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ISSN: 2347-9302 (Online)
IJEEEAR Vol. 2, SP-1, Feb. 2014
SOLAR POWER PLANT AS REACTIVE
POWER COMPENSATOR OF THREE PHASE
ELECTRICAL NETWORK USING
TRANSFORMERLESS INVERTER
TOPOLOGY
S.Saravanalingam1, S.Boobalan2
M.E. Student, 2Assistant Professor
Department of EEE,
Mohamd Sathak Engineering College,Kilakarai
1
[email protected], 2 [email protected]
1
Abstract—This paper discusses the real and reactive power
management of the three phase electrical network. The control of
real and reactive power can be achieved by using a solar panel
based transformerless inverter. The transformerless inverter
topology contains a voltage source inverter (VSI) along with HBZVR technique. The solar panel is used to support real and
reactive power and a proportional-integral (PI) controller is used
to maintain a constant voltage at the dc-bus of the voltage source
inverter working as STATCOM. Switching of VSI is achieved by
controlling source currents to follow reference currents using
PWM control. The solar based VSI is interconnected in the
consumer side hence it eliminates the additional transmission line
and reduces the weight and size of the system. Thus the
transformerless inverter based solar power plant supports real
power in day time and in night time it act as a static compensator
(STATCOM) and provide reactive power at night time. This
topology is simulated under MATLAB environment using
simulink with unbalanced load. The model is performed for a
three phase electrical network connected with transformerless
inverter along with solar panel which was act as a STATCOM.
Keywords—STATCOM, Transformerless inverter topology,
photovoltaic solar panel, proportional-integral (PI) control scheme.
I.
INTRODUCTION
In the past few years solar energy sources demand has grown
consistently due to increasing efficiency of solar cells,
manufacturing technology improvement and economic of
scale. The installation of solar panel to the consumer end
(grid) can be done using various topologies and it is favor to
the consumer. As a result a new topology for grid connected
inverters with higher efficiencies and lower manufacturing
costs has been developed [1].
Transformerless topologies have several associated benefits
against designs using topologies with line or high frequency
transformers. From a practical perspective, transformerless
topologies reduce the size and mass of inverters. The initial
cost of the inverter is also typically reduced. Perhaps the most
advantageous aspect of transformerless inverters is their
increased efficiency at low and partial load. As no reactive
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power is required for the magnetizing of the transformer
windings, losses are reduced and the power factor is also
typically higher than that inverters using transformer [2].
The consideration while constructing a solar panel is the
power storage and dc to ac conversion. Since the Photovoltaic
cell is directly connected to the grid using transformerless
inverter there is no need of storage [3]. And in case
transformer is omitted the generated common mode behavior
of the inverter topology greatly influences the ground leakage
current through the parasitic capacitance of the photovoltaic
cell.
The utilization of solar panel as a STATCOM is the modern
approach. In the night time there is no real power generation in
solar panel and it is not usable. To overcome this problem the
photovoltaic solar panel act as a STATCOM and it supplies
reactive power to the consumer load. Thus the need for
additional STATCOM for night utilization was avoided. By
using transformerless topology the efficiency of the whole
system is increased by 1%-2% [4]. The important advantage of
using transformerless inverter with solar panel is higher
efficiency, smaller size and weight compared to PV system
that has galvanic isolation.
II.
a.
PROPOSED WORK
System model
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A typical solar panel along with three phase load is shown in
fig 1. during the day time the amount of real generation is
higher. Hence the solar panel can inject real power to the grid.
The point of connection of the solar panel to the distributed
generator is called point of common coupling (PCC).The
output of solar panel is dc source and the amount of generation
depends on the radiation. In this system configuration a
transformerless topology is used, to improve the input power
generation a boost converter is implemented.
In night time there is no power generation from solar farm
and the farm is not usable. To overcome this problem the solar
panel can be used as a STATCOM and it will support reactive
power to the grid. This can be achieved by using a DC link
capacitor which was interconnected with transformerless
inverter. A battery is connected with the DC link capacitor to
provide initial voltage. A switch is used to isolate the solar
farm from the inverter at night time.
b.
TRANSFORMERLESS TOPOLOGY ANALYSIS
PV systems connected to the low voltage grid have an
important role in distributed generation systems. In order to
keep up with the current trends regarding the increase in PV
installations, PV inverters should have small weight and size,
due to residential installations and High efficiency. This can
be achieved by using transformerless inverter. It consists of six
IGBT diodes and a switch. According to the level of power
conversion one or more stage can be designed. A three phase
voltage source inverter along with HB-ZVR topology is
implemented in this topology. Depending on the voltage level
of the PV array a voltage boost up stage can be present, which
raises the DC link voltage of the inverter to the required level.
This is the case of the two stage topology, where the PV
system includes the DC-DC boost converter followed by DCAC grid side inverter. In case the voltage level from the PV is
lower than the required minimum then a boost converter is
added between the PV array and the inverter. This boosts the
input voltage from PV so the inverter has a DC link voltage
around 400v for single phase and 700v for three phase grid
connection.
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IJEEEAR Vol. 2, SP-1, Feb. 2014
Fig.2. Model of HB-ZVR topology
c.
HB-ZVR proposed Topology
A new topology called H-Bridge Zero Voltage Rectifier (HBZVR) is proposed, where the zero voltage is achieved by
short-circuiting the grid voltage through the LCL filter, using a
diode rectifier bridge and one switch. During the zero voltage
vector the mid-point of the DC link is clamped to the shortcircuited grid. The topology is detailed in Fig. 2, showing the
bidirectional switch, as an auxiliary component with a grey
background. This bidirectional switch is clamped to the
midpoint of the DC-link capacitors in order to fix the potential
of the PV array also during the zero voltage period, when T1T4 and T2-S3 are open. An extra diode is used to protect the
lower DC-link capacitor from short-circuiting.
During the positive half wave, T1-T4 is used to generate the
active vector, supplying a positive voltage to the load. The
zero voltage state is achieved by turning ON T5 when T1-T4
is turned OFF. The gate signal for T5 will be the
complementary gate signal of T1-T4, with a small dead-time
to avoid short-circuiting the input capacitor. During the
negative half wave of the load voltage, T2-T3 are used to
generate the active vector, and T5 is controlled using the
complementary signal of T2-T3 and generates the zero voltage
state, by short-circuiting the outputs of the inverter and
clamping them to the midpoint of the DC-link.
d.
COMMON MODE VOLTAGE REJECTION
The common mode voltage generated by a topology and
modulation strategy can greatly influence the ground leakage
current that flows through the parasitic capacitance of the PV
array. Generally, the grid does not influence the commonmode behavior of the topology, so it can be concluded that the
generated common-mode voltage of a certain inverter
topology and modulation strategy can be shown using a simple
resistor as a load. Of course in case of transformerless PV
systems connected to the grid, the common-mode voltage will
have a sinusoidal shape with the grid frequency and having
amplitude half of the grid voltage peak.
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IV.
(1)
(2)
(3)
(4)
SIMULATION STUDY
Figure 4 shows the simulink model for unbalanced load with
STATCOM. This system is simulated under, an rms voltage
380V and frequency 50Hz is set and connected with an
unbalanced load. The solar panel injects the real power in the
day time which is connected at the load side. Then in night
time, the STATCOM injects the reactive power to the load by
comparing the transmission line output using a PI controller. If
the generated power in STATCOM is higher, then the
consumed power from the source side (Grid) should be
reduced.
From the above equations 1-4, the common mode voltage is
constant for all switching states. Therefore the leakage current
through the parasitic capacitance is very low.
III.
SOLAR PLANT AS STATCOM
Fig.4. Simulink model of the proposed system
Fig.3. solar plant as STATCOM
The Static synchronous compensator can act either a source or
sink of reactive power. If connected to a source of power it
can also provide active AC power. When the terminal voltage
of the voltage source inverter is higher than the AC voltage at
the point of connection the STATCOM generates reactive
power. A proportional–integral (PI) controller is composed to
regulate the voltage. This controller regulates the PCC voltage
and the dc-bus voltage across solar panel inverter capacitor at
a constant level. The PCC voltage is regulated by providing
leading or lagging reactive power during bus voltage drop and
rise, respectively. A phase-locked loop (PLL) based control
approach is used to maintain synchronization [5] with PCC
voltage. A hysteresis current controller is utilized to perform
switching of inverter switches. To facilitate the reactive power
exchange, the dc-side capacitor of solar panel is controlled in
self-supporting mode, and thus, eliminates the need of an
external dc source (such as battery).
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The tabular column 1 shows the amount of real and reactive
power consumption and injection in day and night time. From
this, when the solar plant act as STATCOM it can support
reactive power to the grid and in the day time the solar plant
inject real power to the grid. Thus the amount of power
consumption from the source side is reduced by using solar
plant.
Table 1: Power generation in source and load side with and
without Solar Plant
PGen
in
source (W)
P Solar (W)
PDemand
in
load (W)
QGen
in
source(VAR)
IJEEEAR 2014
Solar Plant
as a Real
Power
source
3214.00
Solar Plant as
STATCOM
700.00
-
3812.00
3811.00
3921.00
1719.00
3812.00
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IJEEEAR Vol. 2, SP-1, Feb. 2014
QSolar (VAR)
-
2213.00
QDemand
in
load (VAR)
3932.00
3932.00
Fig 4.1 shows the source and STATCOM voltage, when the
solar power plant injects real power in the day time. This
graph shows that inverter voltage is higher than the source
voltage, so that the STATCOM can inject real power.
This work is focused on the optimization of photovoltaic
energy as well as its injection in three phase electrical network
through an inverter with minimum possible losses. This work
proposes the real and reactive power compensation using solar
power plant with no additional transmission lines and passive
compensating devices and improved power factor at balanced
and unbalanced load condition. The adopted approach gives
the real and reactive power support to the system during day
and night and helps to reduce the cost of additional
transmission lines and compensating devices. Also the
proposed VSI based solar STATCOM improves the power
factor and reduce the reactive power drawn from the
generator.
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Fig. 4.1 Source and STATCOM voltage in day time
Fig 4.2 shows the source and STATCOM voltage, when the
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STATCOM.
Fig. 4.2 Source and STATCOM voltage in night time
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V.CONCLUSION
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