Parameter identification-based MTPA control strategy for low-speed permanent magnet synchronous motors
[Objective]The inductance of a permanent magnet synchronous motor is not constant during operation.It fluctuates owing to changes in magnetic field strength and temperature.Conventional MTPA control utilizes fixed inductance parameter values.However,during actual operation,magnetic saturation and load-induced changes in the dq axis current alter the actual inductance parameters.This can lead to parameter deviations during real-time MTPA operation.[Methods]In this study,we employ the high-frequency injection method to identify motor parameters.By injecting a high-frequency voltage signal with a specific amplitude and frequency on the αβ shaft,we can obtain the three-phase current of the motor through a current sensor.Following this,the high-frequency current response is procured through coordinate transformation,enabling the acquisition of actual inductance parameter values from positive and negative sequence currents.A rotation transformation is performed on the high-frequency current response.We perform two specific angle rotations on the vector form of the high-frequency current,obtaining the amplitude of the positive and negative phase sequence current through a filter.The identified inductance parameters are then incorporated into the MTPA calculation.This ensures the accuracy of parameter identification and stability of motor operation,helping avoid control loss caused by mismatches between the maximum torque current control parameters and the motor.This experiment was validated using the DSP LANCHXL-F28379D control core experimental platform.Under conditions of a load torque of 0.9 N·m and a set speed of 800 r/min,the actual value of d-axis inductance is 8.75 mH.This aligns closely with the calculated value of 8.45 mH,marking an error of 3.42%.The identified value of the q-axis inductance is 4.81 mH,which is nearly identical to the calculated value of 4.85 mH,with an error of 0.83%.When the identified inductance parameters are incorporated into real-time MTPA processes,the amplitude of the three-phase current obtained is significantly reduced.This achieves current optimization at maximum torque.[Results]Experimental results show that without using the MTPA module,the maximum amplitude of the three-phase current reached when the maximum torque is achieved is 9.2 A.If the real-time identified inductance parameters are included in the operation of the MTPA module,the maximum amplitude of the three-phase current obtained is 7.6 A,effectively controlling the maximum torque-current ratio.We used the high-frequency injection method to identify the motor's inductance parameters by inputting high-frequency rotating voltage into the αβ shaft and transforming it through rotation.The αβ axis demodulation calculation obtains the inductance parameters,and the real-time identified inductance parameters are fed back to the MTPA link for timely tracking and achieving maximum torque current control.[Conclusions]Compared to the extended Kalman filtering method and recursive least squares method,the high-frequency injection method provides more control and convenience during the parameter identification process.It mitigates issues such as data overflow and slow convergence speed observed in the initial identification stage.At the same time,the MTPA module has been upgraded to no longer rely on fixed parameters.Instead,it accomplishes real-time identification of inductance parameters and adjusts the generated dq axis current in real time.This change ensures current optimization when torque is maximized.
interior permanent magnet synchronous motorrotating high-frequency voltage injectionparameter identificationmaximum torque per ampere
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