Research And Design Of Positionless Drive For Air Pumpless Brushless DC Motor

At present,the motor which is mainly used to drive oil pump is the brushless dc motor(BLDCM);Because the BLDCM is without brush and commutator and has the same performance in some aspects with the DC motor,it is gradually used.That the rotor position sensor of the motor is easy to failure leads the BLDCM can not work nomarlly due to the complex environment of the aerospace oil pump.As a result,the paper does some research and design about the the sensorless control of the BLDCM which used to drive the aerospace oil pump.The main works in this paper are as follows,First,to provide theoretical basis for the follow-up design the present condition and related principle of the BLDCM are analyzed.Then,the key technology of sensorless control of BLDCM — — sensorless starting and running are analyzed in details and the existing technique of starting and rotor detection are compared.In this paper,three-stage start strategy is used.Based on the back EMF zero crossing detection,the principle that three phase back-EMF are equivalent to hall signal is used to detect zero-crossing points of Back-EMF and commutate by using the majority function.Finally,according to the above theory,the hardware and software of the drive system of aerospace oil pump BLDCM without position sensors are designed.The hardware systems based on digital signal controller dsPIC33FJ32MC204 are established and the back-EMF detection circuit,the driver and inverter circuit,over-current and under-voltage protection circuit and orther related peripheral circuit are designed.About software system,by comparing and caculating the relation of three phase back-EMF, the thesis back-EMF are equivalent to hall signal is discussed.The algorithm of the back EMF zero crossing detection is provided by using the majority function to achieve the sensorless communication and running.Through the design of each module program, speed and current double closed-loop system is built.Finally,the experimental platform of the sensorless control of the BLDCM is set up in the laboratory.Some experiments are done to verify the performance of the hardware and software.The experimental results prove the BLDCM can start up smoothly,run normally,its communication is correct and has good performance of speed control.The practical results have proved the feasibility of designed drive system.