Investigations on Common-Mode Capacitive Couplings in Current Sensors for Medium Voltage Converter Enabled by 10kV SiC MOSFETs

Capacitive couplings in current sensors cause common-mode currents from the power circuit to circulate into the signal circuit, which may interfere with the operation of the protection and sampling circuits. To tackle this issue, this paper practically analyses the common-mode capacitance of a current sensor intended for a medium voltage converter enabled by 10kV silicon-carbide MOSFETs. Two methods to reduce the common-mode currents are therefore proposed to ensure a stable operation of the sampling and protection circuits. Experimental tests, conducted at a DC-link voltage of 6 kV and a dv/dt of more than 30 V/ns, show that the common-mode current introduced by capacitive couplings in current sensors can be reduced by both proposed methods. Mathod A optimizes the current sensor implementation by reducing the capacitive coupling, which causes a 50% reduction in common-mode current, whereas method B achieved more than 80% reduction by introducing a common-mode filter on the output of the current sensor.