Direct Torque Control For Bearingless Brushless DC Motor

Bearingless brushless dc motor is one kind of new motor which combined brushless dc motor with magnetic bearing. It has the advantages of simple structure, lower fault-rate, smaller volume, higher efficiency of energy conversion and it also realize the suspension control in high speed. Compare the other bearingless motor, the brushless dc motor has more short axial space, higher rated speed and the rotor suspended by the rotating flux which produced by the permanent magnet in rotor surface. So the rotor suspension needs smaller energy. Because of the advantage of energy conservation and enviroN·mental protection, the bearingless brushless dc motor becomes a new research direction in high speed drives.The direct torque control (DTC) has successful applied in the sine wave control motor and recent years it also made breakthrough in brushless dc motor. Direct torque control is combination of the control method and motor. This method realizes the decoupling of motor and dramatically improves the dynamic and static performance of motor. Now it is one of the main research directions of motor control. But this method has large torque ripple so it can not directly use in bearingless brushless dc motor control. In order to introduce the direct torque control in bearingless brushless dc motor it needs to solve the problem of the large torque ripple.In the first, this paper analyzes the mathematical model of brushless dc motor; establish the suspension control theory of bearingless brushless dc motor. Then deduce the mathematical model of bearingless brushless dc motor which includes the torque control and suspension force control. In the second, deduced multi-level and sectors subdivision control for direct torque control and introduce it to bearingless brushless dc motor. This method can produce the vector tables according to the system requirements and choose the best control vector to obtain the best effect. In the third, improve the suspension control by use closed-loop suspended force direct control. In the forth, combine adaptive genetic algorithm to calculate the optimum parameters of the suspension system. In the end, design and implement the digital control system of bearingless brushless dc motor. Make the simulink of combine multi-level and sectors subdivision control with direct torque control for bearingless brushless dc motor. The results show that this method can inhibit torque ripple and the current distortion obviously, it is able to improve the motor dynamic and static performance effectively. The closed-loop suspended force direct control can track the rotor state accurately and it improves the control’s precision and speed effectively. Verify the method and realize the control method by DSP (TMS320F2812).