Efficiency improvement on wind turbine through bump up stepper motor

This paper presents with the starting torque provision for the wind turbines which are sometimes not rotating even at cut-in wind speed, (rotation sensed through output power of the turbine) here if the power is zero above the cut-in wind speed then the turbine is not in running condition. Here we are using the sensorless sensing method, by providing some extra torque through stepper motor for starting purpose we will improve the efficiency of the wind turbines. Normally the speed of the wind is not a constant, hence by providing this type of set-up can make the wind turbine to rotate to its maximum extent (i


Introduction
The wind energy system is considered to be one of the most promising renewable resources.In which the wind turbine starts to rotate at start-up wind speed and the power gets extract from the turbine at cut-in wind speed.Hence due to some ageing effects of gear box or due to the problem in pitch angle control (i.e.improper alignment in blade) will cause decrease in starting torque of the turbine to rotate at cut-in wind speed.Hence the power extracting time from the turbine gets decrease which cause decrease in efficiency in wind turbine systems.
Hence for to overcome this energy loss we need to provide extra torque to the turbine shaft, for that we are going to provide that deficient torque through stepper motor which should operate during the period where the speed of the wind is above the cut-in wind speed and power output of the turbine is zero.In which the stepper is going to rotate for 20 seconds after that we are monitoring for wind speed and power out output of the turbine if that conditions prevails same again means operate the stepper motor for another 20 second or else stop the stepper motor when the turbine starts rotating.Also the supply to the stepper motor proposed to be provided with solar panels along with mppt and boost converter to make the system more eco-friendly and self-supporting.
The paper is organized as follows: Section II provides the concept of wind energy conversion system.Section III describes the stepper motor mathematical modeling and motor selection.Section IV describes the MPPT technique and solar panel simulation modelling.In Section V, effectiveness and feasibility of the proposed method is demonstrated by simulation results.Conclusions are drawn in Section VI.

Torque calculation 2.1. Torque supplied by the turbine to generator
Figure 1 Torque supplied by turbine Generally the specifications of turbine will provide you the diameter of the turbine hence with that we can able to calculate the mechanical power supplied by the turbine to generator at specified speed can be known.Hence for to drive the turbine at some constant speed during cut-in wind speed we know the torque level.By using this technique we can choose the proper stepper motor for to drive the turbine at stall conditions during cut-in wind speed The equations which are involved in wind turbine torque calculation are as follows: Mechanical turbine torque (turbine) = Pm/ω Pm=mechanical power & ω=speed to rotate or generator speed The power available in the wind is given by the flowing air mass per unit time.The wind turbine produces maximum power when the turbine operates at maximum value of Cp, Where β=pitch angle The tips peed ratio has given by the following equation.
R=Radius of blade swept area,N=Rotatioal speed.

Stepper motor
Here we are going to use stepper motor as the extra drive system for to drive the turbine in stall condition during cutin wind speed.For which the torque required for selecting the motor to rotate the wind turbine at constant speed is calculated using mechanical power of the turbine Hence the equation for designing the hybrid stepper is as follows Mathematical model describing the dynamics of the system [1] can be given as follows Using MATLAB SIMLINK Tool Kit, the dynamic equation ( 4),( 5),( 6),( 7) has been simulated.For dynamic simulation, the voltages (Va,Vb) are given as per the stepping sequence.Stepper motor's rotor rotates through one step angle for every step pulse.The phase Currents, angular speed and rotor position need to be evaluated for a given voltage.Interactions of voltages contribute stepping angle of rotor.The electricity available at the terminals of a photovoltaic array may directly feed small loads such as lighting systems and DC motors.Some applications require electronic converters to process the electricity from the photovoltaic device.These converters may be used to regulate the voltage and current at the load, to control the power flow in grid connected systems and mainly to track the maximum power point (MPP) of the device.….eq (10) Io=saturation current in the diode

Isc=short circuit current
Voc=open circuit voltage a=ideality of the diode(1<a<1.5) ∆T=T nominal in kelvin-273 K

MPPT algorithm perturb and observe
The P&O method is the most popular MPPT algorithm due to its simplicity.Figure 3 shows the flow chart of P&O method.
After one perturb operation the current power is calculated and compared with previous value to determine the change of power ÄP.If ÄP>0, then the operation continues in the same direction of perturbation.Otherwise the operation reveres the perturbation direction.The above simulation shows the value of torque provided by 200W wind turbine(FD 2.1-200-8) with rotor diameter 2.2m with pitch angle=3 o at wind speed=3m/s and with rotational speed=30rpm is 0.05753N

Stepper motor
Figure 5 Stepper motor simulation from eq(4),( 5),( 6)&( 7) Since the parameter for simulation of stepper motor has been brought from "Position Control of a Sensorless Stepper Motor" [6] Figure 6 Half stepping simulation result Which will provide 1.8 o step angle for each step sequence

Boost converter
Since boost converter are used for to provide boost up voltage for the load circuit.Here we are designing for 24v output voltage with input as 18v and input current as 0.6A  Step 1:Check whether the wind speed is greater than cut-in wind speed and also whether the output power of the turbine is greater than zero.
Step 2:If the step 1 condition fails to prevail start the stepper motor and made it run for 20 seconds and again check the system output power and wind speed.
Step 3:If it starts to rotate (ie power extract from turbine starts) then stop the stepper motor and keep monitoring the system

Sheet at cut-in wind speed
Where pitch angle=3deg The torque requirement for stepper motor to rotate the turbine at 30rad/sec is calculated by taking speed of the turbine as 30rad/sec and speed of the wind in turbine as 3m/s.
The calculated value is tabulated as follows from the respective formula in the section 5

Conclusion
In which  Torque requires for different wind turbine to rotate at some constant speed on Cut-in wind speed has been calculated. Different stepper motor ratings have been analyzed. Simulation model for the proposed system has been done. Solar panel modeling with mppt has been done  Proper matching of the stepper motor to the torque requirement has been done. Also available rating of wind turbines and stepper motor in the market has been studied.
A control strategy for a direct-drive stand-alone variable speed wind turbine with a PMSG has been presented in this paper.A simple control strategy for the generator-side converter to extract maximum power is discussed and implemented using Simpower dynamic-system simulation software.The controller is capable of maximizing output of the variable-speed wind turbine under fluctuating wind.The generating system with the proposed control strategy is suitable for a small-scale stand-alone variable-speed wind-turbine installation for remote-area power supply.

Pm = 1 / 2 (
air mass per unit time) (wind velocity) density 1.225 kg/m 3 at sea level (T=273) Vw = Up stream wind velocity.A = rotor area.Cp = power co-efficient Vw=Wind velocity (m/s) Cp = Power output from the wind turbine /Power available in the wind.

Figure 2
Figure 2 Solar cellA photovoltaic system converts sunlight into electricity.The basic device of a photovoltaic system is the photovoltaic cell.Cells may be grouped to form panels or modules.Panels can be grouped to form large photovoltaic arrays.The term array is usually employed to describe a photovoltaic panel(with several cells connected in series and/or parallel) or a group of panels.Most of time one are interested in modeling photovoltaic panels, which are the commercial photovoltaic devices.This paper focuses on modeling photovoltaic modules or panels composed of several basic cells.The term array used hence forth means any photovoltaic device composed of several basic cells.
Hence the equation required for to design the solar panels are,  =  − [[ +  (   ) /] − 1 ….eq(8)Where I is the current from the solar cell(I=Ipv-Id) Ipv=photo voltaic current Nser,Npar=number of series and parallel connected arrays Vt=(NskT/q) is the thermal voltage of the array with Ns cell connected in series K=boltzmann constant[1.38.10-23J/K] q=electron charge[1.6.10-19C]a=diode ideality  = ( + ∆)/ ….eq(9)Where Ipv,n (in amperes) is the light-generated current at nominal condition (usually 25 o C and 1000 W/m 2 )∆T=T-Tn(T and Tn being the actual and nominal temperatures [ in Kelvin],respectively), G (watts per square meters) is the irradiation on the device surface, and Gn is the nominal irradiation  = (,  + ∆T)/(exp (Voc, n + Kv∆T aVt ) − 1)

Figure 3 Figure 4
Figure 3 Perturb and Observe

Figure 11
Figure 11 Boost Converter

Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 5 . 5 . 5 . 6 .Figure 17
Figure12 Current with respect to time Since the current output of the converter provides 0.44A and output voltage as 24V,from which the selection of stepper motor for turbine should have power rating below 12watts.Here we are using 17PY-Z264U stepper motor for 300watts turbine FD2.5-300W consumes less than this power rating only(ie less than 12W)

Figure 18 Figure 19 5 . 7 .
Figure 18 Overall system model Fig 18 shows the Simulink model of wind turbine with stepper motor setup including Po zero at 20-40 sec

Figure 20
Figure 20 Stepper motor placing space on turbine Figure 21 Shaft arrangement to place stepper motor Parallel shaft helical gearbox for stepper motor arrangement in shaft of the turbine

Table 3
Different turbine ratings