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A NOVEL TRANSFORMER-LESS INTERLEAVED FOUR-PHASE STEP-DOWN DC CONVERTER WITH LOW SWITCH VOLTAGE STRESS AND AUTOMATIC UNIFORM CURRENT SHARING CHARACTERISTICS ABSTRACT: In this paper, we propose a novel transformer-less direct current (dc) converter that features low switch voltage stress and automatic uniform current sharing. An interleaved four-phase voltage divider operating from a 400V DC bus is used to achieve a high step-down conversion ratio with a moderate duty ratio. Based on the capacitive voltage division, the proposed converter achieves two major objectives, i.e., increased voltage conversion ratio, due to energy storage in the blocking capacitors, and reduced voltage stress of active switches and diodes. As a result, the proposed converter permits the use of lower voltage rating MOSFETs to reduce both switching and conduction losses, thereby improving the overall efficiency. In addition, due to the charge balance of the capacitors, the proposed converter enables automatic uniform current sharing of the interleaved phases without adding extra circuitry or complex control methods. The operation principles and performance analyses of the proposed converter are presented, and its effectiveness is verified by a 500W output power prototype circuit that converts 400V input voltage into 24V output voltage INTRODUCTION: In this paper, we propose a novel transformer-less direct current (dc) converter that features low switch voltage stress and automatic uniform current sharing. An interleaved four-phase voltage divider operating from a 400V DC bus is used to achieve a high step-down conversion ratio with a moderate duty ratio. Based on the capacitive voltage division, the proposed converter achieves two major objectives, i.e., increased voltage conversion ratio, due to energy storage in the blocking capacitors, and reduced voltage stress of active switches and diodes. As a result, the proposed converter permits the use of lower voltage rating MOSFETs to reduce both switching and conduction losses, thereby improving the overall efficiency. In addition, due to the charge balance of the capacitors, the proposed converter enables automatic uniform current sharing of the interleaved phases without adding extra circuitry or complex control methods Quadratic buck converters were built with cascaded dc-dc buck converters which achieve a high voltage conversion ratio. These converters can be transformed into fewer switch topologies to achieve improved characteristics, such as size, and simplified driver design. It can be operated over a wider range of the step-down conversion ratio without using an extremely low duty ratio. However, it requires an additional power stage that reduces the efficiency. A three-level buck converter was proposed to lower the switch voltage stress to half of the input voltage. By using metal-oxide-semiconductor field-effect transistors (MOSFETs), improved efficiency and enhanced performance are achieved as compared to the conventional buck converters whose switches must be rated for the full dc bus voltage. On the other hand, an IBC uses a high number of components. An IBC with a single-capacitor turnoff snubber was introduced which reduces the switching loss associated with turn-off transition. In this design, a single coupled inductor implements the converter with two output inductors. However, it can only be operated at the discontinuous conduction mode (DCM) and, as such, all elements suffer from a high current stress, resulting in high conduction and core losses. Moreover, the input voltage still applies across all semiconductor devices. To reduce switching losses, an active-clamp IBC was proposed In this converter, all active switches are turned on with zero-voltage switching (ZVS). EXISTING SYSTEM: In the conventional multi-phase IBC, active switches are required to use high-voltage devices that are rated above the input voltage. High-voltage-rated devices generally render a number of undesirable characteristics, such as high cost, large on-resistance, large voltage drop, and severe reverse recovery. For high-input low-output voltage regulation applications, operations at higher switching frequencies are required to achieve a higher power density and better dynamics. However, the buck converter with a high step-down conversion rate yields a significant switching loss due to its extremely low duty cycle. This fact not only limits the achievable switching frequency, but also complicates its implementation. In addition, the efficiency is further compromised due to the short on-time and long freewheeling time within each switching cycle. PROPOSED SYSTEM: In this paper, we propose a novel transformer-less dc converter that features low switch voltage stress and automatic uniform current sharing. An interleaved four-phase voltage divider is used to achieve a high step-down conversion ratio. In the proposed converter, series charging of the two capacitors from the input voltage and parallel discharging to the load facilitated by a new four-phase IBC. This architecture provides a high step-down conversion ratio and a low output current ripple without requiring an extremely low duty cycle. Moreover, due to the charge balance of the capacitors, the converter features automatic uniform current sharing of the interleaved phases without adding extra circuitry or complex control methods. ADVANTAGES: Increased voltage conversion ratio, due to energy storage in the blocking capacitors. Reduced voltage stress of active switches. Reduce both switching and conduction losses, thereby improving the overall efficiency BLOCK DIAGRAM: TOOLS AND SOFTWARE USED: MPLAB – microcontroller programming. ORCAD – circuit layout. MATLAB/Simulink – Simulation APPLICATIONS: Voltage regulator modules (VRMs) for computer central processing unit (CPU) boards. Battery chargers. Distributed power systems CONCLUSION: In this paper, we have proposed a novel transformer-less dc converter that offers a high stepdown conversion ratio, low switch voltage stress, and automatic uniform current sharing. The proposed converter topology yields a low switch voltage stress and, thereby, enables the use of low voltage rating MOSFETs to reduce both switching and conduction losses. It achieves an improved overall efficiency and features automatic uniform current sharing. The operation principle and steady-state analyses of the voltage gain were provided, and the effectiveness and superiority of the proposed converter were verified by experimental studies sing a prototype circuit. REFERENCES: [1] D. D.-C. Lu and V. G. Agelidis, “Photovoltaic-battery-powered DC bus system for common portable electronic devices,” IEEE Transactions on Power Electronics, vol. 24, no. 3, pp. 849855, March. 2009. [2] Kai Sun, Li Zhang, Yan Xing, and Guerrero, J.M., “A distributed control strategy based on DC bus signaling for modular photovoltaic generation systems with battery energy storage,” IEEE Transactions on Industrial Electronics, vol. 26, no. 10, pp. 3032-3045, Oct. 2010. [3] M. Pahlevaninezhad, J. Drobnik, P.K. Jain, and A. Bakhshai, “A load adaptive control approach for a zero-voltage-switching DC/DC converter used for electric vehicles,” IEEE Transactions on Industrial Electronics, vol. 59, no. 2, pp. 920-933, Feb. 20112.