Transient Thermo-Voltages on High-Power Shunt Resistors

In this paper, a detailed analysis of thermoelectric voltages of low-resistance, high-power shunt resistors and the extraction of model parameters for transient simulations and error correction are described. Due to temperature gradients, thermoelectric voltages (thermo-voltages) appear on different metallic conductors. As the shunt temperature rises with power dissipation, thermo-voltages are unavoidable under realistic conditions. Their influence is typically unknown and leads to measurement errors, decreasing the current measurement accuracy. Two methods for the extraction of thermo-voltages from the voltage drop across a shunt resistor are discussed. The first method enables the acquisition of steady state thermo-voltage for a certain power load, the second can measure the transient behavior after a power step. For this purpose dedicated electronic measurement systems have been developed. For different types of thin- and thick-film power resistors in standard transfer molded packages model parameters for thermoelectric simulations are extracted. For real driving current profiles for electric vehicles, the measurement error introduced by parasitic thermo-voltages can reach up to 0.17%, about 17% of the error being due to the thermal resistance variation.