**1.1. Electric drive application background in Alternative Fuel Vehicles (AFVs)**

The current worldwide energy shortage and unbalanced distribution is becoming increasingly serious, and resource competition is getting fierce. The potential petroleum resources gradu‐ ally decline, while global oil consumption continues to increase. Traditional Automobiles have to face an unprecedented impact and challenges. On the other hand, with the traditional automobile production sharply increasing, environmental impact becomes more apparent. The emissions of CO2 and other greenhouse gases and global warming [1] come into our view. Alternative fuel vehicles (AFVs) are gradually becoming an inevitable choice for all countries

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to innovate the automobile industry. For instance, in the United States, the sales volume of battery electric vehicles (BEVs) is expected to account for 12% of that of all registered vehicles in 2025. As an energy-efficient, low-carbon and environment friendly traffic tool, AFVs are expected to become increasingly popular in the future.

Most national research institutions and automobile manufacturers have increased R&D investment in the AFV technology to replace traditional vehicles, forming the trend of different technologies developed in parallel. Some of the technologies have achieved significant success in commercial fields [2], [3]. In the United States, Germany, and Japan, GM, Ford, Volkswagen, BMW, Toyota, Honda, and other major automobile manufacturers have adopted different new technology development strategies, based on the situation of the nation and the company, and successfully developed a number of concept AFVs and utility vehicles. AFVs are usually classified into hybrid electric vehicles (HEVs), electric vehicles (EVs), fuel cell electric vehicles (FCEVs).

Some countries, e.g., Japan, have been committed to the hybrid vehicles and have developed a lot of well-known models, e.g., the Toyota "Prius." Some other countries, e.g., Germany, have unique technology in the pure electric vehicles, fuel cell electric vehicles, and so on. BMW i3 with carbon fiber body is the lightest electric car on the market.

The world's major automobile production countries have policies to promote the development of AFVs to cope with difficulties and opportunities. By 2015, the United States raised the goal to one million plug-in hybrid electric vehicles (PHEVs). Tax incentives have been implement‐ ed. The EU will issue €7 billion loan to support energy-efficient vehicles. The German gov‐ ernment raised million BEV and PHEV goals by 2020. Japan in 2009 proposed a "carbon revolution" program, in which development of electric vehicles is one of the core. In China, basic research and the establishment of public service platform are listed as the focus of development. "Three vertical and three horizontal" development layout is presented to promote the AFV industries.
