Since the slot opening is large in the uniform slot machine, the torque ripple generated by overlapping or misaligning with the rotor cavity is remarkably large in the case of interior permanent magnet (IPM) machine. In this work, it is observed that the magnitude of torque ripple depends strongly on the phase difference between air-gap field harmonics: The ripple is minimized when the two dominant harmonic components cancel each other. Based on this fact, a condition is developed to minimize torque ripple by adjusting the q-flux channel width and d-flux barrier width. The torque ripple minimizing solution is found from a level chart made by subdomain time-stepping analysis. Finite element analysis (FEA) also gives a very similar minimizing solution. A prototype machine is manufactured, and its performances are validated through experiments.

Resolvers are widely used as position sensors to obtain angle information. The resolver requires the excitation signal and its amplitude is modulated by the rotor position. The envelope of the modulated signal can be detected precisely only when the samplings are synchronized with the excitation signal. A large error can occur if the synchronization fails. In this paper, the resolver signals are sampled in synchronization with the pulsewidth modulation (PWM) carrier, not the excitation signal. When the resolver excitation signal frequency and the PWM carrier frequency are different, the envelope cannot be detected, so additional signal processing is required to obtain the angle information. For signal processing, multiple auxiliary signals are synthesized based on the sampled signals and quadrature demodulation is performed. A detailed error analysis according to the PWM frequency and motor speed is also performed. The effectiveness is demonstrated through simulation and experimental evidence.INDEX TERMS Phase-locked loop (PLL), resolver-to-digital conversion (RDC), demodulation, resolver, envelope detection.

A strict fault tolerance is required in urban air mobility (UAM). The motor position sensor is one of the monitoring targets in UAMs, because it is in a harsh environment such as rain, ice, dust, vibration, etc. In this work, a resolver-based sensor method and a sensorless algorithm are fused in cooperative mode. Under normal conditions, the sensored angle and the sensorless angle are weighted equally. However, in case of sensor failure, only the sensorless method is selected. In other cases, only the sensored angle is fully respected. It is assumed here that the sensored method as well as the sensorless method may fail. To determine which of the two methods is faulty, the measured current is used as a reference. The virtual current is obtained by numerically solving the permanent magnet synchronous motor (PMSM) model in the stationary frame using the rotor angles. The position fault is then detected by comparing the virtual current to the measured current. Sigmoid functions with a step at zero are used for fault detection and fusion method robust against sudden error fluctuations or noise. Convincing performance and robustness are demonstrated by simulation and experimental results.INDEX TERMS Urban air mobility, Fault-tolerant control, Permanent magnet synchronous motors, motor control, Runge-Kutta 4th.

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