# Research on Output Voltage Stability of Non-Contact Excitation Motor
## 1 Introduction
In the non-contact excitation synchronous motor, there is no friction from the previous brushes in the motor, and no carbon powder is generated, so the working environment of the motor is safer, and the active life is longer. In a non-contact excitation motor, the core components are a primary coil located on the stator and a secondary coil located on the rotor, and the two coils transfer energy through magnetic coupling, similar to a resolver [16]. Resolvers replace traditional brushes and slip rings. A particular frequency of the alternating current is passed through the primary coil. Due to parameter settings, the primary and secondary waves resonate in the secondary coil. At this time, the primary coil and the secondary coil are not directly connected. Through magnetic coupling, the energy in the direct wave is transferred to the secondary coil, which is fixed on the rotor [17]. There is no direct electrical connection in the circuit. The secondary coil then feeds the current into the rectifier module to rectify the alternating current into direct current, and the rectified direct current is input to the rotor to complete the excitation, avoiding the harm caused by brush friction [18]. In the non-contact excitation process, both the primary and the secondary sides need coils to transmit energy, which will inevitably lead to the loss of reactive power, so it is necessary to add compensation circuits on both sides [19]. Standard compensation circuits include capacitors connected in series on both sides simultaneously. However, the primary side current will be affected by the secondary side parameters, and the circuit is not easy to control. Hence, a high-order compensation circuit needs to be used to compensate for the loss of reactive power [20; 21; 22; 23]. Since the stability of the output voltage needs to be controlled after the full-bridge rectifier circuit, a DC circuit conversion link should be added [24; 25; 26; 27; 28]. Standard DC conversion circuits include the BUCK, BOOST, and BUCKBOOST courses [29; 30; 31]. As the BUCK circuit has a simple structure and convenient control, it is more suitable for stabilizing the output voltage in the circuit [32; 33; 34; 35]. When the motor rotates, the equivalent load of the rotor excitation winding will also change with the change in the speed, so it is necessary to add a control link to stabilize the output voltage. Standard control methods include traditional PI control and sliding mode control [36; 37; 38; 39]. The PI control method is simple and has applications in various fields. However, higher accuracy needs to be guaranteed in the conversion circuit, and the PI control has a significant overshoot, so it cannot be used in this article; this algorithm does not meet the actual requirements. Compared with PI control, traditional sliding mode control has no overshoot, but it also has shortcomings such as short adjustment time [40]. Reference [41] proposes a new control method called capacitor current and capacitor voltage ripple (CCVR) control. It shows that the proposed CCVR control technique can be applied to the SIDO CCM buck converter to extend its stable load range and suppress its cross-regulate [41]. Reference [42] presents a new control method. The global robust output voltage regulation problem for DC-DC buck converter systems is investigated using sampled data and almost disturbance decoupling (ADD) control methodology. Aiming to effectively restrain the output fluctuation caused by load variations, a physically realizable robust controller is proposed by employing a linear discrete-time observer to generate reliable, state-reconstructed information under the conception of sensorless control. The proposed control strategy can achieve ADD by the output feedback domination approach, i.e., the output voltage interference can be arbitrarily attenuated in the L2 gain sense [42]. Due to the limitations of the methods proposed above, an improved sliding mode control algorithm is proposed.