Design and Analysis of Multiinput Buck-Boost Converter with Less Number of Switches

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1 Volume 4 No , ISSN: (printed version); ISSN: (on-line version) url: ijpam.eu Design and Analysis of Multiinput Buck-Boost Converter with Less Number of Switches Mudadla Dhananjaya, Swapnajit Pattnaik 2,2Department of Electrical Engineering, National Institute of Technology, Raipur, India. dhanueee203@gmail.com, swapnajit.pattnaik@gmail.com2 April 4,5-207 Abstract Power electronics offer a cost effective solution for connecting components at either source end or load end based on multiple converter configurations. This paper presents a non-isolated multi input buckboost converter (MIBBC) with less number of switches there by reducing the switching losses. The voltage and current stresses on a particular switch have been analyzed for proper selection of switches. The effect of change in output voltage with respect to delay in the turning on of switches has been investigated. Further, using of a single inductor reduces the cost and complexity of the system. A laboratory prototype have been developed for experimental validation which shows the efficiency and effectiveness of the presented topology by using dspace controller (04). Key Words:Multi input, buck-boost converter, efficiency.. Introduction In recent years, there has been a vast increase in the demand of renewable energy sources due to depletion of fossil fuels in the 29

2 near future and also increase in global warming, greenhouse effect, environmental pollution and problems associated with the conventional sources of energy [-3]. There has been an increased utilization of fuel cell stack over the wind and PV systems [4]. In order to meet the energy demands, hybridization of the energy systems is gaining more importance for various applications like hybrid vehicles and household applications [5]. But this needs a proper interfacing circuitry to combine various energy systems to meet the power demand [6-7]. Multiport converter have grabbed attention in recent years as the system with single input source has the drawback of less power density [8]. Moreover, in hybrid system the V-I characteristics of energy sources differ from each other and hence in order to obtain the required output voltage, multiport converters are to be used [9]. The advantages of these converter include simple circuit topologies, centralized control, high reliability, low manufacturing cost and size [4]. Also, the multiport converter has the benefit of integrating a number of converters either in the input DC-DC converter stage or in the isolation stage, in addition to the commonly shared output stage [0]. The output voltage of the renewable sources such as fuel cell, photovoltaic unit is quite low and fluctuating which prevents the direct connection of these units to the load as they need a constant DC voltage. Power electronic converter plays a vital role for voltage conversion. A buck-boost converter can be used to maintain a constant DC voltage [-2]. Multiinput single output (MISO) converter have been well established in the literature. Early MISO were designed by connecting the input voltage source in series to obtain a multiinput topology [3-4]. To prevent input sources to get shorted, an active switch is connected in series with each input source such that only one source can transfer energy to the load at a time [5]. DC-DC converters can be either isolated structure or non-isolated [0]. Several types of DC-DC isolated converters have been proposed [6-7], their drawbacks include leakage loss due to which the conversion efficiency gets lowered, induces high voltage stress in the switches and also increases the switching losses along-with increased Electro-magnetic interference (EMI) problems. The solution to the above mentioned problems is the active clamp circuit which recycles the leakage energy, but increases the circuit complexity [8]. Hence various multi input topologies were proposed based on non-isolated structures [9-23]. A non-isolated multi-input buck/boost converter time sharing concept has been proposed in [4]. A four switch bidirectional buck boost converter, with similar concept is proposed [9]. In [20], an auxiliary circuit was used to achieve soft switching for 30

3 series connected boost converters. In [2], a general derivation for non-isolated parallel integrated multi-input converters including SEPIC and Cuk has been proposed. In [22], a different approach based on switched capacitor converter has been reported. In this paper, a multi input buck-boost converter is presented which has an advantage of using less number of switches as compared to the other topologies (Table ). This reduction in the number of switches reduces the switching and conduction losses thereby increasing the efficiency of the converter. The input power delivered by different DC sources can be regulated individually. This topology employs only one inductor which indeed reduces the complexity as well as cost of the system. The key features of the presented topology include Less number of switches compared with few other topologies Low cost and simple design High efficiency This paper is organized as follows. Section 2 describes the presented topology and its operation. Whereas Section 3 shows the calculation of loss and efficiency. Simulation and experimental results are shown in Section 4 followed by conclusion in Section Circuit topology and operation of multiport buck-boost converter The Multi-input DC-DC converter is shown in Fig.. With VDC, VDC2 (VDC>VDC2) as input voltage sources. The voltage sources are interfaced through a diode. A common inductance, L has been shared by the energy sources and the output capacitance is C [24-26]. SW SW 2 V DC V DC2 D 2 D D L C R Fig.. Schematic of multi-input DC-DC converter. Modes of operation Mode 0 t t In this interval power switch SW is ON, SW2 is OFF and diode is 3

4 reverse-biased. The inductor is energized by the input power VDC as shown in Fig. 2(a). SW SW SW SW 2 SW 2 V DC V DC2 SW 2 V DC V DC2 V DC V DC2 D 2 D 2 D 2 D L D L D L D C R D C R D C R (a) (b) (c) Fig. 2(a), (b), (c) Equivalent circuit of operation during Modes,2,3 and 4. Mode2 t t t 2 In the second interval, SW is turned OFF and to avoid the simultaneous conduction of both the switches, SW2 is not turned ON immediately. By providing delay between the active periodsof the two sources of the converter. In this mode the energized inductor transfer its energy to the load. The equivalent circuit of Mode II is in the Fig. 2(c). Mode3 t t 2 t 3 In this mode, as shown in Fig. 2(b) switch SW2 is ON, VDC2 supplies the energy to the inductor, and it is energized, switch SW and diode are in to OFF state. Mode4 t t 3 t 4 In this interval power switches SW, SW2 are OFF, Diode will be forward-biased through load and capacitor is charged reversely by the demagnetization of inductor (L). The equivalent circuit of the converter is shown in Fig. 2c. The conduction time for both power switches in the respective modes of operation can be determined by the values of duty ratio of the switches. Applying volt - second balance principle to four modes of the operation dil dil dil dil L t 0 L t 2 t L t3 t2 L t4 t3 0 () dt dt dt dt V t dt s t t V t t V t t 0 DC t VO 2 DC , t 2 t d Ts, t 3 t2 d2ts and t 4 t3 d Ts 32 (2) (3)

5 d T 0 V (4) DCdTs V0d Ts VDC 2d 2Ts V0 s V V d DC DC (5) d V d d where d is the delay time between switches, d is the duty ratio of the OFF time d+ d gives the total OFF state of the switches 2.2Calculation of voltage and current stress The voltage across each switch is calculated as follows [9]. In Mode according to Fig. 2(a) the voltage across the switch SW is zero. Applying KVL to the loop with VDC, VDC2, SW, and SW2 the voltage across the switch SW2 is as follows. V SW2 VDC VDC 2 Vd (6) Similarly in Mode3 according Fig. 2(b) voltage across switch SW2 is zero. Applying KVL to the loop with VDC, VDC2, SW, and SW2 the voltage across the switch SW is as follows V SW VDC2 VDC Vd 2 (7) In Mode2 and Mode4 the switches SW, and SW2 should block the respective source voltages, VDC and VDC2 respectively i.e. V V (8) and SW DC V V (9) SW2 DC 2 Let current passing through the power switches and diode be indicated as isw, isw2 and id respectively i SW il dt s 0 dt s (0) i SW 2 il d2ts 0 dt 2 s () i D 0 dt s, d2ts i L dd2 T s (2) 3. Calculation of power loss and efficiency Power losses across the switch mainly include conduction and switching losses. In the ON state, the IGBT conducts a current for an interval ton for every switching period, TS. Conduction losses are calculated considering the duty ratio(d) of the switch [5], [29]. 33

6 P c _ sw T S t on 0 V I dt C S (3) VC is the voltage drop across the switch when it conducts and ISis current through the switch Diode losses are calculated as P C _ D T S t on 0 V F I F dt (4) VF is forward voltage drop, IF is the forward current of diode In DC-DC converter at high switching frequencies switching losses play an important role in determining the efficiency of the converter. Switching loss are calculated as P V I t t f (5) 6 where SW B on off VB- is the blocking voltage of the switch, I- is the current through the switch, ton - on time, toff - off time of the IGBT, obtained from data sheet of STGW30NC20HD, f - is the switching frequency of the converter The efficiency of the converter is given by P out (6) P P P P out C _ SW SW C _ D Table Comparison of various components in presented topology with other existing multi-input topologies Topology Proposed Khaligh A et.al [9] Kumar L et. al [5] S. Rezaee et. al [28] Gavris et. al [27] No. of sources(n) No.of switches No.of Diodes Total switches Inductor Capacitor Expected efficiency (%) 2 N N N N Presented 2 N Table shows that the presented topology having less number of device count leads to reduce cost, complexity, size, simple controlling and using less number of switches there by reduction in the switching loss to get the higher efficiency. 34

7 4. Simulation and experimental results The simulation of the converter is performed in MATLAB/SIMULINK using SimPower Toolbox. For input voltages VDC=50V, VDC2=40V the output voltage and the various responses of the system are shown in the figures. Fig. 3(a) shows the output voltage of the presented converter. Fig. 3(b) shows the inductor current of the presented converter at different modes operation. (a) (b) Fig. 3. (a) Output voltage, (b) Inductor current Experimental results A low voltage hardware setup is developed to verify the feasibility of the presented converter. The selection of the components and the values of input voltages are VDC=50, VDC2=40, IGBT= STGW30NC20HD, inductor=5mh and capacitor=0uf. The control signals for power switches are generated using dspace controller. Switching pulses are generated in accordance with the modes of operation with appropriate duty ratios as shown in Fig. 4(a) and the output voltage of the converter is shown Fig. 4(b) the variation of inductor current in different modes of operation as shown in Fig. 4(c) the efficiency of the converter is plotted as shown in the Fig. 4(d). Voltage and current stress of the two switches are with in stress tolerance as show in the Fig. 4(e) and (f) and it has small switching loss which can be reduced by using soft switching techniques. (a) 35 (b)

8 (c) (d) Isw Isw2 VCE VCE2 (e) 5. Conclusion A non-isolated multi input BBC has been presented. The advantages of this converter include less number of switches there by decreasing the power loss and increasing the efficiency of the converter, using single inductor reduced the cost and complexity of the system. The operation of the presented converter has been studied and analyzed with two inputs. Simulation and experimental results clearly justifies the effectiveness and efficiency of the presented converter. 6. References [] B. Mangu, S. Akshatha and D. Suryanarayana, "Grid- Connected PV-Wind-Battery based Multi-Input Transformer Coupled Bidirectional DC-DC Converter for household Applications," IEEE Journal of emerging and selected topics in power electronics, vol. 4, no. 3, pp , Sept [2] M. R. Banaei and H. A. F. Bonab, "A Novel Structure for Single Switch Non-Isolated Transformerless Buck-Boost dcdc Converter," IEEE Trans. Ind. Electron., 206. [3] M. Fekri, H. Farzanehfard and E. Adib, "An Interleaved High Step-Up DC-DC Converter With Low Input Current Ripple," in Proc. PEDSTC, Conf.,Tehran, Iran, 206. [4] S. Danyali, S. H. Hosseini and G. B. Gharehpetian, "New Extendable Single-Stage Multi-input DC DC/AC Boost Converter," IEEE Trans. power electron., vol. 29, no. 2, pp , Feb [5] L. Kumar and S. Jain, "Multiple-input DC/DC converter topology for hybrid energy system," IET Power Electron, vol. 36 (f)

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