Study On The Control Of Sensorless Brushless Motor In Automobile Electronic Fuel Pump

The automotive electronic fuel pump can supply a certain pressure and flow of fuel from the tank to the engine, so it is one of the most important parts in the automobile power system. However, the energy crisis leads to the fuel’s diversification and the new energy’s development. The commutator of brush in the fuel pump is susceptible to be damaged when the electronic fuel pump is immersed into the new fuel such as alcohol fuels with the property of corrosion, and then the service life and reliability of the electronic fuel pump is reduced very quickly. The automotive electronic fuel pump based on the Brushless DC motor(BLDC motor) can not only effectively reduce the vibration and noise during commutation but also have extensive adaptability in complex environment as it hasn’t any mechanical commutator parts in the structure. Thus, the BLDC motor has great practical significance in the automobile electronic fuel pump.Based on the motor’s rotation principle, the key technical points are analyzed in this thesis. Combined with the automobile electronic fuel pump for the demand of the BLDC motor with high reliability and low cost, the back electromotive force(EMF) is applied to estimate the rotor position information for it’s simple and reliable. At the same time, in order to diminish the phase shift and cost of resistive capacitive circuit, the virtual neutral point is structured in the program to gain the rotor position information. The twice pre-positioning method is utilized to find the rotor’s location when the motor is in the start stage. It can prevent location failure while rotor magnetic pole position and resultant magnetic field orientation with an angle of 180 °, electromagnetic torque of 0, reduce cost and improve the system reliability. The single chip microcomputer with high performance-cost ratio is chosen as the kernel control chip, and then the hardware circuit and the software program are designed in this control system. The P-type MOSFET is chosen on upper half bridge and N-type MOSFET is chosen on the second half bridge in the main power three-phase full bridge circuit. This design can effectively avoid half bridge bootstrap circuit driving main power circuit caused by floating voltage. To verify the reliability of the control system’s hardware and software, and compared with the BLDC motor with position sensor, the Sensorless BLDC motor is tested, such as the motor rotor positioning test, the start test without load, the start test with load, the abrupt load change test(increasing load and reducing load, heavy load and so on). At last, the test platform is constructed to simulate the work environment of the automobile electronic fuel pump and test the control system’s working state in the whole process.The experimental results show that the control system according to the actual demand for the electronic fuel pump has simple structure and low cost, and the method of the virtual mid-point software construction with back electromotive force can obtain the rotor position accurately, the twice pre-positioning method is applied to start motor and realize the motor’s smooth work. The performance experiments with sensorless BLDC motor show that the whole control system has good stability and adaptability. The simulation environment tests of the BLDC motor show that the control system has good stability and electronic fuel pump can meet the requirements of minicar engine oil supply.