19-06-2014, 11:43 AM
Retrofitted Hybrid Power System Design With Renewable Energy Sources for Buildings
Abstract
Most of the research on Hybrid Power Systems
(HPS) is to provide an economical and sustainable power to the
rural electrification. This paper focuses on the design of an HPS
for the building which is a part of the urban electrification. In
the developing countries, the rate of increase in the demand is
more than the rate of increase in the supply, which is a major
challenge resulting in very frequent outages. There are number
of motives to build integrated and synergistic renewable energy
based HPS including environmental, economic, and social benefits.
Most of these HPS topologies use inverters to interface the
renewable sources to the buildings with an offering of low quality
power. Hence, modern sustainability initiatives call for a design
for both new HPS and retrofitting of an existing HPS topology.
With this aspect, this paper describes the topology of retrofitting
HPS with dc Motor-Synchronous Generator set instead of the
use of inverter to an existing building power system. This can
improve the power quality, reliability of the supply, and ensures
stable plant operation. The proposed HPS topology can be used in
small-to-medium sized isolated constructions like green buildings,
industries, and universities. Different renewable energy sources
like Photo Voltaics (PV), Wind Power (WP), and Fuel Cells (FC)
are integrated to form HPS. An energy management and control
algorithm is proposed to use the energy sources optimally to
upgrade these buildings with more reliability and efficiency. The
modeling and simulation is done using MATLAB/Simulink
INTRODUCTION
ELECTRICAL energy is essential to everyone’s life no
matter for whom or where they are. This is especially true
in this new century, where people aim to pursue a higher quality
of life. It is now a globally accepted reality that electrical
energy is fundamental for social and economic development.
Unfortunately, still one third of the world’s population lives
in developing and threshold countries and has no access to
electricity [24]. It has been estimated that the world population
will reach eight billion by 2020. And this growth is mostly in
Manuscript received November 27, 2011; revised April 29, 2012; accepted
August 28, 2012. Date of publication December 10, 2012; date of current version
December 28, 2012. Paper no. TSG-00622-2011.
Y. J. Reddy, Y. V. P. Kumar, and A. Ramesh are with the Honeywell Technology
Solutions Lab (Pvt) Ltd, Hyderabad, Andhra Pradesh, India (e-mail:
jaganmohan.reddy[at]honeywell.com; yvpavan.kumar[at]honeywell.com;
anilkumar.ramsesh[at]honeywell.com).
K. P. Raju is with the Department of Electronics and Communication
Engineering, Jawaharlal Nehru Technological University Kakinada, Andhra
Pradesh, India (e-mail: padmaraju_k[at]yahoo.com).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TSG.2012.2217512
developing countries [25]. So, to supply the electricity requirements
for them, the extension of utility grid is complicated
and expensive due to geographical and economical barriers.
Besides, the need for unrelenting increment in energy production,
diminution in currently reliant fossil fuel resources, and
the regulations to reduce the emissions is the foremost
factor for stipulating the growth of “green energy” generation
systems. In such circumstances, an alternative is to use locally
available renewable energy sources (e.g., solar, wind, hydrogen,
and etc.) and combine to implement modular, expandable, and
task-oriented systems known as the HPS. HPS combine two or
more energy conversion devices, or two or more fuels for the
same device, that when integrated, overcome the limitations
inherent in either.
Grid connected mode
In general, most of the renewable energy resources operate
on dc. Hence, in a centralized ac-bus architecture all the dc
sources require as many inverters to connect them to the ac
bus. This leads to system power quality issues.
• Themain drawback of distributed ac-bus architecture is the
difficulty in controlling the system when the diesel generator
is in off mode.
• The centralized dc bus architecture eliminates the requirement
for more inverters, leading to a chance of improving
power quality.
“Cumulatively, these architectures lag in terms of power
quality, which limits the system to connect to the central utility
grid. Also, they lack in effective energy management between
energy sources and loads to increase the utilization, reliability,
and stability of the supply.”
The proposed retrofittedHPS architecture can overcomemost
of these limitations and facilitate grid-connected mode of operation
to improve the supply reliability to buildings.
RETROFITTED HYBRID POWER SYSTEM ARCHITECTURE FOR BUILDINGS
The HPS investigated and retrofitted in this paper consists of
renewable energy sources such as PV, FC, WP, and also storage
batteries. Most of these (PV, FC, and Batteries) are producing
dc output. Hence, the centralized dc-bus architecture for grid
connected HPS shown in Fig. 2© has been chosen in this paper
Methodology Used in the Design
The methodology that is implemented in this paper uses dc
Motor-Synchronous generator set instead of Inverter between
the dc bus and the loads/microgrid in the conventional HPS for
buildings. That is, exactly in between the dc bus and the building
loads/grid as shown in the following Fig. 3.
Also, the proposed EMCU takes the power demand and the
power generated at any instant as inputs. Based on these two
factors, it can switch the available resources to meet the instantaneous
connected load. This reduces the wastage of energy,
and hence unit generation cost, also provides the facility to run
the building power generating system in parallel with the utility
power grid.
Proposed System Description
In the system shown in Fig. 4, the output of the renewable
sources cannot feed the load directly, as the voltage fluctuations
due to environmental variations are large enough to damage the
concerned load [14].
The (dc-dc)/(ac-dc) converters are used to condition these
voltages. Thus, the varying voltage can be brought to required
value and specified variations limits by varying the duty ratio of
the converters, and then connected to dc bus. The dc bus voltage
is used to drive the dc motor, coupled to the synchronous generator.
Electrical power should be produced exactly at the same
time when it is demanded by building load. It may not be possible
for renewable energy sources to produce sufficient energy
to drive dc motor coupled to synchronous generator at all the
time, since their operation depends on varying natural conditions.
The WT output power varies with the wind speed, the PV
cell output power varies with both the temperature and irradiance,
and the FC output power varies with input fuel. So, the
diesel engine is coupled to synchronous generator as a standby
prime mover to avoid shortages of power. The dc motor, Alternator
and Diesel Engine are mechanically connected using a
clutch.
CONCLUSIONS
Conventional architectures of the renewable energy based
Hybrid Power Systems are majorly associated with power
quality issues as discussed in Section II. This is the primary
concern which leads for the novelty in this paper. The paper
is focused on the design of renewable energy based HPS with
power quality improvement and energy management features.
The methodology introduced is the use of a dc Motor-Synchronous
generator set instead of an inverter, to interface energy
sources with building loads/grid as shown in Fig. 13. To
have an optimum usage of the available resources, an EMCU is
designed. It works based on the total power generated and the
instantaneous load demand.
From the results obtained in Section VI (A&B), the following
conclusions have been made.