## 1 Introduction  
Wireless power transfer (WPT) technology can transfer electrical energy from a high-frequency power supply to a load through a magnetic field instead of a wire connection [1]. It has considerable development potential given its unique advantages, such as safety, efficiency, convenience, and weatherproof-ness, which make it desirable for application in daily life, similar to WiFi. Owing to such advantages, WPT charging can be used in several fields, such as non-rem removable medical implants [2, 3], underwater equipment [4], portable electronic devices [5, 6], and other industrial fields. In particular, applications in the field of electric vehicles have attracted widespread attention [7] because of the environmental friendliness, high efficiency, and high success ratio of vehicle-to-grid interaction. However, most electric vehicles adopt conventional plugged-in chargers, which are unsafe, inconvenient, and space-occupying. The emergence of WPT technology is regarded as a preferred solution to the problems of traditional charging methods, boosting the development of the electric vehicle industry. In general, most of the energy storage devices use lithium batteries, owing to their inherent advantages of high energy, light weight, and strong power tolerance. However, the equivalent resistance of the battery varies with respect to the charging voltage or current. To obtain the expected charging voltage or current for different modes under a dynamic load, the battery charging was mainly accomplished in two stages: an initial constant current (CC) charging stage and then a constant voltage (CV) charging stage, as shown in Figure 1. First, the battery was charged at a constant charging current \(I_{\text{BAT}}\), but the battery voltage continued to increase with the increasement of the resistance. To avoid the damage of the battery caused by overcharging, while the output voltage of the charger rose to the preset voltage \(U_{\text{BAT}}\), the charger needed to quickly switch to CV mode. Finally, the charging was completed when the charging current was reduced to near zero. However, the drastic change of battery resistance brought great challenges to the design of WPT charging systems. To achieve a high-efficiency CC/CV output under dynamic loads, researchers have proposed many schemes for WPT charging systems. These schemes can be roughly divided into three categories. Category 1: [PERSON] et al. [8] proposed a new two-way control scheme for optimizing the charging efficiency of the system, which involves the addition of a DC/DC converter on the primary or secondary side. [PERSON] et al. [9] proposed an automatic feedback control method with a fast response and simple hardware, which can perform impedance matching and obtain the CC/CV output by adjusting the duty cycle. [PERSON] et al. [10] proposed a maximum efficiency point-tracking control scheme to maximize the system efficiency while adjusting the output voltage. However, the additional DC/DC converter increases the cost of the WPT charging systems and reduces the transmission efficiency. Category 2: [PERSON] et al. [11] proposed a design for WPT systems, which can achieve CC/CV charging modes by adopting the load-independent characteristics under zero phase angle (ZPA) conditions with minimal frequency changes throughout the charging process. [PERSON] et al. [12] proposed a novel inductor-capacitor-capacitor series (LCCC-S) compensation topology and a parameter correction scheme for obtaining the CC/CV modes at two different ZPA working frequency points. [PERSON] et al. [13] proposed a hybrid control method for a limited operating frequency range, which by using frequency modulation control to realize zero-voltage switching (ZVS) operation and phase-switching control to adjust the output voltage. However, a wide range of pulse-width modulation is usually desired, which increases the switch losses and volt-ampere (VA) ratings.