# Research on Output Voltage Stability of Non-Contact Excitation Motor
## 1 Introduction  
The increasingly severe exhaust emissions and fuel consumption of fuel vehicles in the modern world exacerbate environmental pollution and the energy crisis. Most countries have successively announced a complete ban on the sale of fuel vehicles in the next few decades and regard the development of electric cars as a guarantee for environmentally sustainable development and an effective way to improve energy security. Therefore, electric vehicles will receive increasing attention [1; 2; 3]. Breakthroughs have been made in critical technologies such as power batteries, drive motors, and in-vehicle operating systems. The motor is the core component of electric vehicles and one of the critical technologies in electric vehicle research. Therefore, the study of high-efficiency motors for electric cars has significant scientific, economic, and practical social value [4; 5; 6; 7]. With the development of new energy vehicles, increasing attention has been paid to the drive motors used in electric cars. In the permanent magnet motor, the permanent magnet provides the excitation, which has the advantages of simple structure, high efficiency,high power density, and low noise [8; 9; 10]. Nowadays, the drive motors installed in many electric vehicles are permanent magnet motors. However, permanent magnet motors also have inevitable shortcomings, such as expensive permanent magnet materials and easy demagnetization at high temperatures [11]. In the electric excitation synchronous motor, the stator and the rotor are separately excited. The rotor excitation can be adjusted independently to realize the weak magnetic field speed regulation, and the speed regulation is more flexible [12]. In addition, since permanent magnets are not required to provide excitation, the cost of the electric excitation motor is lower. When running at medium and low speeds, the excitation winding resistance of the electric excitation synchronous motor is only about 1/10 of the armature winding resistance, so the efficiency is also high. Compared with the permanent magnet synchronous motor, the excitation current and armature current of the electric excitation synchronous motor are relatively independent. When the power supply reaches the limit, the excitation current can be flexibly adjusted to keep the motor's output torque and power factor under control. Therefore, the electric excitation synchronous motor can obtain a more comprehensive speed regulation than the permanent magnet synchronous motor through the adjusted excitation current [13]. Under different working conditions, the excitation can also be adjusted according to each working condition to optimize the system efficiency. In some exceptional cases, the excitation can even be turned off to ensure the system's safety [14]. According to the excitation method, the electric excitation synchronous motor can be divided into synchronous brush motor and brushless synchronous motor. When the brushed electric excitation motor is working, the friction of the brushes will produce carbon powder, which will affect environmental sanitation. It may also contaminate the base of the bearing, which will reduce the insulation performance and directly affect the system's stability, resulting in a higher failure rate of the system [15]. Therefore, the motor housing needs to be opened frequently for maintenance. Especially in some peaceful places, this kind of friction is more harmful and affects the regular operation of electronic systems. Therefore, a new excitation method is urgently needed to replace the brushes and slip rings and complete the excitation typically. Based on the above research basis, in the excitation process of the electric excitation motor, we propose an innovative excitation method, that is, non-contact excitation, which can replace the brushes in the traditional motor.