Performance Measure of Switching Device (MOSFET) in Photo-voltaic System

Transcription

1 Performance Measure of Switching Device (MOSFET) in Photo-voltaic System Kamala J, Janarthanan V, and Santhosh K College of Engineering Guindy, Anna University, Chennai, Tamil Nadu, India Abstract Battery charging circuits utilize switching devices for its control operations. MOSFET is used as switching device in the charge control circuits. This paper analyze the characteristics of Power MOSFET used to charge batteries from solar energy. N channel and P channel MOSFET Device characteristics are investigated for two cases of photo-voltaic system. First case study is done with the device connected between solar panel and battery. Second case study illustrates the performance of device in Buck converter used as photo-voltaic battery charger. Switching losses and efficiency of converter is analyzed for both devices. Results and discussions of this paper are useful for the selection of switching device and the operating frequency. Index Terms Buck converter, Power MOSFET, Switching losses, Transfer characteristics. DC-DC converter is used between solar panel and battery, if battery voltage does not match with solar panel. Efficiency of converter depends on the switching losses of the device. Efficiency of converter is analyzed for various switching frequencies applied to different types of devices. In this case, solar panel is connected to battery through buck converter as shown in figure. I. INTRODUCTION Photo-voltaic energy storage system uses DC-DC converters for maximum energy transfer [1]. DC-DC converters consist of inductance, capacitance and power electronic semi-conductor devices []. Inductor and capacitor sizing is decided by switching frequency of power electronic components. Higher frequency leads to smaller values of inductor and capacitor with improved output regulation [3-5]. Power electronic components are designed with low on state resistance, fast switching rate, higher voltage and current carrying capacity [6]. In a battery charging system, source voltage of N-MOSFET is fixed at battery voltage and the drain current varies with battery voltage. Therefore, conventional MPPT algorithm does not deliver maximum current for battery charging [7]. Detailed analysis of MOSFET characteristics in a photo-voltaic system is required to find the switching requirements. Transfer characteristics of the device indicate the required gate drive for switching. It is derived by connecting the power component between solar panel and battery, with various gate voltages, as shown in figure 1. In this case, battery charging is possible only if solar panel voltage is sufficiently greater than battery voltage. N channel and P channel MOSFET transfer characteristics curves are obtained in this paper. Figure 1 Power MOSFET coupled between PV cell and battery Figure Battery charging through power converter Photo-voltaic energy storage system with a solar panel of 100W p, V mp of 17.5V, and a battery of 1V, 4Ah are considered in the proposed research work. Section II describes overall photo-voltaic charging system and its hardware specifications. Section III discusses the transfer characteristics of power electronic components connected between solar panel and battery. Converter efficiency is analyzed in section IV for various switching frequencies applied to different devices. Section V discusses the results obtained with the experimental set-up. Section VI concludes with the power component requirement and its characteristics applied to battery charging. II. PHOTO-VOLTAIC BATTERY CHARGING SYSTEM Specifications of solar panel are given in Table I. Battery charging is achieved either by connecting switch between solar panel and battery as shown in figure 3 or by using DC-DC converter as shown in figure 6. TABLE I SPECIFICATIONS OF SOLAR PANEL Characteristics Specification Rated power, P 100Wp Peak power voltage, Vmpp 17.5V Peak power current, Impp 5A Open circuit voltage, Voc 1.4V Short circuit current, Isc 6A ISBN:

2 Figure 3 Switch controlled Battery charger Important parameters of the switching device are given in table II TABLE II SWITCHING DEVICE PARAMETERS IRFP150N IRF9530 V DSS = 100V V DSS = -100V R DS(on) = 0.036Ω R DS(on) = 0.3Ω I D = 4A I D = 1A Figure 5 Buck Converter Charge pump circuit required for gate of MOSFET is achieved by a driver circuit shown in figure 4. Complementary pair switching transistors N907A and PNA are used to improve the drive strength of signal. Opto-isolator TLP50 [10] is used as isolator. HI Figure 6 Converter based Battery charger pwm-in 1 PNA N907A 0 tlp pwm-out 1 TL494 [11] pulse width modulator IC is used to generate the PWM signal of converter. Battery voltage is fed back to PWM generator circuit, using potentiometer that can be adjusted to vary the duty cycle of PWM signal. Frequency of PWM signal is varied by varying the resistance of oscillator circuit. Circuit shown in figure 7 uses resistance R13 (potentiometer) to vary frequency and R16 to adjust the duty cycle. Figure 4 Gate driver circuit Buck converter capable of handling 500W is designed with the following requirements Switching frequency = 5 MHz maximum Current ripple < 0.04A Voltage ripple < 0.01V Charging current = 10A maximum Duty cycle = 5% to 95% Specifications of converter are given as follows and shown in figure 5 Input voltage : varies between 14V-0V Output voltage : fixed by battery voltage MOSFET used : IRFP150N / IRF 9530 [8,9] Diode used:mbr1545 Inductance: 100µH Capacitance: 1000µF III. MOSFET TRANSFER CHARACTERISTICS COUPLED BETWEEN PV CELL AND BATTERY HEXFET N channel power MOSFET IRFP150N and P channel device IRF9530 are chosen to study the transfer characteristics. Connection of MOS devices between PV cell and battery is shown in figure 8. In case of N channel MOSFET, higher gate voltage is required to turn on the device, since the source is at battery potential approximately 1V. Sufficient drain current flows through the device, when gate voltage is greater than 16V. Gate to source voltage required for sufficient drain current is shown in figure 9. Drain current increases with increase in gate to source voltage. ISBN:

3 Figure 7 PWM Generation circuit Figure 8 MOS device connected between PV cell and battery Flow of drain current charges the battery and increases battery voltage with drain to source voltage decreasing from 7V to 0.15V. Maximum drain current is 5.36A with single N channel MOS device and it is increased to 5.41A with two devices in parallel. Parallel connection of devices reduces on-resistance of device and increases drain current. Figure 9 Characteristics of NMOS device In case of P channel devices, gate voltage need not be higher than source. Gate signal can be derived from the input signal and charge pump circuit is not required. On-resistance of P channel MOS is higher and drain current is comparatively reduced. Maximum drain current for this case is 5.16A with single device and 5.3A with two devices in parallel. Characteristic curves of PMOS device is shown in figure 10. Figure 10 Characteristics of PMOS devices IV. CONVERTER PERFORMANCE WITH DIFFERENT MOS DEVICES Conventinal MPPT is not effective for battery charging system, since the output voltage is at battery voltage, which is not V mp of PV cell. Faster Charging is achieved with higher current flow. This paper analyzes the efficiency of converter by varying switching frequency for different MOSFET configurations. Input / output measurements of converter is taken for four cases of power electronic component as given below Single N channel device Two N channel devices in parallel Single P channel device Two P channel devices in parallel The efficiency of the Converter is defind in equation 1, Efficiency = Where, Power output Total Power input (1) ISBN:

4 Output Power =Total input power-total Power losses () Results of this analysis are shown in figure 11. Power losses in the MOSFET is given by Power Losses = switching power losses + Conduction losses (3) Where, P sw = ( V in I out ) (T rise + T fall ) Fsw (4) P con_loss = I out R ds(on) V out (5) V in Based on the experimental results the losses can be estimated for a Single NMOS Device, with following parameters R ds(on) =.036; I in = 4.79; V in = 14.39, I out = 4.89, V out 1.7, F sw = 1000 Hertz, T rise = 00us, T fall = 5us P sw = ( ) (00 + 5)us 1000 HZ (6) P sw = 7.1 Watts Figure 11 Efficiency of converter with different MOS devices Efficiency of converter with two NMOS devices is lowered due to higher switching losses of two devices. PMOS devices provide comparable efficiency with simple gate driving circuit. P con_loss = =.734 Watts P efficiency = =.870 = 87% Figure 1 Experimental Set-up Buck Converter Switching Device PWM Generator ISBN:

5 V. EXPERIMENTAL SET UP AND RESULTS Experimental set-up used to get results is shown in figure 1. Drain current with V ds and PWM signal is shown in figure 13 and 14. Switched Applications, IEEE Transactions on Power Electronics, Vol. 9, No., pp ,, Feb 011 [6] K.C. Daly, "Power Electronic Switching Devices" [Online] Available people.physics.anu.edu.au [7] Nabil Karami, NazihMoubayed and RachidOutbib, "Analysis of an irradiance adaptativepv based battery floating charger," presented in IEEE Photo-voltaic specialists conference 011. Fig. 13 Vds and Id Fig.14 PWM and Id [8] International Rectifer, [Online] Available [9] Power MOSFET, [Online] Available [10] Laszlo Balogh, Design and Application Guide for MOSFET Gate Drive Circuits, [Online] Available [11] Pulse Width Modulation Control circuits, [Online] Available VI. CONCLUSION Power electronic components play vital role in the performance of converters. This paper analyzes various MOSFET configurations with converter. Results show choosing PMOS device with low on-resistance delivers better performance with simple control circuit. N channel MOS devices operate at maximum effeciency with complex driving circuit. ACKNOWLEDGMENT Authors of this paper would like to thank for the funding provided by the Centre for Technology Development and Transfer, Research Support Scheme of Anna University, Chennai. REFERENCES [1] B. ChittiBabu, Sriharsha, Ashwin Kumar, NikhilSaroagi and S.R.Samantaray, "Design and Implementation of Low Power Smart PV Energy System for Portable Applications using Synchronous Buck Converter," International Symposium on Electronic System Design, 011. [] Juan Paulo Robles Balestero, Fernando LessaTofoli, Grover Victor Torrico-Bascop e and FalcondesJos e Mendes de Seixas, "A DC DC Converter Based on the Three-StateSwitching Cell for High Current and Voltage Step-Down Applications,"IEEE transactions on power electronics, vol. 8, no. 1, january 013. [3] Y. Ren, K. Yao, M. Xu and F. C. Lee, Analysis of the power delivery path from the 1-V VR to the microprocessor, IEEE Trans. PowerElectron., vol. 19, no. 6, pp , Nov [4] L. Huber, K. Hsu, M. M. Jovanovic, D. J. Solley, G. Gurov and R. M.Porter, 1.8-MHz, 48-V resonant VRM: Analysis, design, and performanceevaluation, IEEE Trans. Power Electron., vol. 1, no. 1, pp.79 88, Jan [5] Drazen Dujic, Gina K. Steinke,, Bellini, Munaf Rahimo Liutauras Storasta, and Juergen K. Steinke, Characterization of 6.5 kv IGBTs for High-Power Medium-Frequency Soft- ISBN: