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2023/03/16
At present, emerging vehicles represented by new energy vehicles are rapidly replacing traditional fuel vehicles. Although new energy vehicles are becoming the choice of more people, there is no doubt that they still have pain points in consumer experience. One is inconvenient charging experience or slow charging speed, and the other is range anxiety.
To expand the future market of new energy vehicles, it is necessary to start from the perspective of electrification efficiency, and the current important trend is to use 800V electrical architecture + SiC power devices, in which isolation and driver technology is indispensable.
New trend of vehicle electrification
The trend of vehicle electrification is first to develop high-voltage architecture, increasing charging power under the condition of increasing charging voltage and constant charging current, so as to achieve the goal of driving for 200 kilometers by charging for 5 minutes. At present, some domestic and foreign vehicle models have been using super charging pile, and 800V bus voltage has also been applied and mass produced for many models. Market research shows that by 2025, it is expected that the sales volume of new energy vehicles with 800V high-voltage architecture will reach about 1 million units, and the three-year CAGR (compound annual growth rate) will reach 270%; in 2025, global sales of new energy vehicles equipped with 800V architecture are expected to reach 2 million units.
The second trend is the use of high-voltage SiC power devices; its advantage is that the third-generation semiconductor devices features high voltage, low on-off loss, small size and other advantages, helping to improve the electric drive efficiency, optimize the electric drive weight, and increase the range by 10%-15%.
In the motor controller of the new energy vehicle, the power conversion is realized by enabling/disabling IGBT. Limited by the material itself, IGBT cannot work at temperatures above 200℃. High power-density motor controllers require high power conversion efficiency and higher operating temperature, which puts forward higher requirements for power devices, such as lower on-off loss, high temperature resistance, high thermal conductivity, etc.
Changing from traditional silicon-based MOSFETs or IGBTs to SiC power devices can reduce the weight of the entire module by nearly half. Some customers have developed full SiC platforms that can reduce weight by 9kg, reach a maximum power of 220kW, and reduce size by nearly 40%.
The above two trends put forward new and higher requirements for isolation IC and driver IC. Firstly, the voltage level of the battery, motor and electric control systems (including OBC, DC-DC and BMS) of 800V high-voltage platform, as well as the air compressor, PTC and electric driver will be increased accordingly.
Isolation and driver technology in new energy vehicles
Firstly, the isolation of new energy vehicles is based on safety certification requirements to protect personal and equipment safety at the 400V-800V battery voltage, and processors and other weak current devices also require isolation chip for electrical isolation from the high voltage side; the second is the common ground requirement, which needs to use the isolation device to realize the level conversion function; the third is high noise resistance requirements to achieve higher CMTI (common mode transient immunity), and avoid large noise interference, resulting in power tube mis-opening; in particular, the application of SiC can make the switching frequency rise, causing relatively large dv/dt noise.
Creepage is also one of the requirements of the safety compliance, which represents the distance of the chip packaging surface to produce flashover or breakdown (marking). The common creepage distance in the high-voltage battery, motor and electric control system of new energy vehicles is the isolation device of 8mm. With the upgrading of the battery, motor and electric control system to 800V voltage, the creepage distance will also increase.
In addition, the large peak output current requires to turn on the switch tube with larger current to meet the requirement of quick opening and closing the power tube. New energy vehicles rely on electric air compressors to drive, and main motor driver and PTC also require high voltage electrical isolation.
At present, there are several mainstream isolation technologies in the industry, and NOVOSENSE adopts the capacitive isolation technology based on capacitance coupler. Compared with optical coupler, capacitance coupler has a higher transmission rate, which can easily reach the communication rate above Mbps. The same can be done with optical coupler, but the speed increase comes at a cost of doubling. In addition, the optical coupler is limited by the packaging process, so it is not easy to integrate multiple isolation channels in a chip, while the capacitor isolation can be used to easily integrate six channels and eight channels in a chip. In addition, the capacitance coupler does not have the trouble of temperature drift and light decay, and the operating temperature range is wider.
Magnetic coupler is based on the principle of transmitting signals through changes in magnetic flux, whereas capacitance coupler is based on electric field, which has advantages in terms of low emissions.
In a capacitor isolation chip, the isolation capacitors are located on two separate bare chips. Since it adopts superior enhanced isolation technology for electrical isolation, two capacitive plates are connected in series to achieve isolation in an enhanced architecture. The isolation medium between them is silicon dioxide, which is a kind of isolation medium with higher isolation strength. The withstand voltage of each micron isolation can reach more than 400V, which is 5-6 times of the isolation medium (epoxy resin) used by the optical coupler. Theoretically, the isolation grid with thickness of 30 microns can reach isolation voltage of more than 10kV. The measured 60-second withstand voltage can also reach the level of 12kV. In addition, capacitance-isolated differential transmission architecture per channel also helps to improve common-mode noise suppression.
For common-mode suppression, modulation is needed, that is, an input signal is transmitted in a capacitor or other medium through modulation. The prevailing approach is usually to use OOK encoding, which modulates an input signal to more than 400 megabytes of carrier and then transmits it between capacitors. The patented Adaptive OOK coding scheme is optimized by NOVOSENSE, which further improves the capability of the isolator to resist common-mode noise. Compared with the other two approaches, OOK coding modulation has the advantage of strong resistance to common-mode suppression.
NOVOSENSE products feature withstand voltage isolation capability of 12kVrms, EMC performance and surge of > 12kV and both-side capability of ESD > 10kV. These products have obtained UL/CUL/VDE/CQC and other mainstream safety compliance certification in the industry.
NOVOSENSE provides digital isolation chips and isolation power supply, including isolation sampler, isolation driver, as well as some interface related products and automotive grade isolation devices, which are now in full mass production.
The third generation semiconductor has higher requirements for isolation devices. The switching frequency has been increased from 10kHz of silicon base to 100kHz of SiC, and the isolation voltage has been increased to more than 1000V.
In addition, requirements of SiC devices on digital isolators are higher switching frequency and higher transmission rate with common mode inhibition ability of not less than 100kV/ microsecond. NOVOSENSE isolation devices can reach 150kV or even 200kV.
In the new-generation electric drive development platform, CMTI, wide grid voltage swing, large peak output current, fast rise and fall time, fast short circuit protection and soft shutdown ability are the key indicators to be considered when selecting suitable SiC power tube driver chips.
NOVOSENSE system and product solutions
In the application of NEV electric driver main motor driver, NOVOSENSE has mass-produced isolation drivers, including NSi6611 and NSi6651 intelligent protection enhanced isolation driver, as well as enhanced digital isolator and enhanced isolation sampler.
In addition to the driver, it provides bus voltage or current isolation samplers NSi1311 and 1300 for the battery, motor and electric control system with relatively high market shares.
NSi82 is the earliest automotive grade digital isolation product launched by NOVOSENSE. It covers 1-6 channel schemes and adopts different packages, such as narrow body 8, wide body 8 and wide body 16, including ultra-wide body isolation devices that match 800V applications with a creepage distance of 15mm. In addition, there are some interface products such as the 1042, 1051, 1043 for CAN and the 1145 with sample to be ready soon.
The main advantage of the enhanced isolation is the isolation of the operating voltage, with withstand voltage of 5,000V AC per minute. NSi82 enhanced digital isolator is a hero product with nominal isolation voltage of 5000Vrms, measured withstand voltage of 12kV in the insulation oil, sufficient margin and relatively high reliability.
Since the isolation operating voltage is applied to both ends of the isolation grid for a long period of 20 years or more, it is necessary to ensure that the failure rate of the isolator is less than 1 ppm. If it is basic isolation, this requirement is much looser, requiring failure rate of less than 1000 ppm, a difference of 1000 times.
Meet the domestic substitution demand of auto manufacturers
NOVOSENSE isolation and driver products are mainly used in OBC, DC-DC, main motor driver, BMS and thermal management system. The performance of its products are competitive in isolation and drive technology industry, with safe and reliable production supply chain in China. Mature product experience and sound intelligent production system are reflected in the AEC-Q100 qualification, and it has strictly followed the automotive grade process and control concept from product definition and development to the back-end wafer packaging.
Sample application
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