Diagnosis and Classification of faults in IPMSM: Demagnetization and Interturn short fault

Abstract

This thesis proposes a method that diagnose and classifies for a demagnetization and an interturn short fault (ISF) in a interior-type permanent magnet synchronous machines (IPMSM). The proposed method consists of three stages. It diagnose the demagnetization in first stage with a structure analysis of the IPMSM. After then, the ISF is diagnosed by voltage and current residual analysis with a faulty winding model (FWM). Finally, a new method of utilizing currents in synchronous frame of the IPMSM is proposed to diagnose and classifies the demagnetization and interturn short fault simultaneously.

In the first proposed diagnosis for the demagnetization, the structure analysis of the IPMSM is used for estimating the change of inductances. The demagnetization causes flux-density difference and changes the inductances of the IPMSM. Such varying parameters make it difficult to detect and diagnose the exact severity of the demagnetization. With the structure analysis, a varying inductances can be calculated. Combination of the structure analysis with the least square (LS) method allows us to diagnose the fault well.

In the second proposed diagnosis, the ISF is dealt with by analyzing the voltage and current residual components. As the ISF induces decrease of the winding with the fault, it affects both voltage and current; the proposed method uses those components to diagnose the fault. The FWM is introduced to analyze the fault. The model describes a relationship between the voltage decrease of the faulty winding to the characteristics of the fault such as a fault resistance and a fault turn ratio. I suggest a fault index based on the FWM to show the severity of the fault.

In the final proposed method, both demagnetization and ISF are handled. Those two faults show similar characteristics when the machine has either of them. Both of them increase the magnitude of input current compared with normal machines at the same load torque. However, analysis in this thesis suggests that the demagnetization cause increase in the current angle beta, whereas the ISF cause decrease in beta. This difference is exploited to classify the fault if one is detected in the IPMSM. Experimental results on IPMSMs verify that the demagnetization and ISF can be classified and diagnosed in various conditions with the proposed technique.