NON-ISOLATED SOFT SWITCHING DC-DC CONVERTER AND LOAD AT FULL RANGE OF ZVS

International Journal of Electrical Engineering & Technology (IJEET) Volume 7, Issue 5, September October, 2016, pp.62 69, Article ID: IJEET_07_05_006 Available online at http://www.iaeme.com/ijeet/issues.asp?jtypeijeet&vtype7&itype5 ISSN Print: 0976-6545 and ISSN Online: 0976-6553 Journal Impact Factor (2016): 8.1891 (Calculated by GISI) www.jifactor.com IAEME Publication NON-ISOLATED SOFT SWITCHING DC-DC CONVERTER AND LOAD AT FULL RANGE OF ZVS Kirti G. More and Ramling D. Patane Department of Electonics, Terna Engineering College, Navi Mumbai, India. ABSTRACT A non isolated soft switching DC DC converter and load at full range of zero-voltage switching (ZVS) characteristic is proposed. The proposed converter consists of an auxiliary circuit, an inductor, two switches, and 2 diodes to achieving high efficiency at full range of load. At low and heavy loads, ZVS of switching device is achieved by energy storing component. The inductor energy stored varies with load and hence results in minimizes conduction loss. This leads to switching of device for full range of load. The proposed DC - DC converter achieves high efficiency as switching loss is reduced due to soft switching and ZVS operation which severe to reduce conduction loss. The efficiency is improved about 4% in boost mode (2.5% in buck mode) at full range of load. To verify the performance of the proposed converter, experimental results prototype are presented. Key words: High efficiency, Non-isolated dc dc converter, Switching loss, zero-voltage switching (ZVS). Cite this Article: Kirti G. More and Ramling D. Patane, Non-Isolated Soft Switching DC-DC and Load at Full Range of ZVS. International Journal of Electrical Engineering & Technology, 7(5), 2016, pp. 62 69. http://www.iaeme.com/ijeet/issues.asp?jtypeijeet&vtype7&itype5 1. INTRODUCTION RENEWABLE energy sources like sunlight, wind, tides, waves, and geothermal heat are replacing fossil fuels which produce CO2. The electrical energy generated by the renewable sources varies in accordance with climatic conditions. For example, a solar power generation system depends on location and weather condition. A wind power generation system depends on speed and direction of wind. Hence for renewable power system an additional storage system along with DC-DC converter and unified batteries is used to maintain constant supply of power in commercial and industrial applications [1]-[6].The DC-DC converters are of two types, Isolated and Non-Isolated, depending on their application. The converters in which breaking of ground loop is done with an isolated transformer and require more than four switches are the isolated DC-DC converters [2]. While the non isolated converter consists of simple circuitry having inductors and two switches which provides high efficiency than isolated type of converter [3].The nonisolated DC-DC converters are divided into five types. Buck, boost, buck-boost, cuk and full bridge converter. These non isolated converters with application of soft switching method are used to achieve http://www.iaeme.com/ijeet/index.asp 62 editor@iaeme.com

Non-Isolated Soft Switching DC-DC and Load at Full Range of ZVS high efficiency at full range of load. Hence reduce conduction and switching losses of switches in power system [7]. Figure 1 Conventional DC DC Figure 1 shows soft switching dc-dc converter using resonant network formed by series inductor. The zero voltage switching (ZVS) characteristics is achieved at full range of load by large value of circulating current flowing through series inductor. The circulating current is free of conduction losses and load. The efficiency of converter can get degraded due to large conduction loss during light loads. Soft switching converter circuitry was proposed which provides soft switching characteristics and ripple free current by inductor [6]. But the conduction losses are of high value due to large amount of circulating current. To eliminate this problem, a high-efficiency DC DC converter with low current and ZVS characteristic at full range of loads is proposed, in Fig. 2. The varying ON time of switches controls the energy stored in inductor L. During light loads ZVS of switch Q 2 is achieved by the inactive inductor L and hence has minimized conduction loss. This results in providing high efficiency at full range of loads. A theoretical analysis and experimental prototype of the proposed converter are presented to verify the performance of the proposed converter. 2. THE PROPOSED CONVERTER Figure 2 Proposed DC-DC Figure 2 shows the circuit diagram of the proposed DC DC converter consisting of non isolated or transformer less topology. The converter has dc input source, inductor L, diode D, filter capacitor C, controlled switch Q and load as R. When the switch is ON inductor current increases and diode is in OFF state. As the switch is off the energy stored in inductor is transferred to output. Hence no energy is supplied by input during this period. Diode D 1 and D 2 are the freewheeling diodes. Figure 3 shows theoretical waveforms for proposed converter in boost and buck modes, respectively [8]. http://www.iaeme.com/ijeet/index.asp 63 editor@iaeme.com

Kirti G More and Ramling D Patane Figure 3 Buck-Boost Waveform during switch ON and OFF 2.1. Buck Mode A buck converter provides a lower output voltage than the input voltage. The main application is in dc regulated power supplies.the basic buck with a purely resistive load is represented infig.4. Consider a circuit with ideal switch with constant instantaneous input voltage and purely resistive load and then the instantaneous output voltage waveform is represented in Fig.4 [8]. The output voltage is calculated in terms of the switch duty ratio: + 0 Substitute D in Eq. (1) where!"# $%!"# (1) Where $ & '()*+) The output voltage can be controlled by varying the duty ratio!, of the switch which results in linear variation of output voltage V O with control voltage. The fluctuations in output voltage are decreased by low pass filter made up by an inductor and a capacitor. When the switch is ON, the diode is reverse biased and input serves energy to inductor and load. Hence during OFF state of switch the inductor current flows through diode and transfer some of its stored energy to load. Thus the inductor current is equal to output current. (a) (b) Figure 4 Buck converter http://www.iaeme.com/ijeet/index.asp 64 editor@iaeme.com

Non-Isolated Soft Switching DC-DC and Load at Full Range of ZVS 2.1.1. Buck as Continuous Conduction Mode (CCM) Figure 5 shows buck converter operating in continuous conduction mode[8]. Here inductor current flows continuously./ 0 1 02.During t on, switch is on and inductor current flows and reverse bias diode providing positive voltage across inductor, 0 3. Hence inductor current increases linearly to / 0.The stored inductive energy / 0 flows through diode during OFF state of switch and 0 3. (a) (b) Figure 5 Buck converter state (a) switch ON; (b) switch OFF switching states The waveform repeats from one time period to next in steady state operation. Hence the integral of inductor voltage 0 is zero at one time period, since,! + 44 6 5 0 5 0 +5 0 0 or 3!, 3! 7 89 :+/( (2) & Hence for given input voltage the duty ratio of switch varies linearly with output voltage and the voltage across inductor is zero. or! +0. 44,!, Assuming associated power loss of circuit elements to be low, then < < Since And > > & &? 3 http://www.iaeme.com/ijeet/index.asp 65 editor@iaeme.com

Kirti G More and Ramling D Patane Hence by controlling the duty ratio of switch, buck converter in continuous conduction mode works equivalent to dc transformer. 2.2. Boost Mode As shown in figure 6, for this type of DC-DC the output voltage is always higher than the input voltage [8]. The diode is reverse biased as the switch is in ON state. This causes isolation of output stage and inductor receives energy from input. During OFF state of switch output receives energy from input and inductor. Figure 6 Boost 2.2.1. Boost as Continuous Conduction Mode (CCM) Figure 7 represents waveform for continuous conduction current when inductor current flows continuously./ 0 1 02.82. For one time period the time integral of inductor voltage is zero.! + 3 44 0 Figure 7 Continuous conduction mode: (a) switch ON (b) switch OFF http://www.iaeme.com/ijeet/index.asp 66 editor@iaeme.com

Non-Isolated Soft Switching DC-DC and Load at Full Range of ZVS Dividing both sides by, and rearranging Assuming a lossless circuit, < <, & BB C? 4 And > > & 13 5 3. EXPERIMENTAL RESULTS The theoretical analyses of proposed converter are verified by prototype with the given design specifications: V JK 9V, V MN 35V, L 85mH as experimentally found. The switching device IRF640N for switches are used in proposed converter prototype. An ATMEL microcontroller 89C8051 is used. To achieve stable efficiency ADC MCP3201 along with feedback network formed by operational amplifier is used. 3.1. Verification of Boost Mode Figure 8 shows the experimental waveforms for switch in ON and OFF period for boost mode. The conduction losses and switching losses are minimized as compared to the conventional soft switching dc dc converter as shown in Fig. 1.Hence total efficiency is improved. 3.2. Verification of Buck Mode Figure 8 shows the experimental waveforms for switch in ON and OFF period for buck mode. ZVS operation of the switches is achieved in a full range of loads. Figure 8 Observed Waveform http://www.iaeme.com/ijeet/index.asp 67 editor@iaeme.com

Kirti G More and Ramling D Patane 3.3. Measured Efficiency Figure 9 shows the measured efficiency for the conventional dc dc converter and the proposed converter in boost and buck modes. The efficiency of converter in Fig. 1 is measured with the parameters L 85mH and C μf. The proposed converter achieves high efficiency and ZVS of switches for full range of loads.the proposed converter provides the efficiencies of 95.68% in boost mode and 94.02% in buck mode are obtained. Fig.10 shows the photograph of proposed dc dc converter. 98 96 94 92 90 88 Proposed Soft Switching 96 94 92 90 88 Proposed Soft Switching 86 84 50 100 150 200 Conventional Hard Switching 86 84 50 100 150 200 Conventional Hard Switching Figure.9 Measured Efficiency versus Power (a) Buck ; (b) Boost Figure 10 Proposed prototype of DC DC 4. CONCLUSION In this paper, high-efficiency with non isolation soft switching and load at full range of ZVS is proposed. The measured efficiency of the proposed converter is more than 94% from 10% load to full load. At full load as compared with a conventional hard-switching dc dc converter, the improved efficiency is 4% in boost mode (2.5% in buck mode).this is because of reduced switching loss by means of ZVS operation of the switches and the minimized conduction loss The maximum efficiencies of 95.68% in boost mode and 94.02% in buck mode are measured in the proposed converter. The proposed dc dc converter is appropriate for a system between a 9-12 V batteries. http://www.iaeme.com/ijeet/index.asp 68 editor@iaeme.com

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