From electric vehicle battery life to safety, SiC power components are expected to achieve “double solutions”

The power battery is the core energy source of the new energy vehicle. In order to ensure the efficient, reliable and safe operation of the battery, it is necessary to conduct real-time monitoring, fault diagnosis, SOC estimation, short-circuit protection, etc. of the power battery through the battery management system (BMS), and exchange information with the vehicle integrated controller through the CAN bus. BMS is known as the “brain” of the electric vehicle power battery system in the industry. Together with the power battery and the vehicle control system, it constitutes the three core technologies of electric vehicles.

The “China BMS Battery Management System Market Research Report (2019 Edition)” shows that the three core functions of BMS are cell monitoring, state of charge (SOC) estimation and single cell balancing. The BMS monitors the working temperature and power of the single lithium battery cell, and automatically takes measures to balance the charge and discharge current of the single lithium battery cell and prevent the occurrence of overtemperature. It is one of the key technologies for the development of electric vehicles to enable the electric vehicle power battery to obtain the best performance and the longest service life under various working conditions.

However, BMS also faces problems such as integration optimization, miniaturization, and improvement of current accuracy. In the special topic “BMS’s New Mission” planned by Feiwang, we invited Mr. Lin Qifeng, Assistant Manager of Technology Center of Rohm semiconductor (Shenzhen) Co., Ltd. to discuss .

Lin Qifeng, Assistant Manager of Vehicle Vehicle Group 2, South China FAE Department, Technology Center, ROHM Semiconductor (Shenzhen) Co., Ltd.

How to solve the problem of battery life and charging of electric vehicles?

Compared with fuel vehicles, short cruising range and long charging time have always been the pain points of electric vehicles. In what ways can BMS improve the cruising range and charging time of electric vehicles? Lin Qifeng told, “The BMS is responsible for monitoring the status of the battery in real time. One of the ways to improve the cruising range is to effectively use the limited battery capacity by improving the monitoring accuracy of the BMS. A coulomb counter IC that monitors the amount of incoming and outgoing charges. Using this coulomb counter IC, the current integration accuracy can be improved from the conventional ±5% to ±1% through high-precision analog current detection and real-time current calculation by hardware. This will greatly help improve the estimation accuracy of battery capacity.”

In addition, in terms of improving the charging time, Lin Qifeng believes that increasing the battery voltage is a trend in recent years. The battery Voltage has been doubled from the original 400V to 800V, which can significantly shorten the charging time. Therefore, the control power components (conventional mosfets and IGBTs, etc.) arranged in the BMS are also required to improve the withstand voltage performance. The SiC power components provided by ROHM not only have a withstand voltage of more than 1000V, but also have little influence ON product characteristics by temperature, which is very helpful to increase the voltage of the battery.

Effectively solve the safety challenges of electric vehicles, the role of SiC power components is emerging

With the increasing popularity of electric vehicles, the safety of electric vehicles has attracted more and more attention from users. Especially in battery monitoring, chip manufacturers and solution manufacturers are trying their best to achieve higher-precision real-time monitoring through technical means. BMS is not only responsible for preventing abnormal voltage, abnormal current, abnormal temperature, etc. of the battery, but, as the last fortress, it also plays an important role in safely isolating applications (loads) such as batteries and motors, in the periphery of batteries such as xEVs, Use a mechanical Relay to turn off the power. The mechanical relay has the problem of failure caused by the wear and tear of the mechanical part. Therefore, it is expected that the popularity of semiconductor relays will be driven by SiC power components in the future. Using semiconductor relays not only avoids wear failures, but also quickly shuts down the power supply in the event of an overcurrent, enabling safer battery use.

According to Lin Qifeng, ROHM has been developing products for BMS, such as power components led by SiC and resistors for current detection, as well as small-signal discrete components, power supply ICs for microcontrollers for drive control, etc. In the future, ROHM will also launch products that support multi-cell series batteries, and continue to provide BMS solutions that are most suitable for various batteries including next-generation batteries.

Of course, the BMS of electric vehicles also has two issues, one is miniaturization, and the other is to improve the accuracy of current detection. ROHM is involved in both aspects. For the improvement of accuracy, the coulomb counter IC developed by ROHM mentioned above is used to count the amount of charge flowing in and out, which can improve the current integration accuracy from the previous ±5% to ±5%. 1%, can achieve higher-precision current detection; for miniaturization problems, for example, with the increase of the number of battery cells in series, the number of resistors used to balance the power of each battery also increases, which urgently needs a solution. . The LTR series of chip resistors developed by ROHM that support high-power long-side electrode structure have better heat dissipation performance and require only about 1/4 of the mounting area compared to previous products.

BMS integration optimization continues, battery life expected to improve

In the future, BMS still needs to be integrated and optimized. Lin Qifeng proposed another solution. He believes that another issue in the effective use of batteries is the shape of the battery pack. For example, EVs need to be able to fit in a limited space and be able to adapt to the battery shape of various vehicle types. As its solution, BMS is going wireless. A wireless BMS can make it easier to change the battery layout.

Battery life has always been an important issue faced by electric vehicles. To prolong battery life, it is very important to accurately monitor the usage environment of the battery. This requires technology that can detect parameters such as voltage, current, and temperature with high accuracy. Another approach is to improve the load efficiency of the battery-connected inverter. For example, the use of SiC power components provided by ROHM in the inverter can generally improve the efficiency by about 8% compared with the use of Si-IGBT. Reducing the weight of the battery by 8% is also able to travel the same distance, so it is expected to improve efficiency by reducing the weight of the vehicle.

Lin Qifeng emphasized, “As a comprehensive semiconductor manufacturer that supplies power components, LSIs, resistors, small-signal discrete components, and many other components, ROHM can provide the best solutions to customers’ problems. ROHM will improve Electronic Component technology will continue to help BMS improve the performance and quality of batteries.”