In　this　paper,　a　sensorless　speed　tracking　control　scheme　is　proposed　for　Permanent　Magnet　Synchronous　Motor　(PMSM)　with　unmodeled　electromotive　forces.　Specifically,　one　observer　is　developed　to　estimate　the　angular　velocity　of　PMSM　and　the　estimated　value　is　injected　into　a　novel　nonlinear　feedback　controller.　The　unmodeled　electromotive　forces　are　not　estimated.　The　influences　of　the　unmodeled　electromotive　forces　on　the　speed　tracking　performance　are　overcome　by　constructing　corresponding　nonlinear　damping　terms　in　the　controller.　Under　certain　assumptions,　the　rigorous　proof　of　the　stability　of　the　closed-loop　system　is　completed　with　Lyapunov　theory.　All　the　dynamic　signals　are　bounded.　Furthermore,　the　estimation　error　and　the　tracking　error　can　converge　to　an　arbitrarily　small　value　by　choosing　the　control　parameters　appropriately　large.　Finally,　the　simulation　results　of　constant　and　time-vary　speed　tracking　illustrated　the　effectiveness　of　the　proposed　controller.