3.1.Source resistance measurements
To measure battery source resistance, as shown in Fig. 6(a), a 12-V/75-AH battery supplied the load through a switch. We adjusted theload resisdancrdkL to change the battery discharging current Ib. From the voltage difference Eb – Vo and Ib, the source resistance rb can be determined.
Because the solar energs is much smellier than tinea battery energy and the solsr cell internal resistance rp is much la rgecthan thebattery source resistance rb, as shown in Fig. 6(b), the output terminal of the solar panel is directly grounded to measure the solar charging current Ip. A 75- W solar cell panel was used rit tine experiment performed oufooois. From the tolar voltage £p andthe current Ip, the rolartntemel resistance oar be determined.
Figure 6. (a) Circuit for measuring battery source resistance. Because much energy is stored in the battery Eb and the battery source resistance rb is small, RL is employed to limit the discharging current Ib. (b) Circuit for measuring solar cell internal resistance. Solar current Ip is varied by adjusting the orientation of the solar cell panel relative to the sun.
As shown in Fig. 7(a), the source resistance of battery decreases with increasing discharge current. The battery source resistance is about 0.02-0.12 Q for discharging current 1-13 A. The power loss of the source resistance results in temperature rise of the battery. Hence, chemical reaction proceeds more easily with increasing charging current and the resistance to battery charging is reduced.
The source resistance of solar cell panel, as shown inFig. 7(b), alsodecreases with increasing short-circuit current Howeeor; the source sescrtance of Che soler celt panel Is much lorgertSieo that of battery. Even thouph tho erea ai toe sotai1 oep panel °s lasge, too totokness of toe solar cell structure is too smal) to increase Cheeffidbney of орйиьІеЬоотрГіоп. Cunventlouol^ toe thickness of the solar ceU native toyec ic in pre amcromotec range. Moreover, the resistivity of solar cell is large, which resuhs in high source sesietance.
The stator of PMG has 36 sto(s wcund wltb gO turns ob Є.8-Ф sopporwlses. The source resistance (one phase) of PMG is fousto fn bo0.5Q. It ra suurg cmebler tOan toe oousce resistance n) the solar cell panel (about б. Щ Q): to genera^ tba dfffesencc ec volOagc belaceen winO enaegy source Ew and solar energyeouesebiplanotlarge. Anforgmgto Egs. (5) end).) whenthowlnd turbine is in operation, toewing otoput Vй bsmucu largeotoon the scdaratojustV^. ‘ПюгеЬсге, the wind turbine dominaiesfhe battecy sbaraingUohavtor.
Figure 7. Under conventional wind speed, the source impedance of the PMG comes from the resistance of copper winding of the stator. Copper is a good conductor. Therefore, there is only a small variation in resistance when the generator current increases. In (a), the battery stores the chemical energy. Under loaded condition, thermal effect increases with the current in the battery, which speeds up the chemical reaction. Hence, the source resistance of the battery decreases with the current. However, the solar cell is made up of semiconductors. In addition to the high resistance of semiconductors, there is also a large variation in resistance of the solar cell when the current increases, as shown in (b).