| With the support of the new power electronics technology,mechanical advances,more powerful micro-processors and advanced intelligent control theories,the usage of high speed motors is becoming more and more widespread.High speed motors found a usage in a number of applications due to its high rotational speeds and small sizes.Also,it shows the great promises of replacing some classical low speed drive systems with its high speed analogue.At the moment,there are no position sensors on the market that could provide reliable position estimations in the high speed range.For this reason,sensorless control strategy should be adopted for super-high speed drives.Although a lot of sensorless algorithms have been proposed in the literature,not each of them can be applied for high speed motors.There are some limitations that should be considered when choosing a proper sensorless algorithm.One of the main issue in very-high speed motor drives is a constantly changing bandwidth during the acceleration of the motor to its nominal speed,therefore the position estimator that does not depend on the operating frequency should be developed.This article introduces the implementation of very-high speed surface mounted pm motor drive system.The detailed derivation of mathematical model of pm motor together with space vector modulation techniques are presented to give the foundation for the development of sensorless control strategy.Based on the field oriented theory and mathematical model of the motor,the equations to calculate PI controller gains with the given desired bandwidth were obtained.In case of surface mounted PM motor the structure of the rotor is symmetric,therefore the relation between rotor position and spatial saliency is very weak.A novel high frequency injection algorithm based on the square-wave voltage injection,which is less dependent on the machine structure and rotor asymmetry,fast and is well suited for nonsalient-pole PM machines was investigated for its applicability to high speed motors.For a high speed motor,due to the wide frequency change in phase currents(from low frequencies up to 2 kHz),some simple adaptation mechanisms were adopted for expanding bandwidth of current controller and position estimator online.Also,by choosing dq rotor reference frame where the signals are considered as dc signals,thus mitigating the variable bandwidth problem,a reliable and efficient wide speed range sensorless control algorithm based on back-EMF estimation was proposed and applied to air turbo-compressor.Finally,a set of simulations was performed in MATLAB/Simulink environment to verify the feasibility of the proposed method.Simulation results demonstrated that the proposed algorithm is able to control high speed PM motor from low speeds up to its nominal speeds with a great accuracy and robustness.It also confirmed the correctness of the chosen reference frame along with bandwidth correction schemes.Further,the experimental platform on the base of TMS320F28335 and SiC MOSTES?s was built,while the motor control code was generated with the help of Embedded Coder to enable direct deployment of control algorithms on embedded control platforms.Experimental results verify that high speed back-EMF position estimator can accurately track the rotor position even on the very high speeds,however due to the rotor structure of the motor(2 poles surface mounted PMSM)and very weak saliency(),the initial position detection algorithm was unable to provide reliable estimates of the rotor position at standstill,and therefore can?t be applied to the high speed motors.To start the motor from zero,a pre-defined frequency pattern with a controlled magnitude of the current were applied to the motor.Then,when the magnitude of the back-EMF becomes enough to guarantee the reliable estimation of the rotor position the algorithm is switched to the high speed back-EMF estimator. |
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