In power electronics, gate-voltage measurement is used to optimize the design of the gate driver. Therefore a proper measurement technique is vital to ensure the proper operation of the electronic device. Measuring a small signal in a high switching voltage environment is a complicated task especially for high-side switches in a half-bridge configuration with fast semiconductor devices where voltage probes are subject to high common-mode voltages with fast transients. Hence, this article compares experimentally the conventional differential probes with optically isolated probes for measuring a small signal (26V) with a 1200V common-mode voltage and high switching rates created by SiC MOSFET (30kV/µs). The conventional differential probe shows differences of measured voltage amplitude up to 10V compared to optically isolated probe. The experimental results prove that parasitic elements of conventional differential probes change the gate-voltage shape and increase the common-mode current in the experimental setup up to 6dB.

This paper proposes a novel self-controlled SiC MOSFET gate driver circuit. This new gate driver (GD) proposes a dynamic gate-bias modification thanks to a passive feedback of the drain or source current to control the EMI during turn-off switching transition. A Rogowski coil integrated into the terminals of the SiC MOSFET provides the feedback to modify the gate voltage profile. During turn-off, this circuit increases the voltage level of gate and consequently the gate current. This approach has a positive effect on the EMI behavior of converters without harmful effect on converter efficiency compared to the conventional method which consists in increasing the gate resistance. Moreover, with this approach, the gate driver design remains without modification (except the connection to the Rogowski coil) and there is no effect on turn-on transition of the SiC MOSFET. The proposed method is designed and developed for a 1.7kV SiC MOSFET and has been validated experimentally in an inductive doublepulse test platform. The proposed gate driver moderates the switching speed and is validated experimentally up to 1.2 kV 200A with the 1.7kV SiC MOSFET by reducing the common-mode current of turn-off transition.

This paper presents a system-level EMI investigation in a new 3-phase 1.2kV 100kW insulated DC/DC converter. In this prototype, achieving full operation was prevented by false triggering of semiconductors due to large common-mode current through gate drivers. A passive filter embedded into the structure of the transformer to connect it to the ground is proposed as a corrective and cost effective solution to mitigate the electromagnetic interferences. New grounding layout enabled to reduce the common-mode current through gate drivers by up to 75% without decreasing the switching rate. This allowed to proceed to measurements on the prototype at nominal operation. The method is validated in simulation and extensive experimental results have been obtained from the considered prototype. This proved the feasibility of the proposed solution and showed the effect of the transformer design in EMI behavior of insulated DC/DC converters.

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