An energy system is a structure of network consisting of energy sources, storage,
transmission, distribution, and consumption of energy. The basic primary use of energy is
for transportation, heating, industrial and electricity sectors. These sectors are generally
based on traditional fossil fuels. However, the issues, challenges and causes are evolving
due to severe climatic conditions prevailing in the world, and it is important to use
enormous amounts of renewable energy systems to ensure carbon negativity by
encouraging clean and green energy replacing fossil fuels with solar, hydro and wind
energy systems.
Due to population growth, rapid rise in demand can be seen and to meet the demand,
power generation must be correspondingly increased, and hence more renewable energy
systems must be infused into the power grid to meet the rising demand for power
generation. Over the past two decades, deregulation and transition towards the smart grid,
leading to structural changes in the power grid, increased the complexity in the network.
The power from injected renewable is intermittent in nature and hence it is unreliable.
Due to this supply demand mismatch occurs leading to wide frequency oscillations in the
system. However, owing to the complicated structure of the system, regulating the grid
frequency is a major control problem and sometimes it may also give rise to power
disruptions. Among all the renewable energy sources wind energy sources have more
demand due to their availability. Presently, wind energy systems are integrated into the
grid through DFIG and back-to-back converters. As these converters operate at low
voltages, an additional edge of reducing capital cost including protective devices, cost of
maintenance, total harmonic distortion can be achieved. The back-to-back converters
comprise of two converters operating in rectifying and inverting modes respectively.
In general, inverters are classified based on various characteristics like type of output,
single-phase inverters (SPIs) and three phase inverters (TPIs), nature of input source,
voltage source inverters (VSIs) and current source inverters (CSIs). The shunt capacitor
at the input terminals reduces the dc ripple content particularly second harmonics which
are prone to harm the source. This leads to a smoother dc voltage. Though solid-state
power electronic switches, viz. IGBTs and MOSFETs have brought about significant
merits in control complexity, they produce harmonics which are quite detrimental to the
performance of the system.
Harmonic voltages affect the power network and also the critical equipment in the
vicinity of the harmonic source. This may result in erroneous operation of the sensitive
loads. Hence, harmonic content must be reduced to an acceptable level and before
designing a converter, one should consider standards of THD constraints. Nevertheless,
completely eliminating harmonic currents from an electrical system is very challenging
and difficult but can be reduced significantly using harmonic filters. Most power
electronic converters generate distorted wave shape that can further be decomposed into
integral multiples of fundamental component. They can be eliminated using multilevel
inverters, by tuning the controller/adding the respective harmonic filters.
