Small-Signal Dynamics of Interconnected Subsystems in Electric Vehicle

A general electric vehicle (EV) consists of many subsystems such as battery, DC-DC converter, DC-AC inverter, motor, and vehicle body along with their controllers. Therefore, the modeling, simulation, and validation are time-consuming and critical tasks due to its multiple time scale nature of the different subsystems and multi-domain modeling of different subsystems, i.e., battery model using physics, converter as well as inverter model using electrical, and motor-vehicle body model using mechanical engineering concept. Moreover, the selection of the type of modeling has a direct impact on control decisions of high-performance vehicle designs and their analysis. In this paper, small-signal transfer function analysis has been used to capture the overall dynamics of the EV along with controller design and stability analysis. To do this, a constant battery voltage DC-DC converter with equivalent inverter-fed motor-vehicle load in constant torque mode and constant power mode is considered. This assumption is valid because the time constant of the DC-DC converter is low compared to the other subsystems in the EV, therefore the overall dynamics is governed by the closed-loop control of the DC-DC converter.