Design and Control of Multi-port Isolated DC-DC Series Resonant Converter

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Name of the Speaker: Surja Sekhar Chakraborty (EE16D203)
Guide: Dr. Kamalesh Hatua
Venue/Online meeting link:
Date/Time: 17th May 2023 (Wednesday), 11:00 AM

Isolated bidirectional DC-DC converters are found very useful for the applications, such as Battery Energy Storage System (BESS), Solid State Transformer (SST), Intelligent Uninterrupted Power Supply (IUPS), and MV drives, due to their high power density and high efficiency. Among the existing eight-switched topologies, Dual Active Bridge (DAB), Dual Active Bridge Series Resonant Converter (DABSRC), and LLC resonant converter have better performances in terms of control and efficiency. Among these topologies, DABSRC is an attractive choice due to its high efficiency and simple analysis. However, its high frequency (HF) link dynamics are neglected in the existing literature, which increases the RMS and the peak VA rating of the electrical components used in the HF link. Besides the two-port DC-DC converters, series resonant converter based three-port converters are also popular among the other isolated three-port DC-DC converters. A common issue with the three-port DC-DC converter is the power coupling between the two HF links. Due to this coupling, the control system design becomes complex and difficult to implement in low-cost microcontrollers.

In this work, an accurate modelling is carried out of a DABSRC, which can predict the HF link dynamics and helps to design the controller. Two different multivariable controllers, such as (1) fast-slow control, and (2) state feedback control, are proposed in order to attain high efficiency over a wide range of loads. The fast-slow control is simple to design, and the state feedback control is theoretically rigorous but has better transient performance. The proposed state feedback control achieves a settling time of 4 ms for DC bus voltage and reduces the overshoots in HF link voltage and current by 60%.

In addition to the modelling and control of DABSRC, the design of a high frequency transformer (HFT) is also proposed for a three-port DC-DC converter for on-board charging applications. A suitable winding arrangement is proposed for a three-winding transformer to achieve a zero terminal leakage inductance which naturally decouples the active power flow between the two high frequency links of a three-port series resonant converter (TPSRC) and simplifies its operation by converting it into a parallel combination of two DABSRC. Typically, the decoupling is achieved either by complex control system design, or by using a suitable capacitor in the high frequency link. By the virtue of the proposed decoupling method, a multi-port converter with any number of ports can be transformed into the parallel combinations of multiple two-port converters.