DYNAMIC
STABILITY ANALYSIS OF HYBRID SYSTEM INTEGRATED INTO A DISTRIBUTION POWER GRID

 

GAYATHRI MANGALAM

M.E.POWER SYSTEMS ENGINEERING

DEPARTMENT OF ELECTRICAL AND
ELECTRONICS

GOVERNMENT COLLEGE OF TECHNOLOGY

COIMBATORE-13

 

                  Dr.LATHA MERCY.E

                      ASSO.PROFESSOR

DEPARTMENT OF ELECTRICAL
AND ELECTRONICS

            GOVERNMENT COLLEGE OF TECHNOLOGY

COIMBATORE-13

 

 

Abstract— Dynamic stability analysis
of hybrid system comprising hydro power and solar power generation, integrated
into a distribution power grid.A Super Capacitor (SC) is utilized to smooth the
generated power delivered to the distribution power grid

Keywords—Hydro
turbine;Hydro generator;Solar panel;Boost

Converter;Super
capacitor;Utility grid;Power grid

                                                                                                                                                               
I.      Introduction

Renewable energy is collected from variable resources. It  often provides energy in electricity
generation. Solar and hydro energy play a major role in renewable energy
sources. Solar energy has the greatest potential of all the sources of renewable
energy. Solar energy is radiant light and heat from the sun that is harnessed
using a range of ever-evolving technologies such as solar heating, photo
voltaics,solar pumping, etc.., Water is the main soures of hydro power
generation. The kinetic energy of the flowing water strick the  blades or vanes, it starts turns inside the
hydraulic turbine, then, it converted into mechanical energy. In the hybrid
system of hydro and solar energy, to achieve the maximum power. When combining
both hydro and solar, power fluctuation will be occured. By using the super
capacitor  power fluctuation will be reduced
used to reduce kinetic energy.To balancing a two energy sources that will be
produce a unstable condition by using of supercapacitor to reduce this problem.

HYDRO ENERGY

Hydro power plant is a conventional renewable energy source. It has basically its two main sections, firstly the mechanical part
of the plant which includes hydraulic turbine, penstock, controller, hydraulic
servo motor, control valve etc.

 

Fig.1.Hydro Turbine model

Second part
of the plant is electrical section which mainly consists of generator and load.To analysis a generator part convert
mechanical energy to electrical power. HYDRO TURBINE
GOVERNOR is combination of hydraulic turbine and controller.Modelling of hydroturbine describing variation in flow and developed mechanical power
with respect to the turbine speed, gate opening and runner blade movement of
hydro turbine. Synchronous generators or alternators are
synchronous machines used to convert mechanical power to ac electric power.
Synchronous machines are used widely as generators of electrical power. Large
machines generating electrical power in hydro, nuclear or thermal power
stations are the synchronous generators. They can generate active and reactive
power and has an important role in voltage control

SOLAR ENERGY

Solar energy
has the greatest potential of all the sources of renewable energy and if only a
small amount of this form of energy could be used, it will be one of the most
important supplies of energy especially when other sources in the country have
depleted. Energy comes to the earth from the sun. The
solar panel can be used as a component of a larger photovoltaic system to
generate and supply electricity in commercial and residential applications.
Each panel is rated by its DC output power. Solar panels use light energy
(photons) from the sun to generate electricity through the photovoltaic effect.
The majority of modules use wafer based crystalline silicon cells or thin-film
cells based on cadmium telluride or silicon. The structural (load carrying)
member of a module can either be the top layer or the back layer. Cells must also be protected from mechanical damage and moisture.

 

SUPER
CAPACITOR

Supercapacitor is a modern energy
storing device, storing very high value of electric capacitance in a very
compact structure. They are rated in farads, and offers thousands of times
higher storing capacity than the electrolytic capacitor. They are also known as
Ultra capacitors and Double layer capacitors. Differs with the convention
energy storing methods of capacitors, that they are not made up of dielectric
material. They store energy in plates filled with double layer of same
substance.This allows for separating the charge without the need for a
dielectric, the plates are packed with a much larger surface area resulting in
high capacitance .The supercapacitor is ideal for energy storage that undergoes
frequent charge and discharge cycles at high current and short duration. Supercapacitors have much longer life
than that that Lithium batteries, normally of 10 to 20 years.Thay have very
high charging rate, can be charged within seconds. Supercapacitors can be
easily installed and offers easy interface with other devices with flexible
mountings.Super capacitors have very fast transient response as compared to the
commonly available lithium ion batteries.SC used to maintain a stable operation
of connecting two energy sources.

DISTRIBUTION POWER GRID

                An electrical
grid  is an interconnected network for delivering electricity from producers to
consumers. It consists of Generating stations,Transmission and Distribution.
Generation consist of hydro and solar power combination.To transmit a power
generation to distribution to maintain stable condition with help of super
capacitor.DC-link connected to the converter circuit that output passing
through the inverter. That inverter output is connected to the transformer(step
up) power deliver to the Transmission line. Two-way ?ows of electricity and
information could improve the delivery network is called an utility grid. The
protection system of a utility grid provides grid reliability analysis, failure
protection, and security and privacy protection services. While the additional
communication infrastructure of a smart grid provides additional protective and
security mechanisms, it also presents a risk of external attack and internal
failures.

An important problem in unmanageable
generation sources such as photovoltaic and hydro is their power fluctuation

Generation variability can be moderated
through the aggregation of various systems. This method is limited in small
grids, isolated systems or grids with high penetration of renewable energy
sources. This fact can limit the percentage of renewable energy sources in the
grid.

BLOCK
DIAGRAM

Fig.2

The hydro power and
solar power generation integrated into a distribution power grid. The PV system
is connected to a common dc link through a dc boost converter. The hydro power
is connected to a dc link through an inverter circuit. The output voltage of AC
will be converted to DC by means of the inverter circuit. A Super Capacitor
(SC) is utilized to smooth the generated power delivered to the distribution
power grid. To achieve the maximum power extractions
from PV array and hydro power generation system

ANALYSIS OF HYDRO AND SOLAR

Hydro: A Francis turbine is considered in this
paper. It is referred to a fixed head and a constant water flow. It is assumed
that water flow variations are very slow compared to the drive dynamics. The
turbine model is a basic one, i.e. it includes neither blade pitch control nor
upstream guide vane one. According to these assumptions, hydro power turbine
behavior may be taken into account by means of simplified static mechanical
characteristics represented in Fig.2 for a fixed rate of flow.  

The modelling of micro hydro power plant is done
in this thesis by using MALAB/Simulink. Introduction of micro hydro power plant
reduces a lot of burden without any adverse effect on environment while meeting
the localized power requirement. The simulation results shows that with proper
choice of governing system for micro hydro power plant leads to proper load
sharing, constant voltage output and constant speed with variation of load
values. This leads to an economical operation of the system.

The main motive of this
proposed work is an efficient design of solar panel for constant
Current-Voltage (V-I) characteristics of a Photovoltaic array of various
environmental conditions like different irradiance and temperature. A proposed
model uses constant environmental condition in combination with actual solar
radiation and ambient temperature. The new design is developed on Mat
lab-Simulink platform for calculating and analyzing the power output from a PV
panel by taking the values of current and voltage with constantly varying solar
radiation at any geographical location and different day The output power of
solar panel is directly given to dc/dc controller in order to reduce circuit
complexity.

MAT LAB SIMULATION

               In order to compensate the power
fluctuations from the HPGS and the PV array, the SC will continuously exchange
with the dc link a power grid. The difference between the power generated by
both the renewable sources and the power fed to distribution power grid. It
should be noticed that when performing the sizing of the SC, the power profiles
of the HPGS and the PV array must be given in advance and the sum of their
average is taken as the power fed to the distribution power grid. MATLAB is a
powerful electrical engineering software tool that allows engineering to build
electrical models in Simulink environment and change their operating
conditions.

 

Fig
3. SIMULATION MODEL OF HYBRID SYSTEM

 

PV pannel simulation model   PV array was operating very close to the
peak points under the varying solar condition.The PV array is composed of
several PV cells interconnected in series.If required voltage level that cell
arrangement will be varry.Depending on the cell connected in series/parallal
connection required current and voltage collected from the PV cell.

                Boost
converter simulation model:The DC-DC boost converter was use to convert the
variable DC input to a fixed DC output voltage at a required voltage level.The
output of the PV pannel is varriable DC voltage that will be converted to fixed
DC voltage with help of boost converter.

Hydro power plant: The simulation model can be build individual
sub-model like hydro power plant combination of turbine, governor, synchronous
generator, excitation system and RLC loads are connected together.The output of
generating electrical power depending on the rotating speed of turbine.So the
speed and electromagnetic torque will be measured

That output of hydro power plant is pure form of AC voltage that
will be connected to supply through a DC link so that output power convertered
into Dcwith help of  converter
circuit.The combination of converter circuit design by IGBT power electronic
device because of various kind of application like a transistors have low ON
resistance,high voltage capacity, fast switchinf action and various high level
of voltage applications like PWM,SMPS, variable speed control,AC to DC
converter power by renewable energy sources.

Super capacitor simulation model:The super capacitor is combination
with the control scheme to improve the performance of hydro and pv systems.If
any disturbance will be occur in the hybrid system it will be produce a fluctuation
in systems.At the time of period that system may go on to unstable condition.
To prevent this fluctuation condition with help of  super capacitor is placed.

The variable-speed hydro power plant together with SCESD allows
compensating and smoothing the fluctuating wind power, when connected to the
grid. The discharge strategy attempts to maintain the SC at their lowest
operational voltage (half rated voltage) to make available the SC energy
capacity for absorbing power peaks. Once the generator power exceeds a predetermined
value(dependent on the sea state), the SC prevent any excess power ?owing to
the grid and absorb the difference. Once the input power drops below this
value, the SC maintain this power to the grid until the minimum voltageis achieved.

Grid simulation model: Power fluctuations occur in the
main grid under unbalances condition utility grid maintain a stable condition. Advanced electricity generation,
delivery, and consumption of electric power with help of utility grid.

Solar Simulation:The PV array was operating very close
to the peak points under the varying solar condition.The PV array is composed
of several PV cells interconnected in series. The DC-DC boost converter are
used to convert the unregulated DC input to a controlled DC output at a desired
voltage level.

 

 

   Fig 4. VOLTAGE AND CURRENT OF PV PANEL

Hydro: The simulation
model can be build individual sub-models like hydro turbine governor,
synchronous generator, excitation system and 3-phase RLC load are now connected
together to form the complete block diagram of 
hydro power plant.

 

Fig 5:ELECTROMAGNETIC TORQUE OF HT

The output power of generator depending on the turbine
speed so the speed and electromagnetic torque will be measured.

Fig6:Stator Three Phase Current
Characteristics  at Steady State (in
y-Axis Current in pu and in x-Axis Time in Sec)

The speed governing system of
turbine adjusts the generator speed based on the feedback signals of the
deviations of both system frequency and power with respect to their reference
settings. This ensures power generation at synchronous frequency

       Fig 7: VOLTAGE OF
HYDRO GENERATOR

The simulation results shows that
with proper choice of governing system for micro hydro power plant leads to
proper load sharing, constant voltage output and constant speed with variation
of load values. This leads to an economical operation of the system.
Introduction of micro hydro power plant reduces a lot of burden without any
adverse effect on environment while meeting the localized power requirement.

 

Fig 7. STATE OF CHARGE

The physical phenomena associated with supercapacitor charging
create unobservable internal states of charge(SOC)

 

Fig 8:OUTPUT VOLTAGE ACROSS SC

For filtering purpose connected a thyristor circuit give the gate
pulse signal.Then the output fed to the super capacitor.output wave form
displayed by using of scope.super capacitor paves the way for smoothing power
fluctuation of hybrid system

 

Fig 9: BEFORE SUPER CAPACITOR

 

 

Fig 10:AFTER SUPER CAPACITOR

 

 

 

Power fluctuations occur in the main grid under
unbalances condition utility grid maintain a stable condition

Fig 11: GRID VOLTAGE

 

CONCLUSION

           The dynamic stability analysis
results of a hybrid hydro and PV system integrated into a distribution power
grid have been presented. An SC-based energy-storage system has been employed
to support for smoothing out the power fluctuations. A control scheme has been
proposed aiming to suppress the power fluctuations from feeding to the
distribution power grid and maintain stable operation of the studied system
while achieving the maximum power extractions from the PV array and the hydro
power-generation system. Both modal analysis and MATLAB simulations of the
studied system have been performed to examine the dynamic performance of the
studied system under the operating conditions. 
It can be concluded from the simulation results that the proposed
control scheme has the ability to maintain stable operation of the studied
system under various operating conditions while extracting the maximum power
from both the renewable-energy sources. It can also be concluded from the
simulation results that the SC combined with the proposed control scheme can
effectively smooth out the power fluctuations of the studied hybrid hydro and
PV system. For future  scope to a floating of solar array or floating
of  solar panel  refers to an array of photovoltaic
panels on a
structure that floats on a body of water. In order that the renewable
energy generated
is not wasted, and does not become negatively disruptive to the overall energy
system, battery storage should be installed between the point of generation and
the grid system. 

 

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http://www.files.harc.edu/Documents/EBS/CEDP/HydropowerPart2.pdf

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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