MHz High Efficiency & High Power Density Bidirectional Battery Charger with GaN HEMT – Xiucheng
Hi everyone. This is Xiucheng from CPES. Today, I gonna demonstrate a high efficiency high frequency high power density battery charger system using high voltage GaN devices The research target of this project is to evaluate the performance and potential of high voltage GaN switch based on a bi-directional battery charger system This battery charger can be used in non-isolated system, such as dc nano grid Buck/boost converter is used due to its simplicity and high efficiency The top and bottom switch is both 600V GaN switch In current stage, the 600v cascode GaN switch is preferred due to its easier gate drive and better switch performance The right hand side figure shows the switching energy comparison between cascode GaN switch and state of art Si MOSFET It is obvious that GaN switch has much less turn on switching loss The turn off loss is negligible due to current source drive mechanism existing in the cascode configuration This page shows a brief control diagram of one phase module of battery charger system The converter operates at critical mode The required signal includes zero current detection (ZCD), maximum cell voltage and current reference The ZCD signal can be generated by detecting the inductor current polarity The control scheme is simple and is capable for MHz operation This is the one phase module efficiency The bottom curve is the corresponding switching frequency DCM and burst operation is adopted to improve the light load efficiency The right hand side figure shows the four phase system efficiency curve The grey point is the phase shedding point The system efficiency is well above 99% over most load range and peak efficiency is about 99.4% This is the prototype of 4-phase bi-directional battery charger with 600V GaN switch The rated power is 5kW. This is the GaN SW in TO247 package This is the high frequency inductor made of ferrite material and Litz wire The whole system can achieve 99.4% peak efficiency and it requires less thermal management The system power density is 500W/in3 This is full load condition The converter operates at critical mode and the switching frequency is 1MHz The yellow waveform is the PWM signal of top switch and blue waveform is the drain-source voltage of top switch It is obvious that top switch can achieve zero-voltage turn on Meanwhile, the CPES proposed gate drive method can well suppress the noise induced by high dv/dt at turn off transition This is the light load condition The switching frequency increased to 2MHz Zero-voltage turn on for the top switch is always realized The measured efficiency is above 99% over most load range That’s end of the show. Thank you for your attention. Bye bye.