Online Calibration Method for High-Precision On-State Voltage Measurement of Power Semiconductors

This paper presents an online high-precision calibration method for on-state voltage measurement of power semiconductors using active temperature control. Unlike other calibration techniques, this method operates continuously during converter operation, enabling monitoring of long-term changes in component characteristics. The method is implemented in a diode-based measurement circuit, selected for its fast response and simplicity. Despite these advantages, diode-based circuits have limited accuracy due to forward voltage variability caused by different junction temperatures of diodes and their manufacturing tolerances. By actively controlling the temperature of a diode, and exploiting the fact that the forward voltage is temperature dependent, this method compensates for the diode forward voltage variations and other sources of measurement errors, such as resistance tolerances and voltage drop across the relay contacts. The resulting high-accuracy voltage measurements are critical for applications like monitoring transistor degradation, precise conduction loss calculation, and determining the dynamic on-resistance of wide-bandgap devices. However, achieving a high common-mode rejection ratio, essential for reliable measurements, remains a challenge for the practical implementation of this method.