# Design of WPT System Based on Interleaved Boost Converter
## 1 Introduction  
At present, wired power transmission technology using a metal medium to transfer electric power has been widely used. However, the long working time of the transmission line may produce sparks, which will not only increase the line loss but also significantly reduce the safety. In order to solve the above difficulties, an isolated power transmission technology is being widely promoted, namely wireless power transmission technology [1; 2]. Wireless power transmission technology can be applied in electric vehicles [3], underwater equipment charging [4], implantable medical treatment [5] and other occasions [6; 7]. To expand the load lifetime and achieve better performance, the output voltage/current of a WPT system should be stable. Nevertheless, the misalignment between the transmitter (Tx) and receiver (Rx) has a great impact on output voltage/current. Hence, an effective closed-loop control scheme is essential. Three types of control strategies are commonly utilized in WPT systems. They are primary side control (PSC), secondary side control (SSC), and primary and secondary side control (PSSC), respectively [8; 9; 10]. In this study, PSC (SSC) refers to the control that both the sampling and control are implemented at the primary (secondary) side while PSSC refers to the control that the sampling and control are implemented at the secondary and primary sides, respectively. The response of PSC is fast, but the output accuracy is low. It is not suitable for scenarios where high output accuracy is required. The output accuracy of SSC is high, but it increases the volume and weight of the Rx. PSSC feeds the output voltage/current at the secondary back to the primary. Hence, the control accuracy is high. In addition, PSSC is suitable for applications wherethe primary space is large and the secondary space is small, for instance, electric vehicle wireless charging systems (EVWCSs). Therefore, this paper will focus on PSSC. Variable frequency control at the primary and secondary sides can keep the output voltage/current constant, but it results in the loss of resonance and zero phase angle (ZPA) and introduces a large amount of reactive power increasing the stresses over the components [11]. Phase shift control of a WPT system using a full bridge inverter can maintain the resonance of the system, but the disadvantages of low inverter gain (defined as the ratio of the fundamental harmonic of the output voltage of the inverter to the DC input voltage of the inverter) and narrow adjustment range limit its utilization in practical systems [12]. To increase the inverter gain and widen the adjustment range, this paper replaces the full bridge inverter with an interleaved boost converter (IBC). A greater inverter gain indicates a higher output voltage of the inverter and smaller currents and losses in the primary. Moreover, the IBC can reduce the ripple of the DC input current. Consequently, the impact of the WPT system on the power grid is attenuated. Misalignment tolerance is an important issue in electric vehicle wireless charging systems (EVWCSs) [13; 14; 15]. Optimizing compensation topologies and modifying magnetic couplers are two widely employed methods that can effectively improve the misalignment tolerance of WPT systems. However, optimizing compensation topologies may introduce additional resonant components and reduce system efficiency [4; 5; 16]. When the primary and secondary sides are offset, the duty ratio of the primary side interleaved boost is adjusted by the method of closed-loop control to realize the voltage regulation characteristic. The remainder of this paper is organized as follows. Section 2 analyzes the working principles of the WPT system, especially the input and output characteristics of the IBC. Section 3 focuses on the system modeling and closed-loop control strategy. Section 4 introduces the proposed parameter design method in detail.