Error Analysis of An Accurate Bipolar Voltage Measurement Circuit for Online Health Monitoring of IGBTs

On-state voltage is predominantly used in the health monitoring of the IGBT. In this paper, fast, accurate and online on-state voltage measurement circuit is suggested for an IGBT. The circuit is capable of measuring positive on-state collector-emitter voltage (V
_CE-ON
) and negative forward voltage (V
_F
) of anti-parallel diode. The measurement circuit offers the scaling/shifting of the on-state voltage, which facilitates direct connection of Analog to Digital (ADC), to monitor the voltage in digital controllers. The key advantage of the suggested circuit is that the overall measurement error is about ± 0.111%, which is below the allowable error limits (± 0.33%) for condition monitoring of the IGBT. A flexible voltage clamping is provided, during OFF state of device, to minimize the error in the measurement. Different possible errors in the measurement are due to, i) resistor mismatch, ii) diode voltages mismatch, and iii) ADC quantisation and opamp. The detailed analysis of the mentioned errors is presented in this paper. Simulation and experimental validation of suggested circuit is carried out and results are also compared with previously reported measurement circuits.