| The Brushless DC motor has the ascendency of simple structure,low cost,high reliability,good speed regulation performance and high power density.It has been widely used in many fields.The position information of the motor rotor is the key of the speed regulation system.Usually,the rotor position sensor needs to be installed to obtain the rotor position information,but it also has to confront the problems of high cost and complex control structure,which restricts the application of the motor.The sensorless control of motor has become a research hotspot.In the complex working environment,the performance of the control system will be affected by adverse factors such as internal parameter changes and external load disturbances.The controller based on sliding mode variable structure theory can ensure that the system operates according to the set state,ignore the influence of internal and external disturbances,and achieve the purpose of accurate control.Aiming at improving the performance of Brushless DC motor speed regulation system,this thesis combines the vector control strategy of Brushless DC motor with the sliding mode variable structure control method.The main work of this thesis is as follows:Firstly,this paper introduces the vector control theory,coordinate transformation,voltage space vector pulse width modulation technology.Then,the sliding mode variable structure theory and its characteristics are introduced.On this basis,a new type of superspiral sliding mode observer is designed,which uses continuous function T(s)instead of symbolic function sign(s)to optimize the traditional superspiral sliding mode observer,and uses the improved superspiral sliding mode observer to estimate the position and rotation speed of the rotors.Secondly,a new sliding mode reaching law is presented,which is composed of three parts: variable speed term,variable power term and variable exponential term.It can adjust the approach speed adaptively according to the state position of the system,increase the approach speed when moving away from the sliding surface,and reduce the chattering phenomenon when sliding on the sliding surface.The simulation and comparison experiments are carried out with other approaches law control schemes.Experiments show that the new approach law improves both fast responsiveness and dithering,and a sliding mode speed control module is built based on the new approach law instead of a speed PI control module.Moreover,considering the existence of internal parameter perturbation and external load perturbation in the system,the disturbance of the system is difficult to measure in practice.For this reason,a sliding mode disturbance observer is designed,and the observed values are feed forward to the output of the speed controller.A new approach law based on disturbance error is presented,and a sliding mode disturbance observer is designed based on the new approach law to simplify the complexity of real-time calculation of gain factor.At the same time,it avoids the increase of observation jitter caused by the gain factor due to too large disturbance error.Finally,a double-loop speed control simulation model is built on the Matlab/Simulink platform.The validation verifies that the improved superspiral sliding mode observer can more accurately observe the motor speed and the rotor position information,reduce the jitter of the observation signal,and compare with the experimental results of the traditional superspiral sliding mode observer,improve the self-filtering function of the superspiral sliding mode observer,omit the angle compensation link of the traditional sliding mode observer,and simplify the control process.The new reaching law sliding mode speed controller scheme can improve the response speed of the system and effectively suppress the chattering of the sliding mode control system.The combination of the new sliding mode speed controller and the improved disturbance observer proposed in this paper is verified to improve the robustness and speed control performance of the system. |
