Abstract
The in-wheel electric vehicle with distributed drive units has better stability and flexibility than traditional centralized drives, but may encounter a higher failure rate due to additional actuators and sensors, especially that the faults of the wheel-side position sensor make motor torque out of control. To overcome this problem, a fault-tolerant control strategy with a multi-states switching method is proposed. The strategy judges the sensor failure by verifying redundant speed information, realizes sensorless control schemes by flux-observer based algorithm in high-speed range and I-F control algorithm in low-speed range with low acoustic noise, and applies adaptive transition process between different control schemes. To pursuit high stability, the signal-to-noise analysis for fault judgment due to sensorless estimation accuracy is discussed. Meanwhile, the principle of I-F resonant oscillations during the transition process is initially deduced in detail, and the conclusion of stability condition is obtained. Finally, the influence of system parameters on resonance performance is analyzed by simulation, and the effectiveness and reliability of the proposed strategy for the risk-controlling process are verified by experiments.
Highlights
Electric vehicles with in-wheel motor drive systems have the advantages of compact structure, high transmission efficiency and flexible torque controllability
If the power of the faulty wheel being cut off immediately at the moment of failure, strong torque ripples may be generated, which influence the dynamic performance of the torque distribution control in a certain period
I-F control are selected for wide speed range sensorless control when sensor failures
Summary
Electric vehicles with in-wheel motor drive systems have the advantages of compact structure, high transmission efficiency and flexible torque controllability. By using the flux-observer based Field-Oriented Vector (FOC) control in the high-speed range and the self-resonance principle of current frequency (I-F) control in the low-speed range, the reliability of the FTC strategy is improved, and the switching process of multi-state sensorless algorithm is designed to be smooth as well. Considering that the HF injection method is not suitable for vehicle applications, the back-EMF flux-observer-based FOC and I-F control are selected for wide speed range sensorless control when sensor failures. To meet requirements of continuity, the current amplitude and phase angle are designed to converge to the balanced resonance point synchronously, and the torque angle transits smoothly from 0 degrees to θL0, so that the smoothness of torque and speed during switching is significantly improved
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