Speed measurement of a general DC brushed motor based on sensorless method

DC brushed motor (abbreviated as DC motor later) has some outstanding advantages for example cheap and control easy compared to other types of motor. It has already been widely used in industrial machines and household appliances. In many applications of DC motor, the speed of the DC motor is often a basic required to be measured parameter. To achieve this purpose, a direct speed measuring method which a speed sensor with suitable dimension or resolution needs to be coupled with the axis of DC motor and leads to more complicated mechanical structure and control circuit should be included in equipment. Moreover, if the setup place of the speed sensor is insufficient, the direct speed measuring method is then not allowed to be used. The current parameter is one of the independent variables of DC motor. Many important dynamic behaviors of the DC motor will be characterized by this parameter. In this paper, we will propose a new speed measurement of DC motor based on a sensorless speed method. In order to verify the feasibility of our proposed method, we test and compare the measured motor-speed values of electric-spray pump by using the conventional speed measuring method (couple a speed sensor with rotating axis of DC motor) and the proposed sensorless speed measuring method, respectively. The experimental measured results show the method that the speed measurement of DC motor is read and calculated based on the frequency of ripple component of the motor current is actually feasible.