异步电动机采用变频调速时，若要保持磁通不变，应遵循（  ）的原则？（0.5）

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69421' and id < 4494885 and id<>'4494885' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69421' and id > 4494885 and id<>'4494885' order by id asc limit 5