With the continual development of semiconductor device technology, it has been made possible to
increase the switching frequency of power electronic converters to achieve high power density. But high
frequency switching inevitably increases switching loss which degrades the converter efficiency. Significant
reduction in switching loss is possible by incorporating soft-switching techniques viz. zero voltage switching
(ZVS) and zero current switching (ZCS) which are the inherent features of resonant converters (RCs). Since
these converters simultaneously facilitate both compact design and efficient operation, these are reportedly used
in several applications, namely electronic ballasts, induction heating, DC distribution systems, solar
photovoltaic inverters, wireless power transfer and on-board battery chargers.
Resonant converters (RCs) offer efficient performance when switched at the resonant frequency which is decided by the resonant tank parameters. But these parameters drift from their initial designed values due to variation in environmental and/or operating conditions leading to inevitable drift in the resonant frequency. To address this issue, two different automatic resonant frequency tracking (ARFT) schemes are proposed, which always ensure the switching frequency to be equal to the current resonant frequency. One of the proposed techniques detects off-resonance by monitoring phase-relationship of a variable-pair in the resonant tank, while the other method performs detuning detection by observing gain-relationship of a tank variable-pair. Also, a generic procedure is presented to conclusively decide between the phase-based and gain-based ARFT schemes for a given resonant tank. Both the proposed strategies are realized using low-cost analog electronics. Experimental evaluation of steady-state and transient performance of both these ARFT methods is carried out and maximum error in frequency tracking is noted to be below 1%.
Apart from the frequency drift problem, three critical design aspects of RCs are also addressed. First, an existing confusion in literature regarding ZVS analysis of full-bridge switch network is noted and an accurate ZVS analysis is proposed to mitigate this lacuna. Next, the necessity of diode reverse-recovery loss estimation for phase modulated RC design is considered and a structured method is proposed to estimate different reverse- recovery metrics directly from device datasheet. Then unavailability of any voltage gain expression is noted for the series resonant converter operating in discontinuous conduction mode. To resolve this issue, an analytical approach is proposed, which leads to the derivation of converter voltage gain as well as the boundary between continuous and discontinuous conduction modes.
For each of these topics, problem definition, limitations of the existing approaches and key contribution will be presented briefly. However, analytical derivation and hardware realization of the phase-relationship- based ARFT scheme will be discussed in adequate detail. Also, a brief overview on future research directions and teaching plan will be given towards the end of the seminar.
Utsab Kundu received his B. E. in Electrical Engineering from IIEST Shibpur (formerly known as Bengal Engineering and Science University) in 2010. He received his M. Tech in Machine Drives and Power Electronics from IIT Kharagpur in 2012. He received his PhD in Power Electronics from IIT Kanpur on Jan 29, 2019. Currently, he is working as a staff power systems engineer in Maxlinear Technologies Private Limited, Bangalore, where he joined in Aug., 2018. His research interests include resonant mode power conversion, soft- switching, power converter topologies and control techniques in power electronics.