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The so-called ‘Sneak Circuit’ is defined as an unexpected path or operational status in an electric or electronic circuit due to the limitation or oversight in design. Such sneak circuit can be triggered to operate under certain conditions. Whenever the unwanted or unintended operation corresponding to the sneak circuit emerges, the desired functions are likely to be degraded or inhibited. Undoubtedly, the phenomenon of sneak circuit also exists in power electronic converters, which are artificially designed to convert electric energy. In fact, sneak circuits in power electronic converters are not
uncommon. For example, the discontinuous-conduction mode (DCM) in DC-DC converters is a type of sneak circuit corresponding to its continuous-conduction mode (CCM) counterpart, and vice versa. However, the phenomenon of sneak circuit was not well-known in the past, largely due to unawareness of their conception in power electronics. In recent decades, power electronics has undergone intense development in many areas of technology. Better functionality, safety, and reliability of the power electronic system have become increasingly important in the present application of power electronics. In view of catastrophic results, which might be caused by the operation of a sneak circuit under certain conditions, it is necessary for power electronic engineers to understand thoroughly the sneak circuit in power electronic converters designed under all possible practical conditions.
The authors’ understanding of sneak circuits in power electronic converters came from an accidental experiment on the basic step-down RSC (resonant switched capacitor) converter early in 2004. In that experiment, the control strategy for switches was not changed and only some parameters (i.e., the switching frequency, the load, and the input voltage) were adjusted. It was surprising to observe that the converter changed
its status from four normal operating stages to six operating stages, and the adjusting process was completely reversible. Such an observation implied that two unexpected or undersigned operating stages had appeared. Moreover, when the converter worked in six operating stages, we observed obvious hazards of sneak circuit operation in a basic step-down RSC converter, including decrease in the output voltage and increase in the stress of the inductor current and switched capacitor voltage. Apparently, the six operating stages we observed were an example of a sneak circuit in a basic step-down RSC converter. It could be considered as the starting point of our study on sneak circuits in power electronic converters, and this book is a periodic summary of our research achievements in this field over the past ten years. We begin in Chapter 1 as an introduction of sneak circuit, outlining moves onto power electronic converters on sneak circuit phenomena, and an overview of definition, history, and analysis methods for sneak circuits. The following chapters are divided into three parts. The first part, consisting of Chapters 2 to 5, mainly describes sneak circuit phenomena in some typical power electronic converters. In Chapter 2, we present sneak circuit phenomena in families of RSC converters, and derive their expression of output voltage and operational conditions as they were first discovered. In Chapter 3, based on the summary and analysis of CCM and DCM of Buck, Boost, Buck-Boost, Cúk, Sepic, and Zeta DC-DC converters, we argue that DCM can be regarded as a sneak circuit in terms of the definition of these phenomena. In this way, the in-depth understanding on the physical mechanism of the DCM is presented from the viewpoint of a sneak circuit. In Chapter 4, we discuss some sneak circuit phenomena in soft-switching converters, specifically taking the full-bridge ZVS PWM converter, the Buck ZVS multi-resonant converter, and the Buck ZVTPWMconverter as examples. The purpose of this chapter is to illustrate that sneak circuit phenomena
are more complex and abundant in soft-switching converters due to the existence of the resonant tank. The sneak circuit here must be eliminated, otherwise it will give rise to unpredicted effects on the converters. In Chapter 5, we consider two novel power electronic converters, that is, the Z-source inverter and the synchronous rectifier DC-DC converter. The detailed investigations on these two converters further demonstrate that sneak circuit phenomena inevitably exist in a large number of power electronic converters under certain conditions. The second part includes Chapters 6 and 7, where we propose some analysis methods, which are used to investigate sneak circuit phenomena in power electronic converters. In Chapter 6, we use graph theory to study sneak circuit paths. Firstly, the adjacency matrix, connection matrix, and switching Boolean matrix are respectively employed to find all circuit paths in the converters. Then, we identify the sneak circuit paths according to the operating principle of power electronic converters. In Chapter 7, we suggest a systematic method for discovering the sneak circuit phenomena in power electronic converters, which is essentially a method of mode analysis of the sneak circuit and can be taken as the complement of Chapter 6. Chapters 8 and 9 are the last part of this book. In these two chapters, we focus on the guidelines concerning elimination and application of sneak circuits in power electronic converters. In order to eliminate the sneak circuit in power electronic converters, we propose two methods in Chapter 8. One method is to restrict the parameter variation of the converter so that the sneak circuit cannot become active, whereas the other method completely cuts off the circuit path corresponding to the sneak circuit. Since the aim of understanding the sneak circuit is to fully utilize it, this issue is addressed in Chapter 9, where we demonstrate the utilization of a sneak circuit to achieve performance improvement, topological reconfiguration, new function, and fault diagnosis
of power electronic converters with specific examples