## 1 Introduction  
Because of its abundance in nature, solar photovoltaic (PV) energy is gradually becoming one of the most important renewable energy sources. It is pollution-free, requires less maintenance, and is less expensive to run [1]. In a standard PV renewable energy power system, the inverter and DC-DC converter are essential. The system can either be standalone or grid-connected [2, 3]. The traditional two-level inverter is used in a lot of applications. However, due to limitations such as high harmonic content, reduced output resolution, high component stress, and lack of modularity, its applications are now limited to smaller-scale operations [4, 5]. A multilevel inverter (MLI) was later introduced as a better alternative, with which most of the mentioned demerits are solved [6]. However, traditional MLI topologies, such as neutral point clamped (NPC), flying capacitor (FC), and cascaded H-Bridge (CHB), have several drawbacks in common. The demand for a higher number of components is one of them [7]. If the number of required components can be reduced, the overall cost of a system can also be reduced. As a result, MLI topologies with a reduced number of components have been widely published over the years. This newer generation of MLIs uses fewer components, such as switches, capacitors, DC sources, and gate drivers, while maintaining similar or better output characteristics than older MLIs. One of the earliest reduced-component MLIs is known as the multilevel DC-link inverter (MLDCL), which makes use of an H-Bridge as a polarity generator [8]. It is one of the most popular methods of reducing the overall number of switches, but the switches on the bridge need to block a very high voltage that is equivalent to the maximum output voltage [9]. Some other topologies, such as the T-Type and E-Type, avoid using the H-Bridge to reduce the high total blocking voltage at the cost of a higher number of components [10; 11]. An improvement to the standard H-Bridge known as the packed H-Bridge was proposed years later [12]. It requires two extra switches. However, with the interconnection with optimal basic units, as presented in [13], a good balance between the number of components and total blocking voltage was successfully achieved. MLI can also be categorised according to its DC source connection architecture, which has its own set of benefits and drawbacks. There are MLI that require multiple isolated DC sources, while others need only single or several shared DC sources with capacitors. For the latter group, capacitors are needed to provide different voltage levels to generate multilevel outputs. A capacitor voltage balancing control system will be needed for the proper operation, which is rather complex to perform [14]. MLIs with isolated DC sources normally do not have capacitors. In some applications, such as variable frequency drive, isolated inputs can be harder to control. In other applications, such as PV interconnection, where multiple PV modules can be implemented as separate sources, isolated MLI can be simpler to implement and more advantageous [15]. The market for standalone PV energy systems is still available, especially in countries with rural areas where is it is economically expensive to connect these areas to the utility grid [16]. The DC-DC converter is necessary for a PV system to control the output from PV panels before serving as the input to the inverter [17]. In a standalone system, it is crucial to ensure the voltage at the input of the inverter is constant; otherwise, the AC output will be unstable. However, the characteristics of PV panels depend greatly on solar irradiation and operating temperature [18]. The standard modulation index-based DC-link voltage control method used in traditional MLI is not suitable to be applied in newer MLI topologies since the range for modulation index control will be smaller as the number of output levels increases [19]. There is also very little literature discussing this matter, especially in a standalone PV system.