Designing Power Electronic Interfaces and Microsource Controllers for a MicroGrid
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Date
2017-09
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Developing a Microgrid (MG) system supplied with feasible integrated
microsources, such as renewable energy sources and fuel cell, is one of the
major solutions to be envisaged in terms of the current trend of power
demand, i.e. efficient, environmentally friendly and relatively cheap means of
power generation. In a Microgrid the most indispensible devices are the Power
Electronic Interfaces and Controllers which regulate electrical parameters of
the microsources.
This research provides comprehensive overview, design and modelling of
Power electronic interface (PEI) and Microsource Controllers (MCs) for a
Microgrid supplied with Photovoltaic (PV) and Integrated Solid Oxide Fuel
Cell/Gas Turbine (ISOFCGT). The PEIs to be designed includes Inverters and DCDC
boost
converter
for
the
three
microsources,
PV,
SOFC
and
GT,
and
rectifier
for
the
Gas
Turbine
(GT)
unit.
To
avoid
use
of
transformer
in
the
MG,
two-stage
DC-DC
boost converter is used. For the ease of controlling and reduction of
THD, SPWM technique of inversion is applied.
In designing Microsource Controller a control technique known as Droop
control, in which active and reactive powers are controlled during gridconnected
mode
of
operation
of
the
Microgrid,
and
voltage
and
frequency
are
controlled
in island mode, is considered as a better option. By doing so the
control of microsources is distributed and proportional power sharing among
microsources is facilitated so that reliability of control is ensured as there is no
central control unit which needs communication facilities.
In the Microgrid the PV is not dispatchable unless it is backed by battery
storage system due to the intermittent nature of the solar power. But the cost
of battery for PVs is very expensive and makes the system sophisticated due to
power electronic interface for charging and other ancillary devices like charge
controller. There is the possibility of not to use the battery and the ancillary
devices by using the SOFC microsource instead of the battery storage system
when the solar power is reduced or completely unavailable. So this thesis also
considers the possible mechanism of sensing the intermittency of the solar power in such a way that the SOFCGT can take over the PVs in partial or
completely.
The designed PEIs could make the microsources to be integrated in to the
proposed MG by converting their original DC and high frequency AC sources in
to standard three phase AC wave forms of 380 V and 50 Hz. Also using the
designed Microsource Controller it is possible to control V, f, P and Q by
ensuring proportional power sharing among the microsources.
MATLAB/SIMULINK-Simpowersystem is used to simulate the designed PEIs and
the MCs based on a model Microgrid so that the performance characteristics
of the two systems can be demonstrated practically.
Description
Keywords
Microgrid, Microsource, Microsource Controller, Power Electronic Interface, Inverter, DC-DC converter, Rectifier, Droop Control, Photovoltaic, Integrated Solid Oxide Fuel cell/Gas Turbine