In the course of the past three decades, the generation and consumption of energy have increased globally to some exceptional degrees. On an everyday basis, a large amount of energy and power is being utilized for many applications that are linked to residential, commercial and industrial processes. There are many reasons that compel greater attention on energy sources that are renewable, including the ever-increasing Renewable energy sources provide pollution-free and environmentally sustainable alternatives to conventional sources. Source: Adobedemands of today’s world for power, power crises associated with shortages of conventional sources and the impact of these conventional sources on our earth and environment

The energy sources that are renewable, like solar and wind, provide alternatives to conventional sources. These energy sources are pollution-free, environmentally sustainable and technologically efficient.

However, existing grid networks are incapable of handling the transmission and distribution of high renewable energy penetration levels. Complexities stem from interconnections of different types of power generation sources and systems, interconnections of various types of transmission lines and transformers, and the changing nature of different loads.

The stability and power quality of power systems are impacted by the interconnection of impulsive nature of various generators, load fluctuations and the effects of loading in transmission lines. Keeping these things in mind is not an easy task, as it is quite difficult to reliably maintain a healthy power system, regardless of various uncertainties. Before getting started with power quality improvement with a renewable energy source, a review of the definition of renewable energy is in order.

Renewable energy can be defined as the energy that originates from natural resources, which are renewed on a human timescale naturally, for instance, light from the sun, wind energy, rain, tidal energy, waves and geothermal heat. Renewable energy resources can be found in wide geographical areas as compared to other energy sources.

Wind and solar as renewable energy sources

Wind power is harnessed by means of either a windmill or wind turbine. The mechanical energy as a rotation of the wind wheel is generated by the kinetic energy of the wind stream and after that electric energy of the generator is produced by the conversion of the mechanical energy into electric energy. For this purpose, generally, wind turbines with a horizontal axis are used. The maximum practical capacity of a wind turbine is about 2 MW to 4 MW. These units have a hub height of 60 m to 100 m and a wind wheel diameter of about 60 m to 80 m.

Small wind turbines offer outputs of about 0.1 kW to 100 kW and for large-scale applications, many wind turbines provide capacities of 100 kW to 2,000 kW. In some power systems, solar panels can be deployed to augment generating capacity. A basic system consists of the following components:

• The photovoltaic (PV) modules
• Mechanical and electrical connections
• Mountings
• Means of regulating the electric output
• Means of modifying the electric output

The photoelectric effect is the basic principle behind the PV cell operation. In the photoelectric effect, due to the absorption of sunlight of some specific wavelength, the electrons from the valence band get ejected. Electrons that absorb energy greater than the bandgap energy of the semiconductor jump to the conduction band from their valence band. Hole electron pairs are created in the illuminated region of the semiconductors, and are free to move in the conduction band.

These free electrons are induced to move in a particular direction by the electric field action present in the PV cells. The electrons are now bound to flow along a desired path and by the connection of a metal plate on the top and bottom side of the PV cells, the current can be drawn for external use as well. The required power is produced by this current and voltage.

Power configurations with these renewable energy sources are equally important. Power electronics technology affords scope to use these renewable energy resources in various configurations. With the use of power electronics interfaces, we can connect the renewable sources with a distribution grid or we can also interconnect it with other generators, storage systems and loads in microgrids.

It is worth mentioning that a microgrid is not the same as the main grid system. A main grid system is considered to have unlimited power so that system stability is not affected by load variations. For microgrids, abrupt and large variations in the load might account for voltage transitions of large magnitude in the AC bus. Furthermore, non-linear load proliferation can reduce the power quality indicators, for instance, computation technique or switching power converters, especially in microgrids. In the grid, the quality of power is also affected by the non-linear loads but as far as microgrids are concerned, this can be even worse under the same conditions.