A variable magnetomotive force memory motor (VMFM) is a motor that can expand its operating range by changing the magnetization state of a variable permanent magnet. However, changing the magnetization state requires a pulse current several times larger than the armature current rating. To address this challenge, the authors proposed a VMFM drive system that enabled magnetization with one-third of the inverter’s rated current by incorporating dedicated magnetization coils into the stator. The magnetization coils were connected in parallel with the armature coils and powered by the same inverter, eliminating the need for additional power converters and contributing to system miniaturization and cost reduction. Electromagnetic field analysis, however, revealed that mutual induction between the drive and magnetization coils hindered effective magnetization. In this paper, the mechanism of this mutual induction is clarified through simplified prototyping and FEM-based analysis, and an appropriate mitigation strategy is proposed.

This paper proposes a novel method for online inductance estimation for Permanent Magnet Synchronous Motors (PMSMs) using oversampling techniques. In sensorless control at medium to high speeds, inductance errors cause position identification inaccuracies. Conventional online inductance identification methods have problems such as the audible noise generated by the injection of test signals. Since oversampling enables the sampling of current variations within a PWM period, inductance can be identified without the need for test signal injection. In this paper, experimental results demonstrate that the proposed method achieves fast inductance estimation while maintaining robustness against position errors, load and speed fluctuations.

The introduction of the wide bandgap (WBG) semiconductor in power converters and faster switching speeds have increased the radiated electromagnetic interference (EMI), and the demand for its analysis methods has been growing. This paper presents a radiated EMI analysis above 30 MHz for a half-bridge circuit with only output cable among input and output cables, using common-mode (CM) current as an indicator. First, we clarify the problems in the radiated EMI analysis when the input cable is short and the power converter cannot be approximated as a dipole antenna. In addition, we evaluate the effect on the radiated EMI analysis of the existence of Y capacitors, which are often used in the conducted EMI countermeasures. Next, we demonstrate the validity of the radiated EMI analysis including the Y capacitors in power converters with no input cable, together with the modeling of the Y capacitors. Finally, we show the characteristic change of the radiated EMI with resistive load connection and the results of the analysis.

In applications such as outdoor ventilation and cooling fans, the rotor may be unintentionally rotated by external wind. In such cases, conventional initial rotor position estimation algorithms, which typically assume the rotor is at rest, may fail to correctly initiate motor operation due to inaccurate position detection. This can lead to unstable startup behavior, including reverse rotation, vibration, or overcurrent. To address this issue, this study proposes an initial rotor position estimation algorithm capable of accurately determining the rotor position even when it is in motion. The proposed method enables precise position detection across a wide range of rotational speeds, including standstill, low-speed, and medium-to-high-speed conditions. The effectiveness of the proposed algorithm is validated through experimental testing on a 2.2 kW-class Synchronous Reluctance Motors (SynRMs).