Comparative Study of Rectenna Configurations for Satellite Solar Power Station

Transcription

1 2011 International Conference on Circuits, System and Simulation IPCSIT vol.7 (2011) (2011) IACSIT Press, Singapore Comparative Study of Rectenna Configurations for Satellite Solar Power Station Kalpana Chaudhary 1, Babau R. Vishvakarma 2 1 Department of Electrical Eng., Institute of Technology, Banaras Hindu University, India 2 Department of Electronics Eng., Institute of Technology, Banaras Hindu University, India Abstract: In the present paper the investigations on conversion efficiency of two rectenna configurations viz. rectenna using half wave series diode rectifier and half wave shunt diode rectifier for satellite solar power station is presented. The analysis was carried out using equivalent circuit approach with ORCAD 9.1 software. It is found that the conversion efficiency is lowest for maximum load in both configurations. Typically conversion efficiency of rectenna using half wave series diode rectifier is 41.23% at 100Ω load whereas it is 15.34% for 500Ω load. It is also envisaged that the performance of the rectenna should not be judged only by its conversion efficiency for low RF input, instead load current should also be considered. It is also significant to note that the shunt rectifier circuit provided almost constant conversion efficiency for all the loads considered at lower and higher range of RF input. This indicates that rectenna using shunt rectifier is equally good both for lower and higher RF input power. Keywords: satellite solar power station; rectenna; simulation 1. Introduction Glaser (1968) proposed the concept of classic satellite solar power station (SSPS). The proposed system locates the power generator on a satellite, which is located on geosynchronous orbit. Solar power will be converted to dc power and it will again convert to microwave power by cross-field devices, which may be transmitted to earth. The frequency of microwave transmission is 2.45 GHz. This power will be received at Earth by receiving antenna called rectenna. Chaudhary and Vishvakarma (2009) discussed the effect of ionsopheric induced depolarization on satellite solar power station.later on Chaudhary and Vishvakarma (2010) presented the comparative analysis of LEO, GEO and Molniya orbit based SSPS for various locations of India. A system that combines microwave antenna and rectifying devices was termed as rectenna by Brown (1984). In other words, a rectenna is a receiving antenna combined with a rectifying circuit which converts microwave power in to the DC power at the ground station. Researchers such as Rodenbeck et al (2004), Kim et al (2006) and Berland et al (2008) have designed, developed and proposed the methodologies to improve the performance of rectenna system at the ground station. However in the present endeavor, an attempt is made to improve the rectenna performance as well as its effective practical implementations for satellite solar power station. In this paper, the investigations on rectenna system are carried out using equivalent circuit approach with ORCAD 9.1 software for the purpose. Comparative analysis of rectenna configurations for various resistive loads at 2.45 GHz input frequency is carried out on two configurations of rectenna and a most suitable configuration is proposed. 2. Components of Rectenna Rectenna is the power conversion equipment that converts the input RF power to DC. Rectenna mainly consists of a receiving antenna, band pass filter, rectifying circuit and DC filter. The output of rectenna is fed 73

2 to load resistance. Thus load forms a component of rectenna for performance analysis in this study. All the components are discussed individually in the subsections. 2.1 Receiving Antenna In the equivalent circuit approach, a receiving antenna can be modeled as an RF power source of desired frequency as quoted by Park and Youn (1999). In the present analysis, the receiving antenna is transformed as a RF power source at a frequency of 2.45 GHz. 2.2 Input Filter Input filter is required in the rectenna system to prevent the reflection of DC power towards receiving antenna. Input filter should be capable to transmit collected microwave power by antenna power towards the rectifier circuit. The filter is selected and designed to fulfil the following conditions: 1. Filter should give maximally flat response. 2. Minimum number of components to achieve compactness and reduce complexity. 3. Minimum cost. Band pass filter is used in the present study for the analysis of conversion efficiency of the system. The input filter is represented in the equivalent circuit of rectenna configuration in Fig Selection of Rectifying Device The choice of power semiconductor devices plays an important role in the power conversion circuit. Since the rectifier of the rectenna system has to operate at microwave frequency, the power conversion device must have low reverse recovery time ad the conversion efficiency must also be high. Schottky diode is chosen as a conversion device for the analysis of rectenna system in the study. Schottky diode is modeled as an ideal diode in parallel with a capacitor of suitable range (0.16pF-0.3pF). 2.4 Output Filter The output filter in the rectenna system is DC filter whose function is to pass only DC component of voltage and to suppress harmonics. A shunt capacitance of pf range (80pF 100pF) is used as DC filter for analysis of rectenna. In the equivalent circuit approach, all the components of rectenna are transformed in to their electrical equivalent. Comparative analysis of rectenna has been done for two configurations of half wave rectifier viz. Series diode rectifier and shunt diode rectifier. The equivalent circuit model of rectenna is used to calculate its RF to DC conversion efficiency. Accordingly, conversion efficiency as a function of RF input power (high power) were calculated and the data thus obtained for rectenna with half wave series diode rectifier and rectenna with half wave shunt diode rectifier is shown plotted in Fig. 3(a) and Fig. 3(b) respectively. The conversion efficiency as a function of load resistance is shown in Fig. 4(a) for rectenna with half wave series rectifier for RF input power of 10 W and 20 W. Similar plot is also shown for rectenna with half wave shunt rectifier in Fig. 4(b). Zin L1 10uH RF Power source FREQ = 2.45 e9 V1 C1 1n C3 C5 R2 Recievina Antenna Receiving Antenna Input Filter Rectifier Output Filter Load Fig. 2 Electrical Equivalent Circuit of Rectenna Using Half Wave Shunt Diode Rectifier 74

3 Fig. 3(a) Conversion Efficiency vs RF Input Power of Rectenna Using Half Wave Series Diode Fig. 3(b) Conversion Efficiency vs RF Input Power of Rectenna using Half Wave Shunt Diode Rectifier for Large Signal Fig.4 (a) Variation of Conversion Efficiency of Rectenna Using Half Wave Series Rectifier as a Function of Load Resistance 75

4 Fig. 4 (b) Variation of Conversion Efficiency of Rectenna Using Half Wave Shunt Rectifier as a Function of Load Resistance 3. Discussion of Results From the scrutiny of Fig. 3(a), it is found that for higher RF input power (5W- 25W) the conversion efficiency of rectenna is almost same for all the values of RF input power. However there is small decrease in the conversion efficiency at around 10 W for all the loads. The data of conversion efficiency of rectenna using half wave shunt rectifier is shown in Fig. 3(b) for higher RF input power. It is revealed that Conversion efficiency decreases with increasing load for all the RF input. It is also corroborated that conversion efficiency is invariant with RF input power for a particular load. However the conversion efficiency is lowest for maximum load. Typically conversion efficiency is 41.23% at 100Ω load whereas it is 15.34% for 500Ω load. The variation of conversion efficiency of rectenna using half wave series rectifier as a function of load resistance is shown in Fig. 4(a). From this graph it is clearly evident that the conversion efficiency decreases with increasing load and it is higher for higher RF input power at all values of load resistance. This indicates that system efficiency is better for the higher RF input power. The variation of conversion efficiency of rectenna with half wave shunt rectifier as a function of load is shown in Fig. 4(b). It is observed that in this case, the curve for low RF input power (10W) as well as for high input power (20W) overlaps indicating that the efficiency of the system is almost invariant with the input power level. This makes the rectenna with shunt rectifier configuration more efficient as compared to the system with series rectifier configuration for all values of RF input power. 4. Conclusions After the analysis of rectenna performance it is concluded that the performance of the rectenna should not be judged only by its conversion efficiency for low RF input. Instead load current should also be considered. It is also significant to note that the shunt rectifier circuit provides almost constant conversion efficiency for all the loads considered at lower and higher range of RF input. This indicates that rectenna with shunt rectifier is equally good both for low and high RF input power. 5. References [1] P.E.Glaser. Power from the Sun: its future. Science Vol 162, 1968, pp [2] K.Chaudhary and B. R. Vishvakarma. Effect of Ionospheric Induced Depolarization on Satellite Solar Power Station. Progress in Electromagnetics Research Letters (USA), Vol. 9, 2009, pp [3] Kalpana Chaudhary, B. R. Vishvakarma. Feasibility Study of LEO, GEO and Molniya Orbit Based Satellite Solar Power Station for Some Identified Sites in India. Advances in Space Research (Elsevier), 46 (2010), pp

5 [4] W. C. Brown. The History of Power Transmission by Radio waves. IEEE Transaction on Microwave Theory and Techniques. Vol. 32, No. 9, September, 1984, pp [5] C. T. Rodenbeck, M. Yili and K. Chang. A Phased Array Architecture for Retrodirective Microwave Power Transmission for Space Solar Power Satellite. IEEE MTT-S Digest. 2004, pp [6] J. Kim, S. Y. Yang, K. D. Song, S. Jones and S. H. Choi. Performance Characterization of Flexible Dipole Rectennas for Smart Actuator Use. Smart Materials and Structures, Vol. 15, 2006, pp [7] B. Berland, L. Simpson, G. Nuebel, T. Collins and B. Laning. Optical Rectenna for Direct Conversion of Sunlight to Electricity. 2008, US Patent [8] Y. H. Park and D. G. Youn. A Study of Analysis of Rectenna Efficiency for Wireless Power Transmission. IEEE- Tencon, Jeju, September 15-17, 1999, pp