Research On Sliding Mode Control Strategy Of Permanent Magnet Synchronous Motor Based On Three Level Inverter

With the update and iteration of science and technology,frequency conversion and speed regulation technology has become an important means to save electric energy.In China,high-voltage AC is used to directly drive nearly half of the total number of motors with more than 315 KW,resulting in a large amount of waste of electric energy.In order to achieve the goal of carbon neutrality in 2060,it is extremely urgent to develop a high-voltage high-power variable frequency speed regulation system.As an important part of modern industrial production,motor drive control system has been widely concerned and studied by scholars at home and abroad.Permanent magnet synchronous motor(PMSM)has the advantages of small size,high power density,strong reliability,and is widely used in various high-precision servo systems.The traditional PMSM control system is gradually replaced by the high-performance and high-precision PMSM sensorless control system because the mechanical sensor is easily affected by the external environment.Therefore,this paper studies the sensorless sliding mode control system of permanent magnet synchronous motor(PMSM),a three-level diode-clamped(NPC)inverter.First of all,for NPC three-level inverter,neutral-point voltage balance has always been a hot issue,which greatly limits its development and application.This paper mainly discusses its working principle,and puts forward the method of charge compensation by adjusting the positive and negative small vectors,IGBT switch sequence and other control ideas.This strategy introduces a balance factor k,which adjusts the operating time of the power switching device and provides an accurate expression when there are paired positive and negative small vectors in the region.Obtaining an effective range for adjusting the midpoint potential,while once again limiting and correcting k.Based on the fluctuation of the midpoint potential,the reasonable time for the positive and negative small vectors to act is derived.The charging and discharging of the upper and lower capacitors on the DC side can be more efficiently achieved by introducing adjustment factors.The simulation results of the model have verified that the proposed introduction of a balance factor can quickly and effectively achieve neutral point potential balance.Secondly,for the sensorless control system of permanent magnet synchronous motor,sliding mode control is widely used because of its fast dynamic response,strong robustness and small computation.However,there is chattering phenomenon in sliding mode variable structure control,which is not conducive to the effective operation of the motor.The effects of sliding mode gain and switching function on chattering are studied and analyzed.For the sliding mode gain,fuzzy control is used to regulate the gain,and the switching function is used to suppress chattering.Combining the advantages of both,an improved second-order super-spiral sliding mode observer is designed.When the system is close to the sliding mode surface,a proper reduction of the sliding mode gain can effectively weaken the chattering phenomenon and enhance the stability of the system.Finally,in the Matlab/Simulink simulation platform,a simulation model is established for the neutral point potential control method of NPC three-level inverter and sensorless sliding mode control system of permanent magnet synchronous motor,which verifies the feasibility of the method proposed in this paper,effectively controls the capacitance voltage on the DC bus of three-level inverter,and improves the super-spiral sliding mode control observer to weaken the chattering phenomenon of sliding mode control,The accuracy of rotor position estimation by sliding mode observer is improved.