Research On Sensorless Control Of Permanent Magnet Synchronous Motor Used For Plunger Pump

Surface Mounted Permanent Magnet Synchronous Motor(SPMSM)has the advantages of high power density,high efficiency,and high power factor.It is widely used in industrial applications,but for motors operating in seawater,the position sensor is required to be corrosion resistant,high grade of flooding and oil immersion.The application of position sensorless control of motor to the above applications has the advantages of high reliability and low cost.For the problem that the plunger pump has a large load torque at zero speed and it changes with the seawater pressure.This paper deeply studies the initial position identification,start-up and mid-high speed sensorless control of the plunger pump SPMSM.When large current is applied to the stator winding of the SPMSM,the stator core tends to saturate and the cross-coupling phenomenon of the magnetic flux path of the dq axis is very obvious,resulting in a large difference in the dq axis synchronous inductance.Based on this effect,a six-pulse voltage vector injection method is proposed to identify the rotor initial angle.First,six pulse voltage vectors are injected in sequence,the stator current response is sampled at each vector,and then the sector of rotor is located according to the maximum value of the response curve.The initial angle of the rotor is calculated from the sector decision using the pulse and current sampling values.To solve the problem of large starting torque of the plunger pump,this paper combines the SPMSM I/F control method to deeply study the I/F starting method based on the stator current orientation.Firstly,the control strategy of the motor current and rotor angle in the acceleration process is analyzed,and the motor is steadily accelerated to 10% rated speed;then the state switching method using current control function is studied,and the linear and exponential current control functions are analyzed.The simulation and experimental results show that the current-ratio startup method is very robust in the acceleration process,and the state switching instantaneous speed and current fluctuation are small.When SPMSM operating in the high-speed range,large severe jitter is existed in the estimated current in the traditional sliding mode observer,and the unreasonable bandwidth design of the phase-locked loop may cause the estimated speed to diverge.In order to solve the above problems,this paper first studies the effects of current estimation under three SMO switching functions,and concludes that the sigmoid(x)function works well,and then analyzes the estimated current convergence of the function under different indices.Finally,the parameters of each part of the phase-locked loop are designed.The bilinear method used to discrete the low-pass filter has high precision and good robustness.The parameters of the loop filter are designed to achieve accurate estimation of the rotor speed under different speeds.The experimental results show that the rotor position estimation error is 6 degrees at most,and decreases as the rotation speed increases.