Most of the countries in the world are concentrating on renewable energy generation, due to day-day increase in population increasing the energy demand, also to make their environment sustainable. With the many of features, use of megawatts rating solar photovoltaic (PV) power plants are becoming more popular for upgrading the existing power generation throughout the world. Moreover, among the existing renewable energy generations, solar power is the primary choice to meet the rapidly increasing demands; since solar PV plant installing time is relatively quick, say about in 3- 4 months, compared to conventional (thermal, hydro & diesel) plants which may require about 3-4 years. The low voltage (270‒700V) power converters require a filter and a step-up transformer for interconnecting the local grids with solar PV power plants. The advances in power converters without transformers and filters have recently become more attractive for solar PV power plants connected directly to grid. The study of this article describes the essential requirement and the technological developments in the design of power electronics converters, together with their modulation schemes to integrate solar power directly with standard power grid. This article, review ongoing research activities and the probable directions for the future research in developing inverters for cost-efficient grid connected solar PV plants

Philosophers and industries have focused on designing multilevel inverters, which use significantly fewer power switches and dc sources to achieve high power, low switching, and less harmonic output distortion for medium voltage applications. Even so, these multilevel inverters have some downsides like the use of many electronic components, electromagnetic interference (EMI), bulky driver circuit complexity, significant reverse recovery times, and voltage balancing issues. A modern asymmetrical multilevel inverter with fewer switches and drivers than standard topology is introduced in this article. The powerful analogy addresses traditional inverter topologies of a similar structure. The proposed MLI is relatively simple and easy to extend for many output levels. The proposed design of MLI is implemented for 15 level output with precise and high-quality near sinusoidal waveform using seven switches, three dc sources and three diodes and hence the volume, cost and driver circuit complexity is considerably reduced. The novelty in the proposed topology is that reduced ON state semiconductor switching devices. The output of the MLI is evaluated with the parameter of total harmonic distortion (THD). To minimize the THD, optimization algorithms such as GA, PSO, WOA and HHA were implemented at fundamental switching PWM control method. The comparative analysis of these algorithms on proposed inverter performance is integral for this research. The efficacy of this topology enhances the integration of renewable energy sources.

Multilevel inverters have great scope in current developments of grid-connected solar PV systems. Two-level inverters are the simplest kind of multilevel inverter available (MLI). As the number of output levels is raised, the total harmonic distortion decreases. In classic MLI topologies, more electronic components are utilized to get higher-level outputs, which raise the cost, complexity, and volume of typical MLI installations. By reducing the design components, the cost of the system will be reduced. Furthermore, the two- and three-level inverters produce constant dv/dt output, which increases the stress on the power switches. This research proposes an asymmetric MLI topology that is suitable for PV applications and utilizes less number of DC sources and switches. The proposed inverter is controlled by selective harmonic elimination-based pulse width modulation (SHEPWM) to eliminate the lower-order dominant harmonics. The nonlinear equations produced by the SHEPWM are solved for the switching angles of the proposed inverter using the Newton-Raphson (NR) method and particle swarm optimization (PSO) method for various modulation indexes. The performance of the proposed inverter is analyzed based on the total harmonic distortion (THD) of the output for different operating levels of the inverter by comparing similar topologies in the literature. The THD obtained by the NR method is 7.3% and by using PSO is 4.23% at 0.9 modulation index.

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