| Permanent magnet brushless dc (PMBLDC) motors are widely applied because of its simple structure, high efficiency, simple control strategy and convenient maintenance. A common strategy called six-step 120° conduction is usually used in PMBLDC, and it needs six key rotor position signals in a cycle for communication for three phase windings. The six rotor position signals can be obtained by hall sensors in sensor control mode, or obtained by zero-crossing points of back-EMFs in sensorless control mode.Contra-rotating permanent magnet brushless dc (contra-rotating PMBLDC) motoris a special kind of PMBLDC and its electromagnetic structure is exactly the same as common PMBLDC motors. The diffirence is that armature of contra-rotating PMBLDC also can rotate as permanent magnet rotor and they rotate in contra direction. Because of the gyroscopic effect in fluid in underwater propulsion system, the use of contra-rotating propeller can maintain its balance; And the use of contra-rotating propeller can improve the wind utilization; And in the field of new type cars drive system, contra-rotating PMBLDC motors can reduce the mechanical complexity and volumn of machine.This paper did the research on contra-rotating PMBLDC motors by contrast with common PMBLDC motors. Firstly, got the mathematical model, figured out the factors fluencing the speed of rotors, studied sensor and sensorless control strategies of contra-rotating PMBLDC motors. And proposed a special start-up method based on inductance diffirence for sensorless control based on back-EMFs. Secondly, verified the control strategies of common PMBLDC motors can be used in contra-rotating PMBLDC rotors by simulation experiments in MATLAB/Simulink platform. Finally, the hardware platform based on the TI company TMS320F28069 chip was set to complete the experiments of sensor control and sensorless control strategies. |
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