The Research On Sensorless Control System For Five-Phase Brushless DC Motor

The Brushless DC motor in electric vehicle application is very wide. But it also facessome problems like large torque ripple, small output torque, high failure rate and high cost ofmaintenance. Through the sensorless control method, this thesis focuses on how to solvethese problems above by taking Five-phase Brushless DC Motor as the power device. Themain contents are as follows:1) This thesis has analyzed the working principle of the three phase brushless DC motorand the five phase brushless DC motor. Through comparative study, it finds out thesimilarities and differences between the two points, and gives the five phase brushless DCmotor voltage balance equation, electromagnetic torque equation, and mechanical equationsof motion.2) Since it is difficult to detect the rotor initial position in Five-phase Brushless DCMotor sensorless control method, this thesis has analyzed and verified its correspondingrelationship between inductance and the rotor of Five-phase Brushless DC Motor in differentpositions, according to the theory that inductance changes frequently during the motorrunning, namely, the law of the equivalent inductance L of winding coil varies from thechanges of inner magnetic flux; and Indirect inductance measurement is adopted to definethe rotor initial position accurately.3) During the start of the Five-phase Brushless DC Motor sensorless control method, theBack Electromotive Force is not yet built, it is very hard to determine the Phase ChangingPoint. Normally, the forced phase changing method will arise the motor shaking terribly,leading a bad effect. In this thesis, due to the corresponding relationship between the windinginductance and bus current, by measuring the bus current during its periodically change, wecan find the rotor’s corresponding position indirectly, and set a corresponding drive logic toset the motor in its normal running status from startup steadily.4) This thesis has Designed a single-chip control system for the five phase brushless DCmotor. The hardware cheme is based on the XC866. Through the software design, it hascompleted the five phase brushless DC motor control system with a XC866chip as the core finally.5) Based on the five phase brushless DC motor sensorless control system experiment,obtained five phase brushless DC motor in a static state inductance position detection of pulsewaveform and the current waveform stability after the operation, and obtained the actualposition of the rotor; also received the five phase brushless DC motor sensorless operationcharacteristic curve, and with a sensor operation characteristic curve comparison, discoveredtwo are basically identical, which shows that the proposed five phase brushless DC motorsensorless control system is correct.In the research of this subject, by analyzing and researching on the principle ofFive-phase Brushless DC Motor and the working process of sensorless control method, wehave achieved its control method of Five-phase sensorless Brushless DC Motor. By the workof project practice, the project feasibility is confirmed.