# Analysis of AC DC Four-Switch Boost-Buck Battery Charger Converter for EV Applications
## 1 Introduction  
The development of electric vehicle (EV) battery charging has seen significant progress since the introduction of EVs in the late 19 th century. Initially, early EVs faced challenges like a limited driving range and slow charging. However, advancements in battery technology and charging infrastructure have transformed EVs into a practical transportation option for many. Early EVs used lead-acid batteries, which had low energy density and needed frequent charging. In the mid-20 th century, nickel-cadmium (NiCd) batteries became common, offering better energy density and a driving range of about 60 miles per charge, though they charged slowly and did not last long. In the 1990s, nickel-metal-hydride (NiMH) batteries took over as the main EV battery technology. They had higher energy density, allowing for a range of up to 100 miles per charge, and could charge faster with a longer lifespan. Today, lithium-ion (Li-ion) batteries are the most widely used in EVs. They have even higher energy density, providing a range of up to 300 miles per charge, along with fast charging and durability. As battery technology has improved, so has the charging infrastructure. Initially scarce, charging stations are now plentiful worldwide, with many supporting various EV models. Additionally, there are different charging options available to suit different needs, including Level 1 for overnight charging and Level 3 for quick charging during long trips [1, 2]. Regarding On-Board Charger (OBC) topologies, the most used is the two-stage topology composed of an AC-DC converter stage to guarantee PFC, followed by a DC-linkcapacitance and a DC-DC converter stage that offers galvanic isolation and manages the battery charging process. Usually, the AC-DC stage is a step-up topology that boosts the DC-link voltage at a fixed value higher than the peak value of the grid voltage, i.e., above 340 V in 230 V AC. The DC-DC stage is usually implemented using series LLC resonant or Phase-Shifting Full Bridge (PSFB) converters that are responsible for charging the battery for the whole battery voltage range, i.e., 200-450 V for a 400 V battery [1; 2; 3; 4; 5; 6; 7]. However, in the series LLC resonant converter, a wide voltage range of the battery pack implies that the converter operates frequently away from the resonant frequency, which results in the resonant current waveform being far from the ideal sinusoidal waveform and a decrease in the efficiency of the LLC. Also, the efficiency of PSFB topologies decreases when the system operates far away from the nominal input-output voltage gain because of the loss of ZVS operation [8; 9]. To avoid that, in [9], the authors present a variable DC-link scheme that guarantees no variation of the nominal operating point despite battery voltage variation. The efficiency is higher, but it is limited by the available DC-link voltage range because of the use of a boost totem-pole AC-DC topology. Buck-boost converter topologies arise as candidates to improve whole OBC efficiency because of their capacity to establish a DC-link voltage value higher or lower than the peak value of the voltage grid. However, two-switch buck-boost topologies such as Cuk or SEPIC are eliminated because they present high voltage stress and, therefore, have low efficiency at the OBC voltage levels [10; 11; 12]. Four-switch topologies, consisting of a combination of boost and buck converters, offer low device stress and high efficiency when they operate as a buck or as a boost, making them a good candidate to implement a variable DC-link with an AC-DC PFC stage. In [13], the paper explores an advanced control scheme for a non-inverting buck-boost converter used in PFC applications. It emphasizes the reduction in current stress on the converter components, which significantly enhances overall efficiency. The buck-boost converter operates through a dual switch control mechanism, intricately balancing between the buck stage and the boost stage.