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太阳能电池等效电路模型如图1所示,包含一个电流源${I_{{\rm{pH}}}}$、一个二极管、两个电阻即串联电阻${R_{\rm{s}}}$和并联电阻${R_{{\rm{sh}}}}$[15]。
太阳能电池的I-V特性定义如下:
$$ I = {I_{{\rm{pH}}}} - {I_0}\left[ {\exp \left( {\frac{{q(V + I{R_{\rm{s}}})}}{{nkT}}} \right) - 1} \right] - \frac{{V + I{R_{\rm{s}}}}}{{{R_{{\rm{sh}}}}}} $$ (1) 式中:$ I $为经过外接负载的电流;$ {I_0} $为对应的反向饱和电流;$ n $为太阳能电池的理想因子;$ V $为光生电压;$ q $为电子电荷;$ k $为玻耳兹曼常数;$ T $为温度。
用于同步传能和通信的太阳能电池板模型如图2所示,左侧为太阳能电池板内部等效模型,$ r $为小信号等效电阻器,$ {C_0} $和$ {L_0} $分别为电池内部电容和电感;右侧为外接电路[11]。负载${R_{\rm{C}}}$和电容$ C $串联形成通信分支,与通信分支并行的是由电感$ L $和电阻${R_{\rm{L}}}$组成的能量收集分支,光电流由直流分量${I_{{\rm{PH}}}}$和交流分量$i{(\omega )_{{\rm{PH}}}}$组成。
图 2 用于传能和通信的太阳能电池等效电路模型
Figure 2. Equivalent circuit model of solar cell for energy transfer and communication
依据图2,该模型频率响应为:
$$ {\left| {\dfrac{{v(\omega )}}{{{i_{{\rm{PH}}}}(\omega )}}} \right|^2} = {\left| {\dfrac{{\dfrac{{{R_{{\rm{LC}}}}}}{{{R_{\rm{s}}} + j\omega L + {R_{{\rm{LC}}}}}}\dfrac{{{R_{\rm{C}}}}}{{\dfrac{1}{{j\omega {C_0}}} + {R_{\rm{C}}}}}}}{{\dfrac{1}{r} + \dfrac{1}{{\dfrac{1}{{j\omega C}}}} + \dfrac{1}{{{R_{{\rm{sh}}}}}} + \dfrac{1}{{{R_{\rm{s}}} + j\omega L + {R_{{\rm{LC}}}}}}}}} \right|^2} $$ (2) 其中,${R_{{\rm{LC}}}}$为:
$$ {R_{{\rm{LC}}}} = \dfrac{1}{{\dfrac{1}{{j\omega L + {R_{\rm{L}}}}} + \dfrac{1}{{\dfrac{1}{{j\omega C}}}} + {R_{\rm{C}}}}} $$ (3) -
系统实验原理如图3所示。实验系统包括发射端的激光器、准直扩束系统、合束镜、信号发生器以及接收端的太阳能电池及其外接电路、示波器、源表等实验装置。对于系统发射端选用的波长为808 nm的激光器,用于研究太阳能电池的传能特性;选用波长为650 nm的半导体激光器用于信号的传输。合束镜将两束不同波长的光合为一束,准直扩束系统选用GCO-2505扩束镜,通过调节镜头上的调焦和变倍手轮可调整扩束比和光束的发散角。选用DG4000系列任意波形发生器对LD进行内调制,接收端为GaAs太阳能电池,尺寸为1 cm×1 cm。用数字示波器采集输出信号,KEITHLEY 2450型号数字源表进行太阳能电池I-V特性的探测,激光功率采用美国THORLABS公司的PM16-121数字功率计进行测量,其最大测量功率值为500 mW。
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当单独能量传输时,仅采用808 nm激光器经过扩束系统后辐照在GaAs太阳能电池表面,用源表测量不同功率密度激光辐照太阳能电池的I-V特性曲线和P-V特性曲线,如图4所示。
图 4 太阳能电池响应特性曲线。 (a) I-V曲线; (b) P-V曲线
Figure 4. Response characteristic curves of solar cell. (a) I-V curve; (b) P-V curve
GaAs太阳能电池短路电流${I_{{\rm{sc}}}}$、开路电压${V_{{\rm{oc}}}}$和光电转换效率$ \eta $随激光功率密度的变化关系如图5所示。在测量范围内,短路电流${I_{{\rm{sc}}}}$随入射激光功密度增大而增大且呈线性关系;开路电压${V_{{\rm{oc}}}}$随入射激光功率密度的增大而增加,最后变化较小趋于饱和;光电转换效率$ \eta $随入射激光功率密度的增大而减小,当激光功率密度大小为54.9 mW/cm2时,光电转换效率可达46.6%。由此可以看出,激光功率密度是影响太阳能电池传能特性的重要因素。
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对太阳能电池频响特性的测试采用波长650 nm的小功率LD作为入射光源,最大光功率为5 mW。频率响应可由所接收到的交流信号电压$ u(t) $的归一化功率增益$ {\left| {H(f)} \right|^2} $定义,其中$ f $为频率,$ t $为时间,${\left| {H(f)} \right|^2} = {\left| {{v_{{\rm{pp}}}}(f)/\max ({v_{{\rm{pp}}}}(f))} \right|^2}$,${v_{{\rm{pp}}}}(f)$为电压$ u(t) $的峰峰值[15]。发射端、光电探测器、外接电路和整个系统的归一化频响特性分别用$ {H_1}(f) $、$ {H_2}(f) $、$ {H_3}(f) $和${H_{{\rm{system}}}}(f)$,有:
$$ {H_{{\rm{system}}}}(f) = \left| {{H_1}(f)} \right| \times \left| {{H_2}(f)} \right| \times \left| {{H_3}(f)} \right| $$ (4) 首先借助PDA100 A2硅光电探测器间接测量,探测器带宽为11 MHz,用示波器测量其系统归一化频率响应,如图6所示,可以看出在测量范围内该系统各个部分的频率响应近似于平坦,接收端更换为GaAs太阳能电池后,测量系统频响带宽为3.7 kHz,系统中除太阳能电池板外的其他部件均具有较大的带宽,可得GaAs光电池的3 dB带宽约为3.7 kHz。
图 6 接收端为PD探测器和GaAs太阳能电池时系统频响特性曲线
Figure 6. Frequency response of the system when the receiver is PD detector and GaAs solar cell
在接收端接入外接支路,固定能量接收支路的参数为RL=5 kΩ,L=1 mH,研究信号传输支路参数对响应特性的影响。使用信号发生器产生一个电压峰峰值${V_{{\rm{pp}}}}$=500 mV的正弦波信号,添加直流偏置电压${V_{{\rm{ac}}}}$=3 V用于驱动 LD,LD距太阳能电池10 cm。采用控制变量法分别调整${R_{\rm{C}}}$和$ C $的大小进行系统频响特性的测量,由图7 (a)、 (b)可以看出,随着电阻${R_{\rm{C}}}$的增加,系统带宽随之减小;随着电容值$ C $的增加,系统带宽随之减小,电容值从10 μF继续调大,带宽不再发生变化,因此可以通过调整外接电路进而改变系统的频率响应。
图 7 接收端为GaAs太阳能电池时系统频率响应变化曲线。(a)随${R_{\rm{C}}}$变化; (b)随$ C $变化
Figure 7. System frequency response change curves when the receiver is GaAs solar cell. (a) Change with ${R_{\rm{C}}}$; (b) Change with $ C $
用信号发生器输出OOK调制信号,信号峰峰值设置为500 mV,偏置电压3 V,驱动激光器辐照GaAs太阳能电池,测量输出响应波形如图8 (a)、 (b)所示,可实现10 kbps的通信速率。为提高通信速率,改善系统的响应性能,设计放大电路如图9所示,放大电路可以通过增益或衰减的调节使得可检测信号的范围大大扩展,便于信号的采集。
接入放大电路后的测量结果如图8 (c) 、(d)所示,实现了240 kbps的通信速率,输出电压峰峰值从408 mV提高到7.2 V。根据接入电路前后的测量结果对比,可得接入电路能够在较大的范围内有效提高通信带宽,改善输出信号,满足能量传输和信号探测的要求。
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根据图3搭建实验装置进行能量和信号的同步传输实验,传输距离为50 cm,由于用于能量传输的光路会对信号的传输产生干扰,在太阳能电池接收端接入放大电路,并施加反向偏压3 V,使得输出信号波形改善。由图10 (a) 、(b)可以看出,在接入电路前,当通信速率为2 kbps、传能激光功率密度为69.4 mW/cm2时,由于连续激光的干扰,使得输出波形携带较大噪声,接入电路后,输出信号得以恢复,改善通信性能。
图 10 激光无线能量和信号同步传输时输出波形。 (a) 接入电路前; (b) 接入电路后
Figure 10. Waveform received when the laser wireless energy and signal are transmitted synchronously. (a) Before circuit access; (b) After circuit access
通过调节用于传能的激光器所发射激光功率密度,如图11所示,图11(a)、(b)为接收信号波形,图11(c)、(d)为调制信号波形,当功率密度分别为59.5、69.4、80.5、90 mW/cm2 时,可实现信号的通信速率依次为140、100、40、30 kbps。可以看出,当传能激光功率密度较高时,会在一定程度上干扰信号的传输,由于当传能激光功率密度越高时,太阳能电池内部产生的电子-空穴对密度越高,产生越多的光生电流,对所接收到的脉冲光信号要达到动态载流子平衡,数量越多的电子-空穴对响应时间越长,通信速率降低。
Performance test of solar cell under laser energy transmission and signal transmission
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摘要: 激光无线能量传输在为远距离设备供能方面有着潜在的应用前景,在激光无线传能的同时进行激光无线通讯,具有重要的应用价值。针对砷化镓太阳能电池,对激光传能系统在无线能量传输时激光无线通讯性能进行了测试。实验采用波长808 nm激光实现砷化镓太阳能电池的能量传输,采用波长650 nm激光作为信号的传输,分别对单能量传输、单信号传输以及能量和信号同步传输三种情况下的砷化镓太阳能电池的输出特性进行了测试。结果表明:当单能量传输时,太阳能电池的性能与激光功率密度的大小密切相关,激光功率密度在54.9~90 mW/cm2范围内光电转换效率最大值为46.6%;当单信号传输时,通过测量系统的频率响应得到砷化镓太阳能电池的3 dB带宽约为3.7 kHz,并通过设计放大电路提高系统的通信性能,优化输出波形,使得系统的通信速率从10 kbps提升至240 kbps,输出电压峰峰值达到7.2 V。最后实验测量了不同激光强度下可实现的通信速率,当激光功率密度为59.5 mW/cm2时可实现140 kbps的通信速率,使得激光充电系统在无线能量传输下可以进行信号的传输。Abstract: Laser wireless energy transmission has potential applications prospects in supplying energy for long-distance equipment. And laser wireless communication with energy transmission has important application value. For GaAs solar cell, the laser wireless communication performance of the laser energy transmission system was tested during wireless energy transmission. A wavelength of 808 nm laser to achieve the energy transmission of the GaAs solar cell was used in the experiment, and a wavelength of 650 nm laser was used as the signal transmission. The output characteristics of GaAs solar cell under three conditions of single energy transmission, single signal transmission and energy and signal simultaneous transmission were tested respectively. The results show that when the single energy is transmitted, the performance of the solar cell is closely related to the laser power density. In the range of 54.9-90 mW/cm2 of the laser power density, the maximum energy conversion efficiency is 46.6%; when the single signal is transmitted, by measuring the frequency response of the system, the 3 dB bandwidth of the GaAs solar cell is about 3.7 kHz. And by designing the amplifier circuit, the communication performance of the system is improved and the output waveform is optimized, so that the transmission rate of the system is increased from 10 kbps to 240 kbps, and the output voltage peak-to-peak reaches 7.2 V. Finally, the achievable signal transmission rates under different laser intensities were measured experimentally. When the laser power density is 59.5 mW/cm2, the signal transmission rate of 140 kbps is achieved, so that the laser charging system can perform signal transmission under wireless energy transmission.
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Key words:
- solar cell /
- energy transmission /
- signal transmission /
- frequency response
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[1] 桂永雷, 孙立凯, 崔洪亮, 等. 低相噪大面积平衡光电探测器[J]. 光学精密工程. 2018, 26(2): 284-292. Gui Yonglei, Sun Likai, Cui Hongliang, et al. Large area balanced photodetector with low phase noise [J]. Optics and Precision Engineering, 2018, 26(2): 284-292. (in Chinese) [2] 董冰, 佟首峰, 张鹏, 等. 20 m水下无线蓝光LED通信系统样机设计[J]. 中国光学. 2021, 14(6): 1451-1458. Dong Bing, Tong Shoufeng, Zhang Peng, et al. Prototype design of 20 m underwater wireless blue light LED communication system [J]. Chinese Optics, 2021, 14(6): 1451-1458. (in Chinese) [3] Boussaada Mohamed, Abdelati Riadh, Yahia Hedi. Emulating and amplifying an I-V panel based on an electrical model of a PV cell [C]//International Renewable Energy Congress, IEEE, 2019: 1-6. [4] 常浩, 陈一夫, 周伟静, 等. 激光辐照太阳能电池损伤特性及对光电转化的影响[J]. 红外与激光工程. 2021: 1-9. Chang Hao, Chen Yifu, Zhou Weijing, et al. Damage characteristics of solar cells irradiated by laser and its effect on photoelectric conversion [J]. Infrared and Laser Engineering, 2020, 49(S1): 20200262. (in Chinese) [5] 李娟, 俞浩, 虞天成, 等. 用于无线能量传输的高效率半导体激光器设计[J]. 红外与激光工程. 2021, 50(5): 43-50. Li Juan, Yu Hao, Yu Tiancheng, et al. Design of high efficiency semiconductor laser for wireless energy transmission [J]. Infrared and Laser Engineering, 2021, 50(5): 20210147. (in Chinese) [6] 田慧军, 刘巧莉, 岳恒, 等. 高比探测率和高速石墨烯/n-GaAs复合结构的光电探测器[J]. 中国光学. 2021, 14(01): 206-212. Tian Huijun, Liu Qiaoli, Yue Heng, et al. High specific detection rate and high speed photodetector with graphene/n-GaAs composite structure [J]. Chinese Optics, 2021, 14(1): 206-212. (in Chinese) [7] 孟立新, 赵丁选, 张立中, 等. 机载激光通信中气动光学的影响及补偿[J]. 光学精密工程. 2014, 22(12): 3231-3238. Meng Lixin, Zhao Dingxuan, Zhang Lizhong, et al. Influence of aerooptics on airborne laser communication and its compensation [J]. Optics and Precision Engineering, 2014, 22(12): 3231-3238. (in Chinese) [8] Kim Sung-Man, Won Ji-San. Simultaneous reception of visible light communication and optical energy using a solar cell receiver [C]//International Conference on ICT Convergence, IEEE, 2013: 896-897. [9] Wang Zixiong, Tsonev Dobroslav, Videv Stefan, et al. Towards self-powered solar panel receiver for optical wireless communication [C]//IEEE International Conference on Communications, IEEE, 2014: 3348-3353. [10] Wang Zixiong, Tsonev Dobroslav, Videv Stefan, et al. On the design of a solar-panel receiver for optical wireless communications with simultaneous energy harvesting [J]. IEEE Journal on Selected Areas in Communications, 2015, 33(8): 1612-1623. [11] Zhang Shuyu, Tsonev Dobroslav, Videv Stefan, et al. Organic solar cells as high-speed data detectors for visible light communication[J]. Optica, 2015, 2(7): 607-610. [12] 孔美巍. 水下无线光通信系统的设计与实验研究[D]. 浙江大学, 2018. Kong Meiwei. Design and experimental study of underwater wireless optical communication system[D]. Hangzhou: Zhejiang University, 2018. (in Chinese) [13] Xiong Mingliang, Liu Qingwen, Wang Gang, et al. Resonant beam communications: Principles and designs [J]. IEEE Communications Magazine, 2019, 57(10): 34-39. doi: 10.1109/MCOM.001.1900419 [14] Sheng Quan, Wang Meng, Ma Hanchao, et al. Continuous-wave long-distributed-cavity laser using cat-eye retroreflectors [J]. Opt Express, 2021, 29(21): 34269-34277. doi: 10.1364/OE.442385 [15] Fakidis John, Videv Stefan, Haas Harald, et al. 0.5-Gb/s OFDM-based laser data and power transfer using a GaAs photovoltaic cell [J]. IEEE Photonics Technology Letters, 2018, 30(9): 841-844. doi: 10.1109/LPT.2018.2815273