基于共模电流模态的逆变器供电电机线端与内部绕组绝缘在线状态监测

Addressing cable insulation parameter effects in practical applications, this article proposes an online method using common-mode current modes to assess line-end and internal coil insulation conditions in inverter-fed machines. First, a common-mode equivalent model incorporating cable insulation parameters is established. Analyzing the machine’s common-mode impedance characteristics reveals dominant modes and paths of common-mode current under common-mode voltage step jumps. This yields the relationship between high-frequency common-mode current oscillation frequency ( $f_{\mathrm {HFCM}}$ ) with line-end coil insulation, along with the coupling relationship between mid-frequency oscillation frequency ( $f_{\mathrm {MFCM}}$ ) coupled with both line-end and internal coil insulation under varying cable inductance. To overcome the limitations of classical fast Fourier transform (FFT), which is primarily suitable for stationary signals (single-frequency signals), and the empirical modal decomposition (EMD) algorithm is computationally complex and may have frequency aliasing, this article uses the variational mode decomposition (VMD) algorithm to obtain $f_{\mathrm {HFCM}}$ and $f_{\mathrm {MFCM}}$ . The monitoring strategy employs ${f} _{\mathrm {HFCM}}$ to determine line-end coil insulation degradation; combined with cable inductance and the insulation degradation condition of line-end coil, $f_{\mathrm {MFCM}}$ assesses internal coil insulation degradation. Experiments demonstrate that the proposed method can sensitively detect incipient degradation in both line-end and internal insulation of inverter-fed machine windings.