Phase Compensation Research Of Brushless DC Motor Based On Virtual Neutral Point Voltage

Permanent-magnet brushless DC (BLDC) motor is increasingly being used in automotive, computer, industrial, and household products because of its high power density, small geometry, fast dynamic response, high efficiency. The use of position sensor limits application of the motor with position sensor, therefore, brushless dc motor without position sensor technology research has high research and application value. At present, scholars proposed the method of back emf, inductance measurement method, the speed-independent position function method, kalman filtering method, the state observer method and other methods. Especially the application of back EMF method is researched more widely, but the method can bring the phase lag of winding voltage because of filter and it need to be modified according to different running speed of the motor. In addition, the sensorless permanent magnet brushless dc motor’s start problem is also a key problem affecting the operation of the motor starting, based on the above questions this article mainly aims at the reversing of the terminal voltage method without position sensor technology position correction, the motor starting method study, basically have the following conclusion:First, in view of the terminal voltage method detecting rotor position of brushless dc motor, analysis of three methods for PWM chopper was deduced to motor winding end voltage and Virtual neutral point voltage, points out the characteristic of voltage changes, on the basis of detection, commutation position detection and correction methods was proposed based on neutral point voltage of brushless motor winding. Further derived the method of winding commutation position calculation expression and logical analysis of a relational table, and then, by dynamic finite element simulation to verify the accuracy and feasibility of the method, so as to provide theoretical reference basis for the application of this method.Secondly, in view of the low speed starting of brushless motor without position sensor problem, based on the analysis of the traditional method of "3-step" start are introduced on the basis of pointed out" boost upsampled ratio "is success for motor starting, too high or too low " boost upsampled ratio "will flood back EMF zero crossing, and motor fails to start. Based on this, this article has given some improvements to the traditional way of "3-step" start. The low-speed range boost upscaling synchrotron simultaneous detection of back EMF zero crossing. If not reliable detection under low speed threshold n1to zero, then continue to accelerate to high speed threshold n2, then, winding without electricity for a power cycle, detect back EMF zero crossing directly to enter without position sensor running state. Under the premise that guarantee starting reliability, this method improves the quickness and the state switch of motor starting stationarity. It is usefull for the starting research of brushless motor without position sensor.Finally, based on the above study, this paper based on flash memory dsPIC30F3010enhanced16-bit digital signal controller, design of brushless dc motor without position sensor operation control circuit.The hardware circuit mainly includes the brushless motor winding terminal voltage sampling circuit, motor drive circuit, over-current protection circuit, etc. Software mainly includes the main program, the open-loop starting subroutine, induction electric potential zero detection subroutine, method2detection subroutine, A/D interrupt subroutine, and T2interrupt subroutine. Preliminary implement the sensorless operation of the motor by hardware and software debugging, and the experimental waveform is ideal, the speed of the motor, the torque is more smooth.