This　paper　presents　a　method　of　designing　the　phase　locked　loop　(PLL)　for　rotor　speed　estimation.　The　transfer　function　from　the　torque　current　to　the　estimated　rotor　speed　is　derived　and　is　compared　with　that　from　the　torque　current　to　the　real　rotor　speed.　The　damping　ratio　of　the　PLL　is　selected　to　make　the　two　transfer　functions　as　close　to　each　other　as　possible.　A　first-order　filer　is　further　added　to　compensate　the　differences　between　the　two　transfer　functions　at　high　frequencies.　Simulation　results　show　that　the　proposed　design　of　the　PLL　method　improves　the　accuracy　of　the　rotor　speed　estimation.