Digital Inverleaved CRM PFC
In order to solve problems caused by sub-harmonic oscillation phenomena and utilize the high efficiency advantage of Critical Conduction Mode, Powerland has done a complete analysis of the sub-harmonic oscillation phenomena and proposed a novel phase-shift interleaving control scheme, where the slave phase can work at critical conduction mode and phase-shift is almost 360º/N, N is the number of phases. Due to inherent variable switching period, a digital implementation in FPGA has been realized in a 250W two-phase interleaved CRM boost PFC.
Digital DAB DC-DC Converter
Instead of using LLC topology, a ZVS-PWM converter with similar performance as LLC resonant converter was proposed for DC/DC Front-end converter. By controlling the phase shift between primary side and secondary side voltages, the converter can achieve optimal efficiency at normal operation condition, when AC line exists. Additionally, the circuit has the capability of boost voltage gain, which can help extend the holdup time and reduce bulky capacitor requirement. This novel topology features small holdup capacitor, ZVS switching all switches, easy SR driving, optimal efficiency at normal operation condition, and inherent current-sourcing characteristic for convenient module paralleling. Because no commercial controller is available for this novel topology, DSP-based digital control has been developed for series applications. Furthermore, a digital pulse-skipping method is proposed to achieve flat efficiency for whole load range.