## 1 Introduction
However, the above methods are mainly applied to electric vehicles, and there are few research methods to reduce magnetic flux leakage in rotary equipment. For a pot core rotating transformer, the different winding topologies in the rotating transformer were designed and optimized according to total core volume and power losses [17]. Furthermore, a multi-physical design method for high-frequency rotating transformers was proposed, where the PTE was optimized for different core geometries [18]. The design of the rotary transformer is mainly based on the combination of multiple physical fields, such as electric field, magnetic field, and thermal field, which increases the complexity of system design. On the other hand, compensation topology was researched for performance improvement. The capacitor compensation schemes of MCRWPT mainly included four categories, namely series-series (SS), series-parallel, parallel-series, and parallel-parallel, and the characteristics of these schemes were analyzed [19]. The SS capacitor compensation scheme has the characteristic that resonance frequency is independent of load resistance and is more suitable for the variable load resistance on the rotating part. However, the output voltage of the WPT increases with increasing load resistance under the condition that the input voltage is constant. A direct current to direct current (DC-DC) boost-buck converter with a limited input voltage range was applied to adjust the output voltage of the rectifier [20,21]. The efficiency of the DC-DC converter was related to the load resistance, and its maximum efficiency was between 60% and 90% [22]. A closed-loop control scheme was applied to achieve the maximum efficiency under the non-optimal equivalent load resistance condition [23]. However, the application of the closed-loop control method introduced wireless communication into the MCRWPT system, which increased the complexity of the system. Some methods without wireless communication were proposed. Adjusting frequency and input voltage by monitoring input voltage and input current achieved system efficiency above 70% [24]. In addition, the maximum energy efficiency tracking method was achievedby adjusting the equivalent load resistance inside the receiving unit to the optimal value and then finding the minimum input power in the transmitting unit [25]. However, this method requires a fixed system output power. In addition, the MCRWPT scheme with DC-DC converters needs closed-loop control, which makes the system design complex on the premise of improving the system performance. Most research focuses on applying WPT technology to electric vehicles and rotating shaft equipment. However, there are few types of research on the application of WPT technology in an RMINS. To enhance the safety of the RMINS and improve the flexibility of the rotation control scheme, the WPT technology is introduced into the RMINS in this paper. Since the existing WPT system's coil shape is matched to the circuit parameters, it cannot be directly applied to the limited size structure within the RMINS. This paper proposes a simple design method for the MCRWPT system applied in the RMINS. The magnetic shielding structure is designed to reduce magnetic leakage, and the excitation frequency is studied to improve the efficiency of the MCRWPT system with a DC-DC converter. This system can provide a stable power supply for the rotating unit without feedback control. Finally, the experiment verifies that MCRWPT technology can be successfully applied in the RMINS. The structure of this paper is arranged as follows. The principle and characteristics of the MCRWPT system is analyzed in Section 2. The MCRWPT system is designed from two aspects of magnetic shielding structure and excitation frequency in Section 3. The experiment results are analyzed, and the prototype is given in Section 4. A brief conclusion is given in Section 5.