Permanent magnet (PM) synchronous motors are gaining wide recognition over other types of motors in drive systems, mainly due to their inherently advantageous features. For successful operation of PM motor drives, position and speed sensing are of critical importance. Due to the drawbacks of conventional sensors the speed and position sensorless PM motor drive draws wide attention. In this paper, an algorithm is developed which enables the PM motor drive to operate successfully at any speed without any mechanical speed and position sensors, while keeping the maximum output voltage of the inverter constant. New expressions have been derived for the rotor speed and position in terms of stator voltages and currents. A method has been suggested to calculate the input voltage of the motor. The present work is also an attempt to provide a brief review of speed and position sensorless PM drives with simulation and experimental results.