . However, the problems caused by the increase in power are the increase in the size of the charging pile, thermal management and other problems. It is critical to take into account the size, efficiency and power of the charging pile, and to increase the switching frequency of the power device.
The advancement of semiconductor technology has rapidly and effectively increased the switching frequency of power MOSFET devices. IGBTs have 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 driving method is the key to achieving the switching frequency that these switching devices can support, and the switching frequency determines the balance between system design cost, size, and efficiency. Higher switching frequencies have higher and higher requirements for gate drivers. The transmission delay, dead time, and common mode transient immunity (CMTI) of the gate drivers used play a key role in improving the power and efficiency of Separated DC fast charger . Impact.
To unlock high-power DC charging, isolated gate driver is the key
In order to operate a MOSFET/IGBT, a voltage is usually applied to the gate, and a dedicated driver is used to apply the voltage to the gate of the power device and provide driving current. The isolation performance, common-mode transient immunity, and total propagation delay of isolated gate drivers will determine the overall power, efficiency, and system size of the DC module. The correct choice of such solutions is critical. Compared with traditional optically isolated gate drivers, ADI's iCoupler isolated gate drivers provide good gate drive characteristics and isolation performance.
The traditional optical coupling isolation method has a long transmission delay time (150-200 nanoseconds), while the transmission delay of the iCoupler isolated gate driver is about 50-60 nanoseconds, which greatly reduces the transmission delay and the transmission delay. Time consistency is better, and lower transmission delay and delay consistency play an important role in improving switching frequency and efficiency. In addition, the dead time of the isolated gate driver is also one of the key features. The lower dead time of the iCoupler isolated gate driver will effectively reduce the loss. For a large-scale deployment of Separated DC fast charger , even a fraction of a percentage point increase in efficiency has great economic and social benefits.
Take ADI’s new 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 and drive the SiC MOSFET at a switching frequency of hundreds of kHz; plus fast desaturation protection and other fast With fault management function, designers can correctly drive single or parallel SiC MOSFETs up to 1200V. The inherent advantages of iCoupler magnetic isolation make these characteristics significantly better than optically isolated gate drivers, which can ensure that the charger can achieve ultra-high power density in the power converter without sacrificing efficiency.
In addition, in terms of functional safety and user life and property safety, good isolation performance is also very critical. The "2019 New Energy Vehicle Consumer Market Research Report" disclosed that 20.65% of public Separated DC fast charger failed. In addition, CCTV once reported that among the 10 batches of charging pile products from 9 companies, 7 batches did not meet the requirements of the national standard. Risk monitoring found that the four items of the samples did not meet the requirements of the national standard, which could cause fire or electric shock. 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 safety performance.
The destruction test proved that in a bad situation, the iCoupler isolated gate driver will not affect the isolation tolerance performance.
Dr. Bernhard Strzalkowski, an ADI expert in power management/digital power/iCoupler applications, once wrote that in highly reliable and 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, it is necessary to ensure that electrical isolation can be maintained even if the chip itself fails when making the driver chip. To this end, he conducted a special destructive test: that is, in a bad situation, when the high-power MOSFET/IGBT fails, the inverter capacitor bank of several thousand μF will quickly discharge, and the released current will cause the MOSFET/IGBT to be damaged. , The package explodes, the plasma is discharged into the environment, and part of the current entering the gate drive circuit will cause electrical overload. The test result proves that under bad conditions, when high power is applied to the output chip, a small range of damage will occur near the output pin of the driver. This test will not affect the isolation tolerance performance.
How to "empower" Separated DC fast charger under the trend of high-power popularization under the new infrastructure?
Not long ago, the State Grid’s marketing department issued the 2020 Smart Power Professional Work Points, which clarified State Grid’s development plan for charging facilities in 2020, and mentioned a number of tasks related to energy storage, including closely tracking distributed photovoltaics and storage. Energy policy, technology, industrial development, research on the impact on the power grid and load balancing involving electric vehicles, customer-side energy storage, and distributed power generation, etc. The Xinjiang Autonomous Region Development and Reform Commission recently 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 Separated DC fast charger 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, a charging station with twenty Separated DC fast charger must meet the all-weather charging state, and the power grid needs to provide local charging peak power exceeding 1MW. Such high peak load power may cause the grid to collapse at multiple points, or require huge investment in improving transmission lines and centralized power plants to substantially increase the base load capacity. Adding an energy storage system can use this stored energy to increase the charging load capacity of electric vehicles. The energy storage system can maintain the stability of the grid by adjusting the power peak value, or provide charging power in the event of a power failure.