Analysis of An Non-Isolated Interleaved Buck Converter with Reduced Voltage Stress And high Step down Ratio

Transcription

1 Analysis of An Non-Isolated Interleaved Buck Converter with Reduced Voltage Stress And high Step down Ratio SHEETAL NAND DR. R. DHANALAKSHMI Department of Electrical and Electronics Engg. Dayananda Sagar College of Engineering Bangalore, INDIA Abstract-An Interleaved Buck Converter for high gain and reduced voltage stress DC-DC converter is proposed. A very high step down conversion is achieved by using IBC.The main objective is by using voltage divider circuit for both storing energy in capacitors and for reducing voltage stress on the switches. Input capacitors in the proposed circuit are series charged by the input voltage and parallel discharged by new twophase interleaved buck converter. The proposed converter has low voltage stress on the switches this is achieved by using lower rating MOSFET S which reduces switching and conduction losses both. Therefore overall efficiency is improved by using thesemosfets and the cost is also reduced. This IBC has uniform current sharing characteristics by using voltage divider circuit and there is no need of adding any extra circuitry. This proposed converter has 200V input voltage 12V output voltage.analysis of the proposed IBC are presented through simulation by MATLAB Simulink. Index Terms-The main feature of this proposed topology is to achieve high gain by step down conversion and to reduce voltage stress on the active switches. I.INTRODUCTION DC-DC converters are widely used in Power Electronics devices for step-up or step-down conversion depending on the application and requirement. Buck converter is used to achieve step down conversion ratio because of its reduced size, Simple structure, low cost and in application ranging from low power regulators to very high step down converters this buck converter are having very less components and used in non-isolation application. In this project we are making use of Interleaving Buck Converters (IBC) because it is a parallel combination of two Buck converter having two switches, diode and inductors connected to common capacitor and output load. Interleaving also known as Multi-phasing.The frequency of IBC is twice as large as individual inductor currents this will lead to smaller peak to peak variation in capacitor current. Multiphase interleaving technique is also used to handle large output current requirement to improve transient response. They are able to share current equally and handle bulk power. Interleaving operations include N converters to operate in parallel so that the frequency is N times the single converter frequency. IBC is used where large step down conversion is required like 3.3 to 5 V for Telecom and Datacom fields, In Automobile industry its 12 V to 14 V for battery charging application, Personal computers for Voltage regulator module (VRM), Microprocessor, LED drives, Renewable energy system, Military and Medical domain etc. In this project we are implementing for battery charger for automotive applications which require 12 V. Automotive battery is a type of rechargeable battery that supply energy to the automobile that uses lead-acid type of battery made of six galvanic cells to provide 12V system. Each cell provides around 2.1V so that total voltage for full battery is 12.6 V and for heavy vehicles like trucks it will require two batteries in series for 24V system. IBC has received lot of attention due to its low complexity control and has many advantages compared to buck converter. Fig 1: Conventional Interleaved Buck Converter (IBC) In the conventional Interleaved buck converter shown in Fig.1,due to high input voltage all semiconductor active switch devices are effected. So, voltage devices used must be of higher rating than the input voltage applied. High-voltagerated devices has disadvantages like high cost, high onresistance, high forward voltage drop, severe reverse recovery, And the converter operates in hard switching condition. Therefore, the cost becomes high and the efficiency becomes poor. For higher power density applications, it is required for the converter to operate at high switching frequencies. A 516

2 double frequency buck converter (DF) is proposed [1] to increase the switching frequency which can improve the dynamics of power converters, buthigher switching frequencies results in increased switching losses. Consequently, the efficiency is further reduced. In case of high-input and low-output voltage applications active switches experience an extremely short duty cycle. To overcome the drawbacks of conventional IBC many step down converters have been proposed. Three level ZVS active clamping PWM [2] has been proposed. Active clamp circuits can implement zero voltage switching of active switches during turn on and turn off transition.but the drawback is more components are required for the use of IBC and this makes the circuit complicated.a single-capacitor turn off snubber [3]is introduced in the above IBC. By using snubber switching loss during turn-off transition can be reduced. But this circuit operates at discontinuous conduction mode (DCM) and all elements suffer from high-current stress, resulting in high conduction and core losses.in future analysis made on automotive dc-dc bidirectional converter [4] in this proposed topology much higher number of interleaved phases are connected in parallel together using interleaving technique the power stages is divided into several smaller power stages and therefore the size of the components is reduced, current stress is reduced and efficiency is improved. But the drawback is that controlling of current loop per phase will be difficult and cost effective.[5] Quadratic buck converter with single switch is proposed. In this dc conversion ratio is dependent on duty ratio. It is equal to two-buck converters connected in cascade by using only one active switch. the drawback is that current mode control and voltage mode control is needed for quadratic buck converter and its complicated due to inner coupling of inductor. Voltage control mode requires compensator which makes the performance poor.two IBC without coupling inductors is presented [6]. This interleaved buck converter has received a lot of attention and has advantages compared to single converter the input and output ripple is very low, the ripple frequency can be doubled the size of the filter is very small and less components are involved and transient response is improved. due to smaller filter components reduction in the peak current will have lower electromagnetic induction noise.the drawback is higher number of switches and gate drive circuits are needed so the control is more complexconverters [7] in this they have used TL ( three level ) to reduce voltage stress on the switches and to have improved step down conversion for medium to high power applications. The output voltage of these have lower harmonics and the size of the filter is also smaller. This TL converter is essentially a half bridge converter. This uses feed forward control scheme this makes the control of circuitry complicated this is an major drawback of this work.an interleaved synchronous buck converter [8] is the solution for achieving very high current and to handle high current powered microprocessors because input and output current ripple are lower. It also enables dissipated power over the PCB area by using equal current sharing circuit. Drawback is more components are needed and the cost is very high.automotive Interleaved Buck Converter in this [9] application the power management system should be smart enough to handle the key off loads from high voltage batteries. Where volume, cost and weight are important therefore the choice is single battery system 12V. The power converter should be able to cover all the requirements needed for 12V load. In non-isolated converters there is no need for isolation between input and output buses it s an added advantage for automotive power net over transformer isolation type of configuration where cost will be also high.in further analysis of work done they have used zero current transition Interleaved converter [10] turn on transition is done at zero current and two set of switches are operating out of phase in this to share load power equally. The losses associated with diode are reduced by employing two small inductors. This uses IGBT S to reduce turn off losses by the current tailing. the major disadvantage of this approach include very high peak current in the switch, therefore conduction losses increases and circuit control is more complicated. II.Proposed Circuit: Fig 2: Circuit diagram of proposed interleaved buck converter The Proposed topology consists of voltage divider circuit as shown in figure 2.The voltage divider circuit consists of capacitors across the MOSFET switches connected in parallel by doing this kind of arrangement voltage stress on the active switches is reduced by equal sharing of current and by storing energy in the capacitors which gives very high step down conversion ratio.there are four modes of operation with the duty cycle less than 0.5 so that the circuit operates in the CCM mode and current sharing will be uniform during operating in CCM mode. Mode 1: III. Modes of operation: 517

3 The figure 3 shows the equivalent circuit In this mode of operation switch S1a, S1b is on and diode D1 freewheels in this mode switch S2b and S2a are off the energy stored in the inductor is retrieved to the load by following the current path through C1, S1a,C A,L2 and then to Co and R. in this mode energy stored in C1 is released to C A, L2 and the output load. Energy stored in the C B is released to L2, Co and R which follows another path. Therefore inductor current I L2 is increasing and inductor current I L1 is decreasing. The voltage stress across the C1 is equal to V C1 = V in /2 and V ca and V cb = V in /4. Fig 5: mode 3 equivalent circuit for proposed IBC Mode 2: Fig: 3: mode 2 equivalent circuit for proposed IBC Figure 5 shows the equivalent circuit of mode3 operation in this mode of operation switch S2b and S2a are turned ON and diode D2 the current in the inductor I L1 follow two paths that is through C A, L1, Co and R then freewheels through D2, C B and S2b back to C2 again. The energy from capacitor C2 is discharged to C A,, L1 and load. Another path is from C A,, S2a, L1 and to the load freewheels through diode D2 again to capacitor C A,. The energy from C A, is retrieved to L1 and the load. So the current in I L1 is increasing and I L2 is decreasing. V C2 = V ca + V CB Because of S3 and S2 are ON. V C2 = V in 2 andv ca = V cb = V in /4. Mode 4: Fig: 4: mode 2 equivalent circuit for proposed IBC The equivalent circuit for mode 2 is shown above in fig 4. In this mode of operation S1a, S1b, S2aand S2b are turned off. Both the inductors currents will flow through freewheeling diodes D1 and D2 Therefore inductor current I L2 and I L1 are decreasing in this mode due to release of energy to the load. The voltage across the inductors V L1 and V L2 will be equal to - V o respectively. Mode 3: Fig6: mode 4 equivalent circuit for proposed IBC Figure 6 shows the equivalent circuit for mode 4 operation in this mode all the switches S1,S2a, S2b and S1b are turned off and its operation is similar to mode 2. The energy stored in inductors L1 and L2 are released to the load and freewheels through the diode D1 and D2 therefore current in inductor I L1 and I L2 are decreasing and its equal to -Vco. 518

4 Frequency ( Hz) Inductors ( L1 & L2) 65Hz 150µ H Capacitors ( C1 & C2) 250µF C3 & C4 10µF Output Capacitor ( Co) 250µ F R L 1.56Ω Table V shows the specification which is used in designing the parameters values in the Simulink model which is given in the figure 8. Fig 7: waveform of the modes of operation VI. Simulation waveforms results: Figure 7 shows the waveform of different modes of operation for duty cycle less than 0.5 The voltage stress on the active switches are reduced and current through the inductors I L1 and I l2 are verified. IV. Circuit arrangement of Simulink model: (a) (b) Fig : 8 Simulink model of proposed IBC converter V. SPECIFICATIONS: Fig 9: waveforms of the (a) input voltage 200V and (b) output voltage 12V. Parameters Input Voltage Values 200 V 519

5 (a) (d) Fig 10 : (a) shows the voltage across Vc1, (b) across Vc2 (c) acrossvca (d) across Vcb. (b) Fig 11: Current through inductor L1 & L2 which is 4V ( c ) (a) 520

6 [7] J. P. Rodrigues, S. A. Mussa,M. L. Heldwein, and A. J. Perin, Three level ZVS active clamping PWM for the dc dc buck converter, IEEE Trans.Power Electron., vol. 24, no. 10, pp , Oct [8] Optimal design for an interleaved synchronous buck converter, System Engineering, Power Management Products, Texas Instruments Incorporated. [9] Automotive Interleaved Buck Converter, System Engineering, Power Management Products, Texas Instruments Incorporated (b) [10] Interleaved Zero-Current-Transition Buck Converter, ieee transactions on industry applications, vol. 43, no. 6, november/december Fig 12: (a) voltage across the Diode D1 (b) voltage across the diode D2 VII.Conclusion In this paper A non-isolated interleaved Buck converter with reduced voltage stress and switching losses have been proposed in this proposed converter has two input capacitors which is used for series charging and parallel discharging and for providing higher step down conversion ratio. The main objective is by using voltage division principle. As a result the proposed converter has very low voltage stress on the switches which will allow us to choose lower rated devices which will reduce the cost of our project. Current stress is also reduced by uniform sharing of the current. The operating principles and relevant analysis of the converter are verified using Matlab software for input voltage 200V, output voltage 12V, 100W output power has been verified. VIIIReferences: [1] X. Du and H. M. Tai, Double-frequency buck converter, IEEE Trans.Ind. Electron., vol. 56, no. 54, pp , May [2] J. P. Rodrigues, S. A. Mussa,M. L. Heldwein, and A. J. Perin, Three levelzvs active clamping PWM for the dc dc buck converter, IEEE Trans.Power Electron., vol. 24, no. 10, pp , Oct [3] Y. M. Chen, S. Y. Teseng, C. T. Tsai, and T. F. Wu, Interleaved buckconverters with a single-capacitor turn-off snubber, IEEE Trans. Aerosp. Electron. Syst., vol. 40, no. 3, pp , Jul [4] C. Garcia, P. Zumel, A. D. Castro, and J. A. Cobos, Automotive dc dc bidirectional converter made with many interleaved buck stages, IEEE Trans. Power Electron., vol. 21, no. 3, pp , May [5] J. A. S. Morales, J. Leyva-Ramos, E. E. G. Carbajal, and M. G. Ortiz- Lopez, Average current-mode control scheme for a quadratic buck converter with a single switch, IEEE Trans. Power Electron., vol. 23, no. 1,pp , Jan [6] Interleaved buck converter havin low switching losses and improved step-down conversion ratio, Digital Object Identifier /TPEL

7 International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE) 522