ABSTRACT
This paper proposes a two-stage battery charger using an bridgeless power factor correction (PFC) AC-DC converter at the first stage. The converter at the front end improves the input current shaping and power factor while providing adequate DC link voltage. At the back end, a half-bridge LLC converter is used to charge the battery. This onboard charger (OBC) executes nearly unity power factor throughout a broad input voltage range. Furthermore, input current and voltage sensors are not required for AC-DC conversion due to the discontinuous inductor current conduction mode (DICM), further increasing the converter’s reliability and reducing the overall cost. This OBC solution practically suits the majority of low-voltage (LV) battery chargers. The design equations and a thorough steady-state analysis of the proposed charger are also presented. Simulation work is carried out using MATLAB/Simulink.

INTRODUCTION
Recent years have seen a surge in interest and study of electric and hybrid electric vehicles (HEVs). The battery is the heart of electric and hybrid vehicles because it stores the energy that powers them. A non-power-factor-corrected charging system consumes a current that is high in harmonics from the input mains supply as the batteries are mostly capacitive. As a result, the nearby devices that are connected to it suffer severe consequences. Any EV charging solution must have a PFC stage in order to meet defined power quality standards. With approximately 80% of the total EVs on road are accounted by two-wheelers and three-wheelers, EV sector in India sees enormous opportunities in charging solutions for EVs. To power an electric vehicle’s battery, a charger can be installed either within the vehicle (called an “on-board charger”) or outside (called an “off-board charger”). Off-board chargers are utilized for high-power AC and DC charging, whereas the on-board chargers are used for low-power AC charging as shown in Fig. 1. On-board battery chargers (OBCs) usually incorporate an AC-DC converter followed by a DC-DC converter with galvanic isolation. AC-DC conversion at the front end plays a pivotal role in OBC solutions. Conventional front-end converters have low THD, power factor, and device count. These demerits will make the battery heavier. In an OBC, it is essential to fulfill requirements like reduction in current harmonics at the input, better regulation of output voltage and power factor correction (PFC). Obtaining an effective OBC is facilitated by PFC-based AC-DC converters, a crucial component of an EV charger. These converters provide the same flexibility as any other power converter, allowing for operation in either continuous inductor current conduction mode (CICM) or DICM or boundary inductor current conduction mode (BICM). Boost PFC converter topologies are widely preferred in the PFC converter based on-board charging. These configurations convert AC to DC with a diode full bridge rectifier (DBR) and then power up with a boost converter. However, this design introduces issues including heat dissipation due to the high output capacitor current ripple and worrisome amounts of DBR losses. The common-mode (CM) noise, ripple current, sensing circuit complexity, and voltage stresses of many bridgeless (BL) topologies are all higher than that of their boost, buck-boost, Cuk, SEPIC, Luo, and Zeta-derived counterparts. Though bridgeless dual-boost and totem-pole dual-boost reduce CM noise, they do so at the expense of additional conducting devices for each half cycle. Majority of single-stage, isolated and non-isolated topologies contain high conduction losses demanding bulky heat sinks, further leading to thermal failure. Hence, they are unfit for low-voltage and high-current applications. Whereas high-voltage and lowcurrent single-stage OBC applications in the literature fails to discuss heating issues. Two-stage topologies with PFC converters can either work in a post-regulator mode at the back end or a pre-regulator mode at the front end. At front-end, PFC is accomplished, while back-end voltage and current are controlled by a pre-regulator type. In CICM operation, PFC needs three sensors at the front end to work. Back-end converters, on the other hand, use two sensors to keep the charging voltage and current in control. Because the input phase must be tuned to match the grid, these converters are difficult to control and cost higher. For input sinusoidal current shaping and power factor correction (PFC), the CICM control at the front-end uses the inner current control loop. In contrast, the outer voltage control loop regulates the output voltage. Phase-locked-loop (PLL) and the requirement of current controllers with larger bandwidth at the inner-side drive it towards more complexity. This complexity and difficulty in establishing natural PFC for AC-DC in CICM open the way for DICM, which possesses intrinsic qualities such as built-in PFC, reduced number of sensors, effortless control, zero current switching (ZCS) turn-on of the power switches, as well as the inherent zero diode reverse recovery losses. In DICM mode, achieving UPF operation at AC mains is possible without input sensors. Further, the voltage-doubler configuration can reduce voltage stress on semiconductor switches. A DICM-operated bridgeless buck-boost converter for e-rickshaw on-board chargers is presented. Since the main switch is operating in DICM, an LC filter is deployed to reduce switching harmonics in the ac line. This work only involved front-end PFC converters. Whereas, converter is used at the front-end for PFC and at the back-end a half-bridge LLC resonant converter achieves zero voltage switching (ZVS) turn-ON only. The two-stage EV charger utilizes a bridgeless Cuk front end and a back-end isolated flyback dc-dc converter. Due to its minimal component count, the flyback converter is easy to operate and very cheap, but it only suits for low power rating. Since the flyback does not employ the buck boost operation of the Cuk converter to lessen switching losses, the front and backend converters can be operated independently. Wide range of output voltage is achieved by employing a phase-shifted dc-dc converter, followed by a front-end PFC converter, for EV chargers. The high output voltage is a result of the high frequency transformer, whereas the low output voltage is the result of duty cycle management. In this setup, the phase-shifted converter offers a wide output voltage range while the PFC converter controls the dc link voltage and shapes the ac current.

PROBLEM STATEMENT
In this work, the front-end converter is obtained from boost topology where inductor operating in DICM is connected either to input or output.. Single sensor for output DC link is sufficient for the operation of PFC converter due to inherent power factor correction property due to DICM operation. The load side voltage doubler is formed in this OBC by shifting the diode rectifier from the supply side to the load side. Turning ON of switch Sa/Sb will automatically reverse bias the diodes thereby reducing the magnitude of conduction losses. Reduced stress can be achieved along with the charger’s suitability for higher kW operation due to the converter at the front end. More importantly, the converter’s ability to dynamically operate over a range of AC variation and load variations guarantees the practicality.

LITERATURE SURVEY:
Y. Sato, M. Uno, and H. Nagata, proposed “non-isolated multi-port converter integrating PWM and phase-shift converters,”. Multi-power-source systems containing multiple power sources have gained considerable attention since the advent of renewable energy sources, electric vehicles, etc. These systems tend to increase complexity and costs because multiple converters in proportion to the number of power sources are required to individually control each source. Multi-port converters (MPCs) that combine multiple converters into a single unit have been reported to achieve simplified systems at lower costs. Most conventional MPCs, however, pose major challenges such as the necessity of a transformer and low effective duty cycle. This paper presents a novel non-isolated MPC integrating a PWM converter and phase-shift converter. The proposed MPC, with simple topology containing only four power switches, achieves individual control of each source and bidirectional power flow. The detailed operation analysis was performed, and a 100-W prototype of the proposed MPC was built for the experimental verification. The experimental results showed that two output ports could be individually controlled with PWM and phase-shift controls, respectively, verifying its operation.
S. Venkataraman, C. Ziesler, P. Johnson, and S. Van Kempen, proposed “Integrated wind, solar, and energy storage: Designing plants with a better generation profile and lower overall cost,”. Colocating wind and solar generation with battery energy storage is a concept garnering much attention lately. An integrated wind, solar, and energy storage (IWSES) plant has a far better generation profile than standalone wind or solar plants. It results in better use of the transmission evacuation system, which, in turn, provides a lower overall plant cost compared to standalone wind and solar plants of the same generating capacity. IWSES plants are particularly suitable for regions that have set high targets for wind and solar generation but have limited land available for project development.
A. Bhattacharjee and I. Batarseh, proposed “An interleaved boost and dual active bridge-based single-stage three-port DC–DC–AC converter with sine PWM modulation,”. In this article, a new three-port converter is proposed that interfaces two dc voltage sources of different magnitudes and an output ac port in a single stage. The proposed converter is primarily based on the dual active bridge topology where the secondary bridge is composed of four quadrant bidirectional switches, which allows it to be directly connected to an ac port. The primary bridge can also be used as an interleaved bidirectional boost converter by connecting two inductors across the transformer primary, which forms an additional input DC port. The power flow between the dc ports to the ac port is based on dual phase-shift modulation where a phase shift is introduced between the two legs of the primary bridge switches and another phase shift between the primary and secondary bridges. This enables the standard sine pulsewidth modulation to be used for synthesizing ac output. For the power flow mode between the two dc ports alone, a parallel boost modulation is proposed that improves the system efficiency by removing any circulating current introduced by traditional interleaving. The proposed converter achieves fully soft switched three-port power conversion with a reduced number of active devices compared to the existing topologies. The modulation scheme is also much simpler and requires no optimization or complex control. A PowerSim-based simulation program is used for validating the proposed converter. A 200-W prototype is built to experimentally verify the theoretical analysis of the proposed converter.
J. Zhang, W. Jiang, T. Jiang, S. Shao, Y. Sun, B. Hu, J. Zhang, proposed “A threeport LLC resonant DC/DC converter,”. This paper proposes a new three-port LLC resonant converter which integrates input port, storage port, and load port in one converter. A pulse-frequency modulation and phaseshift combined control method are adopted for the proposed topology. It has four different operation modes with different gains and different power directions between input port, storage port, and load port, which are attractive for renewable energy with energy storage system applications. The proposed topology operates under resonant frequency, which is easy to implement with digital control, and it can achieve soft switching for almost all the switches and diodes similar to conventional LLC resonant converter. The performance of the proposed converter is validated by the experimental results from a 500-W prototype with 1.25-A maximum output current.
J. Zeng, J. Ning, X. Du, T. Kim, Z. Yang, and V. Winstead, proposed “A four-port DC-DC converter for a standalone wind and solar energy system,”. This article proposes an integrated, four-port, dc-dc converter for power management of a hybrid wind and solar energy system when it works in the standalone mode. Compared with existing four-port dc-dc converters, the proposed converter has the advantage of using a simple topology to interface sources of different voltage/current characteristics. The proposed converter is constructed for power management of a hybrid energy system, which consists of a photovoltaic panel, a wind turbine generator, a rechargeable battery bank, and a load. The simulation and experimental results show that the proposed converter is capable of not only controlling the charge and discharge of the battery according to the state of the charge, but also maintaining the dc-link voltage to be constant.
P. Prabhakaran and V. Agarwal, proposed “Novel four-port DC–DC converter for interfacing solar PV–fuel cell hybrid sources with low-voltage bipolar DC microgrids,”. Bipolarity in dc microgrids is desirable as it enhances the system reliability and efficiency. However, a bipolar dc microgrid (BDCMG) demands multiple conventional dc-dc converters to feed power to both the poles of the BDCMG. To handle this requirement and to maintain high efficiency, a new four-port, dual-input-dual-output dc-dc converter topology is proposed for interfacing the solar photovoltaic (PV) and fuel cell sources to a low-voltage BDCMG. The proposed topology is unidirectional, efficient, and compact. It has fewer circuit elements with only one inductor compared to the conventional nonisolated dc-dc converters. The proposed converter regulates one of the pole voltages of the dc bus and also ensures maximum power point tracking of the PV source. Furthermore, the converter can be operated as a single-input-dual-output converter. The control complexity of the proposed converter is low as it can be operated in various modes with only one set of controllers. To design the control system for the proposed converter, a small-signal model is derived for each operating mode. Loss modeling and efficiency analysis of the proposed converter are carried out, and its efficacy and performance are validated by detailed simulation and experimental results under various operating conditions.
Q. Tian, G. Zhou, M. Leng, G. Xu and X. Fan, proposed “A nonisolated symmetric bipolar output four-port converter interfacing PV-battery system,”. A bipolar dc microgrid is desirable as it enhances the system reliability and efficiency. However, the conventional bipolar dc microgrid requires multiple dc-dc converters to feed the power to the load, which leads to large volume and weight and high cost. In this article, a novel four-port converter is proposed to integrate photovoltaic (PV) module and battery to the bipolar dc microgrid system, realizing the single-stage energy conversion. The main advantages of this converter are that three switches are used to realize PV generation, battery charging and discharging, as well as symmetrical bipolar output voltage, and all input ports and output ports share the common reference ground. Depending on relationships between the energies of the source and the load, three different operation modes are defined. Then, the detailed parameter design is provided by analyzing different operation modes of the converter. Energy management and control strategies of the bipolar dc microgrid using this converter are explained in detail. Finally, experimental verifications are given to illustrate the feasibility and effectiveness of the proposed converter.
T. Chaudhury and D. Kastha, proposed “A high gain multiport DC–DC converter for integrating energy storage devices to DC microgrid,”. Interfacing multiple low-voltage energy storage devices with a high-voltage dc bus efficiently has always been a challenge. In this article, a high gain multiport dc-dc converter is proposed for low voltage battery-supercapacitor based hybrid energy storage systems. The proposed topology utilizes a current-fed dual active bridge structure, thus providing galvanic isolation of the battery from the dc bus, wide zero voltage switching (ZVS) range of all the switches, and bidirectional power flow between any two ports. The dc bus side bridge uses voltage multiplier cells to achieve a high voltage conversion ratio between the supercapacitor (SC) and the dc bus. Moreover, as the proposed topology employs only one two-winding transformer to achieve a three-port interface, the number of control variables are reduced, which decreases control complexities. The operation of the proposed converter is analyzed in detail, including the derivation of ZVS conditions for the switches and transformer power flow equations. A decoupled closed-loop control strategy is implemented for the dc bus voltage control and energy management of the storage devices under different operating conditions. A 1-kW laboratory prototype is built to verify the effectiveness of the proposed converter, along with the control scheme.
P. Kolahian, H. Tarzamni, A. Nikafrooz, and M. Hamzeh, proposed “Multi-port DC-DC converter for bipolar medium voltage DC microgrd applications,”. In this study, a new bipolar DC–DC converter based on the combination of a multi-port dual active bridge and a neutral point clamp topology is proposed. This topology provides the integration of multiple renewable energy sources, with different types and capacities, to a bipolar medium voltage DC micro-grid. The main advantages of the proposed topology are its high power density and the reduced number of switches with respect to the combination of different converters. Moreover, it provides isolation which is crucial for some micro-grid power conditioning converters. The proposed converter is employed for a typical hybrid generation system consisting of a photovoltaic (PV) system, a fuel cell (FC), and a battery (BAT) considering the characteristics of each power generation system like maximum power point tracking of PV, optimum operating region of FC and over-charge/discharge of BAT. In addition, the proposed converter is simulated in different power sharing modes in MATLAB/Simulink software environment. Eventually, the theoretical and simulation analyses are validated by experimental prototype results.
Y. Liang, H. Zhang, M. Du and K. Sun, proposed “Parallel coordination control of multi-port DC-DC converter for stand-alone photovoltaic-energy storage systems,”. Aiming at the low inertia DC micro-grid poor bus voltage quality and the energy storage SOC balanced problem, considering the urgent demand of high up/down ratio, electrical isolation and high-efficiency converter for distributed micro-source. An improved virtual capacitor (IVC) parallel coordination control strategy based on multi-port isolated DC-DC converter is proposed. First, MPIC is used to replace the traditional Buck/Boost circuit to achieve the electrical isolation from the micro sources of the energy storage system. Secondly, by analogy of IVC control, design the control frame of single voltage outside circle and multiple currents inside the ring, IVC control suitable for Four-port isolated DC-DC converter(FPIC) is obtained. Then, the parallel and coordinated control strategy under the control of IVC for multiple energy storage interface converters is established.
X. Du, J. Zeng, J. Ning, T. Kim and V. Winstead, proposed “Modeling and control of a four-port DC-DC converter for a DC microgrid with renewable energy sources,”. In this paper, modeling and control design of a four-port bidirectional DC-DC converter for integration of various energy sources to a DC microgrid is proposed. The power transferring through the transformer is first derived from the steady-state waveforms. Based on the power analysis, three controllers are developed to regulate the battery voltage/current, and the power flow between the energy sources and the DC microgrid, respectively. The converter is used to interface a wind turbine generator, a PV panel, battery, and the DC microgrid. With the designed controllers, the four-port DC-DC converter is not only capable of performing the maximum power point tracking (MPPT) for the two renewable energy sources, but can achieve bidirectional power flow between the energy sources and the DC microgrid as well.
N. Dao, D. Lee, and Q. Phan, proposed “High-efficiency SiC-based isolated threeport DC/DC converters for hybrid charging stations,”. This article proposes a novel isolated three-port dc/dc converter based on a series resonant converter and a dual active bridge (DAB) converter for electric-vehicle charging stations with fast and slow charging functions. With this three-port structure, the proposed converter has fewer components, which results in lower system cost and volume compared with separate charger systems. A simple control method using phase-shift and frequency modulations was developed to control the output power of the fast and slow charging ports simultaneously. An optimal phase-shift angle was also derived to minimize the transformer current for when only the DAB converter is operated for slow charging. To verify the converter operation, a 5-kW SiC-based prototype with a power density of 2.74 kW/dm 3 was built and tested with an input voltage of 600 V. A high-efficiency performance over a wide output voltage range has been achieved, and the peak efficiency is 98.2% at the rated conditions.