ac dc dc dc dc/ac ac/dc ac ac/dc Input Filter Output Filter Interleaved PFC Converter dc Isolated Full-Bridge LLC Resonant dc/dc Converter Figure 3. The overall topology selected for OBC. Table 2. The front-end converter topology comparison. ac dc Figure 4. The conventional interleaved PFC topology. ac dc Interleaved PFC Bridgeless PFC Efficiency 97-98% 98% Voltage sensing Simple More complex Current sensing Simple More complex EMI Smaller filter components Larger filter components one return current path. Instead, a current transformer or hall-effect current sensor is typically used at the input port. Finally, the bridgeless design leads to increased common mode noise, which can be difficult to filter. These drawbacks led to the selection of the conventional interleaved PFC topology. Table 2 compares the front-end converter topologies. Output Converter Topology Figure 5. The bridgeless PFC topology. current measurement is more complicated. The conventional PFC design allows current to be monitored with a shunt resistor in the return current path. However, monitoring current with a single shunt resistor is not feasible for the bridgeless converter because it has more than The output converter transforms the intermediate dc voltage to the required output dc voltage. Multiple topologies are suitable for this converter, and the topologies investigated were the following: 1) phase-shifted fullbridge (PSFB) converter, as shown in Figure 6, and 2) LLC resonant converter, as shown in Figure 7. GM's benchmarking indicated the PSFB topology was the most popular design for automotive OBCs. This topology uses fixed frequency pulsewidth modulation (PWM) switching control, and a delay is introduced between the turn-on commands of diagonal switches. This switching technique makes use of parasitic circuit elements to IEEE Electrific ation Magazine / march 2 0 1 7 39