Page 114 - Hybrid-Renewable Energy Systems in Microgrids

98 Hybrid-Renewable Energy Systems in Microgrids

be classified as technical difficulties related to control and protection system, regulation
challenges and client cooperation challenges. Subsequently, in this section depicts the
control techniques and its specialized technical challenges for an inverter in the microgrid.

2 Grid inverter synchronization

Distributed energy resources (DERs) have become more popular due to numerous
technological been development compared to oil based energy production. It has some
advantages such as less emission on greenhouse gases, less maintenance cost if plugged-
in hybrid electric vehicle, smart energy infrastructure, etc. The inverter is implemented
to connect with the DERs to AC grid with the ultimate objective of sharing loads burden
and power by integrating power processing converter with power control strategies.
Synchronization method is one of the main technical challenges in the grid integration
[1,3]. It is used to secure the DG if grid network contains faulty cases and to get the
desired output voltage with improved stability of the power transfer during power shar-
ing. Phase locked loop (PLL) and trigonometric based on synchronous reference frame
PLL are the conventional methods to evaluate the grid parameters such as phase estima-
tion and frequency tracking of the grid connected inverters [3]. Recently, synchronous
method characteristics have been used in the controller strategy at multilevel program-
ming without having the PLL. This method is effectively utilized for power processing
method to synchronize the inverter with grid or other synchro-inverter.
Many techniques have been proposed to focus on the grid synchronization for bet-
ter power transfer from DERs to the conventional AC grid. The maximum method of
DERs supplies DC source with the storage batter bank inputs, which are integrated to
AC grid through the inverter with synchronization method. Sometimes, the distributed
generator is also operated during the standalone operation in which voltage source
inverter or current source inverter for sending the power to the loads. Here, the voltage
source inverter requires an external reference to keep it synchronized even if it works
in AC input source systems. This is especially with regards to frequency and voltage
droops for outlining the microgrid performance. The inverter can inject a good quality
power into the grid even if there is any change in voltage, frequency and phase- angle
on the grid side when maintaining the grid-inverter synchronized condition.
The concept of power distribution between DG converter and the grid is shown in
Fig. 6.1. The exchange of power occurs when the real power is transferred with phase

Figure 6.1 Synchronous Generator bus connection model connected to an infinite bus.