Current Loop Optimal Control Of Permanent Magnet Synchronous Motor Based On Double Second-order Observer

In recent years,the compact joint module composed of multipole surface mounted permanent magnet synchronous motor and reducer has attracted extensive attention from in robot field.Its special structure and application scenarios put forward higher requirements for the current loop of permanent magnet synchronous motor-higher response bandwidth and lower torque pulsation.The high bandwidth current inner loop can improve the dynamic response of the system and reduce the tracking error of the outer loop.But it also amplifies the system noise and brings greater uncertainty and disturbance to the system.Combined with state observer and disturbance observer,the state variables and disturbances are estimated at the same time to improve the response speed and stability of the system.In order to improve the estimation accuracy of state variables and realize the decoupling of d-axis current,q-axis current and rotor speed,an observer is designed based on the high-order state space model of permanent magnet synchronous motor.Focusing on the design and optimization of the current loop of permanent magnet synchronous motor,starting from the two basic points of reducing sensor measurement noise and improving current waveform,this paper aims to improve the response bandwidth and robustness of current loop.The specific work is as follows:(1)Realize current and speed estimation based on double second-order state observer.Firstly,establish the third-order state model of permanent magnet synchronous motor,and propose a linearization strategy for the nonlinear part of the model.Secondly,the third-order observer based on Kalman filter is designed to fuse the data collected by the sensor to estimate the stator current and rotor speed.Finally,in order to make the high-order observer easy to apply in practice,propose a strategy to reduce the order of observer.Considering the system disturbance,propose a state space model based on disturbance estimation,and complete the design of double second-order observer based on double Kalman filter.(2)Based on Kalman observer,complete the design of current loop considering flux weakening control.Firstly,based on the double second-order observer,realize the vector control scheme of permanent magnet synchronous motor.Secondly,in order to expand the speed regulation range of the motor to apply the occasions that require run above base speed,realize the automatic field weakening function of the current loop.Finally,compare two flux weakening control methods.The method based on current amplitude adjustment can improve the speed and maintain the torque output as much as possible.The other method based on current phase adjustment can realize the smooth transition from constant torque region to flux weakening region.(3)Research on current harmonic suppression strategy based on driving pulse and current harmonic monitoring.In order to solve the serious current harmonic when the motor is running at low speed and light load,and the influence of cogging torque,friction torque and external disturbance in addition to the dead time effect of inverter,propose three current harmonic suppression strategies.The experimental results show that the current harmonic suppression strategy based on adaptive neural network reduces the current harmonic from 34.33% to 8.40%.It suppresses the current harmonic through self-learning,improves the robustness of current loop and reduces torque ripple.The simulation and experiment are carried out on the module with rated voltage of 24 V,rated speed of 3500 rpm,number of motor poles of 14 and reduction ratio of1:9.1.The simulation and experimental results show that the double second-order observer based on double Kalman filter can achieve the effect close to the third-order observer.Moreover,the current loop based on state and disturbance observer has higher response bandwidth and robustness.The two flux weakening control methods proposed in this paper can increase the motor speed from 3527 rpm to 3680 rpm.The three current harmonic suppression algorithms proposed in this paper can improve the sinusoidal degree of stator current and reduce current harmonic from 34.33% to22.21% and below.