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Citation information: DOI 10.1109/TIA.2019.2951510, IEEE Transactions on Industry Applications 1 A PFC Based EV Battery Charger Using a Bridgeless Isolated SEPIC Converter Bhim Singh, Fellow, IEEE Department of Electrical Engineering Indian Institute of Technology, New Delhi bsingh@ee.iitd.ac.in Radha Kushwaha, Member, IEEE Department of Electrical Engineering Indian Institute of Technology, New Delhi radhakushawaha@gmail.com Abstract- Conventional PFC (Power Factor Correction) circuits in EV (Electric Vehicle) battery chargers have the efficiency limitation due to high conduction loss associated with a diode bridge rectifier (DBR) at the input. To mitigate this issue, a bridgeless (BL) single ended primary inductance converter (SEPIC) with improved power quality, is presented in this paper. The input current shows a unity power factor operation over the entire charging duration. Due to elimination of DBR and the current conduction through relatively fewer number of devices, conduction losses are significantly reduced. This, in turn, improvises the charger efficiency as compared to conventional BL SEPIC converter. The overall performance of proposed charger is illustrated with the help of various operating modes, design equations, simulation based performance and experimental validation under steady state as well as over wide fluctuations in AC mains voltage. The EV battery is charged at constant current/ constant voltage control mode, which provides satisfactory results for improved efficiency and inherent PFC, thus, improving overall performance of the charger. Keywords—BL SEPIC converter; Constant Current/Constant Voltage control; Diode bridge rectifier (DBR); Electric Vehicle; Power Quality I. INTRODUCTION The need for a good fuel utilization and further preventing of greenhouse gas emissions, is shifting automotive industry to electrified vehicles and, thus, electric vehicle (EV) has come into existence to stabilize the transport sector to a greener side. The recent and upcoming vehicle technology comprises an energy storage known as BES (Battery Energy Storage), which charging incorporates certain power electronic interfacing circuit as illustrated in [1-2]. These power electronics circuits that regulate the charging voltage for BES, should be designed efficient enough to maintain the input power quality (PQ) indices as per the IEC 61000-3-2 standard [3]. However, conventional EV battery chargers are supplied from an AC source using filtered output of a diode bridge rectifier (DBR). This type of charging draws a highly distorted current from AC mains. Therefore, losses in the conventional system, are increased and various PQ indices, such as input power factor (PF) and displacement power factor (DPF), are observed to be very poor. The specifications for a conventional EV battery charger under test, are shown in Table-I and various input side waveforms are recorded as per Fig.1. It is noticed that conventional EV charger shows a PF as low as 0.82 and the input current THD is found to be as high as 55.3%. Moreover, it is clearly seen the reactive power requirement of the charger is significantly high. Being a key component of an EV charger, the front-end PFC converter should be designed to achieve the efficiency and size goals as per [4] along with conforming the international PQ regulations. To provide the improved PQ indices at AC mains, an additional PF correction (PFC) stage is added in conventional charger, which challenges the abovementioned size and efficiency goals due to increased size and cost of the charger. Therefore, single stage PFC converters are being extensively researched in the market for EV [5]. A topology based survey on various front end PFC converters for EV battery chargers are reported in [6]. An EV charger may be designed based upon the on-board and off board configurations. Several on-board configurations based single stage EV chargers with improved power density and efficiency, are discussed in [7-9]. However, an off-board configuration seems to be more promising with the advantage of lightening vehicle weight and facility of charging at higher power ratings. In this context, a new front-end interleaved PFC converter for off-board EV charger has been proposed in [10], which reduces the high frequency input ripple current. This, in turn, reduces the size of EMI filter. Moreover, the semiconductor losses are reduced in the system since the switching devices have been employed in parallel. However, interleaving does not abolish the problem of excess heat in the input side diode bridge rectifier, like the conventional boost rectifier. Several converters with interleaved input and zero voltage switching (ZVS) PFC based EV chargers are presented in [11-13], which provide inherent advantage of reduced output current ripple and. inductor size. However, interleaving inputs in improved PQ based converter, suffers from the drawback of high current stress in PFC switches. TABLE I. SPECIFICATIONS OF EV FOR TEST Parameter Specification Speed 0-25 km/hr in Power Mode Battery 4*12V, 100Ah (48V) Range 120 km per Charge Motor BLDC: 48V, 850W Charger Specifications Charger Output voltage:63-65V Charger current at Output:10-12A Supply voltage range:160-260V Fig. 1 Conventional Charger for EV: Test results for mains current, input power analysis and harmonic content in mains current