Characteristics of PHEV
Fig. 2 shows a schematic graph of usage of charged
electricity in HEV and PHEV. The battery's state of
charge (SOC) is controlled to maintain an intermediate
level and an almost constant state by using regenerated
electric energy in conventional HEV. SOC control
operation in PHEV is different from the HEV. Operation
of PHEV vehicles change significantly after reaching a
certain running distance. It is characteristic event of
PHEV. PHEV is operated by charge depleting (CD)
mode when battery SOC have some capacity. At CD
mode, the vehicle is operated by consuming electric
energy supplied from external source. The operation
mode is switched to charge sustaining (CS) mode when
minimum or suitable level of SOC level is reached
achieved. The CS mode uses regenerated electric
energy. The vehicle is controlled to keep the SOC
constant. It is like the conventional HEV control but
SOC level is kept lower than that of HEV. Battery SOC
range of PHEVs is wider than that of HEVs. This affects
battery durability and performance.