# An Overview of Non-Isolated Hybrid Switched-Capacitor Step-Up DC-DC Converters
## 1 Introduction  
Climate-change-related problems have focused the attention on renewable energy sources as an option to fossil fuels for electric energy generation [1; 2; 3; 4; 5; 6; 7; 8]. Photovoltaic (PV) panels and fuel cells (FC) stacks are among the most studied renewable energy sources, but they produce electrical energy at a relatively low voltage; their voltage levels need to be boosted before being injected into the utility grid. This is one reason why much attention has been put on high-voltage gain dc-dc converters in the power electronics research field. DC-dc converters usually perform the first energy conversion on PV generation systems to feed Voltage Source Converters (VSC) and integrate renewable energy into the utility grid [9; 10; 11; 12]. Power electronics-based converters have been used extensively in this application [9; 10; 11; 12]; several converters, such as the boost, buck-boost, Cuk, etc., can be used to increase the voltage to an adequate level. Traditionally, dc-dc converters are made by inductors, capacitors, and switches. Switches can be synthesized with diodes, transistors (such asMOSFETS), or thyristors. Additionally, magnetic elements, such as coupled inductors or transformers, can be used [9]. The inductor is usually the largest and heaviest component in a power converter. An important research area related to the power electronics circuits is to achieve power conversion without inductors; in this case, Switched-Capacitor (SC) circuits are being investigated [13; 14; 15; 16]. They are composed of capacitors and switches, and their research is not new, but their combination with traditional converters and/or with small inductors that produce a resonant charge interchange is giving a new breed to the research of SC converters [40; 41; 15; 16], converters in which capacitors get charge interchange between them to increase or reduce the voltage. This article presents an overview of hybrid SC converters. It starts with a short review of pure SC circuits [13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39], but it focuses on modifications of those circuits mainly with the use of small resonant inductors, which leads to resonant SC circuits [40; 41; 42; 43; 44; 45; 102; 45; 103; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78; 79; 80; 81; 82; 83; 84; 85; 86; 87; 88; 89; 90; 91; 92; 93; 94; 95; 96; 97; 98; 99; 100; 101], and the combination of traditional converters, such as the boost converter topology, with capacitor-based voltage multipliers [47; 48; 49; 102; 103; 104; 105; 106; 107; 108; 109; 100; 101]. It is important to emphasize that inductors used in resonant SC circuits are much smaller than energy storage inductors used in traditional converters. Their inductance is so small that some articles utilize air-core inductors or parasitic inductance in wires to achieve the resonant charge interchange [108; 110; 111; 112]. The resonant charge interchange is a relatively new tendency among designers of SC circuits; it is relevant since several converters have been investigated with relatively large efficiency [40; 41; 42; 43; 44; 45; 102; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 75; 76; 77; 78; 79; 80; 82; 83; 84; 85; 86; 87; 88; 89; 90; 91; 92; 93; 94; 95; 96; 97; 98; 99; 100; 101]. The efficiency of pure SC circuits is limited due to an effect in which the charge interchange among capacitors produces a type of loss which can be called discharging loss. It has been proved before that SC converters with a resonant charge interchange have no discharging losses, as will be discussed later. The overview includes contributions introduced to the state-of-the-art in the last decade.