In this paper to estimate the rotor position in sensorless BLDC motor drive, the method of the ratio functions line by line flux is used. This method, compared to other methods which are evaluated to estimate the rotor position, has low software volume and therefore, its implementation is easy and also manufacturing cost is less. Also this method has an appropriate efficiency in a wide range of speed and estimate the rotor position is independent of speed and rotor frequency. Also in this paper, from two methods Direct Torque Control (DTC) and switching function are used to design sensorless BLDC motor drive. DTC method is one of the most innovative and efficient methods in control of the electrical machine. High speed in response to changes in torque, simplicity of implementation, independence to machine parameters and needs of less computation are the advantages of this method. At the end of this paper, simulation results by using software MATLB shows good function of sensorless BLDC motors with DTC method than the switching function method
