Embedded Controlled Isolated Bidirectional Full-Bridge DC-DC Converter with Flyback Snubber

An isolated bidirectional full-bridge DC-DC converter with flyback snubber for supplying a resistive load is simulated and experimentally verified. The DC-DC converter for high conversion ratio, high output power, and soft start-up capability is presented in this paper. The circuit consists of a capacitor, a diode, and a flyback converter. These components help to clamp the voltage spikes caused by the current difference between the current fed inductor and leakage inductance of the isolation transformer. The switches are operated by soft-switching technology. The suppression of inrush current which is usually found in the boost mode start-up transition is presented here. The simulated and experimental results for output voltage, output current, and power for both buck and boost modes are presented. 1. Introduction A DC-DC converter converts a source of direct current(DC) from onevoltagelevel to another. These converters are important in portable electronic devices such as cellular phonesandlaptop computers, which are supplied with power from batteries primarily. The ordinary circuit of a DC-DC converter for high power applications typically includes a bidirectional full-bridge DC-DC converter [1–3]. The current difference between the inductor and isolation transformer does not ensure a well-defined output voltage and is characterized by less reliability and efficiency. The output voltage contains voltage spikes. An active commutation can be used to control the current in the leakage inductance [4]. But it requires an additional clamping circuit to suppress the voltage spikes. An RCD passive snubber can be used to clamp the voltage. A buck converter was employed to replace RCD snubber. But it still needed complex clamping circuit [5, 6]. Active clamping increases the current stress on switches. Soft-switching capability can be used, but it is not suitable for step-down operation. In this scheme of DC-DC converter with flyback snubber (Figure 1), the snubber recycles the absorbed energy in the clamping capacitor. The voltage of the clamping capacitor can be regulated by operating the flyback snubber independently. The current does not circulate through the full-bridge switches, and hence the current stress can be reduced, improving the system reliability significantly. Figure 1: Isolated bidirectional full-bridge Dc-Dc converter with flyback snubber. 2. Configuration and Operation The operating principle of the circuit consists of two modes: (i)step-up conversion,(ii)step-down conversion. The modes of operation of boost mode are shown in Figure 2 and of