Design And Research Of Vector Control System For Position Sensorless BLDCM

Brushless DC motor (BLDCM) is widely used in military, industrial, civil and other fields for its advantages of simple structure, high operation efficiency and good speed regulation performance. BLDCM is usually driven by 120° square-wave current. Under this control method, the mutation of reversing current will lead to the torque ripple and a big noise. Due to the magnet manufacturing process and magnetization, the waveform of BLDCM's back EMF is close to sinusoidal wave. It will achieve smaller torque ripple and better performance when the sinusoidal-wave current is used to control BLDCM.The key to achieve precise control performance of BLDCM lies in obtaining accurate rotor position. The reliability of position sensors is reduced in the high temperature and high corrosive occasions. In order to solve this problem, the sensorless BLDCM vector control technology is researched in this thesis. Several key technologies such as the starting control method, the switching strategy, the rotor speed and rotor position estimation are performed.On the basis of analyzing the constant voltage frequency ratio method, the starting strategy with speed-open-loop and current-closed-loop is presented. Compared with the constant voltage frequency ratio method, the method effectively prevents the rotor out of step and avoids the stator windings over current. In this thesis, the switching process based on decreasing the current amplitude is analyzed. When the rotational speed is higher, the sliding mode observer is used to estimate the rotor's position and speed.The hardware design and software design of the vector control system for the sensorless BLDCM are researched to test the feasibility of the strategy. The hardware circuits mainly include power supply circuit, driving circuit, inverter circuit, current sampling circuit and conditioning circuit. The rotor position and the rotor speed calculation subroutine, the AD sampling subroutine, and the SCI communication interrupt subroutine are included in software design.At last, the designed control system is tested and the feasibility of the control algorithm is verified by the experiment results.