Gate-driver Integrated, Junction Temperature Estimation of SiC MOSFET Half-bridge Modules
SiC MOSFET power modules are becoming the global solution in harsh environment systems due to the benefits of higher power density and efficiency. Achieving high reliability of such systems is of upmost importance due to large economic implications. Intelligence on the gate driver can lead to significant improvement of both short-term and long-term reliability of the SiC MOSFET devices by providing insight on the real-time behavior of relevant switch information. The device switch-current Id can be used for short-circuit detection under various fault impedances assessing the short-term reliability. In combination with Vds(on), the on-state resistance Rds,on and thus the online junction temperature (Tj) estimation is possible. This enables monitoring the status of the SiC MOSFET device such as state-of-health, remaining useful life, maintenance scheduling, etc., tackling the long-term reliability aspect.
Taking all of this into account, an intelligent gate driver is developed, containing the described measurements. A stacked gate driver is shown in Fig. 1. with the indicated controller part of the gate-driver, the actual driver board, Rogowski coils for switch current measurement, and a utilized circuit for on-state voltage measurement. A 2-diode circuit is employed as an on-state voltage mea- surement sensor, due to benefits it has over similar circuits utilized in the literature, including high blocking capability, no offset prob- lem, non-temperature-dependent sensing diode circuit, low delay, small losses, good accuracy and sensitivity. These benefits render it perfectly suitable to be used in combination with a Rogowski coil and have accurate on-state resistance and thus junction temperature estimation. Fig. 2. shows initial Rds,on measurement results. Online junction temperature estimation will be performed with the aid of a field programmable gate array (FPGA) that will sample current and voltage information at the same time. Based on the pre-characteriza- tion results of the device stored in the flash memory (current, voltage and temperature look-up table) located on the controller board of the gate driver, FPGA will assess and compare voltages and currents, as well as estimate junction temperature.