High-Bandwidth High-CMRR Current Measurement for a 4.8 MHz Multi-Level GaN Inverter AC Power Source

Abstract

The control of very high switching frequency power electronic converter systems featuring latest generation wide bandgap (WBG) devices requires current measurements with a very high bandwidth (BW) to achieve high closed-loop control dynamics. One example is a ultra-high BW 4.8 MHz parallel-interleaved multi-level GaN inverter AC power source with a target output BW of 100 kHz. This work investigates the combination of state-of-the-art Hall-effect current sensors with a suitable high-frequency (HF) sensor to extend the BW of the commercially available current sensor by a factor of 20 – 50, i.e., up to 10 − 20 MHz. The main focus lies on a small form factor and a low realization effort. HF current sensors based on a Rogowski coil, an inductor integrated voltage sensing and a current transformer (CT) are analyzed and compared. Additionally, their respective performance limitations are highlighted. Furthermore, a precise combiner network to combine the low-frequency (LF) and HF signal is analyzed. The combiner circuit is designed in a way that component tolerances have no influence on the behavior in the transition frequency range from LF to HF. Thereby, also the immunity to Common-Mode (CM) disturbances, i.e., the high dv/dt occurring for the switching transitions of WBG semiconductors is considered. Finally, a hardware demonstrator featuring the two most promising current sensor approaches, i.e., the inductor voltage sensing and the CT, is presented and verified with comprehensive measurements in frequency and time domain. A BW from DC up to 35 MHz is measured. The realized sensors are further tested with a hardware prototype of the aforementioned AC power source switching 600 V at an effective switching frequency of 1.6 MHz. The measurements clearly reveal that both proposed sensor concepts are well suited for accurate measurements in fast switching converter systems with negligible additional volume.