Nonlinearity of inverters

cogging effect of motors and temperature drift of current sensors lead to DC offset and 5th/7th harmonics in the observed back electromotive force of sensorless control systems

which seriously degrade the control performance of high-speed maglev trains. To address this issue

a sensorless control strategy based on the multi-resonant extended state observer(MRESO)was proposed for suppressing the impacts of DC offset and the 5th/7th harmonics. First

the influence mechanism of harmonics on sensorless control was analyzed

and a resonant extended state observer(RESO)was developed on the basis of the fundamental back electromotive force dynamic model to accurately observe the fundamental back electromotive force and suppress the effect of DC offset. Then

to enhance the suppression capability of RESO against the 5th and 7th harmonics at low speeds

the MRESO with a parallel structure of multi-resonant controllers was further proposed. Hardware-in-the-loop experimental results show that the proposed sensorless control strategy can effectively suppress the DC offset and the 5th/7th harmonics in the observed back electromotive force

significantly improve the accuracy of the observed angle

and realize the closed-loop sensorless operation of high-speed maglev trains in the speed range from 10 to 600 km/h.