Development of a Differential Voltage Probe for Measurements in Automotive Electric Drives

Accurate efficiency determination is very important in the field of electric drive research and development. Modern inverters generate pulse width modulated signals with short rise times and high frequencies. Thus, high-accuracy power measurements under nonsinusoidal conditions have to be performed. This requires high precision voltage and current probes, including frequency response flatness over a wide bandwidth and a high linearity up to a few hundred volts. This paper describes the development and characterization of a high-voltage differential probe, suitable for precise measurements in automotive electric drives. The main parts of the probe are two input voltage dividers with a further frequency compensation circuit and a difference amplifier. The complete circuit design and the compensation of parasitic effects are explained in detail. Final experiments show that the developed probe outperforms commercially available probes. The probe has a very flat frequency response up to 1 MHz, a bandwidth of 20 MHz, and a linearity better than 250 ppm up to the maximum differential input voltage of 1 kV.