原创 光伏电池电气性能的评测——光伏电池的总体效率的测量参数2

PV电池的串联电阻（r_s）可以从至少两条在不同光强下测量的正偏I-V曲线中得出。光强的大小并不重要，因为它是电压变化与电流变化的比值，即曲线的斜率，就一切情况而论这才是有意义的。记住，曲线的斜率从开始到最后变化很大，我们所关心的数据出现在曲线的远正偏区域（far-forward region），这时曲线开始表现出线性特征。在这一点，电流变化的倒数与电压的函数关系就得出串联电阻的值：

The series resistance of a PV cell (r_s) can be determined from at least two forward-biased I‑V curves, measured at different light intensities. The magnitudes of the light intensities are not important, because it is the change in voltage with the change of current, or slope of the curve, that is meaningful in all cases. Bearing in mind that the slope of the curve changes dramatically from beginning to end, meaningful data can be found at the curve’s far-forward region, where the curve starts to take on linear characteristics. The inverse of the change in current as a function of voltage at this point gives the value for the series resistance:

r_s = ΔV/ΔI

到目前为止本文所讨论的测量都是对暴露在发光输出功率下，即处于正偏条件下的PV电池进行的测量。但是PV器件的某些特征，例如分流电阻（r_sh）和漏电流，恰恰是在PV电池避光即工作在反偏情况下得到的。对于这些I-V曲线，测量是在暗室中进行的，从起始电压为0V到PV电池开始击穿的点，测量输出电流并绘制其与加载电压的关系曲线。利用PV电池反偏I-V曲线的斜率也可以得到分流电阻的大小（如图5所示）。从该曲线的线性区，可以按下列公式计算出分流电阻：

The measurements discussed so far have been made with a PV cell exposed to light-generating output power, under forward-biased conditions. But some of the characteristics of a PV device, such as the shunt resistance (r_sh) and the leakage current, are best found with the PV cell shielded from light and operating under reverse-biased conditions. For these I‑V plots, measurements are made in a dark enclosure, from a starting voltage of 0 V to a point at which the PV cell begins to break down, with the output current measured and plotted as a function of the applied voltage. The shunt resistance can also be found by using the slope of a PV cell’s reverse bias I‑V curve (Fig. 5). From the linear region of the curve, the shunt resistance can be found from

r_sh = ΔV _{Reverse Bias}/ΔI _{Reverse Bias}

                     V_反偏

                                   用于估算r_sh的线性区

                                         ΔI_反偏

ΔV_反偏

      log I_反偏

图5. 利用PV电池反偏I-V曲线的斜率可以得到PV电池的分流电阻。

Fig 5. A PV cell’s shunt resistance can be found by using the slope of a PV cell’s reverse bias I‑V curve.

除了在没有任何光源的情况下进行这些测量之外，我们还应该对PV电池进行正确地屏蔽，并在测试配置中使用低噪声线缆。

In addition to making these measurements in the absence of any light sources, the PV cell should also be properly shielded and low-noise cables used in the test setup.