With the advancement in planar magnetic technology as well as wide band-gap (WBG) devices such as Gallium Nitride (GaN), Silicon Carbide (SiC) MOSFET and high electronic mobility transistor (HEMT), the utility of resonant converters has remarkably expanded. These converters can be used in applications requiring power density since they naturally possess zero voltage switching (ZVS) and zero current switching (ZCS) capabilities. Recently, they are gaining popularity in point-of-load (POL) DC-DC converter applications, such as electric vehicle (EV) chargers. As majority of the EV chargers are grid-connected, cascading a front-end (FE) AC-DC power factor corrected (PFC) converter with POLs becomes necessary. It is well-known in the literature that in cascaded systems, the impedance interaction of any FE converter with POL converters may lead to issues with system stability. The individual converters should be designed with sufficient stability margin to meet Middlebrook's stability criterion. Therefore, the knowledge of small-signal impedances becomes a prerequisite for applying the stability criterion. This paper focuses on determining the small-signal impedances of the LLC resonant converter, which are then used to analyze the stability of an EV charger employing the LLC resonant converter as a POL converter. The analysis is experimentally verified in a laboratory-developed prototype of 800W grid-connected EV charger.

With the advent of new electric vehicle technologies, research into electric vehicle chargers have also progressed immensely in the recent times. This paper discusses the modeling and design considerations involved in a bidirectional isolated electric vehicle charger. An electric vehicle charger comprises of a front end rectifier with power factor correction capability, with or without bidirectional feature cascaded with an isolated or non isolated DC-DC converter. The small signal impedance models of these converters are developed which aids in analysing the interaction between the two converters, while they try to meet their own control objectives. It is imperative to ensure that these interactions will not induce unintended oscillations at the DC link or instability in the cascaded system. Detailed simulation results of this cascaded system are presented to validate the analysis.

Various power conversion applications require the power converters to be cascaded with one another, to meet the load requirements. However, generally the trend is to cater to the control system design of individual converters and then cascade them with the other converters. Such cascaded systems can give sub optimal performance with poor stability margins. This paper tries to address this issue by investigating the interaction of the individual converters along with their control systems on the other converter, at their point of coupling. An active front end three phase rectifier cascaded with a voltage controlled buck converter is considered here to demonstrate the stability oriented control system design. Detailed impedance modeling of these converters are presented and their mutual interaction is studied for understanding the system stability. Extensive simulation results are presented to validate the analysis.

Triple active bridge converters are an extension of dual active bridge converters and used to combine multiple energy sources. The advantages of using a triple active bridge converter are its high power density, providing isolation along with elimination of low frequency transformer and high efficiency power conversion. To address the intermittent nature of solar energy, it is always appropriate to include a energy storage device along with it. Triple active bridge converter acts a viable option in integrating these two energy sources in the most efficient manner. Further, this energy can be fed to the grid by using a voltage source converter cascaded with this triple active bridge converter. This paper discusses the cascaded converter with its control algorithms and different operating modes. A laboratory prototype of a triple active bridge converter integrated with the grid through a voltage source converter is developed and the different control and operating modes are verified, which are also included in this paper.