Study On The Control For High-speed BLDC Motor Without Position Sensor

Due to the advantage of high speed, small volume, high power density, and rapidresponse, high-speed magnet brushless DC motor(BLDCM) has been wildly applied in thesearea such as turbocharger, air compressor, centrifugal pump, blower, molecular centrifuge,navigation test platform, high speed machining fields (high speed grinding, high speed milling,etc) and medical equipment. Without the work of installing and replacing rotor positionsensor, BLDCM can work on that field where there is hot or humid, or is limit to the size ofmotor. As these obvious advantages, high-speed BLDCM has been the focus in the field ofmotor control.Among all the strategies of high-speed BLDCM control without rotor position sensor,the method based on detection of zero crossings of the phase back electromotive force(B-EMF) of BLDCM is one of the major approaches for rotor position estimation because ofthe advantages of simple and reliable detection. This paper introduces in detail the operatingprinciple of BLDCM, then establish its mathematical model. Based on detection three phaseB-EMF, a system of high-speed BLDCM control without position sensor is proposed. And themotor run as three-phase six state conduction mode, every time three are only two phasewindings conduction. When the motor is standstill or at a low speed, the B-EMF is too little tobe accurately detected, so the motor can’t run well. Therefore a particular method, which iscalled three-step-initial staring is applied to during the period of BLDCM start up. The paperanalyzes process of startup in detail, firstly, the rotor rotates to the certain orientation;secondly, the rotor speeds up while the voltage of the motor increases, the voltage linearrelation with the frequency of rotor; thirdly, the motor convert to run synchronously bydetection of phase B-EMF, thus the period of startup is over.The key difficulty of hi-speed control is the protection of inverter circuits, high-speedand large current will bring huge electromagnetic interference (EMI), lead to the powerswitch turn on at wrong time. A practical protection circuit is proposed by analyzing theequal model for inverter circuits and researching the oscillating of voltage on grid electrode ofMOSFET. As well, other circuits are designed, including MCU interface circuit, detectioncircuit of B-EMF, detection circuit of current on invert circuit, and power change circuit. Inorder to eliminate the interference in current to affect the detection of B-EMF, a algorithm ofdetection of B-EMF is proposed, which designs a window to filter interference. The systemcontrol the high-speed BLDCM during the interrupt period, two-level interrupt guarantees thereal tome control. Then the BLDCM starts up in open loop, while enter speed closed loop byusing the measure of detection the zero crossings of the phase B-EMF. All the software workis completed in the compiler environment of IAR Embedded Workbench. At last, the experimental platform with STM32F103VCT6as the control core is built,which can be used for the high-speed BLDCM control system. The experimental research isdone with the BLDCM rated power4KW, speed at50000r/min, which has verified thecorrectness of the proposed strategy.