Development of New Power Control Unit with Small Size and Low Cost for Small Hybrid Vehicle with Two-motor Hybrid System

A new power control unit (PCU) has been developed for a Honda small hybrid vehicle with a two-motor hybrid system launched in 2020. For small hybrid vehicles, downsizing and reducing costs of hybrid systems are major challenges. As such, there were emphatic requirements for the newly developed PCU to be small and affordable. To satisfy these requirements for the PCU, new technologies and components have been introduced such as an all-in-one type intelligent power module (IPM) with integrated functions and reverse conducting IGBT (RC-IGBT), a new control sequence for voltage control unit (VCU), and revised PCU packaging to improve cooling performance. The new IPM has a printed-circuit board (PCB) equipped with an electric control unit (ECU) and gate drive circuits, 7 current sensors, and a power module with RC-IGBTs. This functional integration led to a reduction in the number of main electrical PCU assembly components from 9 in the previous PCU to 2 in the new PCU. In addition, the number of mounted parts on the PCBs was reduced from 2,200 to 1,300 by means of various methods such as the integration of the ECU and gate drive circuits. Moreover, the size of the power module, the area of the RC-IGBTs, and the number of parts in the power module were reduced owing to the introduction of RC-IGBTs instead of conventional IGBTs and a diode pair, reduction of loss in the RC-IGBTs, and increased operating temperature of the RC-IGBTs. A new VCU control sequence suppresses the fluctuation in high DC line voltage, while a cooling structure that covers the surrounding of a high voltage capacitor reduces the capacitor temperature. These measures reduce capacitance of the capacitor almost by a half compared to that of the previous model. The newly developed technologies and components dramatically decreased the number and volume of parts in the PCU. Thus, a new PCU with small size and low cost was realized.