# Research on Three-Phase Wireless Power Transfer System
## 3 Experiment and Analysis
### Comsol Simulation
Finally, we obtain the optimal mutual inductance model by thoroughly studying the overlap angle and coil span of the three-phase, three-coil wireless charging system. The span of each phase coil in the model is 180 degrees, and the angle difference between the three phases is 120 degrees. The structural diagram is shown in Figure 5.  
This paper also compares the electric field and magnetic field distribution of single-phase and three-phase coils, and the COMSOL simulation parameters refer to the data in Table 1.  
The COMSOL simulation results of the electric field mode comparison of the coil coupling model of the WPT system are shown in Figure 6, it can be clearly seen that the three-phase coil divides the current of the single coil into each bridge arm of the three-phase, and the effective value of the current flowing through is smaller than that of the single-phase coil. Because the voltage and current stress of the circuit are positively correlated with the current, the smaller the current, the smaller the voltage and current stress on the coil. Therefore, this three-coil design enables higher power charging requirements under the same current stress constraints. By evenly distributing the current to different phases, the current load on each phase can be reduced, thereby improving the stability and reliability of the system, reducing the loss of the system, prolonging the service life of the system, and providing a more reliable and efficient solution for high-power charging. Figure 4: COMSOL simulation of the influence of horizontal misalignment on coil efficiency. (\(D=100\) mm). Figure 5: Coupling mechanism model of three-phase WPT system. In Figure 7, the COMSOL simulation results show the magnetic field mode and magnetic flux density streamline when the coupling mechanism is working under the excitation of a circuit current of 220 V and 47.5 kHz. The structure of the three-phase sector coil enables it to provide high-density winding in a smaller space. By comparison, it can be seen that under the same input excitation, the magnetic field of the three-phase coil is relatively stronger and the leakage flux is less. This characteristic enables the three-phase coil to generate a stronger magnetic field while providing a high-density winding, which is suitable for wireless power transfer applications. In addition, because the three-phase currents in the three-phase coil are staggered by 120 degrees, a rotating magnetic field can be generated. Compared with the traditional wireless power transfer method, the transmission of the rotating magnetic field does not require direct alignment between the transmitter and the receiver, which can improve the anti-offset performance of the system and realize energy transmission more flexibly. The transmission efficiency of the three-phase coil reaches 96.49%, while the efficiency of the single coil is only 93.67% under the same size and excitation conditions, and the power transmission efficiency is increased by 2.82%. The magnetic flux density effect of the working area between the three coils is more obvious, so this structure design helps to reduce the volume of the coil, improve the compactness and efficiency of the equipment, and improve the energy transmission efficiency of the system without increasing the original size. Figure 6: Comparison of electric field COMSOL simulation results of WPT system coil coupling model. Figure 7: Comparison of magnetic field mode and magnetic flux density line of WPT system coupling model.