In systems where the HV-LV DCDC converter lacks bidirectional capability, an independent isolated DCDC Boost design represents a viable alternative. This approach also facilitates the utilization of LV batteries for pre-charging DC-link capacitors. Given the average power requirements, push-pull topology is generally preferred.

Figure 3-7 shows the block diagram for an independent isolated DCDC design. The MCU for OBC/DCDC/Inverter receives HV battery voltage information from the BMS, configures the output voltage for the isolated DCDC converter, and initiates the pre-charging process for the DC-link capacitor. Upon completion, this transmits a READY signal to the BMS to activate RELAY1 and RELAY2.

Figure 3-7 Block Diagram for Independent DCDC Design

Using a 400V DC Bus voltage and 600μF DC-link capacitor as an example, with LV battery voltage ranging from 9V to 16V, a transformer turn ratio of 1:50 can be established. According toEquation 1 , the average current is 1.2A. Setting delta IL to 0.3Iout and the switching frequency to 100kHz:

The calculated inductance is 924μH; however, in simulation, considering inrush current and winding turns of the inductor, 500μH is used. Figure 3-8 presents the SIMetrix Simulation circuit based on these calculations, while Figure 3-9 displays the simulation results.

Figure 3-8 SIMetrix Simulation Circuit for Independent DCDC Design

Figure 3-9 SIMetrix Simulation Results for Independent DCDC Design

TI Components enumerates the primary components used in independent DCDC design. The existing MCU of OBC/DCDC/Inverter can be repurposed to generate PWM signals and implement closed-loop control. If MCU bandwidth constraints exist, LM25037-Q1 can be used for control functions and ISOM8810-Q1 for isolated feedback.