JOURNALOF THE TECHNICAL UNIVERSITY - SOFIA

PLOVDIV BRANCH, BULGARIA

FUNDAmENTAL SCIENCES AND

APPLICATIONSVolume 21, book 1, 2015

СПИСАНИЕНА ТЕХНИЧЕСКИ УНИВЕРСИТЕТ - СОФИЯ

ФИЛИАЛ ПЛОВДИВ, БЪЛГАРИЯ

ФУНДАМЕНТАЛНИ НАУКИИ

ПРИЛОЖЕНИЯтом 21, книга 1, 2015

ISSN 1310-8271

Copyright

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N 1310 - 8271

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Copyright © 2015 by Technical University - Sofia, Plovdiv branch, Bulgaria ISSN 1310 - 8271

Fig. 10. Amplifier section schematic diagram

The accurate solar radiation level comparison may be performed only if the

sensitivities of the 9 measurement channels (sensors and amplifiers) are identical (Fig.10). This is the reason to use a special channel sensitivity calibration procedure. On it the sensor array PCBs, after assembling, are placed on the rotating disk horizontally and the standard sun lite source is situated in front of the assembly. By rotating the disk and measuring the maximal voltage level, produced by the each one channel, the sensitivity coefficients (for all the channels) are determined.

3. Sensor control section The control unit is based on

PIC24FJ128GA010 microcontroller using Microchip’s Explorer 16 development board [5]. The board is equipped with various interfaces, including digital I/O, serial UART module, ADC inputs and USB device module. RAM memory is 8K bytes which is sufficient for storing input values from sensors. Processor instruction execution speed of 250 ns allows processing of input data to be done in the given time window (Fig.11).

PV sensor array is connected to 9 channel transimpedance amplifier for amplification and signal level matching and then to analog-to-digital module of the microcontroller. The ADC module is high-speed, pipelined 12-bit A/D converter.

Fig. 11. Control system block diagram

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Fig. 10. Amplifier section schematic diagram

The accurate solar radiation level comparison may be performed only if the

sensitivities of the 9 measurement channels (sensors and amplifiers) are identical (Fig.10). This is the reason to use a special channel sensitivity calibration procedure. On it the sensor array PCBs, after assembling, are placed on the rotating disk horizontally and the standard sun lite source is situated in front of the assembly. By rotating the disk and measuring the maximal voltage level, produced by the each one channel, the sensitivity coefficients (for all the channels) are determined.

3. Sensor control section The control unit is based on

PIC24FJ128GA010 microcontroller using Microchip’s Explorer 16 development board [5]. The board is equipped with various interfaces, including digital I/O, serial UART module, ADC inputs and USB device module. RAM memory is 8K bytes which is sufficient for storing input values from sensors. Processor instruction execution speed of 250 ns allows processing of input data to be done in the given time window (Fig.11).

PV sensor array is connected to 9 channel transimpedance amplifier for amplification and signal level matching and then to analog-to-digital module of the microcontroller. The ADC module is high-speed, pipelined 12-bit A/D converter.

Fig. 11. Control system block diagram

Copyright 2015 by Technical University - Sofia, Plovdiv branch, Bulgaria ISSN 1310 - 8271

The start/end position sensor is used to indicate start point and the full turn end point in measurement movements. The Texas Instruments DRV8824 [6] provides an integrated bipolar stepper motor driver solution. It has built in micro-stepping indexer and simple step/direction control interface.

The system parameters, such as a scanning time interval, a number of averaged measurement samples, sensor array sensitivity data etc. may be added or changed by using a keyboard and LCD display.

Output data are available through RS485 interface connection. The USB port supports controller program development.

MCU read PV sensors array signals at every step and find the maximum value. At the end of the rotation the algorithm finds the maximum value of all and interpolates with its near sensor value to find the exact optimal angle of elevation. The simplified algorithm diagram for the measurement procedure is presented on Fig.12.

Fig. 12. The simplified algorithm diagram for measurement procedure

4. Conclusions The sensor, proposed in this article, allows

the user actual, real time information about the optimal inclination and azimuth orientation of the PV panels, in case to produce maximal electricity power. The obtained data are based on the fast and practically full sky observation procedure. Linear interpolation is used only in elevation access, between two sensors positions, reporting best

values. The inclination difference for these two sensors is only 10 degrees.

The azimuth resolution is set to 0,9 degree and match to a half step size of the stepper motor.

For the best results in optimal position measurements, the type of the sensors in photocell array should be the same, as in PV plant panels.

The chosen data interface (RS485) is convenient to cover long distances - up to 1200 m.

Copyright © 2015 by Technical University - Sofia, Plovdiv branch, Bulgaria ISSN 1310 - 8271

This feature adds flexibility in sensor placement, inside the PV plant arrangement.

5. Acknowledgement This work has been supported financially by

the: Research project 152ПД0046-24/ 27.03.2015

of the Technical University of Sofia; Research project 152ПД0045-24/ 26.03.2015

of the Technical University of Sofia. REFERENCES

1. E. Ritchie, E., Argeseanu, and A., Leban, K. “Robust Solar Position Sensor for Tracking Systems”. Proc. of the 9th WSEAS Int. Conf. on POWER SYSTEMS, ISSN: 1790-5117, ISBN: 978-960-474-112-0, pp. 49-54.

2. P. Roth, A. Georgiev, H. Boudinov. “Design and construction of a system for sun-tracking”. Renewable Energy. vol. 29 (3), 2004, pp. 393-402.

3. P. Roth, A. Georgiev, H. Boudinov. “Cheap two-axis sun-following device”. Energy

Conversion and Management. vol. 46 (7-8), 2005, pp. 1179-1192.

4. J.C. Sáenz-Díez Muro, E. Jiménez Macías, J.M. Blanco Barrero, J. Blanco Fernández. “Optimal orientation procedure of photovoltaic solar systems through the use of a multicellular photovoltaic sensor”. Proc. of the Int. Conf. on Renewable Energies and Power Quality (ICREPQ’12), Santiago de Compostela, Spain, 28th to 30th March, 2012.

5. Explorer 16 Development Board User’s Guide: DS51589A Microchip Technology, 2005.

6. DRV8824 - Stepper motor controller IC, Datasheet: SLVSA06H – Texas Instruments October 2009 – Revised December, 2013.

Contacts e-mail: rum_pop@yahoo.com e-mail: stefan_lishev@abv.bg e-mail: ageorgiev@gmx.de e-mail: vasileva_nadezhda@abv.bg

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