Research on High-Frequency Deduction Method for Distribution Network Measurement Data Based on Differential Mode Switching Oscillation

The insulation at the motor phase terminals of variable frequency drives is prone to degradation due to transient overvoltage impacts caused by high-frequency switching of pulse-width modulation. The switching oscillation resonance effect offers the potential for sensitive detection of subtle changes in insulation condition; however, the insulation characteristic signals are influenced by multiple factors coupled at high frequencies, increasing the difficulty of accurate identification. To address this issue, this paper proposes a high-frequency extrapolation method for distribution network measurement data based on differential-mode switching oscillations. First, by analyzing the dominant switching oscillation modes of the system, high-frequency differential-mode switching oscillations are selected as sensitive modes to decouple the influence of the inverter power device’s parasitic capacitances. Second, a variational mode decomposition algorithm is employed to extract differential-mode frequency features from multimodal switching oscillations, mitigating the interference caused by the dynamic switching timing of power devices under transient operating conditions. Finally, by leveraging the amplitude ratio of differential-mode switching oscillation currents at both the inverter and motor sides, the impact of cable high-frequency distributed parameters is further decoupled. By extracting high-frequency differential mode oscillation frequency characteristics and combining them with the current amplitude ratio on the inverter side and the motor side to construct Index_<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>g</i>1</sub>, the method effectively decouples the influences of multiple factors, such as cable, inverter parasitic parameters, and operating conditions, highlighting its advantages as a sensitive indicator of insulation status. The proposed method is validated on a 380V/3kW permanent magnet motor variable frequency drive system. Results demonstrate that the method can sensitively reflect subtle changes in phase terminal insulation condition and effectively decouple the coupling effects of the inverter, cables, and operating conditions, providing a novel technical approach for high-frequency feature extraction and dynamic analysis of distribution network measurement data.