CHAPTER 6
CONCLUSION
6.1 CONCLUSION
This thesis presents a possible solution for power quality issues in a
Microgrid
connected
utility
and
fixed
speed
induction
wind
turbine
generator(FSIWTG). This solution can be achieved by integrating the UPQC and
Matrix Convertercalled Universal power line manager (UPLM). This can do
simultaneous compensation of voltage imbalance, voltage sag, voltage swell, control
of reactive power and frequency regulation.
To achieve the research objectives, the work focused on two main areas of
the investigation. Firstly it mitigates the power quality issues of the matrix
converter’s input current harmonics and output voltage harmonics. Secondly the
integration of the matrix converter and Unified Power Quality Conditioner is
implemented for regulation of the Microgrid’s frequency, mitigation of voltage sag,
voltage swell, current harmonics and control of power flow.
Based on the simulation results given in the second chapter it can be
concluded that the total harmonic's level of the input current is found to be 60 %.
Even after a passive active filter is implemented it does not minimize the harmonics
efficiently. After that the shunt active filter (SAF) method of compensation is
implemented in the matrix converter for power quality improvement. The shunt
active filter strategy reduces up to 30 % of higher order harmonic components. When
the shunt active filter system is operated in a matrix converter the current harmonics
are removed effectively when compared to the passive filter’s implementation. After
that the power quality issues of the matrix converter’s output voltage is analyzed, and
it is found that the matrix converter delivers voltage harmonics and that the total
harmonic distortion level is 60 %. After the implementation of the passive filter it is
found to minimize the matrix converter’s output voltage harmonics, but not
efficiently. The series active filter (SAF) method of compensation implemented in
the matrix converter results in the improvement of the power quality in matrix
converter’s output voltage. It does eliminate 80 % of harmonic components. Based
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on the final
simulation, the research concludes that two active filters i.e. a
combination of a series active filter and a shunt active filter (Unified Power Quality
Conditioner) simultaneously compensates the current and voltage variations and
mitigates the harmonics in the matrix converter’s input and output side.
The simulation results presented in chapter 3shows that the voltage sag,
voltage swell and supply frequency variations affect the performance of a fixed
speed induction
wind turbine generator. The basic
model of custom power
equipment, namely a constant frequency unified power quality conditioner (CFUPQC) has been proposed. The proposed method can regulate the supply frequency
efficiently using a CF-UPQC’s matrix converter. Based on the simulation results , it
can be concluded that the proposed system has the ability to control all the important
power quality issues. The CF-UPQC also works effectively in the FSIWTG
connected to a Microgrid system. This new power quality conditioner compensates
the voltage sag, voltage swell, supply frequency and mitigates the current harmonics
in a FSIWTG. But through the simulation result it is found that the CF-UPQC does
not control the real power flow. Because without power flow control micro grid
frequency varies.
In the fourth chapter the CF-UPQC is further modified (called UPLM) to
control the power flow in addition to regulating the load frequency. Based on the
simulation results described in this chapter it can be concluded that the UPLM
effectively mitigates voltage sag, voltage swells and supply frequency variations.
Moreover the UPLM effectively controls the power flow in a Microgrid connected
utility. This new power quality conditioner also mitigates the voltage sag, voltage
swell, supply frequency, current harmonics and controls the flow of the real and
reactive powers in a Microgrid connected FSIWTG. The simulation shows that the
UPLM behaves satisfactorily during the steady-state and transient periods. The
proposed system effectively mitigates all important power quality issues present in a
Microgrid connected utility and FSIWTG.
The final chapter shows the interfacing of a Microgrid (60 Hz) with a main
grid (50 Hz) by using a UPLM . The active power flow from the Microgrid can be
controlled at the PCC of a main grid to a desired value determined by the UPLM’s
controllers. With the change in the load’s demand the micro sources operate at
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different frequencies causing an increase or decrease in the Microgrid frequency.
However, the UPLM constantly monitors the Microgrid frequency and if any
frequency drop is not restored in the Microgrid UPLM performs rapid load sharing to
main grid achieve power balance in order to ensure the Microgrid’s frequency
stability. The simulation results show that the proposed system has the ability to
transfer the power flow between the main grid and the Microgrid with a preset value.
The proposed system injects the real and reactive power to the Microgrid and the
PCCof main grid and maintains the frequency and voltage as constant and it is
validated through Matlab/Simulink software.
6.2 LIMITATION AND FUTURE WORK
At the end of the thesis it would be mandatory to give suggestions as to how
this research can be continued and what aspects may need to be investigated further
on.
As was made clear in this thesis no artificial intelligence control system
investigated
for
UPLM’s control system. This did not really impair the
investigations but further work should be dedicated to building a control system .
A laboratory prototype of the proposed UPLM system should be built and
tested to verify the validity which hasn’t been done this thesis. Results elaborated in
this thesis are all based on the same simulation program. To confirm the results,
simulations for larger and differently configured test systems should be performed.
The used program MATLAB/SIMULINK is definitely a widely spread
software in research and industry, but especially for industrial applications there are
other software tools that should be considered too. A well known program used
intensively in industry is PSS/E™ that allows for instance dynamic simulations of
very large power systems. It should be a next step to implement and affirm the
functionality of our developed control concepts in PSS/E™.
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