Design and Comparison of Standalone Bladeless Wind Solar Hybrid System with the Conventional Standalone Wind Solar Hybrid System

Now a days the power consumption is more compared to the available power and the pollution is also increasing. So, one of the solutions to overcome the above mentioned two disadvantages is producing the power with the renewable energy sources which are unlimited and non-pollutant. Among the available renewable energy sources, wind and solar sources [1] have number of advantages like unlimited, clean.

Using wind as a source there have been number of wind turbines like Horizontal axis wind turbine, vertical axis wind turbine, Darrius wind turbine but the disadvantages with these wind turbines is high investment, noise, fatal to birds, higher wind speed requirement and no availability of wind all the times. So solar can be used for power generation but even it has disadvantage that it is not available at night times and no power generation. So, using of single renewable source at a time may not meet the load requirement and so by combining these sources [2, 3] they can be effectively used which leads to hybrid system.

Standalone Hybrid power generation system [4-6] produces electrical energy with the use of more than one source and if one is not available another source can be used +for running the load. Standalone Solar wind hybrid power generation system uses solar and wind as sources, but the conventional wind turbine has disadvantages like higher wind speed requirement, high investment, fatal to birds, noise.

Bladeless wind turbine is an alternative solution of generating power with wind and getting rid of the disadvantages of conventional horizontal axis wind turbine and the basic principle behind the bladeless turbine is vortex induced vibrations [4]. Vortex vibrations are the vibrations that are induced with in a structure when wind is passed through it and producing oscillatory motion. These oscillations can be converted into electrical energy using devices like piezoelectric cells, crank and shaft mechanism, linear alternator but producing low energy, high maintenance and so transducer [7] can be opted for energy conversion. But the produced energy may not be sufficient for usage and so high gain step up DC-DC converter can be used for boosting the voltage up to the required value instead of using conventional boost converter. To reduce the filter requirements and to reduce total harmonic distortion of output energy three level inverter [8] can be used instead of conventional two-level inverter.

The paper is organized as follows; the first section of the paper is dealing with the comparision of proposed bladeless hybrid system and conventional hybrid system, the second section of the paper is dealing with the mathematical modelling of proposed bladeless hybrid system and the third part discusses with controller for wind turbine and the fourth part deals with the software realization of proposed system, result and discussion of the proposed system and the fifth part deals with the conclusion.

Bladeless wind turbine is basically a system consisting of mass $m$  and spring having stiffness of $S_{\text {stiff}}$  can be shown with mass spring system which is shown in below Figure 3.

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Figure 3. Mass spring system

The following are the designing equations [9, 10] involved for the spring mass system.

A tapered cylindrical structured mast made of fiber whose mass is given as

$m=\frac{\pi}{3} \rho L\left(D^{2} / 4\right)$         (1)

where $L$ is length of the mast, $\rho$ is density of $\operatorname{arr}, D$  is the diameter of mast.

The flow of wind over the mast induces vortex vibrations which can be characterized by the Reynolds number and strouhal number given as

$R_{n}=\frac{U_{W} D}{\mu}$           (2)

where $U_{W}$  is velocity of wind, $\mu$  is kinematic viscosity. For the Reynolds number vs strouhal number data strouhal number, $S_{t r n}=0.2$  for considered wind speed.

These vortex vibrations can be determined with a frequency called strouhal frequency $f_{s t r}$  [9] can be given as

$f_{\text {str}}=\frac{S_{\text {trn}} U_{W}}{D}$           (3)

A spring used for increasing oscillations of the mast with spring stiffness [9] given as

$S_{\text {stiff }}=m w_{\text {nat }}^{2}$           (4)

where $W_{n a t}$  is natural frequency of the mass spring system.

The resultant of the vortex vibrations produces alternating lift forces $F_{\text {lift}}$  [9] can be given as

$F_{l i f t}=\frac{1}{2} \rho U_{W}^{2} A_{m} L_{c o e f f}$           (5)

where $A_{m}$ is area of the mast, $L_{\text {coeff }}$ is coefficient of lift force.

The resulting displacement $Z$  of the mast [9] can be given as

$\ddot{z}=\frac{F_{\text {lift}}}{m}-\frac{S_{\text {stiff}} Z}{m}$         (6)

3.2 Solar panel

A solar panel consists of solar modules which intern contains solar cells. A solar cell basically consists of a p-n junction diode and internal resistance which is shown in below Figure 4.

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Figure 4. Equivalent circuit of solar cell

When sun rays fall on the solar cell, the total current that is generated is $I_{p h}$ .

The following are the designing equations [1-5] involved for the solar cell.

The diode current can be given as

$I_{d i}=I_{o}\left(e^{\frac{q V_{P V}}{n K T}}-1\right)$          (7)

The current through the shunt resistance can be given as

$I_{s h}=\left(\frac{V_{P V}+I_{s e} R_{s e}}{R_{s h}}\right)$          (8)

The current collected at the output of the solar cell can be given as

$I_{P V}=I_{p h}-I_{d i}-I_{s h}$          (9)

The voltage across the solar cell can be given as

$V_{P V}=\frac{K T}{q}\left[\ln \left(1-\frac{\left(I_{P V}-I_{p h}\right)}{I_{o}}\right)\right]$          (10)

where $K$ is Boltzmann constant, $T$ is the temperature, $q$  is charge of electron.

The bladeless hybrid system is an integration of bladeless wind turbine and solar panel. When wind passes over the mast due to vortex action displacement whose value is 0.22m is the resultant motion for wind speed U=2m/s, which is shown in below Figure 7.

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Figure 7. Displacement of mast

The displacement has been converted into AC power using AC transducer whose value is 52VAC shown in below Figure 8.

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Figure 8. Output voltage of an AC transducer

The AC electrical power has been converted into DC power using diode bridge rectifier whose voltage value is 50VDC, current value is 4.7A and is shown in below Figure 9.

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Figure 9. Voltage and current of diode bridge rectifier

A solar panel of 48V DC has been designed and its output voltage and current whose values are 48V DC and 4.8A is shown in below Figure 10.

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Figure 10. Voltage and current of solar panel

The voltage and current obtained from the bladeless wind turbine, solar panel are integrated and fed to high gain step up DC-DC converter and the voltage, current & power which are boosted which is shown in below Figure 11.

The hybrid system has been simulated for different wind speed conditions U=0.5m/s, U=1m/s, U=1.5m/s, U=2m/s and the four outputs are shown inbelow Figures 12,13 & 14.

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Figure 11. Voltage, current and power of hybrid system for U=0.5m/s

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Figure 12. Voltage, current and power of hybrid system for U=1m/s

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Figure 13. Voltage, current and power of hybrid system for U=1.5m/s

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Figure 14. Voltage, current and power of hybrid system for U=2m/s

The output from the DC-DC converter is fed to three level inverter and the resultant voltage ,current whose values are 400VAC, 8A are shown in below Figure 15.

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Figure 15. Voltage, current and power of three level inverter

Table 2. Proposed hybrid system

Table 3. Proposed hybrid system vs conventional hybrid system

The proposed hybrid system and the conventional hybrid system are simulated using MATLAB Simulink and the voltage, current & power are shown in above Table 3.

Table 4. Specifications of bladeless hybrid system

The above Table 4 shows the specifications of the bladeless hybrid system.