In rail transit application, the multimode pulsewidth modulation (PWM) is used to take full advantage of the dc-bus voltage in wide speed range. To improve the sensorless control performance of interior permanent magnet synchronous motor (IPMSM) drives in this condition, an overall system delay compensation method is proposed for a hybrid position observer that combines a simple square-wave voltage injection with a nonsingular terminal sliding mode observer. Due to the delay effect, the currents and position estimation performance are deteriorated, such as more severe dq-axis currents coupling and fluctuation of estimated position error. In order to solve these problems, the analysis of delay characteristics in the IPMSM sensorless drives is first presented. For carrier-based modulation, the compensation time is obtained through a self-tuning PI regulator based on predictive q-axis voltage error. Then, the three-phase reference currents are utilized to judge the direction near zero-crossing point and the parameters robustness is also analyzed. For optimal PWM modulation, the voltage vector angle and modulation depth are predicted in a simple way, and the delay effect can be eliminated. Furthermore, the harmonics distribution in sensorless control is described by power spectral density. Finally, the effectiveness of proposed strategy is verified by experimental results with a 3.7-kW IPMSM sensorless drive platform.
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