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Hybrid based Wind-Photovoltaic system for isolated condition using Direct Power Control Technique
1Justin Simon, 2Akhil P.G
1,2PG Scholar, Dept of EEE
1,2Amrita School of Engineering Bangalore, Karnataka
Email : 1[email protected], 2[email protected] Abstract—Hybrid system are attracting widely due to its
operating features which can operate in all aspects of climatic changes. In this work, a Self excited induction generator (SEIG) combined with PV Array is used for the Hybrid system. A variable wind speed is incorporated in this work. The simulation has been designed using MATLAB/Simulink. The control scheme verified using Direct Power control (DPC) technique. It provides full control of Active and Reactive power. An LCL filter is used to reduce the higher order harmonics. A detail analysis of the controller on load side is verified were presented in this paper to show effectiveness of controller in hybrid systems.
Keyword: Direct Power control (DPC), Self Excited Induction Generator (SEIG)
I. INTRODUCTION
Renewable energy defined as the energy generated from natural resources such as sunlight, wind, rain, and geothermal heat, which are renewable. Wind energy is the kinetic energy associated with the movement of atmospheric air. It has been used for hundreds of years for sailing, grinding grain, and for irrigation. Wind energy systems convert this kinetic energy to more useful forms of power. A wind turbine converts the energy of wind into kinetic energy. Wind speed usually increases with height and where there are no natural or man-made obstructions and this why you'll often see them on hilltops or perhaps in the middle of wheat fields owing to intermittent in nature storage of the available energy is the challenging task there are lot of study on storage and distribution of wind energy for the past few decades [1]-[2].In order to optimize the wind turbine system and improves the power quality of the systemwind energy conversion systems (WECS) in order to keep more economical power quality under limits proposed by its own standard for the given compensation several control complexity [3]-[4] .Open loop feed-forward technique can implemented in remote or isolated mode[5] the efficiency of the system is reduced due to environmental impacts.
Now a day’s voltage oriented control (VOC) Technique which offers a stable performance and high dynamic using an internal current loops the method is developed using the conventional Proportional and Integral (PI) controllers. PI Controllers having its own disadvantages due to slower for fast transients and control range.
Wind is an intermittent in nature so that there is always a peak demand due to unpredictable weather condition to mitigate the demand there should be additional source which can fulfilled the need.
Photovoltaic or solar cells as they are also called semiconductor devices, convert sunlight into direct current or electricity. Groups of PV cells are electrically configured into modules and arrays, which can be used to charge batteries, operate motors and to power any number of electrical loads. The growth of semi conductor industry reduced the investment in power electronic components used for poly crystalline materials.
Generalized PV model easily simulated and analyzed in conjunction with power electronics for the maximum power point tracker. Equations to model a PV cell, module and array, its characteristics, and interfacing PV modules[6]
A details of different control algorithm is discussed in this paper based on maximum power point tracking[7]- [10].
Hybrid power systems usually integrate renewable energy sources with fossil fuel based generators to provide. It offer better performance, flexibility of planning environment benefits compared to diesel generators based isolated mode of operating. In order increase the demand Hybrid system gives the opportunity expanding the generation.
II. WIND ENERGY CONVERSION SYSTEM
Air has a mass. As wind is the movement of air, wind has a kinetic energy. To convert this kinetic energy of
the wind to electrical energy, in a wind energy conversion system, the wind turbine captures the kinetic energy of the wind and drives the rotor of an electrical generator The mechanical energy developed in wind flow is known as the Betz theory[11]
Power (P) =0.5ρπV3Cp(λ, ß)D2 (1)
Where ρ is the air density, V is the wind velocity in m/s, D is the diameter of the wind turbine power, Cp Co- efficient of wind depends on the, ß blade pitch angle and, λ tip speed ratio
λ= ωrR/v
(2)
ωr is rotor speed of the wind turbine, R is the radius of the blade, v is the wind velocity
Tw=P/ωr (3)
Where Tw is the torque developed due the rotor speed and P is the total mechanical power developed in the system
III. SYSTEM MODELING
A. Variable Wind Speed Generator
Variable speed wind turbine are preferred for high output power generation, There lorts of configuration available among that DFIG double fed induction generator concept(DFIG).It is concept based developed due to wound rotor induction generator (WRIG), The main advantage of DFIG is the rotor energy can fed to grid with the help power converters. The system is complex because the need of Gear Box. Different sequences in the stator and rotor cause fatigue to structural components to gear box [11].
Permanent Magnet Synchronous generator (PMSG) is widely getting popular in recent years due to cost reduction high efficiency and absence of any mechanical components such as slip rings due to this the weight also getting reduced. However the material used in manufacturing PMSF is high cost and de-magnetization also reduce the remote area operation [12].
Owing to find a best configuration in variable speed operation, a self excited induction generator (SEIG) is used in this paper.
B. Self Excitation
In an externally driven three phase induction motor if a three phase capacitor bank is connected across its stator terminal an EMF is induced in the machine winding due to its self excitation provided by the capacitor. The magnetizing requirement of the machine is supplied by the capacitor for the self excitation need to satisfy two
conditions the rotor should have sufficient residual magnetism and the three phase capacitor bank should be sufficient value. The capacitance required for self excitation is calculated by using the below equation Q = VL2/XL (4).
Where VL is the line voltage and XL is the reactance of the Induction generator
C = Q/VL2 *2πf (5)
Where Q is the reactive power, f is the frequency of the system.
A detail test is conducted to model the Induction generator the rating of the machine and test conducted tables are given below to this
TABLE I. MACHINE DETAILS Sl.
No Machine rating
1 Self Excited Induction
Generator 5 HP
2 Rated Voltage 7.5 A
3 Frequency and Poles 50hz 4 4 Rotor & Stator
Resistance 1.5ohm 3.83oh
m 5 Rotor and Stator
Reactance
5.117oh m 6 Mutual Reactance 0.217oh
m TABLE II. TESTDATA
Sl.
No Test Conducted
Voltage(v) Current(A)
1 No load test 415 4.9
2 Blocked rotor test 80 7.5
C. Three phase Bridge Converter
To supply a constant-voltage dc link of the inverter stage, a dc-dc stage is introduced between the uncontrolled diode rectifier and inverter rectifier stage cause considerable loses like increases the total harmonic distortion (THD).Three phase bridge rectifier are used in high power application. The ripple voltage is about 4.2%.The average value of the output voltage can be found using the below equation
Vdc = 1.654*Vm (6) Vrms = 1.6554*Vm (7) R = Vdc2/Prated (8)
Irms = 1.73* Vm /R (9) Irms = 0.5518*Im (10)
Where Vm is the Peak phase voltage, Im is the Peak current through the diode, Irms is the Root Mean square (RMS) Current, Vrms is the Root Mean square (RMS) Voltage, Vdc is the DC voltage across Capacitor. Prated is the active power
Inverters are power electronic circuits which transform a DC signal into an AC signal. When applied to PV systems the DC power produced by the PV generator is converted into AC power.
Single-phase VSIs cover low-range power applications and three-phase VSIs cover the medium- to high-power applications. The main purpose of these topologies is to provide a three-phase voltage source, where the amplitude, phase, and frequency of the voltages should always be controllable. Although most of the applications require sinusoidal voltage waveforms (e.g., ASDs, UPSs, FACTS, VAR compensators), arbitrary voltages are also required in some emerging applications (e.g., active filters, voltage compensators).
IV. SOLAR PHOTOVOLTAIC SYSTEM
A. Modelling of PV Array
A solar cell represented by the equivalent circuit is shown in the Fig 10.1. When the solar cells is illuminated by the sunlight, electron-hole pairs are generated and the electric current I is the difference between the solar light generated current (IL) and the diode dark current (ISH). This phenomenon is called photovoltaic effect, expressed as
I = IL – ISH (11) I = NpIph – NpIs[exp(qV/NskTcA)-1] (12) Where Ip is the light generated current or photocurrent, Is - cell saturation of dark current, q - is an electron charge, k is the Boltzmann’s constant, Tc is the cells working temperature
A is theIdeal factor, Np is theparallel number of cells for a PV module, Ns is theSeries number of cells for a PV module
Iph = [Isc+K1(Tc-Tref)]*lambda (13) Where Isc is the cell’s short circuit current at 25degree Celsius and 1kW/sq.m, K1 - cell’s short circuit current temperature co-efficient, Tref - cells reference temperature, Lambda - solar insolation in kW/sq.m Is = Irs(Tc/Tref)^3exp[qEg(1/Tref-1/Tc)/kA] (14)
Irs=Isc/[exp(qVoc/NskATc)-1] (15) Where Irs - cell’s reverse saturation current at a reference temperature and solar radiation, Eg - band- gap energy of the semiconductor used in the cell, Voc - open circuit voltage at reference temperature
V. DPC TECHNIQUE
This control method is a simplified VOC strategy. The difference between this two control strategies is that the current controllers are eliminated. The power controllers produce directly the voltage references for the PWM and this can be also the reason why this method is called direct power control. A conventional PLL is used also in this strategy in order to detect the grid phase angle Φ.The power used to balance the DC voltage is estimated using the DC voltage controller output and other PI controllers are used for active and reactive power controllers
Fig 1 Block diagram for DCP Technique Where VABC and IABC measured phase voltage V*DC, P*DC, Q*DC are the reference DC voltage , Active power, Reactive power using conventional PI controller the error is controlled and fed back to switches using PWM Technique
VI. RESULTS
All the results are verified in MATLAB/Simulink a variable wind speed is considered throughout of the simulation work. A detail data record has been collected for the different weather conditions based wind speed is varying due to seasonal changes a
Fig 2 Variable wind speed generation
Fig 3 DPC algorithm
Fig 3 Active power
Fig 4 Constant Voltage from PV Panel
Fig 5 Load voltage and current
VII. CONCLUSION
In this Paper, SEIG based WECS is used for simulation.
The DPC technique has good performance in control operaton in isolated mode. An LC filter is inserted in between Load and Inverter to obtain sinusoidal voltage and current with negligible harmonic content and improves the stability. The simulation are carried out based on the test reading conducted for squirrel cage induction generator
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