Permanent-Magnet Magnetization State Estimation Using High-Frequency Signal Injection

Permanent-magnet (PM) magnetization state estimation is important both for torque control and monitoring in conventional permanent-magnet synchronous machines (PMSMs). Furthermore, this can be critical for variable flux machines (VFMs). Use of high-frequency signal injection methods for PM magnetization state estimation in NdFeB magnets has already been proposed. These methods make use of the variation of the PM high-frequency resistance with the PM magnetization state due to the magnetoresistive effect. This paper addresses the generalization of magnetization state estimation using high-frequency signal injection to other types of magnets like SmCo and ferrite, as well as to other magnet structures, e.g., isolated and nonisolated segmented magnets. Use of the magnetoresitive effect for the detection of irreversible/reversible PM demagnetization will also be shown to be viable.