Zero/low speed magnet magnetization state estimation using high frequency injection for a fractional slot variable flux-intensifying interior permanent magnet synchronous machine

This paper focuses on zero/low speed magnetization state (MS) estimation using high frequency injection for a fractional slot variable flux-intensifying interior permanent magnet synchronous machine (VFI-IPMSM). For VFI-IPMSMs, the knowledge of the MS is necessary to achieve loss minimizing control, since loss properties vary with MS. The MS can be estimated by measuring EMF, however, voltage sensors are not commonly used in standard drives. If a flux observer is used, accurate estimation is difficult at zero/low speed due to the diminishing EMF signal. To solve this issue, a superimposed high frequency (HF) injection method for MS estimation is proposed. Physically, higher MS implies a higher saturation condition which results in lower differential inductance. With a constant HF voltage injection, lower inductance (higher MS) results in a larger HF current response and vice versa. As a result, by imposing a HF voltage signal, the MS can be estimated through the HF current response. The proposed MS estimation methodology is evaluated experimentally with a fabricated fractional slot VFI-IPMSM and demonstrates effective MS estimation within 5 % error.