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
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
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