In the development direction of the automobile industry, electric vehicles
(EV) and hybrid electric vehicles (HEV) are becoming an obvious trend. From a
technical perspective, hybrid power is currently more feasible. A hybrid vehicle
is a vehicle equipped with two power sources at the same time - a thermal power
source (generated by a traditional gasoline engine or diesel engine) and an
electric power source (battery and electric motor). In this way, the vehicle's
power system can be flexibly adjusted according to the actual operating
conditions of the entire vehicle, helping the engine to operate in the area with
the best overall performance, thereby reducing fuel consumption and exhaust
emissions.
For end consumers, hybrid models have gained increasing recognition.
Starting from the Toyota Prius, which first entered the public eye, Honda Civic,
Ford Escape, BMW Hybrid X6, Escalade Hybrid, Porsche Hybrid Cayenne, Lexus
RX450H, etc., as well as some domestic hybrids including Chery A5, Changan
Jiexun hybrid vehicles, BYD F3DM, etc. have gradually entered the market.
However, for semiconductor manufacturers, there are still two major challenges
that require long-term research.
Challenge 1: Collective concerns about the safety of lithium battery
packs
Taking a closer look at the EVs and HEVs at major auto shows in 2009, one
obvious trend is the use of lithium-ion batteries to replace nickel-metal
hydride batteries, and the industry generally believes that lithium-ion will
dominate the market in 2015. However, considering the instability of lithium-ion
batteries, careful design and advanced monitoring solutions are needed to ensure
safe operation. For example, battery overvoltage will cause the battery
temperature to rise rapidly, causing fuel leakage and an overheating runaway
state.
Even though lithium-ion batteries have outstanding advantages in terms of
size, weight, recharge speed, life cycle and resistance to memory effects, they
often overheat during overcharge or deep discharge. Therefore, protection and
safety features are extremely important in the use of lithium-ion batteries.
Claus Mochel, senior marketing manager of Atmel's high-voltage product line,
pointed out. Atmel's lithium-ion battery management chipset ATA6870/71
integrates hot-swappable functionality, 6 integrated analog-to-digital
converters with a cutoff frequency below 30Hz and a stackable microcontroller
power supply, eliminating the need for external filters and making it easier to
Comparable solutions require fewer external components.
Brian Black, product marketing manager for signal conditioning products at
Linear Technology, also holds the same view. The difference between hybrid
vehicles and conventional vehicles using gasoline is that hybrid vehicles use a
large battery pack. This battery pack must be carefully managed to maximize
vehicle range, battery pack life, and of course system reliability and safety.
Each lithium-ion battery pack is typically composed of series-connected battery
cells connected in parallel, resulting in a battery pack with hundreds of volts
and a discharge current that may exceed 200A. The use of lithium-ion batteries
increases the complexity and required accuracy of the battery management system
circuitry.
For applications that require multiple battery management functions, the
ideal solution is an integrated battery monitor that can perform battery
measurement, fault detection, temperature measurement and cell capacity
balancing. The LTC6802 can measure up to 12 individual cells, and several
LTC6802s can be stacked to test >1000V systems. In the battery management
system, the LTC6802 performs the heavy analog functions, delivering digital
voltage and temperature measurements to the host processor for state-of-charge
calculations. The LTC6802's high accuracy, excellent noise rejection, high
voltage tolerance and extensive self-diagnostics make it extremely rugged and
easy to use. Its high level of integration means customers can achieve
significant cost savings compared to discrete component data acquisition
designs. Since HEV usually requires hundreds of batteries to be connected in
series, the consequences of failure are serious: the failure of one battery may
cause the entire battery pack to burn or explode. Most common protection
circuits use multiple 3 or 4-channel fault monitors, and use expensive galvanic
isolators between the monitors and analog circuits and passive components
(resistors, multiplexers, etc.). Maxim's MAX11080 has a 12-channel fault monitor
and uses a proprietary capacitively isolated daisy chain interface to greatly
reduce component count. This unique architecture allows up to 31 devices to be
connected to a series battery pack to monitor up to 372 cells. At the same time,
the capacitor-based interface provides extremely low-cost isolation between
battery packs, eliminating cascading electrical failures. By eliminating
expensive isolation components, Maxim's solution saves 75% of space compared to
discrete solutions, reducing the cost of a typical battery management system
from US$250 to US$50. In addition, the MAX11080 has the industry's highest
accuracy, extremely low power consumption, integrated safety and self-diagnostic
functions, and multiple configurable functions, effectively solving problems
related to safety monitoring of large-capacity battery packs.
Compared with traditional car power supplies, the power supply of hybrid
electric vehicles has greater power and higher voltage. For power management,
the object that needs to be managed is not a single power supply, but a
large-scale battery array composed of battery cells connected in series or
parallel. Due to the differences in the production of battery cells, it brings a
great workload to power management. , the health of each battery cell needs to
be monitored and adjusted. Cao Hongyu, senior marketing engineer of the
Automotive Electronics Business Department of Infineon Technologies (China) Co.,
Ltd., added that in addition, the impact of sudden power demands and brake
energy feedback must be well handled during the operation of the entire system.
Security + response rate determine the success or failure of the system.
Because lithium-ion batteries are very sensitive to overcharging and deep
discharge, they have the potential to burn or explode under these conditions.
Atmel's secondary protection device ATA6871 provides a special safety strategy
to monitor the voltage and temperature of the battery cell to prevent thermal
runaway or explosion of lithium-ion batteries. Once one of the above abnormal
conditions occurs in the battery unit, it will be shut down through the
emergency relay device. With a built-in self-test routine that requires no
external microcontroller or software, and hardware-implemented monitoring
thresholds, the ATA6871 provides the highest safety level of Li-ion battery
monitoring. Even if the primary device is damaged, normal operation is
ensured.
Group concerns about the safety of lithium battery packs have prompted the
industry to develop more sophisticated and safer battery detection and
management chips. Automotive semiconductor manufacturers continue to introduce
new battery management and power solutions in an effort to extend battery life
while ensuring safety. and reduce cost, volume and weight.
Challenge 2: Removing barriers to high-voltage electrical systems
Another challenge in HEV design is high voltage. Traditional cars use a 12V
power supply system, while mild, full-scale and plug-in HEVs require
high-voltage electronic systems between 600V and 1,200V, making the design more
challenging.
The most important revolutionary change in HEV is the electrification of
the power system, which requires a powerful electric engine and must run at a
higher voltage than a car powered by a standard 12V internal combustion engine.
In addition, the battery and energy management of HEV are based on a dual power
grid of 12V and a high-voltage battery of hundreds of volts, as well as a DC/DC
converter and power management solution that are newly designed for the
automotive field. Dr. Henning M. Hauenstein, Vice President and General Manager,
Automotive Products, International Rectifier Corporation (IR) stated:
The vehicle structure of HEV requires the use of high voltage. Therefore,
power management ICs must withstand voltage levels of typically 600V, and may be
as high as 1,200V in some high-horsepower HEV models. IR provides advanced motor
drive solutions for mild hybrid vehicles, and those powertrain motors in the
10-15kW range typically use products with 600V capabilities. As for full hybrids
and plug-in hybrids, as well as those with motors up to and beyond 100kW, IR has
a supply of switching and driver ICs up to 1,200V.
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