A Wideband Current Sensing Method Based on Real-Time Resistance Identification

This present article introduces a wideband current measurement method for PWM-controlled power systems, based on the combination of the voltage drop on a resistive conductor element in the current path, such as current bar or Cu-trace on a printed circuit board (PCB) or direct copper bonding (DCB), and of the inductive signal coming from an auxiliary coil system coupled to the same current. The main principle behind this both AC- and DC-capable, cost-effective current sensing approach, which is on top potentially superior to shunts from the thermal management point of view, is the real-time resistance identification (RTRI) of the Cu-trace in situ through the auxiliary inductive current sensor (ICS) and a band-selective signal processing algorithm. The ICS does not need to have high bandwidth since the temperature-driven resistance drift takes place at low rate and the PWM frequency is typically between 1 and 100 kHz. Still, the resultant composite current sensor can be part of high-speed converters' current control loop. The feasibility of the method was demonstrated by designing, manufacturing, calibrating, and testing a PCB-based prototype of the sensor system. We excited it with unipolar triangle-like current waveforms having high DC content to emulate the expectable current signals with current ripples. The dynamic current measurement results were verified using a series shunt as a reference. Based on this, the achieved accuracy of our method, for the applied waveforms up to 100 A and beside Cu-temperatures between 17 C-degrees and 62 C-degrees, was shown to be between 0.93% and 1.10%. For completeness, the expectable Cu-resistance was also determined in parallel, by direct onboard temperature measurement, showing excellent correlation with our algorithm.