Theoretical and practical analysis of a current sensing principle that exploits the resistance of the copper trace

The output current of contemporary AC-DC front-end converters is steadily increasing due to higher power density requirements. The use of shunt resistors to sense the output current is becoming unacceptable due to high power losses and new techniques for current sensing need to be investigated. In this paper, we investigate the possible use of the voltage drop across the trace resistance to sense the output current. This approach promises very low cost since no dedicated shunt resistor is required, no additional power losses occur and no extra space on the printed-circuit-board (PCB) is necessary. To overcome the problems associated with the temperature drift of the copper, and variability in the trace resistance of the copper track, a digital controller can be used to calibrate the trace resistance and implement a temperature drift compensation. This form of microcontroller is readily available on todaypsilas AC-DC front-end converters. However, theoretical and practical investigations revealed that the parasitic inductance and skin effect may limit the bandwidth of this measurement principle down to several hundred Hz. To overcome this limitation, we proposed a compensation technique that has the potential to increase the bandwidth beyond ten kilohertz. Experiments with output currents of up to 240 A demonstrated that the measurement uncertainty for DC currents is less than plusmn1 A for temperatures between 25 to 60 degrees, and that the effective bandwidth can be enhanced using a compensation technique.