描述
孤島現(xiàn)象是指當(dāng)電網(wǎng)由于電氣故障或自然因素等原因中斷供電時(shí)，光伏并網(wǎng)逆變器仍然向電網(wǎng)輸送電能，從而形成一個(gè)電力公司無法控制的自給供電孤島，稱之為“孤島效應(yīng)”。光伏并網(wǎng)發(fā)電系統(tǒng)中孤島的發(fā)生會(huì)產(chǎn)生嚴(yán)重的后果，對(duì)用戶的用電設(shè)備和檢修人員的安全造成重大危害。孤島發(fā)生時(shí)，若孤島中的電壓和頻率超出允許的范圍，可能會(huì)對(duì)用戶的設(shè)備造成損壞；電網(wǎng)的掉電可能使光伏發(fā)電系統(tǒng)過載運(yùn)行，易被燒毀；與光伏發(fā)電系統(tǒng)相連的線路仍然帶電，對(duì)檢修人員造成危險(xiǎn)。所以當(dāng)電網(wǎng)停電后，必須立刻中止系統(tǒng)對(duì)電網(wǎng)的供電，防止孤島效應(yīng)的發(fā)生。反孤島效應(yīng)的關(guān)鍵是電網(wǎng)斷電的檢測(cè)，且檢測(cè)時(shí)間越短效果越好。一般采取被動(dòng)檢測(cè)法和主動(dòng)檢測(cè)法。被動(dòng)檢測(cè)法是實(shí)時(shí)檢測(cè)電網(wǎng)電壓的頻率和相位，通過頻率和相位的異常來判斷電網(wǎng)是否失電。采用被動(dòng)的孤島檢測(cè)方法不足以在負(fù)載匹配的情況下有效檢測(cè)出孤島現(xiàn)象，為此，必須采用主動(dòng)式的檢測(cè)方法。主動(dòng)檢測(cè)法是通過實(shí)時(shí)對(duì)電網(wǎng)參數(shù)發(fā)出干擾信號(hào)，通過檢測(cè)反饋信號(hào)來判斷電網(wǎng)是否失電。常見的方法有主動(dòng)頻率偏移法、滑模頻率偏移法和輸出功率擾動(dòng)檢測(cè)法等。
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