Ultra-capacitor based three level bi-directional isolated DC-DC converter for the regenerative breaking energy recovery system

Ultracapacitor has a many advantage over the conventional capacitor and electrochemical battery so it is used as energy storage devices in many application. Ultracapacitor is connected to the dc bus using a dc-dc converter. The control strategy is of the converter depends upon system requirements: the control of the dc bus voltage, the ultracapacitor state of charge, the active sharing of the energy between the drive and ultracapacitor, and so on. When the ration of dc bus voltage to ultracapacitor voltage is less than 2 than isolated converter with the soft switching is a best solution but for the higher ration its efficiency is less than the non isolated converter. Three-level converters are a best solution where the high frequency and voltage are required. In this stress on the switches are half of the dc bus voltage so the gives the better switching performance. so, the converter's overall performance, including cost and efficiency, can significantly be better compared to two-level converters. This paper presents a three-level bidirectional dc-dc and its control strategy for the ultracapacitor power conversion applications.