CR1625 battery.Key technologies of fuel cell vehicles

　　Electric vehicles are clean, efficient and sustainable means of transportation in the 21st century. Electric vehicles include battery electric vehicles or pure electric vehicles (BHE), hybrid electric vehicles (HEV) and fuel cell electric vehicles (FCEV). Due to the emergence of the oil crisis, fuel saving has attracted widespread attention. Electric vehicles have shown an accelerated development trend and have developed rapidly in the past few decades. However, due to cost factors, hybrid electric vehicles failed to achieve marketization in the following 30 years.

　　1 The development status of electric vehicles at home and abroad

　　1.1 Domestic development status

　　At present, China has made progress in the industrialization of electric vehicles, and some pilot lines have made small profits. This achievement is not available in other countries. Currently, 10 battery-capacitor hybrid electric vehicles are in operation on Shanghai's No. 825 bus, and will be expanded to other bus lines in Shanghai in 2009. In addition, the 10 electric vehicles for the Olympic Games presented to Shandong by the State Grid Corporation of China also used battery-capacitor hybrid powertrain technology. This battery-capacitor hybrid electric vehicle has the main advantages of long driving range, fast charging speed and high number of charge and discharge cycles. The maximum driving distance on a single full charge can reach 100~300 km, and the top speed can reach 80~100 km per hour. The full charging time is about 3 hours, and the power consumption is less than 1.6 (kW·h)/km. Relevant testing data shows that using this hybrid pure electric vehicle can reduce vehicle exhaust emissions by 97% to 98%, while saving energy costs by 70% to 80%.

　　1.2 Current situation of foreign development

　　In the past 20 years, the research and development of electric vehicles has become a new trend in the world. The United States, France, Japan, Germany, the United Kingdom, Italy, Switzerland and other countries have taken the lead in the industrialization and commercialization of electric vehicles. Judging from the current overall situation in the world, Japan is one of the few countries with the fastest development of electric vehicle technology. Especially in terms of product development of hybrid vehicles, Japan leads the world. Relevant statistics show that Toyota Motor Corporation has occupied 90% of the global hybrid vehicle market, and its global hybrid vehicle sales have exceeded 100,000 units, reaching 115,000 units. By 2012, all its models will be equipped with hybrid engines. Japan's goal for fuel cell vehicles is to popularize 50,000 fuel cell vehicles in Japan by 2010.

　　The production and sales of electric vehicles in the United States started earlier, but there is a certain gap compared with Japan in the industrialization of electric vehicles. The three major automobile companies have only produced and sold pure electric vehicles in small batches, while hybrid and fuel cell electric vehicles currently Industrialization has not yet been achieved.

　　The UK has been the only country that has insisted on using electric vehicles on a large scale for more than 50 years. There are currently about 120,000 electric vehicles in the country. Among them, there are tens of thousands of them used only for delivering milk and 1,000 electric sweeping vehicles. At the same time, relevant companies continue to invest and set up factories at home and abroad to mass produce electric vehicles. In addition, Italy, Denmark, Austria, Finland, Canada, Sweden, the Netherlands, the Czech Republic, Hungary, Norway, the former Yugoslavia, Israel, Mexico, Australia, India and Malaysia are all researching and developing electric vehicles or key components of electric vehicles.

　　2 energy sources

　　The energy source of electric vehicles is considered to be the main issue for the commercialization of electric vehicles. Therefore, how to develop energy devices will be a major issue in the development of electric vehicles at present and in the near future. Criteria for the development of energy devices: 1) high proportion of energy and energy density; 2) high specific power and power density; 3) ability to charge quickly and deeply discharge; 4) cycle and long service life; 5) high charging and discharging efficiency; 6) Safe and low cost; 7) Maintenance-free; 8) Environmentally friendly and recyclable.

　　3 Key technologies in the development of fuel cell vehicles

　　The key technologies of electric vehicles include electric technology, automation technology, electronic technology, information technology and chemical technology. Although energy is the most important issue, the optimization of body structure, electric drive and energy management systems is also crucial.

　　Compared with internal combustion vehicles, electric vehicles have a shorter driving range, so in order to maximize the use of on-board stored energy, a suitable energy management system must be selected. Sensors can be installed in various subsystems of the car, including temperature sensors inside and outside the car, current and voltage sensors for charging and discharging time, current and voltage sensors for electric motors, vehicle speed sensors, acceleration sensors, and external climate and environment sensors. The energy management system can achieve 9 functions:

　　1) Optimize system energy flow;

　　2) Estimating the energy generated to estimate the distance that can still be traveled;

　　3) Provide reference for effective operation;

　　4) Obtain energy directly from braking and store it in energy storage components, such as batteries;

　　5) Adjust temperature control according to the outside climate;

　　6) Adjust the light brightness according to the external environment;

　　7) Estimate the appropriate charging algorithm;

　　8) Analyze energy sources, especially battery work records;

　　9) Diagnose any inappropriate or ineffective operation of energy sources.

　　Combining the energy management system with the navigation system, it is possible to plan energy-efficient routes, locate charging stations and predict the driving range based on traffic conditions. In short, the energy management system combines the significant advantages of multi-function, flexibility and variability, so that limited on-board energy can be rationally utilized.

　　3.1 Fuel cells

　　Compared with electrochemical cells, the significant advantage of fuel cells is that fuel cell electric vehicles can achieve the same driving range as fuel vehicles. This is because the driving range of fuel cell electric vehicles is only related to the amount of fuel in the fuel tank, not to the amount of fuel in the tank. The size of the fuel cell is irrelevant. In fact, the size of the fuel cell is only related to the level of power demand of the electric vehicle. Advantages of fuel cells: 1) The reactant feeding time is much shorter than the charging time of electrochemical batteries (except for mechanical rechargeable batteries); 2) The service life is longer than that of electrochemical batteries and the battery maintenance workload is smaller.

　　Compared with ordinary batteries, a fuel cell is an energy generating device and continues to generate energy until the fuel is used up. The advantages of fuel cells are: 1) Convert fuel into electrical energy with high efficiency; 2) Work quietly; 3) Work with zero or low emissions; 4) The remaining heat generated can be reused; 5) The fuel is replenished quickly and the fuel is easy to use. Obtain; 6) Durable and reliable work.

　　Fuel cell electric vehicles are an integrated product of the latest achievements in engineering technologies such as automobiles, electric drive, power electronics, automatic control, chemical power sources, computers, new energy and new materials. Therefore, the development and industrialization of fuel cell electric vehicles require solving many key technologies, such as fuel cells, motor control, body and chassis design, testing technology and system optimization.

　　3.2 New fuel cell technologies

　　Fuel cells use the electrochemical reaction of hydrogen and oxygen to generate clean energy without producing CO2. However, due to limitations of hydrogen storage technology, current vehicle prototypes and demonstration models powered by fuel cells can only reach a maximum driving distance of 322 km. Under standard temperatures and pressures, to store enough hydrogen to reach a driving distance of 483 km would require an onboard fuel cell with a volume equivalent to a double-decker bus; other methods include compressing and storing hydrogen in cylinders or Liquefied hydrogen is stored in tanks, etc., which are impractical due to quality and volume issues.

　　Researchers from the UK-SHEC project team are trying to store hydrogen at a higher density to control battery quality within an acceptable range. They use chemical adsorption methods to draw gas molecules into the crystal lattice of solid compounds and release them when needed. Now, researchers have developed a series of lithium hydride compounds that can meet these requirements well. The project coordinator, Professor Peter Edwards of the University of Oxford, UK, said that this is a long-awaited breakthrough for the fuel cell industry and the transportation sector. This key breakthrough will enable the mass production and application of fuel vehicles in the next 10 years. possible.

　　3.3 Drive motor technology

　　In order to enable the vehicle to travel more miles with enough fuel at once, to maximize the use of hydrogen energy and to minimize the vehicle's curb weight after modification, the electric drive system is required to have high efficiency and power-to-weight ratio. Drive motors should develop towards high power, high speed, high efficiency and miniaturization.

　　Current drive motors mainly include induction motors (IM) and magnetic brushless motors (PMBLM). In particular, permanent magnet brushless motors have the advantages of high power density and efficiency, small size, low inertia and fast response. In terms of electric vehicles, It has broad application prospects. When designing and selecting a drive motor, it should be ensured that the torque/speed characteristics of the motor match well with the load characteristics of the vehicle, the dynamic performance of the motor torque is good, and the efficiency of constant speed, constant power and variable operating conditions should be high.

　　3.4 Electronic control technology

　　Like traditional vehicles, electronic control will play an increasingly important role in the development of fuel cell vehicles. Various control systems of automobiles will develop in the direction of electronics and electrification, realizing wire control, that is, using wires to replace mechanical transmission mechanisms, such as wire braking and wire steering.

　　The existing 12 V power supply can no longer meet the needs of all electrical systems in automobiles, and the implementation of the new standard for 42 V automobile electrical systems will cause major changes in the design and structure of automobile electrical components; at the same time, mechanical relays and fuse protection circuits will also be eliminated. The characteristics of the fuel cell have its own characteristics: 1) low voltage and large current; 2) the output current will increase with the increase of temperature, and the output voltage will decrease with the increase of the output current; 3) the output voltage will start from , the current gradually enters a stable state, and the dynamic reaction time staying within the transition zone is relatively long. It is precisely because of the above characteristics that most electrical appliances and motors cannot adapt to their voltage characteristics, so they must be used in conjunction with DC/DC converters and DC/AC inverters. A large amount of power adjustment is required for the fuel cell system to ensure voltage stability. .

　　3.5 Vehicle system optimization technology

　　The entire vehicle system of a fuel cell electric vehicle is a complex system involving multi-disciplinary technologies, and its performance is affected by multi-disciplinary related factors. Therefore, the entire vehicle system must be optimized based on full consideration of various influencing factors, and the fuel cell system can be improved. Battery electric vehicle performance and reduced vehicle design and manufacturing costs.

　　In the overall design concept, lightweight materials and full utilization of aerodynamics are placed in the most important position. Because when a car is driving, only a small part of the energy generated by fuel consumption is actually used to propel the car and passengers, while most of the energy is lost through heat loss, rolling resistance, air resistance and the inefficiency of the control system. etc. are consumed, during which the mass and aerodynamic factors of the car itself play a very important role. In the overall design process, the emphasis is on mass reduction, that is, a lightweight body requires lighter chassis components and a smaller powertrain. The interconnections and combinations of these components are small, but they can reduce volume and weight. It's even possible to eliminate original components, further reducing the system's mass.

　　4 Conclusion

　　As a clean and efficient power source, fuel cells are expected to become the next generation of vehicle power devices. The widespread application of fuel cells helps save fuel and reduce air pollution. Fuel cell engines will not be able to replace internal combustion engines in the short term. To make fuel cell vehicles practical, a series of key technical issues need to be improved. (Cui Shujuan, Wuhan University of Technology)

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