INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING & TECHNOLOGY (IJEET) Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14) ISSN 0976 6545(Print) ISSN 0976 6553(Online) Volume 5, Issue 12, December (2014), pp. 277-283 IAEME: www.iaeme.com/ijeet.asp Journal Impact Factor (2014): 6.8310 (Calculated by GISI) www.jifactor.com IJEET I A E M E VERY HIGH VOLTAGE BOOST CONVERTER BASED ON BOOT STRAP CAPACITORS AND BOOST INDUCTORS USED FOR PHOTOVOLTAIC APPLICATION USING MPPT Mr. AMAR C S 1, Prof. V.M VIJAYAN 2 1,2 Electrical and Electronics Engineering Department, Sree Narayana Gurukulam College of Engineering, Kolenchery, Kerala, India ABSTRACT Very high voltage-boosting converters based on Bootstrap Capacitors and Boost Inductors used for Photovoltaic application using MPPT are presented. These converter are constructed based on bootstrap capacitors and boost inductors. In this method of improving the voltage conversion ratio, this is based on the fact that the number of inductors and capacitors are increased, and these inductors and capacitors are connected in series during the demagnetizing period, thereby pumping the energy created by the input voltage and the energy stored in the inductors into the output terminal to obtain the high voltage conversion ratio. There are five switches in each converter, only two half-bridge gate driver and one low-side gate driver are needed, but no isolated gate driver would be needed. This proposed topology makes a very high voltage conversion ratio than the existing methods with higher efficiency and reliability Keywords: Boot Strap Capacitor, Boost Inductor, MPPT. I. INTRODUCTION Now a days, the grid-connected photovoltaic (PV) systems, especially the low-power single- phase systems, call for high efficiency, small size, light weight, and low-cost grid connected dc-dc high voltage step up converters. High step-up converters have been widely used in the industry, such as in high intensity discharge lamp driver, uninterruptible power supply, and solar cell system[2],[3]. For the solar cell system to be considered, it needs the high voltage-boosting converter to transfer the low voltage to the high voltage which will be transferred to the ac output voltage via the dc-ac converter. Such a high voltage-boosting converter consists of the traditional boost or fly back converter. The boost converter is simple in structure, but the voltage conversion ratio is not so high, whereas the fly back converter possesses a high voltage conversion ratio but the corresponding leakage inductance is large. This method of improving the voltage conversion ratio, these converters are constructed based on bootstrap capacitors and boost inductors and this is based on the fact that the number of inductors is increased, and these inductors are connected in series during the demagnetizing period, thereby pumping the energy created by the input voltage and the energy stored in the inductors into the output terminal to obtain the high voltage conversion ratio [1]. A high voltageboosting circuit, based on three bootstrap capacitors and two inductors, are presented here. Although two inductors are connected in series during the demagnetizing period, variations in values of these inductors allow such converters to work appropriately. The proposed voltage conversion ratio is higher than all the other voltage conversion ratios in other converters. For this converter, only two half-bridge gate driver and one low side gate driver are needed, but no isolated 277
gate driver would be needed. In this paper, a brief illustration of the operation of this converter is given along with some experimental results provided to demonstrate the effectiveness of the converter. II. PROPOSED TOPOLOGY The block diagram of the entire system is shown below. A PV module is used to generate the dc input voltage. The proposed high voltage boost converter with MPPT control is placed between the panel and the inverter. Fig1.block diagram for the proposed converter with MPPT PV Module PV module represents the fundamental power conversion unit of a PV generator system. The output characteristics of PV module depends on the solar irradiance, the cell temperature and output voltage of PV module. Since PV module has nonlinear characteristics, it is necessary to model it for the design and simulation of PV system applications. Maximum Power Point Tracking Maximum power point tracking (MPPT) is a technique that grid connected converters, Solar battery chargers and similar devices use to get the maximum possible power from one or more photovoltaic devices, typically solar panels. The proposed boost converter has controlled semiconductor switches and it is controlled by applying appropriate gating pulses. The turn off resistance of the switch is very much higher than the turn on resistance. Thus by varying the duty cycle of the gating pulse, the effective resistance offered by the circuit is varied. The boost converter is placed right between the inverter and the PV panel to ensure maximum power transfer. The resistance of the circuit as seen from the PV panel must be equal to the internal resistance of the PV module for maximum power transfer. The duty cycle of the boost converter is adjusted in such a way that maximum power is transferred from the module to the output terminal. The performance of the PV panel depends highly on then environmental conditions which vary throughout the day. The efficiency of the PV panel is very less and hence it becomes necessary to extract the maximum power from the panel by shifting the operating point to the maximum power point. The operating point of the PV panel is fixed by the load resistance. Incremental conductance algorithm [5] is adopted in this work due to its simplicity. In this algorithm, module voltage is changed according to the feedback voltage thus by made the PV panel operating point to force tracking in the direction towards maximum power point. Incremental Conductance Algorithm The basic idea is that the slope of P-V curve becomes zero at the MPP. It is also possible to find a relative location of the operating point to the MPP by looking at the slopes. The slope is the derivative of the PV module s power with respect to its voltage and has the following relationships with the MPP = 0 at MPP (1) > 0 at the left of MPP (2) < 0 at the right of MPP (3) 278
The flowchart shown in Fig 2. explains the operation of this algorithm. It starts with measuring the present values of PV module voltage and current. Then, it calculates the incremental changes, di and dv, using the present values and previous values of voltage and current. Fig 2. Flowchart of Incremental Conductance Algorithm III. MODIFIED HIGH VOLTAGE BOOST CONVERTER BASED ON BOOT STRAP CAPACITORS AND BOOST INDUCTORS Fig.3 Modified High Voltage Boost Converter Based On Boot Strap Capacitors and Boost Inductors Converter contains five MOSFET switches S 1, S 2, an S 3,S 4, and S 5 three bootstrap capacitors C b1,c b2 and C e, three bootstrap diodes D b1, D b2,d 1, and D 2, one output diode Do, two inductors L 1 and L 2, one output capacitor Co, and one output resistor R L. In addition, the input voltage is signified by Vi, the output voltage is represented by Vo, the voltages across C b1,c b2, C e, D 1, and D 2 are shown by V Cb1,V Cb2, V Ce, V D1, and V D2, respectively, and the currents flowing through L 1, L 2, and D o are denoted by i L1, i L2, and i Do, respectively is noted that the proposed converters are based on the charge pump of the KY converter[4] and the series boost converter. By doing so, the conversion ratios can be upgraded further. Above all, if the anode of the diode D 1 is connected to the cathode of the diode Db, the conversion voltage ratio 279
in continuous conduction mode (CCM) from the controller. Basic Operating Principles The converter operated in the CCM are to be analyzed in the following, under the condition that L 1 is equal to L 2. However, actually, L 1 is different from L 2. Mode 1 is (4 + D)/(1 D), where D is the duty cycle of the PWM control signal created Fig 4. Proposed converter operating in mode1 As shown in Fig 4. S 1, S3 and S 5 are turned on, but S 2,S 4 is turned off. Due to S 5 being turned on, Do is reverse biased, but D 1 and D 2 are forward biased, thereby causing Ce to be abruptly charged to V i plus 2V Cb, whereas due to S 1 being turned on, D b1 is reverse biased, thereby causing C b to be discharged and due to S 3 being turned on, D b2 is reverse biased, thereby causing C b2 to be discharged. At the same time, the voltages across L 1 and L 2 are V i plus V Cb, thereby causing L 1 and L 2 to be magnetized. Also, C o releases energy to the output. In this mode, the voltages across L 1 and L 2, V L1 ON and V L2 ON, can be written as V L1 ON =V i + V Cb1 +V cb2 V L2 ON =V i + V Cb1 +V cb2 (4) (5) Mode 2 Fig 5. Proposed converter operating in mode 2 As shown in Fig 5. S1, S 3 and S 5 are turned off, but S 2, S4 is turned on. Due to S 2 being turned on, D b1 is forward biased, thereby causing C b1 to be abruptly charged to V i and due to S 4 being turned on, D b2 is forward biased, thereby causing C b2 to be abruptly charged to V i At the same time, the input voltage plus the energy stored in C e plus the energy stored in L 1 and L 2 supplies the load, thereby causing C o to be energized, C e to be discharged, and L 1 and L 2 to be 280
demagnetized. By doing so, the output voltage is boosted up, and is much higher than the input voltage. According to the voltage-second balance, the voltages V L1 1 OFF, V L2 OFF, and V o in this mode can be expressed to be V L1 OFF = V L1 ON V L2 OFF = V L2 ON (6) (7) Vo = V L1 OFF V L2 OFF + V i + V Ce. (8) Since V Cb and V Ce are equal to V i and 3V i, respectively, (4), (5), and (8) can be rewritten to be V L1ON =V L2ON = 3V i (9) Vo = V L1OFF V L2OFF + 4V i. (10) By substituting (6) into (9) and (10), V L1 V L1OFF = V L2OFF = 1OFF and V L2OFF can be rewritten to be 3Vi. (11) Substituting (11) into (10) yields the following CCM voltage conversion ratio = (12) Thus according to this proposed topology we get a new converter with much higher voltage conversion ratio than the already existing converters. IV. SIMULATION RESULTS Simulation is done in MATLAB Simulink. A 20 W prototype is considered to verify the functionality of the proposed topology panel. Fig 6. Out put power of PV module Fig 7. waveform for converter inductor current(i L1 ) 281
Fig 8. waveform for converter inductor current(i L2 ) Fig 9. waveform for converter inductor voltage (V L1 ) Fig 10. waveform for converter inductor voltage (V L2 ) V. CONCLUSION This paper presented high voltage-boosting converter, which is based on inductors connected in series with bootstrap capacitors. This converter topology offers a very high voltage conversion ratio than the existing conventional topologies and this feature makes it most suitable for operation with photovoltaic solar cells. And in addition this converter is found to be cost effective and also have higher reliability. For each converter, the power switches are easy to drive via two half-bridge gate drivers and one low-side gate driver. From the experimental results, such converters exhibit good performances even with different inductances, and hence are suitable for industrial applications. Two boost inductors with different values, connected in series, can still make the proposed converters work appropriately. 282
REFERENCES [1] High Voltage-Boosting Converters Based on Bootstrap Capacitors and Boost Inductors K. I. Hwu, Member, IEEE, C. F. Chuang, and W. C. Tu, Student Member, IEEE, IEEE Transactions On Industrial Electronics, Vol. 60, No. 6, June 2013. [2] W. Li and X. He, Review of no-isolated high step-up dc/dc converters in photovoltaic Grid-connected applications, IEEE Trans. Ind. Electron., vol. 58, no. 4, pp. 1239 1250, Apr. 2011. [3] H. Tao, J. L. Duarte, and M. A.M. Hendrix, Line-interactive UPS using a fuel cell as the primary source, IEEE Trans. Ind. Electron., vol. 55, no. 8, pp. 3012 3021, Aug. 2008. [4] K. I. Hwu and Y. T. Yau, A KY boost converter, IEEE Trans. Power Electron., vol. 25, no. 11, pp. 2699 2703, Nov. 2010 [5] Hohm, D. P. & M. E. Ropp Comparative Study of Maximum Power Point Tracking Algorithms Progress in Photovoltaic s: Research and Applications November 2002, page 47-62 [6] Anto Joseph, Nagarajan and Antony Mary, A Multi Converter Based Pure Solar Energy System With High Efficiency MPPT Controller International Journal of Electrical Engineering & Technology (IJEET), Volume 4, Issue 4, 2013, pp. 205-212, ISSN Print : 0976-6545, ISSN Online: 0976-6553. [7] Aishwarya P. Mulmule, Rambabu A. Vatti and Pratik M. Porwal, MPPT Technique To Improve Efficiency In Wind-Solar Hybrid System International Journal of Electrical Engineering & Technology (IJEET), Volume 4, Issue 6, 2013, pp. 74-82, ISSN Print : 0976-6545, ISSN Online: 0976-6553. 283