# A Comprehensive Review of Developments in Electric Vehicles Fast Charging Technology
## 5 Status of DC Fast Charging Stations and DC-DC Converters Classification  
Efficiently and quickly charging electric vehicles demands high-power DC-DC converters to adjust the charging infrastructure's high-voltage DC power to the battery's required voltage. Various converter topologies are used, with recent studies proposing designs with fewer active and passive components [146]. To minimize switching losses, soft-switching power electronic switches are being introduced [147; 148]. These converters, used in both on-board and off-board chargers, include buck, boost, buck-boost, SEPIC, Cuk, Zeta, and Super-lift Luo converters [24; 25; 26].  
Higher power chargers typically employ isolated DC-DC converters with options like fly-back, forward, push-pull, half-bridge, full-bridge, and multilevel converters [144; 149]. The bidirectional operation of the transformer is achievable in multiple switch topologies through the alternate operation of the switches [65]. However, this approach has limitations, including transformer core saturation and the strain on primary-side switches caused by operating in discontinuous mode [145]. Newer topologies, like bridgeless and interleaved configurations, aim to enhance efficiency, reduce voltage/current ripples, and streamline the number of components. Soft-switching techniques with resonant converter topologies may further boost charging efficiency [150]. For high-gain applications, multilevel converters are another multi-switch alternative. Additionally, their use guarantees less electromagnetic interference (EMI) because there are fewer voltage jumps [146]. Prioritizing EV charger design effectiveness and charging time is crucial, considering most EVs require 3-4 h to charge fully, a critical factor for their potential use in public transportation [147]. Figure 6 outlines a general classification of DC-DC converter topologies for EV powertrains.  
Figure 7 illustrates the key components of a typical DC fast charger power system, featuring two conversion stages for converting three-phase AC power to DC, along with a DC-DC stage incorporating galvanic isolation [121]. The AC-DC rectification stage includes a Power Factor Correction circuit to meet grid codes' power quality requirements. The DC-DC stage facilitates parallel connectivity at the charger's output stage, ensuring isolation between the EV and the grid [121]. Two main approaches for achieving galvanic isolation are presented: One method involves utilizing a low-frequency transformer (LFT) positioned between the grid and the AC-DC stage, as depicted in Figure 7a. These techniques have been extensively discussed in various sources [66; 149; 150]. Alternatively, a high-frequency transformer (HFT) can be incorporated within the DC-DC stage, as shown in Figure 7b. These methods have also been explored in multiple references. Figure 7 visually represents the two isolation options, focusing on a single module charger for simplicity. However, as the power requirements of DC fast chargers increase, the system's output power can  
Figure 6: Classification of DC-DC converters utilized for EV charging systems.  
be enhanced by connecting multiple identical modules in parallel. This approach enables the system to meet the growing demand effectively. For those seeking more detailed information and comprehensive insights into LF and HF transformer configurations, we advise you to refer to the aforementioned references [144; 148; 149; 150; 151; 144]. The article proposes integrating a filter at the input stage to address the harmonic distortion originating from the rectifier. This filter aims to mitigate the inherent harmonic distortion in the current drawn by the rectifier. LC or LCL filters are typically favoured over L filters due to their superior performance characteristics. Additional information on the advantages and specifications of LC or LCL filters can be found in references [152; 153; 154; 155].