通过改变异步电动机的同步转速而实现对转子调速的方法有（        ）。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='68476' and id < 4421267 and id<>'4421267' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='68476' and id > 4421267 and id<>'4421267' order by id asc limit 5