A61L-0001-0076

A61L-0001-0076

除了大負荷減速場合需要增加制動電阻和制動單元來快速剎車外，實際上如果符合比較重，啟動時間時間要求非?？炷欠N，也需要制動單元和制動電阻來配合啟動的，以往我試過用變頻器帶動一種特殊的沖床，要求把變頻器的加速時間設(shè)計成0.1秒，這時候滿負荷啟動，雖然負荷并不是非常重，但是因為加速時間太短了，這時候母線電壓波動非常厲害，也會出現(xiàn)過壓或者過流的情況，后來增加了外置的制動單元和制動電阻，變頻器就能正常工作了。分析起來，是因為啟動時間太短，母線電容的電壓瞬間被掏空了，而整流器瞬間有大的電流充進來，引起母線電壓突然變高，這樣母線的電壓波動太厲害，瞬間可能會超過了700伏，加上了制動電阻，就可以及時這個波動的高壓，讓變頻器工作在正常狀態(tài)。

還有一種特殊的情況，是矢量控制場合，電機的扭矩和速度方向相反，或者工作在零轉(zhuǎn)速扭矩輸出的場合，比如吊機掉了重物停在半空中，收放卷場合需要力矩控制，都需要讓電機工作在發(fā)電機狀態(tài)，源源不斷的電流會反充到母線電容中，通過制動電阻，就可以及時消耗掉這些能量，保持母線電壓平衡穩(wěn)定了。

很多小變頻器，比如3.7KW的，往往都內(nèi)置了制動單元和制動電阻，應(yīng)該是考慮到母線電容調(diào)小的緣由吧，而小功率的電阻和制動單元并沒有那么貴。

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