The acoustic noises caused by the fixed-frequency signal injection scheme limit the applications of saliency tracking based sensorless control methods for interior permanent magnet synchronous machine (IPMSM) drives at low-speed operation. In this paper, a pseudo-random-frequency sinusoidal injection (PRFSI) considering the sample and hold effect in practical applications is proposed to reduce the undesired acoustic noises. Since the power spectral density (PSD) of the excited high-frequency (HF) current could be dispersed and continuously distributed with PRFSI, the additional HF acoustic noises can be reduced. Through the comparative analysis of HF response currents PSD results for PRFSI and fixed-frequency sinusoidal injection (FFSI), the principle of acoustic noises reduction with PRFSI is analyzed theoretically. Furthermore, the optimal selection of the injection signals is derived considering the sample and hold effect. Whereby, a comparative evaluation of the proposed PRFSI versus FFSI is carried out on a 2.2-kW position sensorless IPMSM drive, in terms of position estimation and PSD results, which verified the effectiveness of the proposed scheme.

Paralleling an external SiC Schottky barrier diode (SBD) with an SiC MOSFET redistributes the reverse-conduction current and may reduce the reverse-recovery energy. However, the benefit depends on device selection and operating conditions, and an unsuitable SBD can increase the reverse-recovery energy. This paper presents simplified interval-specific models for turn-on, forward conduction, and turn-off and evaluates their qualitative trends using double-pulse tests. For the tested devices and operating conditions, the observed turn-on current distribution is qualitatively consistent with the combined influence of capacitive displacement currents and branch parasitic impedance. The forward-conduction waveforms exhibit case-temperature-dependent RL-type current redistribution. Compared with the configuration without an external SBD, the best-performing SBD group reduces the mean reverse-recovery energy $E_{\mathrm{rr}}$ by 19.8–54.5% at $T_{\mathrm{c}}=25 °\mathrm{C}$ and by 70.0–81.4% at $T_{\mathrm{c}}=175 °\mathrm{C}$ across four voltage–current operating points. Other SBD selections increase $E_{\mathrm{rr}}$ at low case temperature. Reducing the dead time from 3 μs to 500 ns increases the peak magnitude of the total reverse current by 36.8%. These results provide design considerations for the tested devices and operating range.