Research On Cogging Torque Suppression Of Brushless DC Motor In Electro-hydraulic Brake System

Electric and intelligent new energy vehicles are the development trend of future cars.Brake-by-wire control system（BBW）can cooperate with the car’s drive motor to realize regenerative braking,increase the endurance mileage by more than 25%,effectively alleviate the short range and low efficiency problems faced by new energy vehicles;at the same time,it can be combined with the intelligent driving function to achieve the leap to automatic driving,which is an important development direction for automotive braking system.Adopting the form of"power-assisted motor+deceleration and torque-increasing mechanism",the electro-hydraulic brake system（EHB）is the mainstream of BBW application.As the source of brake fluid pressure in the braking system,the power-assisted motor performance largely determines working characteristics of EHB.Brushless DC Motor（BLDCM）has been widely used in EHB because of its high power density and high reliability.However,there is cogging torque in BLDCM,which has more significant impacts on EHB after amplification by torque-increasing mechanism,restricting the precise control of brake fluid pressure,affecting the driver’s control experience and even threatening driving safety.This paper takes BLDCM for EHB as the research object and focuses on the research on the cogging torque suppression of BLDCM.The specific research contents are as follows:（1）Based on the parameters of a certain EHB,the design index of BLDCM was determined.The main structure design and electromagnetic parameter calculation were carried out by using the electromagnetic design method.The structure and basic parameters of BLDCM were preliminarily determined,and a three-dimensional model was established.（2）ANSYS Electronics Desktop software was used to simulate the performance of BLDCM.The parameters of magnetic circuit were quantitatively analyzed by no-load simulation to judge the design and rationality of magnetic circuit.Motor performance was observed through load simulation to judge whether it conforms to the rated index;The simulation of the cogging torque was conducted to obtain its curve waveform and spectrum distribution,and to determine the subsequent optimization objective.（3）After analyzing and deriving the analytical expression of the cogging torque through the energy method,it is found that its value is determined by the structural parameters and the Fourier expansion coefficient.Based on this,under the three situations of BLDCM eccentricity change,pole arc coefficient change and auxiliary slot addition,the changes of two important parametersB_rn andG_n were studied,the acquisition method of structural parameters that can effectively suppress cogging torque was given,and the corresponding finite element analysis and verification were carried out.（4）From the control point of view,vector control was introduced into the BLDCM control system.Based on the mapping relationship between the rotor position and the cogging torque,a real-time current compensation control strategy for the output torque was designed according to the rotor position signal.The BLDCM control circuit model and ontology finite element model were established respectively on Simplorer and Maxwell platforms,and the co-simulation was carried out to verify the effectiveness of the proposed control strategy.