A Simple and Accurate Software Technique for the Dynamic Measurement of the Current in Fast Switching Devices using a Resistive Shunt

A series resistive shunt, also called Current Viewing Resistor, CVR, is one of the simplest and most commonly used methods for measuring the current flowing through an electronic device. However, the non-ideality of the shunt resistors creates several measurement problems, particularly when the devices undergo high-speed switching, as in wide-bandgap devices. In this case, the parasitic inductance associated with the CVR causes an overvoltage, which affects the current estimation during the initial stages of the transients, when the current gradient can become very large. To solve this problem, two types of solutions have been proposed in the literature. The first, which is hardware-based, is oriented both to reducing the shunt’s parasitic inductance and to compensating it by adding external circuits that cancel its effect on the voltage signal measured across the CVR. For these hardware solutions, techniques are used to cancel the magnetic field produced by the shunt, and, therefore, axial resistors with parallel windings, printed resistance sheets, or coaxial shunts are used, which lead to an increase in both the complexity of the layout and the cost of the circuit, making them unsuitable for PCB integration and large-scale production. In the second type of solution, the signal measured on the CVR in the presence of stray inductance is fed into software procedures that enable an accurate, wide-bandwidth current measurement. The current extraction software techniques presented in the literature so far require very sophisticated calculations and mathematical procedures, and are suitable only for offline analysis of experimental characterization, such as double-pulse measurements. The procedure proposed in this paper falls within the scope of software procedures and is based on a simple technique that uses the implicit solution of the circuit equations to extract the current from the dynamic measurement of the voltage drop across the CVR. Only the leakage inductance is used as a parameter that can be measured directly on the circuit. It is shown that the proposed procedure exploits the advantages of a cheap, easy-to-manufacture sensor, enabling accurate, widebandwidth current measurement even on high-speed devices. The method is experimentally validated, and the results are compared with those obtained by a commercial Rogowski coil and a coaxial shunt.