High voltage drives multiple industrial chains

The core adjustment of the three-electric system meets the requirements of the high-voltage platform

Upgrading to an 800V high-voltage platform requires adjustments to the three-electric system to meet the reliability requirements for withstand voltage and insulation brought about by the increase in electrical voltage.

Battery system:

The BMS cost of 800V battery pack is about 1/3 higher than 400V. On the cost side, an 800V battery pack requires twice as many cells in series, thus requiring twice as many battery management system (BMS) voltage sensing channels. According to calculations by Iman Aghabali et al., the total BMS cost of a 400V battery pack is about $602, and that of an 800V battery pack is $818, which means that the cost of an 800V battery pack is about 1/3 higher than that of a 400V battery pack. The voltage increase puts forward higher requirements on the reliability of the battery pack. Analysis of the battery packs showed that a pack with a 4p5s configuration could reliably perform about 1000 cycles at 25C, while a pack with a 2p10s (double the voltage than 4p5s) configuration could only achieve 800 cycles. The voltage increase will reduce the reliability of the battery pack mainly because the life of a single cell is reduced (after the charging power is increased, the charging rate of the battery cell will be increased from 1C to ≥3C, and the high charging rate will cause the loss of active materials, affecting the battery capacity and life). In lower voltage battery packs, more cells are connected in parallel for higher reliability.

The 800V high voltage platform has a smaller wire harness diameter, reducing cost and weight. The cross-sectional area of ​​the DC cables that transfer power between the 800V battery pack and the traction inverter, fast charging ports, and other high-voltage systems can be reduced, reducing cost and weight. For example, the Tesla Model 3 uses 3/0 AWG copper wire between the battery pack and the fast charging port. For an 800V system, halving the cable area to 1 AWG cable would require 0.76kg less copper per meter of cable, thus saving tens of dollars in cost. In summary, 400V systems have lower BMS cost, slightly higher energy density and reliability due to less creepage distances and less electrical clearance requirements around the bus and PCB. The 800V system, on the other hand, has smaller power cables and higher fast charging rates. In addition, switching to 800V battery packs can also improve the efficiency of the powertrain, especially the traction inverter. This increase in efficiency can make the size of the battery pack smaller. The cost savings in this area and in terms of cables can make up for the 800V battery. Package additional BMS cost. In the future, with the large-scale production of components and the mature balance of cost and benefit, more and more electric vehicles will adopt the 800V bus architecture.

2.2.2 Power battery: super fast charging will become a trend

As the core energy source of new energy vehicles, the power battery PACK provides driving power for the vehicle. It is mainly composed of five parts: power battery module, structural system, electrical system, thermal management system and BMS:

1) The power battery module is like the "heart" of the battery pack to store and release energy;

2) The mechanism system can be regarded as the "skeleton" of the battery pack, which is mainly composed of the battery pack's upper cover, tray and various brackets, which play the roles of support, mechanical shock resistance, waterproof and dustproof;

3) The electrical system is mainly composed of high-voltage wiring harness, low-voltage wiring harness and relays, among which the high-voltage wiring harness transmits power to various components, and the low-voltage wiring harness transmits detection signals and control signals;

4) The thermal management system can be divided into four types: air-cooled, water-cooled, liquid-cooled and phase-changing materials. The battery generates a lot of heat during charging and discharging, and the heat is dissipated through the thermal management system, so that the battery can be kept within a reasonable operating temperature. Battery safety and extended life;

5) The BMS mainly consists of two parts, the CMU and the BMU. The CMU (Cell Monitor Unit) is a single monitoring unit, which measures parameters such as the voltage, current and temperature of the battery, and transmits the data to the BMU (Battery Management Unit, battery management unit), if the BMU evaluation data is abnormal, it will issue a low battery request or cut off the charging and discharging path to protect the battery. car controller.

According to the data of Qianzhan Industry Research Institute, from the perspective of cost splitting, 50% of the power cost of new energy vehicles lies in the battery cells, power electronics and PACK each account for about 20%, and BMS and thermal management systems account for 10%. In 2020, the installed capacity of global power battery PACK is 136.3GWh, an increase of 18.3% compared with 2019. The market size of the global power battery PACK industry has grown rapidly from about US$3.98 billion in 2011 to US$38.6 billion in 2017. The market size of PACK will reach USD 186.3 billion, and the CAGR from 2011 to 2023 will be about 37.8%, indicating a huge market space. In 2019, China's power battery PACK market size was 52.248 billion yuan, and the installed capacity increased from 78,500 sets in 2012 to 1,241,900 sets in 2019, with a CAGR of 73.7%. In 2020, the total installed capacity of power batteries in China will be 64GWh, a year-on-year increase of 2.9%. The technical barriers to fast charging of power batteries are high, and the constraints are complex. According to Lithium-ion battery fast charging: A review, the factors affecting the fast charging of lithium-ion batteries come from various levels such as atoms, nanometers, cells, battery packs, and systems, and each level contains many potential constraints. According to Gaogong lithium battery, high-speed lithium insertion and thermal management of the negative electrode are the two keys to fast charging capability. 1) The high-speed lithium intercalation ability of the negative electrode can avoid lithium precipitation and lithium dendrites, thereby avoiding the irreversible decline in battery capacity and shortening the service life. 2) The battery will generate a lot of heat if it heats up quickly, and it is easy to short-circuit and catch fire. At the same time, the electrolyte also needs high conductivity, and does not react with the positive and negative electrodes, and can resist high temperature, flame retardancy, and prevent overcharging.
Obvious advantages of high pressure

Electric drive and electronic control system: New energy vehicles promote the golden decade of silicon carbide. The systems involving SiC applications in the new energy vehicle system architecture mainly include motor drives, on-board chargers (OBC)/off-board charging piles, and power conversion systems (on-board DC/DC). SiC devices have greater advantages in new energy vehicle applications. The IGBT is a bipolar device, and there is a tail current when it is turned off, so the turn-off loss is large. MOSFET is a unipolar device, there is no tail current, the on-resistance and switching loss of SiC MOSFET are greatly reduced, and the entire power device has high temperature, high efficiency and high frequency characteristics, which can improve energy conversion efficiency.

Motor drive: The advantage of using SiC devices in motor drive is to improve controller efficiency, increase power density and switching frequency, reduce switching loss and simplify circuit cooling system, thereby reducing cost, size and improving power density. Toyota's SiC controller reduces the size of the electric drive controller by 80%.

Power conversion: The role of the on-board DC/DC converter is to convert the high-voltage direct current output by the power battery into low-voltage direct current, thereby providing different voltages for different systems such as power propulsion, HVAC, window lifts, interior and exterior lighting, infotainment, and some sensors . The use of SiC devices reduces power conversion losses and enables miniaturization of heat dissipation components, resulting in smaller transformers. Charging module: On-board chargers and charging piles use SiC devices, which can take advantage of their high frequency, high temperature and high voltage. Using SiC MOSFETs can significantly increase the power density of on-board/off-board chargers, reduce switching losses and improve thermal management. According to Wolfspeed, using SiC MOSFETs in car battery chargers will reduce the BOM cost at the system level by 15%; at the same charging speed of a 400V system, SiC can double the charging capacity of silicon materials.

Tesla leads the industry trend and is the first to use SiC on inverters. The electric drive main inverter of the Tesla Model 3 uses STMicroelectronics' all-SiC power module, including 650V SiC MOSFETs, and its substrate is provided by Cree. At present, Tesla only uses SiC materials in inverters, and SiC can be used in on-board chargers (OBC), charging piles, etc. in the future.