This paper focuses on the stability of the vehicular integrated power system in terms of its island operation

the slow dynamic response of engine

and the complex working conditions. Firstly

the small signal models of each source and loads converter are proposed

based on which the output impedance and loads input impedance are obtained. Then

the instability criterion of small signal of the vehicular integrated power system is established based on an improved impedance criterion. Furthermore

the instability prediction of the system is analyzed from three aspects

such as its engine speed

vehicle speed

and the torque of each driving motor

by using the Bode diagram. Finally

the theoretical analysis is certificated by the Hardware-in-Loop simulation and prototype vehicle tests. The research results indicate that the engine speed should be controlled between 1 900 r/min and 2 000 r/min

and the vehicle speed shall not exceed 100 km/h

when the vehicle is in high-speed mode. The stability of system is heavily influenced by the torque of each driving motor

and the system will be collapsed caused by the torque when it is more than 48 N·m. It is concluded that the proposed instability criterion can precisely predict the system state

and help optimize the control structure and design the assistant system.