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Wound field synchronous motor

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1001775827613736960


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With the rapid development of new energy vehicles, high-performance electric drives and efficient power managements are becoming the core components of new energy vehicle technologies. Many famous automobile companies set out to seek and develop high-performance motors taking both cost and performance into considerations. The most representative examples such as the induction motors used by Tesla’s Model S and Audi e-tron, and the permanent magnet synchronous motors independently designed by Porsche. However, due to historical reasons, the wound field synchronous motors have been widely used in power plants. Therefore, wound field synchronous motors are naturally considered to have low-power density by the industry. In addition, complex rotor structures of this particular type of machine prevents it from being implemented at highspeed region. This cognitive inertia from industry leads to in sufficient research efforts spent on wound field synchronous machines under the emerging future for transportation electrification.

 

However, the advantages of wound field synchronous motor compared with other types of motors are also evident. For example, the performance characteristics of the motor are independent of temperature alteration. Thanks to its rotor field control lability, the field weakening region or speed expansion capability for wound field synchronous machines is far better than permanent magnet synchronous motors and induction motors. The budget control for wound field synchronous machines is easier than that of permanent magnet motors due to no rare earth elements such as neodymium, dysprosium and terbium are implemented. Circulating oil cooling is more popular than low-cost forced air cooling for automotive industry for which budget is quite sensitive. With the iteration of new energy vehicles, the choice and balance between the cost and performance of electric drive systems will become an eternal topic in the automotive industry.


Based on the above considerations, Nottingham Electrification Centre (simplified here after as NEC ) decided to break the barriers and shackles of the industry on wound field synchronous motors and began to investigate and develop 250kW, 540V high-voltage DC, high-performance, high-speed wound field machines based on forced air cooling for new energy vehicles in 2017. The goal of the first-generation prototype is to approach or obtain the power density of existing induction motors or permanent magnet synchronous motors.

The first-generation prototype was successfully manufactured and assembled at NEC in early 2020 (as shown in Figure 1). The testing jobs were completed at the Key Laboratory of University of Nottingham Ningbo (Figure 2). Coincidentally, the BMW iX3, which will be mass-produced by BMW in 2020, also uses wound field synchronous machines as its fifth-generation electric drive systems. This shows that the advantages of wound field synchronous machine are being gradually recognized by the industry, and the journey of this type of motor in the field of transportationelectrification has just begun.

The first-generation prototype was successfully manufactured and assembled at NEC in early 2020 (as shown in Figure 1). The testing jobs were completed at the Key Laboratory of University of Nottingham Ningbo (Figure 2). Coincidentally, the BMW iX3, which will be mass-produced by BMW in 2020, also uses wound field synchronous machines as its fifth-generation electric drive systems. This shows that the advantages of wound field synchronous machine are being gradually recognized by the industry, and the journey of this type of motor in the field of transportation electrification has just begun.

 

NEC is committed to promoting the development of transportation electrification. The Boeing 787, the most advanced more electric aircraft at present, uses a three-stage generator similar to wound field synchronous machines. That is why NEC considered the technical requirements and possibilities of applying the motor to more electric aircraft at the beginning of the design stage of wound field synchronous machines. The wound field synchronous machine developed by NEC can be adapted to the most advanced variable frequency AC power grid of235V, while providing grid power of 250kVA. At the same time, NEC has also improved the structure of the machine, which reduced the total harmonic distortion of the prototype to 1% under the condition of variable frequency power generation. This greatly reduces power grid losses when the generator operates at power generation mode. Experience gained during the manufacturing and design process will help NEC to improve and optimize the design features which enables capability to develop, manufacture and assemble the high-power three-stage starter generator for the Boeing 787.

 

According to a report published by US market research company IDTechEx in 2019, themarket for diesel generators will reach 4.8 billion U.S. dollars in 2029, ofwhich wound field synchronous generators will be an essential component ofdiesel gen-sets other than diesel engines. It can be seen that wound fieldsynchronous generators still have broad market prospects and space fordevelopment of technology in the field of new electrified transportation andtraditional power generation. Therefore, NEC will continue to cultivatecutting-edge technologies and processes in the fields of new energy vehicles,more-electric aircraft and traditional generators with the University ofNottingham, Ningbo to make efforts and contributions to provide the societywith economic, efficient, and clean high-tech power equipment.

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