Contents I. Introduction
Considering many benefits such as low harmonic distortion, low dv/dt, low voltage stress, low power losses, ability to operate at medium/high power and so on, multi-level converters have recently attracted considerable attention in the scientific community of power electronics [1]–[3]. Conventional multilevel converters are arranged into three categories: 1- Floating Capacitor (FC) 2- Diode Clamped or Neutral Point Clamped (NPC) 3- Cascade H-Bridge [4]–[8]. The difficulty of natural voltage balancing of the capacitors in FC and NPC and the high number of diodes and capacitors required in FC and NPC, respectively, as well as the large number of DC sources in CHB, have drawn the attention of researchers to switched capacitor multilevel inverters (SCMLIs) [9]–[11]. SCMLIs are divided into two categories: 1-Unity gain SCMLIs, 2-High gain SCMLIs [12], [13]. The first category is related to applications in which voltage conversion is important, and in the second category, the issue of increasing the input voltage level is important. SCMLIs use capacitors instead of DC sources and have lower voltage standings and lower power electronics than other converters [14], [15]. In these structures, the capacitor voltage is supplied by a parallel connection to the input source in different operating modes [16], [17]. This leads to the passage of high-amplitude currents through the capacitors, which are called inrush currents. This can damage the capacitor in the long run and also increase power losses. In addition, it limits the industrial applications of these converters. In the following, we will examine the structures that all suffer from inrush current of capacitors. In [18] a new structure for switched capacitor based multilevel converters has been presented. This structure requires an H-bridge to produce negative voltage levels, which in turn leads to an increase in the Total Standing Voltage (TSV) of the proposed structure, so this is one of the major disadvantages of this structure. The advantages of this structure are its modularity and natural voltage balancing of the capacitors. A 9-level converter with the ability to double the input voltage is presented in [19]. The merits of this structure are the inherent production of negative voltage levels, low number of switches and low TSV. The inrush current of the capacitors is one of the most important drawbacks of this structure. An H-bridge based switched capacitor structure is presented in [20]. The shortcomings of this structure are the large number of DC sources and the high TSV. Low number of switches and capacitors are important advantages of this structure. A new 19-1evel high-gain converter is presented in [21]. High TSV is the main disadvantage of this structure, while the high gain of the converter as well as the use of only one DC source are the merits of this structure. According to the above explanations, a quasi-resonant switched capacitor multilevel inverter (QRSC-MLI) is presented to solve the inrush current problem of capacitors. The advantages of this structure are the natural voltage balancing of the capacitors, the ability to increase the input voltage, the very low ratio of the number of sources to the number of steps, the low TSV and most importantly the limitation of the capacitor's inrush current. The proposed structure and how it works are described in Section II. In Section III, the proposed topology is compared with other structures. The simulation results extracted from PSCAD software are presented in Section IV. Finally, the conclusion is presented in Section V.
