High Interference-Resistant Magnetic Field Probe for Non-Invasive Current Distribution Monitoring in Press Pack IGBTs of HVDC Valves

Current imbalance in press pack insulated-gate bipolar transistor (PP IGBT) impacts the device's lifespan and high-voltage direct-current (HVDC) valves' safe operation. The external magnetic field can reveal the internal current distribution of PP IGBT, warning current imbalance. However, the compact structure and high-frequency electromagnetic environment of HVDC valves introduce significant interferences in monitoring, involving both busbar current interference, device dv/dt interference and eddy current interference from the probe. This article proposes a high interference-resistant magnetic field probe featuring a bipolar coil structure and comb structure shielding, which is decoupled from busbar current, reduces dv/dt interference and avoids additional eddy current interference. Following a detailed theoretical analysis, a series of experiments was conducted. The results demonstrate that the proposed probe is sensitive to the current distribution in PP IGBTs, with busbar interference limited to 2 mV and dv/dt interference reduced to 2.9%, while eddy current interference is effectively canceled. These findings validate the feasibility of the proposed method.