16-02-2013, 02:36 PM
A Hybrid Wind-Solar Energy System
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Abstract—
Environmentally friendly solutions are becoming more
prominent than ever as a result of concern regarding the state of our
deteriorating planet. This paper presents a new system configuration
of the front-end rectifier stage for a hybrid wind/photovoltaic energy
system. This configuration allows the two sources to supply the
load separately or simultaneously depending on the availability of
the energy sources. The inherent nature of this Cuk-SEPIC fused
converter, additional input filters are not necessary to filter out high
frequency harmonics. Harmonic content is detrimental for the
generator lifespan, heating issues, and efficiency. The fused multiinput
rectifier stage also allows Maximum Power Point Tracking
(MPPT) to be used to extract maximum power from the wind and
sun when it is available. An adaptive MPPT algorithm will be used
for the wind system and a standard perturb and observe method will
be used for the PV system. Operational analysis of the proposed
system will be discussed in this paper. Simulation results are given
to highlight the merits of the proposed circuit.
INTRODUCTION
With increasing concern of global warming and the
depletion of fossil fuel reserves, many are looking at
sustainable energy solutions to preserve the earth for the
future generations. Other than hydro power, wind and
photovoltaic energy holds the most potential to meet our
energy demands. Alone, wind energy is capable of supplying
large amounts of power but its presence is highly
unpredictable as it can be here one moment and gone in
another. Similarly, solar energy is present throughout the day
but the solar irradiation levels vary due to sun intensity and
unpredictable shadows cast by clouds, birds, trees, etc. The
common inherent drawback of wind and photovoltaic systems
are their intermittent natures that make them unreliable.
However, by combining these two intermittent sources and by
incorporating maximum power point tracking (MPPT)
algorithms, the system’s power transfer efficiency and
reliability can be improved significantly.
When a source is unavailable or insufficient in meeting the
load demands, the other energy source can compensate for the
difference. Several hybrid wind/PV power systems with
MPPT control have been proposed and discussed in works [1]-
[5]. Most of the systems in literature use a separate DC/DC
boost converter connected in parallel in the rectifier stage as
shown in Figure 1 to perform the MPPT control for each of
the renewable energy power sources [1]-[4]. A simpler multiinput
structure has been suggested by [5] that combine the
sources from the DC-end while still achieving MPPT for each
renewable source. The structure proposed by [5] is a fusion of
the buck and buck-boost converter. The systems in literature
require passive input filters to remove the high frequency
current harmonics injected into wind turbine generators [6].
The harmonic content in the generator current decreases its
lifespan and increases the power loss due to heating [6].
In this paper, an alternative multi-input rectifier structure
is proposed for hybrid wind/solar energy systems. The
proposed design is a fusion of the Cuk and SEPIC converters.
The features of the proposed topology are: 1) the inherent
nature of these two converters eliminates the need for separate
input filters for PFC [7]-[8]; 2) it can support step up/down
operations for each renewable source (can support wide ranges
of PV and wind input); 3) MPPT can be realized for each
source; 4) individual and simultaneous operation is supported.
The circuit operating principles will be discussed in this paper.
Simulation results are provided to verify with the feasibility of
the proposed system.
PROPOSED MULTI-INPUT RECTIFIER STAGE
A system diagram of the proposed rectifier stage of a
hybrid energy system is shown in Figure 2, where one of the
inputs is connected to the output of the PV array and the other
input connected to the output of a generator. The fusion of the
two converters is achieved by reconfiguring the two existing
diodes from each converter and the shared utilization of the
Cuk output inductor by the SEPIC converter. This
configuration allows each converter to operate normally
individually in the event that one source is unavailable. Figure
3 illustrates the case when only the wind source is available.
In this case, D1 turns off and D2 turns on; the proposed circuit
becomes a SEPIC converter and the input to output voltage
relationship is given by (1). On the other hand, if only the PV
source is available, then D2 turns off and D1 will always be on
and the circuit becomes a Cuk converter as shown in Figure 4.
The input to output voltage relationship is given by (2). In
both cases, both converters have step-up/down capability,
which provide more design flexibility in the system if duty
ratio control is utilized to perform MPPT control.