太陽能系統中的故障分析與診斷可保護光伏元件受到損壞，並避免可能使安全受到危害的潛在危機。太陽能系統故障可分為交流側故障及直流側故障，雖然已有許多保護太陽能系統相關的國際規範，但對於某些直流側的故障卻無法有效保護，且大部分故障分析仍集中在交流側，導致直流側故障診斷成為太陽能領域的困難點。其中線對線故障根據桑迪亞國家實驗室(Sandia National Laboratories, SNL)統計結果，儘管發生頻率不高，但其造成的危害卻更嚴重而且難以防範。
有鑑於此，本研究針對直流側的線對線故障提出基於啟發式之故障診斷法。此法分別使用電路模擬方式得到相對門檻值，與使用理論估算方式得到絕對門檻值，再結合兩種門檻值來判斷故障。電路模擬法透過MATLAB的Simulink軟體建置太陽能系統模型，以模擬方式取得各種環境條件及故障程度下，正常和故障狀態的陣列輸出電壓瞬時值，先進行有效值計算後，再以陣列開路電壓為基準值做標么化，隨後將兩者之間的變化程度當作判斷故障的相對門檻值，若測量的陣列輸出電壓標么與前一次測量值相減，兩者之間的變化程度大於相對門檻值則判斷為發生故障。理論估算法透過理論值計算方式，求得故障狀態之陣列輸出電壓標么當作絕對門檻值，若測量的陣列輸出電壓標么小於絕對門檻值則判斷為發生故障。經模擬驗證，相對門檻值在低失配故障發生時，依然能夠有效偵測故障，而絕對門檻則有待實務測量後，透過補償係數修正理論估算造成的誤差。

Fault analysis and diagnosis protects the components of photovoltaic (PV) systems from damages and mitigates risks to system safety. Faults in a PV system are divided into alternating current (AC)-side faults and direct current (DC)-side faults. Although many international standards have been proposed to protect PV systems, standards remain unable to effectively protect PV systems from DC-side faults. Moreover, most fault analyses have solely focused on AC-side faults, rendering DC-side faults a major problem in PV systems. In particular, line-to-line faults are very dangerous to PV systems and are difficult to prevent—although they occur relatively infrequently, according to statistics by Sandia National Laboratories.
This study incorporated a heuristic fault diagnosis approach for line-to-line faults. The approach use circuit simulation method to get the relative threshold values, and use theoretical estimation method to get the absolute threshold values. Finally, combine the two threshold values to detect faults. The circuit simulation method uses the Simulink program in MATLAB to establish a PV-system model; the model simulates the instantaneous values of the array output voltage under normal and faulty operation statuses and under various environmental conditions and fault severities. The effective values are calculated before being standardized using the array output voltage as the reference value. The difference between the values of the two statuses is then determined as the relative threshold value for fault occurrence. The difference between the standardized value and the value calculated in a preceding measurement is calculated; if this difference is larger than the relative threshold value, a fault has occurred. The theoretical estimation method involves obtaining the standard array output voltage during a faulty status through theoretical calculations; this voltage is then used as a absolute threshold value. If a measured standardized value is lower than the absolute threshold value, then a fault has occurred. After verified by simulation, the relative threshold values are effective to detect the fault, even when low mismatch fault occurs. However, the absolute threshold values must be corrected by using compensation coefficients in subsequent actual measurements.

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