Compact and high power inverter for the Cadillac CT6 rear wheel drive PHEV

Electric drive system for the Cadillac CT6 plug-in hybrid electric vehicle (PHEV) comprises a power-split hybrid transmission utilizing two motors, a traction power inverter module (TPIM) having two inverters and a liquid-cooled lithiumion battery pack [1, 2]. The resulting propulsion system provides a combination of exceptional fuel economy, crisp acceleration, and strong electric-only driving range. To meet all these performance, reliability and robustness targets and package the TPIM into a compact under hood environment is a challenge. This paper describes indispensable and collaborative design efforts by Hitachi Automotive and General Motors to meet this challenge. Enhancing heat dissipation performance and using high efficient power semiconductor enables reduced inverter size and increased power output. Elimination of heat impeding thermal grease and developing direct water cooled power module made generational improvements in this area. Hitachi went further by developing a direct double-sided cooling power module to achieve ∼35% improvement in heat dissipation utilizing a proprietary cooling structure that immerses the module in coolant [3]. This paper elaborates on the integration, structure and the selection of power transistor switch for this TPIM to meet Cadillac CT6 PHEV tractive and special maneuver needs. Among other coherent steps are to design low inductance busbar, optimize the gate drive circuit elements, provide protection functions for detecting over-temperature, over-current, over-voltage ranges and thus maximizing the performance from the power devices. Design efforts were also directed to surround the Bulk DC capacitor by the vertical water channels of the power module and maintain life expectancy by not exceeding rated hot spot temperature. This paper describes predictions, component and vehicle level test results to justify design competence.