Data Acquisition System for a

Vertical Axis Wind Turbine Prototype

KOCH-CIOBOTARU C.

Department of Automation and Applied Informatics

“Politehnica” University from Timisoara

Bvd. V. Parvan, Nr. 2, Timisoara, 300223

ROMANIA

cosmin.koch@aut.upt.ro

Abstract: - This paper illustrates the design of a prototype model of a Savonius vertical axis wind turbine (VAWT),

including a few dynamic tests. This prototype is physical realised and equipped with a data acquisition system (DAQ).

Further, a virtual instrument (VI) is implemented on a PC to collect data from the DAQ device through the USB port,

to compute them, and to monitor the evolution on the PC. In the end are presented tests done on the system, on

different wind speed regimes. The results obtained by the VI are discussed.

Key-Words: - Vertical Axis Wind Turbine, Data Acquisition Systems, Microcontroller, USB Communication,

LabView

1 Introduction The two major directions in the development of wind

turbines, according to the position of the axis, are the

Horizontal Axis Wind Turbines (HAWT) and the

Vertical Axis Wind Turbines (VAWT)[1].

Both of them present advantages and disadvantages.

The HAWT have a higher power coefficient, so they

present a better efficiency being more attractive for large

scale turbines and wind farms, on- and off-shore. The

largest turbines, to date, are rated 5MW and are HAWT

[2][3].

The VAWT are used especially in low power, until a

few tens of kW, for insular, off-grid, applications or in

the crowded areas, on top of buildings. VAWT have the

tip speed ratio smaller then HAWT, run at lower speeds,

and therefore are more silence. Another advantage is the

high start-up torque, the VAWT being used in the past

for numerous mechanical actions, like running water

pumps [2].

For controlling the turbine during operation, to

achieve an optimal regime, there are used transducers,

data acquisition modules, digital signal processing units

This paper illustrates the design and realization of a

Savonius vertical axis wind turbine of low power, as a

laboratory model. Numerous softwares were used to

design the turbine, the data acquisition (DAQ) system

that monitors the VAWT and the virtual instrument for

data processing

The paper is structured as follows: II – the

mechanical part of the wind turbine, III – data

acquisition system circuit, IV – Virtual Instrument

application and the communication between the PC and

DAQ system through the USB port.

2 System description The first part of the system consists in a Savonius

type VAWT prototype. The turbine captures the wind

energy and converts it into mechanical energy, in the

form of rotation motion around the vertical axis. This

motion is transferred to a direct current generator

through a transmission belt and a system of two wheels

having the multiplication factor of 10. In this way, in the

generator’s windings, electric power is produced. The

electric voltage at the generator end is read by a DAQ

system controlled with a PIC18F4550.

The DAQ system also reads the voltage of a thermic

sensor. This sensor can be used to ensure the

functionality of the turbine in normal safety parameters:

if the temperature is too high, the system works in a

danger zone, where the structural integrity is in danger,

or even the destruction of the installation is possible.

Fig. 1 Block diagram of the application

3 Mechanical part of the VAWT The chosen profile of the turbine is the Savonius

vertical axis wind turbine concept which dates back tho

the '30. The horizontal section resembles the letter “S”,

Selected Topics in Energy, Environment, Sustainable Development and Landscaping

ISSN: 1792-5924 / ISSN: 1792-5940 422 ISBN: 978-960-474-237-0

Fig. 2 Horizontal plan section of a Savonius VAWT turbine

having a concave and a convex scoop. The working

principle of this design may be seen in Fig. 2 [5].

Unlike the HAWT, where the rotational movement is

due to the wing effect (the difference in the pressure on

the two sides of the blade results in a lifting force, that

moves the turbine around its central axis), in the case of

Savonius design, the wind acts directly, with a drag

force, as in the case of a sail [1].

For every type of wind turbine, the plot of the power

coefficient against the tip-speed ratio is of great interest.

The power coefficient (Cp) represents the percent of

power collected from the wind; the theoretical maximum

point is called Betz coefficient and has the value of

0.593. The tip-speed ratio is defined as the product

between the linear speed of the tip of the blade and the

wind speed. For larger values of tip-speed ratio, the

problem of noise emission is of serious concern [2].

In Fig. 3 are presented the efficiency curves of

different types of wind turbine designs, by plotting the

power coefficient against the tip-speed ratio of the

turbine.

The designed model has two levels. Each level

consists of a classic two scoops Savonius design, joined

together with a phase angle of 90 degrees between the

horizontal axes.

For the design of the turbine and simulation of

aerodynamic tests, the software SolidWorks 2006 was

used, with the modules CosmosWorks (see Fig. 4) – for

deformations study, and FluidWorks – for aerodynamic

study (see Fig. 6).

Fig. 3 The power coefficient (Cp) of various types of wind

turbines plotted against the tip-speed ratio

Fig. 4 SolidWorks 2006 model of a Savonius VAWT

The manufactured Savonius VAWT prototype (Fig. 5)

has the following characteristics:

• height of the rotor : 50 cm

• diameter of the rotor : 45 cm

For dynamic balance of the rotor at high speeds, the

base of each level is a full disc, having the diameter with

5% larger than that of the two scoops.

The air mass in motion with a certain speed – the

wind speed, at the contact with the two scoops profiles,

the concave and the convex side, will create a pressure

region on each. As it may be seen in Fig. 6, the pressure

builds up on the side with the wind action. The

difference of pressure between the two sides of a profile,

acts as a force on the surface. The action of this force is

at a certain distance of the rotation axis, and therefore,

results a torque.

At this level it is obvious the cause of the reduced

efficiency: on each moment of the Savonius wind

turbine function, there is a part of the turbine that acts in

the opposite direction.

Fig. 5 Savonius VAWT prototype

Selected Topics in Energy, Environment, Sustainable Development and Landscaping

ISSN: 1792-5924 / ISSN: 1792-5940 423 ISBN: 978-960-474-237-0

(a)

(b)

Fig. 6 FloWorks 2006 simulation of the wind action on the

two sides of the Savonius blade

The FloWorks module offers the fluid dynamic study

on designed modules.

The study from Fig. 6 was realized under the

following simulation conditions:

• the air pressure: 101325 Pa

• the air temperature: 20° C

• the profiles are situated in a field where

the wind speed has only an Ox component,

of value 10m/s

As it may be seen from Fig. 6, the difference between

the two faces of the scoop, in the case when the wind

acts from the concave side, is around 200 Pa. In the case

when the wind acts from the convex side of the scoop,

the pressure difference is only 40-50 Pa. This difference

gives the resulting force that moves the rotor.

The rotation motion is sent from the turbine to a DC

machine that is used in this case in its generator

operation regime through a transmission belt and a

couple of wheels, one on each end, having the ratio of

10.

4 Data Aquisition System For this circuit was used the microcontroller

PIC18F4550, product of Microchip company. It

provides analog inputs and analog to digital converters

on 10 bits [4].

The advantage of using this particular controller is

the fact that provides the hardware capability to use the

Universal Serial Bus (USB) communication.

The functionality of an USB device is structured on

many levels, in a framework. Each level is associated to

a specific function level of the device. The highest level,

except the device, is the configuration. A device can

have multiple configurations, for example for different

power supplied applications. A configuration can have

many interfaces. Under the interface is the endpoint. At

this level the data is handled. There can be 16

bidirectional endpoints. The endpoint 0 is always for

control and it must be free when the device is connected,

for the configuration to take place.

There are four types of transfers for USB:

- Isochronous – used for large packages of data, with on

receiving time assurance. Used in cases where low

losses are not critical, as in audio field

- Bulk – used for large packages, with integrity

assurance; the receiving time is not controlled

- Interrupt – used for low size packages transmission.

Both the receiving time and integrity is assured

- Control – used for device setup

The devices use “high-speed” or “low-speed”

communication. The first one supports all the above

mentioned types of transfer, as for the “low-speed”

communication, it support only the last two.

SIE can be external supplied with 3.3 V, or by an

internal circuit, case in which SIE is connected directly

by USB cable to the other device and the conversion

between the 5V to the 3.3V is made internal. The block

diagram of the SIE is shown in Fig. 7.

Fig. 7 General overview of the USB peripheral and its features

Selected Topics in Energy, Environment, Sustainable Development and Landscaping

ISSN: 1792-5924 / ISSN: 1792-5940 424 ISBN: 978-960-474-237-0

The controller has a dual port memory, which allows

the access of the controller's central unit, as well as of

the SIE module.

PIC18F4550 has the capability to set descriptors for

optimizing the applications through control registers.

Those registers are:

• USB Control Register (UCON)

• USB Configuration Register (UCFG)

• USB Transfer Status Register (USTAT)

• USB Device Address Register

(UADDR)

• Frame Number Registers (UFRMH:

UFRML)

• Endpoint Enable Registers – from 0 to

15 (UEPn)

The circuit acquires two signals: from the generator

and from a temperature sensor. It is necessary to

calibrate the inputs for values between 0 and 5V.

The electronic circuit design was realized in

Pads 2005.

The firmware for the microcontroller was

implemented in MPLAB, in the C language. It has two

major objectives

• Acquiring data from the sensors

• USB communication with the PC

The logic – flow structure of the firmware is

presented below:

• Descriptors setup

• Set the analog port inputs; in the case of this

application there will be used two inputs: 0 and

1

• Set the input channel used by the analogic port;

this function loads in the ADCON0 register the

active port input address

• SIE verifies the USB port for commands; it is

identified, analysed, and executed by the

firmware as follows

• The input signals are subject to an analog – to –

digital conversion; the voltage on the input is

read as a 10 bits value

• Return the result of the analog – to – digital

conversion under a short signed value (on 16

bits); the two registers that represent this value

are ADRESH and ADRESL

In the firmware, descriptors are configured for

identifying, initializing, and setup of the communication

between the host PC and de DAQ device. The following

types are used.

• Device descriptors- they have a role in the

identification of the device by the host PC

• Configuration descriptors- they define the

number of interfaces, the current maximum

value,

• Interface descriptors- very important for the

setup of the communication type, of the

input/output endpoint address and the size of the

transit data

5 The virtual instrument implementation The data are processed with the help of a Virtual

Instrument (VI) realized in LabView 6.1 software.

For the communication between the two systems (PC

and DAQ) NI-VISA is used. VISA is a high level API

used for the bus communication on different

instruments. It is an independent platform: the same API

is used for communication between a device and

LabView and for communication of a GPIB device and

a Mac [6][7].

The USB is a message based communication bus.

This means that the PC and the DAQ device

communicate through commands and data send in text

or binary form. Each USB device has its own command

set. NI-VISA Read and NI-VISA Write can be used to

send these commands to a device or to be able to read

data from it. Information about the command set of the

device is necessary in order to be able to communicate

effectively; this set of commands is specified by the

producer [8].

Beginning with the version 3.0, NI-VISA supports

USB communication. There were implemented

communications with two VISA classes: USB INSTR

and USB RAW.

The devices that use the USBTMC (USB Test and

Measurement Class) protocol use the class USB INSTR.

A special configuration for the communication with

such a device is unnecessary.

The USB RAW instruments are those instruments

that do not respect the USBTMC protocol. This is the

case of the presented DAQ device.

The communication with a USB RAW device is

more complicated because the device uses its own

communication protocol. For an application to be

interfaced with such a device, the producer has to

provide all the necessary data.

NI-VISA implement three types of data fluxes:

control, bulk, and interrupt. When NI-VISA detects the

USB device, it automatically scans for the lowest

endpoint associated to each flux type.

The DAQ device designed and used in this paper has

a BULK type data flux.

For using NI-VISA, the operation system must have a

driver installed for the considered device. In Windows,

this operation is done by installing an “.inf” file. The

device driver, which consists in this “.inf” file, is

realized using VISA Driver Development Wizard

(DDW).

Selected Topics in Energy, Environment, Sustainable Development and Landscaping

ISSN: 1792-5924 / ISSN: 1792-5940 425 ISBN: 978-960-474-237-0

Fig. 9 VISA Driver Development Wizard panel

By selecting the device and communication type and

entering the Vendor ID and the Product ID (must be the

same as the ones set in the device descriptors) DDW

returns the necessary “.inf” file. Fig. 9 shows the DDW

panel.

The resulting “.inf” file is to be installed in

Windows\Inf directory. At the first connection of the

device, the device is installed using this file.

The Virtual Instrument, in a repetitive structure,

presents two sequences of device interrogation code. By

two commands, “A1xxx” and “A0xxx”, the VI

interrogates the device to return the read data from input

1 and input 0, which correspond to the generator voltage

and temperature sensor. This response, sent on 10 bits,

must be interpreted by the VI in order to reproduce the

correct value; this is the reason why the VI designer has

to know the exact structure of the response given by the

DAQ device, in order to correctly interpret the received

bits.

The read data is represented on the front panel of the

application with the help of control blocks. The voltage

is represented in an interval of 60 seconds, for a better

view of the phenomenon. Fig. 10 represents the control

panel of the VI, the user interface of the device. In Fig.

11 is presented the block diagram of the application.

For a better comprehension of the interface, a

division in four quadrants was realised.

In the first quadrant, are present the start and stop

controls, which activate the necessary LabView

commands to setup or to close the communication with

the device. After the start control is activated, the VI

interrogates the device descriptor and returns in a text

box the manufacturer name. The installed driver for the

operation system has also a name; this name, of the

driver, is reproduced in the first textbox, in this case,

“USB_AAAA”.

I II III

IV

a b c

Fig. 10 LabView 6.1 Virtual Instrument interface

Fig. 11 LabView 6.1 Virtual Instrument block diagram

In the quadrant II is represented the temperature

value read by the thermic sensor.

In quadrants III and IV is represented the voltage at

the generator end. In III is presented the momentary

voltage, and in IV is presented the voltage plot on a 60

seconds time interval.

5 Experimental results

During tests, there were considered three wind

regimes, depicted in Fig. 10 with a,b, and c:

• the rise of the wind speed is presented with “a” –

the wind speed increases, the turbine collects

larger amount of energy which is passed to the

generator; it can be seen in the figure the inertia

of the turbine

• constant wind speed regime is presented with

“b” – it may be observed that the generator

produces a constant amount of energy during

this regime

• decrease of the wind speed is presented with “c”

– the turbine collects a smaller amount of energy

and the generator is producing less voltage

Selected Topics in Energy, Environment, Sustainable Development and Landscaping

ISSN: 1792-5924 / ISSN: 1792-5940 426 ISBN: 978-960-474-237-0

6 Conclusions

This paper uses numerous dedicated software for

turbine design, mechanical stress and fluid dynamic

simulation, developing the firmware, writing the

firmware on the microcontroller, design of the electronic

circuit, design of the virtual instrument.

The developed acquisition device replaces the

National Instrument’s own device, hence reducing the

cost of the application. This type of devices can use the

LabView software for user interface and application

monitoring.

This particularly acquisition device is developed

around a Savonius Vertical Axis Wind Turbine for

monitoring the generated voltage.

The DAQ device is supplied from the USB port of

the PC and it doesn’t need an external power source.

This feature gives the device autonomy and simplicity.

7 Acknowledgment This work was partially supported by the strategic

grant POSDRU 2009 project ID 50783 of the Ministry

of Labour, Family and Social Protection, Romania, co-

financed by the European Social Fund – Investing in

People.

7 References

[1] Gary L. Johnson, Wind Energy Systems,

Electronic Edition 2006

[2] Mukund R. Patel, Wind and Solar Power

Systems, CRC Press Florida, 1999

[3] European Wind Energy Association, Wind energy –

The facts 2009

[4] http://www.microchip.com

[5] http://www.aerospaceweb.org

[6] Gani, A.; Salami, M.J.E.; A LabVIEW based data

acquisition system for vibration monitoring and analysis,

Research and Development, 2002. SCOReD 2002.

Student Conference on, 2002, pp. 62-65

[7] Swain, N.K.; Anderson, J.A.; Ajit Singh; Swain, M.;

Fulton, M.; Garrett, J.; Tucker, O.; Remote data

acquisition, control and analysis using LabVIEW front

panel and real time engine, SoutheastCon, 2003.

Proceedings. IEEE, 2003

[8] Chance Elliotta, Vipin Vijayakumara, Wesley Zinka

and Richard Hansen, National Instruments LabVIEW: A

Programming Environment for Laboratory Automation

and Measurement, Journal of the Association for

Laboratory Automation, Volume 12, Issue 1, February

2007, Pages 17-24

Selected Topics in Energy, Environment, Sustainable Development and Landscaping

ISSN: 1792-5924 / ISSN: 1792-5940 427 ISBN: 978-960-474-237-0