Compensation of Temperature Dependence in a Module Parasitic Based Current Measurement System

This paper presents a current sensing method, which evaluates the voltage across the parasitic resistance and inductance in power modules. Such a sensing method requires an appropriate low pass filter to achieve a signal that is proportional to the current to be measured. In inverter operation, however, the parasitic resistance in the measurement section is variable due to its temperature dependence. This requires firstly a temperature estimation for the measurement section in the semiconductor module and a correction of the deviations arising from that circumstance. At a first glance, three different possible temperature estimation methods seem possible. The first approach by using an additional temperature sensor is only considered as a trivial solution and not examined further. Its disadvantage is the additional component, which is then necessary for current measurement. The second and third method are investigated in detail, which is on the one hand the use of mostly present negative-temperature-coefficient (NTC) thermistors in the module and on the other hand, a completely new approach that exploits the temperature dependence of the sensed signal waveform. Both approaches were tested in inverter operation. They improve current sensing errors by means of module parasitics from ± 25 % to ±2...5%.