Stability Criteria for the Energy Storage Bi-directional Dc/Dc Converter in the Toyota Hybrid System II

Distributed DC power systems are becoming increasingly common in advanced electric and hybrid electric vehicles. In these systems, secondary energy storage component is connected to the main high voltage DC bus and consequently traction machine as well as other loads through a bi-directional DC/DC converter. In this paper, it has been shown that, during discharging mode of battery, the traction machine, which is being fed through this converter may act as a CPL. Constant power load (CPL) behavior of tightly regulated DC/DC converters, inverters, and motor drives in distributed DC power systems is equivalent to the dynamic negative impedance, destabilizing the DC bus and consequently the system. We investigate the stability of bi-directional converter of the energy storage systems of a Toyota hybrid system II. Stability of converter in presence of loss components is analyzed and design criteria are presented.