Design and implementation of a position sensorless control method for brushless DC motors

Because brushless direct current(BLDC) motors have the advantages of a compact size, high power density, high efficiency, and long operating life time, they are widely used in many industrial products and electric traction systems. It is known that the BLDC motors have no brushes for commutation. They are commutated with electronically commutation. So, the rotor position information of the BLDC motors must be known to understand which winding will be energized according to the energizing sequence. In most of the existing BLDC motor drivers, rotor position information is detected by Hall effect sensors. This kind of mechanical position sensors will bring additional connections and costs, reliability decrease and noise increase. In order to improve the control performance and extend the range of speed regulation for BLDC motors, a position sensorless control method is proposed in this paper. In the proposed control method, rotor position information of the BLDC motors is detected from the back electromagnetic forces(back-EMFs) which are estimated by an unknown-input observer with line to line currents and line to line voltages. For the purpose of verifying the effectiveness of the proposed control method, a model is built and simulated on the Matlab/Simulink platform. The simulation results show that the speed regulation performance of BLDC motors is improved compared with using Hall effect sensors. At the same time, the reliability of the BLDC motors is improved and the costs of them are reduced because the position sensor is eliminated.

Position Sensorless Control System of Permanent Magnet Synchronous Linear Motor Based on Sliding Mode Observer with an Improved Phase-Locked Loop

In this paper,position sensorless control system of permanent magnet synchronous linear motor(PMSLM)based on sliding mode observer(SMO)with an improved phase-locked loop(PLL)is studied.Firstly,according to the mathematical model,a SMO is designed for sensorless control PMSLM drive.Thereafter,an improved PLL is proposed to tackle the imperfection of data overflow existed in the traditional PLL.The designed SMO incorporating with the improved PLL can be effectively suppress the pulsation of the estimated position and hence the chattering of the derived electrical angular velocity.At last,simulated and experimental results are presented to verify the effectiveness and feasibility of the position sensorless control system.