A　sliding　mode　stator　flux　linkage　estimator　based　on　active　flux　principle　is　proposed　for　a　direct-torque　controlled　permanent　magnet　synchronous　motor　(PMSM)　drive　to　improve　the　performance　of　the　stator　flux　estimation　for　PMSM.　The　stator　current　and　active　flux　sliding　mode　estimators　were　firstly　constructed　in　stator　coordinate　frame,　and　secondly,　the　stator　flux　linkage　was　calculated　with　estimated　active　flux.　The　experimental　results　show　that　the　presented　observer　is　able　to　deliver　more　accurate　estimation　than　an　open-loop　estimator.　The　novel　estimator　has　better　disturbance　resistance　to　inductances　change.　With　the　integrated　flux　observer,　the　PMSM　DTC　drive　system　can　operate　at　very　low　speed　down　to　7.5　r/min　with　half　full　load.　©　2013　Chin.　Soc.　for　Elec.　Eng.