In　reality,　through　the　special　winding　connection　mode,　it　can　be　realized　that　only　one　set　of　driving　systems　controls　the　series　or　parallel　decoupling　and　independent　operation　of　multiple　multiphase　motors.　It　not　only　reduces　the　size　of　the　system,　but　also　saves　much　cost　of　designing　the　drive　system.　As　the　number　of　motors　increases,　the　number　of　encoders　used　to　detect　rotor　position　angle　and　speed　increases,　and　the　cost　increases.　Therefore,　sensorless　control　technology　has　become　the　main　research　direction　in　the　field　of　motor　control　for　pursuing　low　cost　and　high　control　accuracy.　For　permanent　magnet　synchronous　motors　(PMSM),　especially　six-phase　series　three-phase　double　motor　systems,　accurate　decoupling　observation　of　initial　rotor　position　is　the　first　step　to　realizing　sensorless　control　of　dual　motors　and　the　key　to　ensuring　a　smooth　start.　Therefore,　this　paper　proposes　a　method　of　rotating　high-frequency　voltage　injection　to　realize　the　decoupling　observation　of　the　initial　rotor　position　of　a　six-phase　series　three-phase　PMSM　system.　Firstly,　rotating　high-frequency　voltages　are　injected　simultaneously　in　the　six-phase　and　three-phase　planes,　and　the　preliminary　rotor　position　angles　of　the　two　motors　are　obtained　by　demodulating　the　negative　sequence　components　of　their　current　responses.　Secondly,　to　improve　the　estimation　accuracy,　the　error　angle　contained　in　the　positive　sequence　component　of　the　current　response　is　extracted　and　used　to　compensate　for　the　rotor　position　angle.　In　addition,　the　two　motors　are　designed　as　shallow　magnetic　saturated　PMSM　to　prevent　the　over-current　caused　by　magnetic　circuit　saturation.　When　the　pulse　voltage　of　equal　amplitude　and　width　is　applied　to　the　positive　and　negative　sides　of　d-axis,　the　current　response　amplitude　of　the　d-axis　forward　is　smaller　than　that　of　the　reverse.　Consequently,　the　polarity　of　the　magnetic　poles　of　the　two　motors　is　judged.　As　a　result,　the　decoupled　observation　of　the　two　motors’　rotor　initial　position　is　completed.　An　experimental　study　was　carried　out　on　a　set　of　six-phase　series　three-phase　PMSM　systems.　In　the　experiment,　18　positions　of　the　two　motors　were　randomly　selected　for　estimation.　Without　compensation,　the　experimental　results　show　that　the　average　of　the　absolute　value　of　the　estimation　error　of　the　six-phase　PMSM　is　10.89°,　and　that　of　the　three-phase　PMSM　is　5.59°.　After　compensation,　the　value　of　the　six-phase　PMSM　is　3.72°,　and　that　of　the　three-phase　PMSM　is　1.81°.　It　shows　that　the　compensation　method　can　improve　observation　accuracy.　The　rotor　polarity　judgment　of　the　two　motors　at　0°　and　180°　is　also　studied.　The　results　show　that　for　shallow　magnetic　saturation　PMSM,　the　phenomenon　that　the　amplitude　of　the　d-axis　forward　current　response　is　smaller　than　that　of　reverse　can　be　used　to　complete　the　rotor　polarity　judgment.　It　is　consistent　with　the　current-time　curve　fitted　by　the　finite　element　simulation.　The　following　conclusions　can　be　drawn:　(1)　The　error　angle　obtained　from　the　positive　sequence　component　in　the　current　response　is　used　to　compensate　for　the　rotor　position　angle　obtained　from　the　negative　sequence　component,　which　improves　the　estimation　accuracy.　(2)　Based　on　the　shallow　magnetic　saturation　characteristic,　the　rotor　polarity　of　the　two　motors　is　judged　by　the　phenomenon　that　the　current　response　amplitude　of　the　d-axis　forward　is　smaller　than　that　of　the　reverse.　(3)　Experimental　results　show　that　the　estimated　position　angle　can　be　used　to　start　two　motors　simultaneously　with　load,　and　the　process　is　stable.　©　2023　Chinese　Machine　Press.　All　rights　reserved.