# Analysis of AC DC Four-Switch Boost-Buck Battery Charger Converter for EV Applications
## 1 Introduction
The buck stage meticulously manages the input current, ensuring unity power factor (PF) operation, while the boost stage is tailored to minimize the current stress, reducing the wear and potential failure of the converter components. However, despite the advanced control scheme, it presents a discontinuous input voltage that is difficult for the design of the input filter. Another drawback is related to the expected efficiency that must not be so high due to the system always operating in the buck-boost mode, which implies that all the switches are always commutating. Other four-switch buck-boost converter candidates are the two-inductor topologies shown in Figure 1, which implicitly include an input filter that ensures continuous input current. These kinds of converters present a fourth-order frequency response with two resonance peaks at frequencies lower than the switching frequency that can provoke internal oscillations. The converter shown in Figure 1a is presented as a novel PFC stage for EV battery charging in [14]. The simulation results demonstrate a high PF of 0.99. Moreover, the  
Figure 1: Four-switch cascaded boost-buck converters. (**a**) Converter A [14; 15]. (**b**) Converter B [16]. converter can provide a wide range of output voltages. It emphasizes the converter's potential in enhancing the efficiency of on-board battery chargers in EVs. The ability to maintain high power quality at the input while adapting to various battery voltages makes it a promising solution for the evolving EV industry. The paper concludes that this converter is an effective and adaptable solution for EV battery charging, offering high efficiency and versatility in meeting diverse charging requirements. In [15], there are a deeper analysis and control of the converter presented in [14] and they are shown in Figure 1a. The paper outlines the critical issue of Right-Half-Plane Zero (RHPZ) in the duty cycle to input current transfer function in the boost mode and the duty cycle to output voltage in both operating modes. This RHPZ presents limitations in closed-loop operation, leading to slower dynamics and suboptimal performance parameters. To overcome these limitations, the researchers explored various modifications in the converter's design and parameters. An important development in this research is the incorporation of an RC-damping network. This network successfully addresses the RHPZ limitation, enabling a broader closed-loop bandwidth operation. A distinctive control strategy was devised and applied for both operational modes of the converter, demonstrating rapid transient response, minimal harmonic distortion, and high PF. The theoretical predictions made in the study were validated through simulated results using PSIM software. These results demonstrate the applicability and effectiveness of the proposed solutions in improving the performance of AC/DC converters for PFC applications. This paper presents a deep dynamics and control analysis of the two-inductor four-switch buck-boost converter topology shown in Figure 1b and its application as an AC/DC PFC stage of an OBC of an electric vehicle. This converter was previously addressed in [16] without a detailed analysis for its instability. In this paper, the internal dynamics instability problem, due to high-Q oscillations, is solved using an RC-damping network rather than reducing the closed-loop system bandwidth, which represents the main contribution of this paper. This is a cost-effective solution, which allows the implementation of simpler controllers, avoiding the use of complicated control laws such as the one presented in [13]. The proposed strategy enhances the PF and reliability of the converter. The simulation results validate the feasibility and effectiveness of the proposed analysis and control strategy. In Section 2, this paper introduces the different operation modes of the two-inductor four-switch boost-buck AC/DC converter of Figure 1b, providing a comprehensive understanding of its circuitry.