Digital Adaptive Frequency Modulation for Bidirectional DC-DC Converter

This paper introduces a digital adaptive control method for a bidirectional dc/dc charger/discharger, which is the core element for reliable and efficient energy storage systems. The proposed method achieves zero-voltage switching (ZVS) without the use of an auxiliary zero-crossing detection (ZCD) circuit. To satisfy ZVS conditions, proper switching frequency is determined through a digital calculation. It features soft switching over wide input and output ranges. Because this method does not require a ZCD circuit, it is easily implemented with bidirectional operation and reduces instability and noise susceptibility problems. To reduce conduction loss, a multiphase interleaving technique is applied. This interleaving method reduces the required capacitance by decreasing the current ripple. A phase shedding technique is also implemented to achieve higher efficiency over a wide load range. The operation of the proposed digital adaptive control method is analyzed. For experimental verification, a 200-W two-phase-interleaved bidirectional synchronous buck converter with 30-38-V bus voltage and 15-25-V battery voltage is implemented.