In　view　of　the　problem　of　instantaneous　torque　observation　in　permanent　brushless　DC　motor　(BLDCM)　with　two-phase　conduction　without　position　sensors,　an　instantaneous　torque　estimation　method　is　proposed　for　the　BLDCM　with　two-phase　conduction　mode　based　on　high-frequency　current　injection.　Based　on　the　high-frequency　signal　model　with　two-phase　conduction　mode,　the　estimator　of　rotor　position　angle　was　constructed　to　obtain　the　rotor　position　angle　observation　value.　The　instantaneous　torque　was　observed　according　to　the　relationship　of　torque,　rotor　position　angle,　back　EMF　coefficient　and　stator　current.　In　order　to　avoid　the　effect　of　the　q-axis　inductance　change　on　the　estimation　accuracy,　the　estimator　of　q-axis　inductance　was　also　built　according　to　the　high-frequency　signal　model,　which　was　updated　in　the　instantaneous　torque　estimation.　It　is　shown　from　the　experimental　results　that　the　proposed　instantaneous　torque　closed-loop　drive　system　can　operate　at　low　speed,　even　at　zero　speed　with　the　rated　load.　©　2018,　Harbin　University　of　Science　and　Technology　Publication.　All　right　reserved.