Standardization of electrical energy can simultaneously achieve economies of scale and eliminate the infrastructure needed for local fuel consumption. Superior electrical energy storability facilitates power generation (the most efficient, and not "on-demand" type), as is currently the case. For example, wind power and solar power are not necessarily consistent with peak power demand patterns, while storable features can alleviate this problem. Superior portability allows electrical energy to be used as an energy source for cars (large energy consumers). Over time, other applications that tend to use green energy will certainly benefit from this technology. Electric vehicle requirements for battery systems Electric vehicles provide a huge opportunity for the green revolution for a number of reasons. Electric vehicles use grid power to replace gas power. Grid power generation is very efficient and can be obtained from almost all sources of energy. In addition, electric vehicles are also more energy efficient than fuel vehicles. Most cars will experience a continuous cycle of "acceleration, deceleration, and idling" while running. In contrast, variable loads (such as acceleration or deceleration) are more conducive to electric motors (rather than fuel engines) because they provide high torque at low speeds. The fuel engine's operating efficiency is only reached at a very narrow speed/load range, and it must be very large to meet peak acceleration needs. The engine used to convert gasoline energy into kinetic energy is typically 20% efficient, while electric motors can achieve 90% typical efficiency in converting electrical energy into kinetic energy. In addition, the electric motor does not need to consume energy unnecessarily during idling due to idling, and the electric system has the potential to recover mechanical energy through regenerative braking. The overall improvement in energy efficiency can be seen by the fact that the typical energy cost of an electric vehicle is only $0.013/mile. Unfortunately, in today's market, pure electric vehicles are not a viable solution because their travel distance is limited by the energy stored in the car. Today's common battery packs can drive an electric car for 100 miles after 8 hours of charging. An ordinary car tank can provide a standard car with a 300-mile distance and can be refueled in just a few minutes. If you want to be widely accepted by American consumers, electric vehicles must extend the distance and / or shorten the recharge time. The solution that emerged was the Hybrid Electric Vehicle, which combines a fuel engine with an electric drivetrain to provide sufficient travel distance while still having most of the benefits of green energy. Hybrid vehicles use on-board gas engines (for battery charging) and operate the engine at the most efficient speed/torque range when needed. There is no doubt that the success of electric vehicles will help other applications of high-performance battery systems to find their own living space, thereby driving its price decline and performance improvement. For local power generation (including small photovoltaic or wind power systems), the battery can play a vital balancing role, and it can also act as a backup power system when grid power is available. Current battery systems are quite expensive and bulky, and have reliability and safety issues. The next generation of battery systems will provide higher energy density and are designed to achieve smaller, lower cost, more reliable and safer solutions. Design challenges for high voltage battery packs For high-power battery applications, lithium-ion batteries are the preferred chemical battery, primarily because of its high energy density. Today's electric vehicles and hybrid electric vehicles use NiMH batteries, which will increase energy storage density by 400% if lithium-ion batteries are used. However, in order to keep lithium-ion batteries reliable for up to thousands of charge and discharge cycles, battery systems must address many technical challenges. The performance of a lithium-ion battery depends on battery temperature and life, battery charging and discharging rates, and state of charge (SOC). These factors are not independent. For example, a lithium-ion battery generates heat when it is discharged, thereby increasing the discharge current. This has the potential to create a thermal runaway condition and lead to catastrophic failure. In addition, charging a Li-Ion battery to 100% SOC or discharging to 0% SOC will quickly reduce its capacity. Therefore, the operation of the lithium ion battery must be limited to a certain SOC range, such as 20% to 80%, and the available capacity at this time is only 60% of the specified capacity. Not only that, lithium-ion batteries also have a flat discharge curve (Figure 1), where a 1% SOC change may only appear as a voltage difference of a few millivolts. To take full advantage of the available voltage range of the battery, the battery system must monitor the battery voltage very accurately (it directly corresponds to the SOC). In addition to the sensitive nature of lithium-ion batteries, the method of combining batteries is also an important consideration. To provide efficient power from an electrical system, such as the electrical system needed to accelerate a vehicle, hundreds of volts are required. For example, delivering 1 kW of power at 1 V requires 1,000 A, while delivering 1 kW at 100 V requires only 10 A. The inherent resistance in system wiring and interconnects is converted to IR losses, so designers need to use the highest possible voltage/lowest current.
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Charging control of high-voltage battery packs for hybrid vehicles
The Green Revolution may soon have a major victory. When large-scale electricity becomes “storable†and “portable†energy, energy efficiency will be significantly improved, and the promotion of renewable energy will also progress. Storability and portability are the main advantages of liquid fuels, while the power provided by battery systems has the potential to provide a viable alternative. Electrical energy can be used in almost all energy consuming devices, and electrical energy can be generated from almost all available energy sources. Nuclear, solar , wind, geothermal and liquid fuels (gasoline, diesel, ethanol, hydrogen, etc.) can be easily converted into electricity. Therefore, a significant advantage of electricity compared to petroleum fuels is the ability to generate energy anytime, anywhere, using the most cost-effective solutions.