An improved multilevel inverter (MLI) topology using a new basic unit structure with a reduced number of components is proposed in this study. Its single compact module is made up of two basic units connected to the left and right sides of a packed H-bridge. The topology produces 9-Level output when operated symmetrically and 17-Level output when operated asymmetrically. Identical magnitude of DC sources is used for the symmetrical operation, while non-identical magnitudes in a trinary sequence are used for the asymmetrical operation. The low-frequency modulation scheme is applied for the switching control where the switching angles are pre-calculated. The mathematical formulations for the switching are also considered to reduce the total harmonic distortion (THD) at the output. The proposed topology is also found to be superior in terms of the required number of switches per output level and total blocking voltage compared to conventional and recently reported MLIs. With these merits, real-time installation of the proposed topology will potentially require lesser space and become cheaper. The feasibility of the proposed topology is validated for its 9-Level and 17-Level operations through experimental verification on output characteristics, THD, blocking voltage, power-sharing and efficiency.

Multi-level inverters (MLIs) have been widely used in recent years due to their various advantages in industrial and grid-connected applications. Traditional MLI topologies are being hampered by the rapid surge of renewable energy systems (RES) as a result of performance difficulties such as poor power reliability, an economically unviable structure, and a lack of efficiency. These difficulties are due to the traditional MLI topologies’ inability to keep up with the increasing demand for RES. Because of concerns about performance and limitations posed by classic MLI topologies, researchers have found themselves driven to the idea of building innovative hybrid MLI topologies. This study provides a comprehensive analysis of multilevel inverter systems that are wired into the main power supply. Grid-connected inverter types and their configurations are discussed in depth in this review. Diverse multi-level inverter topologies, as well as the different approaches, are divided into various categories and discussed in depth. Additionally, a number of control reference frames for inverters were brought forward for discussion. Furthermore, different inverter control strategies were investigated, followed by a tabular summary of recent developments in the inverter-related literature for the convenience of the readers. Moreover, the recently proposed grid-connected multi-level inverter systems were discussed including their findings and innovations. In conclusion, a brief description of the study’s scope was offered and research directions for future studies were provided.

In this paper, a perturb and observe (P&O) based voltage regulator (POVR) and a capacitor compensator (CC) circuit are proposed for the implementation on 31-level asymmetrical switch-diode based multi-level DC-link (MLDCL) inverter. Since the application of MLDCL in a standalone photovoltaic (PV) system requires constant DC voltages from PV panels, the POVR strategy is deployed to regulate the voltage along with the capability to deliver the maximum power at full load. Boost DC-DC converters are used as the interface between the panels and the inverter for the POVR operation. The results show that POVR is capable of achieving the desired fixed DC voltages even under varying environmental and load conditions, with a steady 230 V at the output. At full load, the standalone system successfully delivers 97.21% of the theoretical maximum power. Additionally, CC is incorporated to mitigate voltage spikes at the output when supplying power to inductive loads. It successfully eliminates the spikes and also reduces the total harmonic distortion (THD) of output current and voltage from more than 10% to less than 5%, as recommended in IEEE 519 standard.Index Terms--Multi-level inverter, photovoltaic (PV) system, maximum power point, voltage regulator, capacitor compensator (CC).

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This paper presents a comparative evaluation of multilevel DC link inverter of photovoltaic (PV) renewable energy system using either symmetrical or asymmetrical dc sources. The four units of dc source can have the same dc voltage level, ie 81.32 V, resulting in symmetrical dc sources. The asymmetrical dc sources consist of input dc voltages in binary sequence, 21.68 V, 43.37 V, 86.74 V and 173.48 V. The boost converters with maximum power point tracking (MPPT) capability which is regulated by perturb and observe (P&O) based control are connected between the PV panels and the four dc sources. The varying dc voltages from the PV panels are regulated to track the maximum power available regardless of the irradiance and temperature conditions. The symmetrical dc sources will facilitate the generation of 9 levels of staircase ac waveform rms of 230 V after the H-bridge inverter. Whereas, the asymmetrical dc sources are able to produce 31 levels of staircase ac waveform also with rated rms 230 V. Detailed analysis and comparison on the powers, ac output voltage, output current, total harmonic distortions, and MPPT achievement are described.