Over the last decade, energy demand from the power grid has increased significantly due to the increasing number of users and the emergence of high-power industries. This has led to a significant increase in global emissions with conventional energy generation. Therefore, the penetration of renewable energy resources into the power grid has increased significantly. Photovoltaic systems have become the most popular resources as their protentional is enormous, thus, the worldwide installed PV capacity has increased to more than 635 gigawatts (GW), covering approximately 2% of the global electricity demand. Power electronics are an essential part of photovoltaic generation; the drive for efficient power electronic converters is gaining more and more momentum. Presently, multilevel inverters (MLI) have become more attractive to researchers compared to two-level inverters due to their abilities to provide lower electromagnetic interference, higher efficiency, and larger DC link voltages. This paper reviews multilevel inverters based on their classifications, development, and challenges with practical recommendations in utilizing them in renewable energy systems. Moreover, PV systems with various maximum power point tracking (MPPT) methods have been extensively considered in this paper as well. The importance and the development of a modified multilevel inverter are also highlighted in this review. In general, this paper focuses on utilizing multilevel inverters for PV systems to motivate and guide society to focus on inventing an efficient and economical multilevel inverter that has the combined capabilities of these converters reported in the literature.

With the rapid development of modern energy applications such as renewable energy, PV systems, electric vehicles, and smart grids, DC-DC converters have become the key component to meet strict industrial demands. More advanced converters are effective in minimizing switching losses and providing an efficient energy conversion; nonetheless, the main challenge is to provide a single converter that has all the required features to deliver efficient energy for different types of modern energy systems and energy storage system integrations. This paper reviews multilevel, bidirectional, and resonant converters with respect to their constructions, classifications, merits, demerits, combined topologies, applications, and challenges; practical recommendations were also made to deliver clear ideas of the recent challenges and limited capabilities of these three converters to guide society on improving and providing a new, efficient, and economic converter that meets the strict demands of modern energy system integrations. The needs of other industrial applications, as well as the number of used elements for size and weight reduction, were also considered to achieve a power circuit that can effectively address the identified limitations. In brief, integrated bidirectional resonant DC-DC converters and multilevel inverters are expected to be well suited and highly demanded in various applications in the near future. Due to their highlighted merits, more studies are necessary for achieving a perfect level of reducing losses and components.

This study thoroughly compares multiple single bidirectional and multiport converters (MPCs), highlighting the significant role of MPCs in multi-input and multi-output (MIMO) systems. MPCs offer a more efficient and cost-effective solution than multiple single converters, especially in applications involving photovoltaic (PV), electric vehicles (EVs) with storage systems, and power grids. This research emphasizes the importance of multi-input converters (MICs) in integrating diverse voltage sources. It notes the rising popularity of multi-output DC-DC converters in portable electronics, owing to their reduced component count, lower costs, and compact design. This paper emphasizes comparisons based on diverse aspects and applications, shedding light on recent developments in basic bidirectional converters. Additionally, it delves into the advancements in MPC topologies, focusing on efficiency, reliability, and modularity improvements. These advancements are crucial for harnessing cost reduction, simplicity, and compactness. Furthermore, this paper introduces an innovative multiport DC-DC converter tailored for integrating and managing renewable sources. This new converter design enhances PV system and battery storage performance by reducing power conversion steps, using fewer components, and improving voltage-boosting capabilities. Its unique bidirectional buck-boost structure allows for versatile connections between sources and loads with varying voltage and power requirements. The performance of this novel converter is evaluated through MATLAB/Simulink simulations under different scenarios. Experimental studies further validate its effectiveness, marking a significant contribution to power conversion and management in integrating renewable sources such as DC microgrids.

This paper presents proposal of a five-level LLC resonant DC–DC converter design procedure for battery chargers. The five-level inverter side of the proposed converter is connected to a transform-less LLC resonant tank to ensure operating at high frequency and achieve soft switching. The proposed converter has less weight, size, and cost. It is also much simpler in terms of implementation, and has smooth energy conversion to the load. The proposed converter is designed to work within the range close to the resonant frequency, to ensure higher power density and efficiency. Thus, the range of operating frequency is set to be (91 kHz < fsw < 110 kHz), while the LLC parameters is designed to achieve resonant frequency fr = 100 kHz. Therefore, it is designed to achieve zero voltage switching (ZVS) for all switches, which enhances the efficiency as well. The theoretical analysis outcomes were confirmed by simulation studies conducted using MATLAB/SIMULINK. An experimental model was also developed and validated with 100 VDC input voltage, which delivered output power of 100 W, 48 V, with efficiency around 96.9%. Selected findings are presented to confirm the effectiveness of the suggested converter.

The persistent energy problems facing developing nations can be addressed by investing in renewable energy sources and technologies as these RES, such as fuel cell, PV energy, wind energy, and biomass energy can provide the needed energy to overcome energy shortages in such nations. MLIs are commonly used for high power high/medium voltage applications as they are considered an advanced topology for power conversion. Studies are currently focusing on the design of “reduced switch MLI (RS MLI) topologies” to facilitate the production of high-quality output without using numerous numbers of switches. These RS MLI are currently emerging techniques for various reasons, such as cost reduction, optimal sizing, reduced volume, minimized losses, and high efficiency. This study presents the design and development of a Multilevel Inverter (MLI) structure with fewer switch count for PV application. The proposed inverter architecture comprises of an H-bridge unit that acts as the polarity generator and the level generating unit comprising independent voltage sources with switches and diodes. It combines the proposed inverter with a PV array through a DC-DC converter. The boost converter will improve the output voltage of the solar photovoltaic system to its maximum value using MPPT (P&O). The proposed inverter is designed and tested for structures of five, seven, and nine levels by using MATLAB/Simulink. Selected results are presented to verify the validation of the 5, 7, and 9 levels MLIs. As a result, the proposed system successfully managed to achieve 96 % efficiency.

This study presents the design of a phase-shifted DC-DC series-parallel full bridge resonant converter (PSFB-LLC) for battery charger application. The proposed converter is controlled by phase-shift pulse width modulation that switches the full bridge inverter connected with a resonant tank; it is equipped with an isolated transformer (high frequency) and backed with a battery for energy transfer and for achieving zero current switching (ZCS) at all the primary active switches. The magnetizing inductance was implemented in parallel with the phase-shifted angle to improve the capacitance of the tank and facilitate the achievement of ZCS for the active switches. The analysis and evaluation of the proposed system was done using MATLAB/SIMULINK software for a 48V 150 Ah lead-acid battery and selected results were adopted to prove the system validity. As a result, the state of charge (SOC) is increasing during charging, thereby confirming the suitability of the developed converter for use energy storage systems.