An alternative low-cost current-sensing scheme for high-current power electronics circuits

A lightweight and low-cost current sensor for application in high-current, high-frequency inverters and power converters is described. The current sensor consists of three elements. The first is a Rogowski coil, also known as a Maxwell Worm, which is a nonmagnetic toroid wound like an inductor. The output voltage at the open terminals of this winding is proportional to the time derivative of the current flowing in a conductor passing through the toroid. The second element of the sensor is an integrator which has as its input the output of the Rogowski coil. The third element of the sensor is a circuit to reset the integrator to zero whenever the current through the Rogowski coil is known to be zero. Resetting the integrator prevents the error generated by the integration of offset voltages and biases, which cannot be avoided in practical integrators, from becoming unacceptably large. For the case of a semiconductor switch, the current through the switch is known to be zero when the switch is gated off. The results presented using this current sensing scheme demonstrate its feasibility for use in high-power motor drive applications. The sensor has its largest advantage for measuring currents with peak values greater than 50 A and with switching frequencies greater than 1 kHz