Research On Starter/Generator System Of Sensorless Brushless DC Motor

Brushless DC motor has become one of the important models for hybrid electric vehicles and electric vehicles that need to use the starter/generator dual-function motor,due to its simple structure,compact size,smooth operation,high efficiency and large starting torque.In this paper,the starter/generator system of BLDCM in the range extender of the auxiliary power generator system of electric vehicles is taken as the research object,and a series of key technical problems are studied.Accurate detection of rotor phase displacement is the premise of BLDCM operation.For sensorless BLDCM,the principle of detecting the zero-crossing point of back EMF based on the motor terminal voltage to obtain the phase displacement of the rotor is analyzed.The influence of PWM modulation is studied to back EMF zero crossing point detection.The back EMF crossing-zero detection circuit to eliminate the PWM chopper interference is designed.A method is proposed to modify the phase shift caused by resistor-capacitance filtering,device delay and software calculation.The phase shift correction formula was deduced.The experimental results show that the method can accurately obtain the position of rotor phase change,and sensorless BLDCM can run stably and reliably.Aiming at the disadvantages of acceleration and self-synchronization failure caused by traditional three-phase open-loop start of sensorless BLDCM,a compound three-phase start method was proposed.In the rotor positioning stage,short-term pulse voltage vector is sent out,and the rotor position is determined in the range of 30 degree electric angle.In the acceleration phase,a set of short and long pulse voltage vectors interspersed are sent for rotor acceleration and quasi-closed-loop positioning respectively.When the motor is added to a certain speed,the switch from external synchronization to self-synchronization can be realized.In the stable operation stage of self-synchronization,the time between the adjacent phase change point and the zero crossing of back EMF can be obtained.It will be a power cycle on the time and the corresponding time averaging 30° electrical angle,to forecast the next 30° electrical angle corresponding to the time.Thus,the next time of phase change is determined,and the smooth transition of the motor from external synchronization to self-synchronization is realized.The experimental results show that this method is effective and feasible of compound three-stage startup method,and the motor can start quickly and smoothly.The starter/generator system of BLDCM of electric vehicle range extender needs to be put into operation quickly at any time according to the on-board battery status,which requires high dynamic performance.The direct torque control is chosen as the control strategy of starter/generator system of BLDCM.The BLDCM-DTC principle is studied.The voltage vector selection tables based on direct torque control are established with runtime starter/generator BLDCM respectively.The establishment method of starter/generator of BLDCM' experiment platform is described.The BLDCM generator system principle of voltage pumping is studied.The generator system of BLDCM has carried on the comprehensive analysis of the simulation.The experimental results show that the BLDCM starter/generator system can realize starting and generating working which has good performance.This paper introduces the software and hardware design of the starter/generator system of BLDCM without position sensor.The hardware part is divided into control module,power module,signal acquisition module and power module according to its function.The design idea of each sub-program module is introduced in detail.Finally,TI DSPTMS320F28335 as the control core of the sensorless BLDCM starter/generator system simulation platform is demonstrated.