4 Maximum Power Point Traking Controller for Pv

8/13/2019 4 Maximum Power Point Traking Controller for Pv

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Technical note

Maximum power point traking controller for PVsystems using neural networks

A.B.G. Bahgata, N.H. Helwab, G.E. Ahmadb, E.T. El Shenawyb,*

a

Electrical Power Engineering, Faculty of Engineering, Cairo University, Cairo, EgyptbSolar Energy Department, National Research Center, El Tahrir St., Dokki, Cairo, Egypt

Received 17 March 2004; accepted 27 September 2004

Available online 16 December 2004

Abstract

This paper presents a development and implementation of a PC-based maximum power point

tracker (MPPT) for PV system using neural networks (NN). The system consists of a PV module via

a MPPT supplying a dc motor that drives an air fan. The control algorithm is developed to use the

artificial NN for detecting the optimal operating point under different operating conditions, thenthe control action gives the driving signals to the MPPT. A PC is used for data acquisition, running

the control algorithm, data storage, as well as data display and analysis. The system has been

implemented and tested under various operating conditions.

The experimental results showed that the PV system with MPPT always tracks the peak power

point of the PV module under various operating conditions. The MPPT transmits about 97% of the

actual maximum power generated by the PV module. The MPPT not only increases the power from

the PV module to the load, but also maintains longer operating periods for the PV system. The air

velocity and the air mass flow rate of the mechanical load are increased considerably, due to the

increase of the PV system power. It is also found that, the increase in the output energy due to using

the MPPT is about 45.2% for a clear sunny day.

q 2004 Elsevier Ltd. All rights reserved.

Keywords: PV module; Maximum power point tracker; Neural networks; Matching factor

0960-1481/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.renene.2004.09.011

Renewable Energy 30 (2005) 12571268

www.elsevier.com/locate/renene

* Corresponding author. Fax:C20 2337 0931.

E-mail address:[email protected] (E.T. El Shenawy).
http://www.elsevier.com/locate/renenehttp://www.elsevier.com/locate/renene


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2. The PV module

The PV module is a thin film solar cells type with maximum output of 64 W at STC.

The complete specifications of the PV module are listed in Table 1. The PV module

generates the dc power that is transferred to load through the MPPT. The PV module is

supported up on a tilted structure from steel frames. The tilt angle can be adjusted simply

Table 1

The PV module characteristics at STC (25 8C and 1000 W/m2)

Rated power 64 W

Operating voltage 16.5 V

Operating current 3.88 A

Short circuit current 4.8 ADimensions 136.6 cm!74.1 cm!3.2 cm

Weight 9.71 kg

Fig. 1. Schematic diagram of the PC-based MPPT for the PV system using neural networks.

A.B.G. Bahgat et al. / Renewable Energy 30 (2005) 12571268 1259


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by choosing the appropriate bolt position on the lower support. The structure is mounted

such that the module is facing south direction. The PV module is implemented in the test

field of Solar Energy Department, National Research Center, in Egypt.

3. The data acquisition system

The main part in the data acquisition system is the AD574 analog to digital module,

which receives the voltage analog signals from the measuring devices and converts them

into digital signals to be processed by the PC. The AD card has 8 input analog channels

each with 12-bit resolution.

The following parameters are measured using the data acquisition system:

The PV module voltage can be measured accurately by using a bipolar LV 25-P voltage

transducer, with galvanic isolation between the primary circuit (high voltage) and the

secondary circuit (low voltage).

A current transducer LA 25-NP is used to measure the PV module current.

A thermopile pyranometer of type Kipp and Zonen (model CM5-774035) is used to

measure the solar radiation intensity. The pyranometer is mounted at the PV module

structure and parallel to the module.

A type K thermocouple is used to measure the PV module surface temperature.

4. The maximum power point tracker (MPPT)

Fig. 2shows the MPPT connecting the PV module to the dc load. The MPPT consists of

a step-down dcdc converter with the input and output filters, and the driving circuit. The

MPPT drives the operating point of the PV module to the maximum power point detected

by the control system.

The main circuit components, as shown in Fig. 2, are as following:

The power transistor (200 W).

The input filter (C1Z1500 mF).

The output filter (C2Z470 mF, LZ150 mH). The freewheeling diode (8 A).

Fig. 2. The PV system with the maximum power controller.

A.B.G. Bahgat et al. / Renewable Energy 30 (2005) 125712681260


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The power transistor is NPN MJ802 transistor. It is used as a switch which is turned on

and off by an external driving circuit with adjustable duty ratio. The duty ratio is adjusted

according to the error signal between the PV module operating power and the maximum

power identified by the neural network.

5. The load

The present load is a permanent magnet dc motor driving an air fan. This load is used to

feed air to a solar drying system for drying agriculture products or wood.

6. The control algorithm

A PC is used for data acquisition, control action, storage and data display. Fig. 3

shows the flow chart of the software program that controls the system operation. The

program is written in BASIC language and stored in the PC. Once the program starts,

it reads four signals from AD module. These signals are the solar radiation level, the

PV module surface temperature, the module current, and voltage. Then, the operating

power is calculated directly from the module current and voltage. While, the

maximum power is calculated from the neural network. For comparison, the direct

power drawn by the load, when it is directly connected to the PV module without

using the MPPT, is also calculated by another neural network, using the measured

solar radiation and module temperature. This power is called the normal operating

power of the PV module (NOP).

The program compares the module power with the maximum power and gets an error

value. If the error value is within the permissible error, then the system is working at its

maximum power point and the load receives the optimal power from the PV module. If the

error is greater than its maximum value, the program generates a control signal,

corresponding to this error, based on the control algorithm.

The control algorithm uses the perturb and observe method, because of its inherently

simple feedback structure, also it needs few measured parameters. In this method, the

system operating point (operating voltage) is changed (increased or decreased) in onedirection. These changes can lead to a change in the PV module output power. The next

changing direction can be determined by comparing the output power of the PV module

with that of the previous perturbation cycle. If the module power is increasing, the next

change will be made in the same direction. But if the power is decreased, the next change

must be in the opposite direction[1012].

The PM7548GP DA converter module is used to send the control signal required,

depending on the software program. The DA module has 12 bits resolution and sends the

control signal from 0 to 10 V.

The control signal is sent to the driving circuit for biasing the power transistor on and

off. This produces a square wave-driving signal with a certain duty ratio that changes theoperating point of the PV module. If the atmospheric conditions change (solar radiation or

module surface temperature), the maximum power point is considerably changed, that



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makes an error between the maximum power point and the new operating power point.

Due to this error the system adjusts its working point to the new maximum power point.

7. The experimental results

The performance of the PV system with the MPPT is studied for clear sunny days with

high and moderate radiation levels.Fig. 4shows the maximum power (MP), the module

power (PVP), and the normal operating power (NOP) measured for a clear sunny day. It isclear that the module power is almost tracking the maximum power all the day. In other

words, the MPPT maintains the load operating at the maximum power point of the PV

Fig. 3. The flow chart of the software program that controls the system operation.



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module.Fig. 4shows also that the NOP is much less than the power taken by the load in

the case of using the MPPT. This arises the importance of using the MPPT to get a good

matching between the dc load and the PV module. The same results are obtained for the

PV system at a moderate sunny day as shown inFig. 5.

Figs. 6 and 7show the MP, PVP, and NOP of the PV system in high and less cloudydays, respectively. These figures show that the MPPT maintains continuously the module

power at its maximum value. The result is valid for the 2 days although they are different in

the nature of the solar radiation and module temperature changes. This means that, in

cloudy days, whatever the nature of the clouds passing, the MPPT tracks accurately the

peak power point.

Fig. 4. The MP, PVP and NOP of the PV system measured in a clear sunny day.

Fig. 5. The MP, PVP and NOP of the PV system measured in a moderate sunny day.



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The performance of the MPPT can be detected according to the matching factor. The

matching factor is the ratio between the power drawn by the MPPT, from the PV module to

the load, to the maximum power generated by the PV module. The matching factor during

a clear day is shown in Fig. 8. The figure shows that about 97% of the actual maximum

power generated are drawn by the MPPT. Similar results are obtained in case of acloudy day.

Fig. 9 shows the PVP (with MPPT) and the NOP (without MPPT) and the

corresponding percentage of the energy increased by the MPPT. This figure shows that

Fig. 6. The MP, PVP and NOP of the PV system measured in a high cloudy day.

Fig. 7. The MP, PVP, and NOP of the PV system measured in a less cloudy day.



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using MPPT increases the module energy. This increase is due to the correct matching of

the dc load to the PV module.Fig. 10shows the daily percentage increase in the system

output energy by the MPPT during 1 month.

The operating periods are the periods at which the dc load operates from the PV modulewithout stopping.Figs. 11 and 12show the module power and the normal operating power

for two cloudy days. The discontinuous periods in the figures mean that the system is

stopped.

Fig. 11shows that the direct coupling system stops more than 2 h through the day,

whileFig. 12shows that the stop periods lie at the day ends for more than 212

h. The system

Fig. 8. Matching factor of the MPPT during a sunny day.

Fig. 9. The PVP and NOP of the PV system and the corresponding increase in energy output by MPPT during a

sunny day.



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stops when the solar radiation falls below approximately 230 W/m2. On the other hand,

when using the MPPT (PVP curve) the system operates all the day hours without stopping

(the starting of the dc motor occurs at lower solar radiation). The continuous operation is

another advantage of using the MPPT, to connect the load to the PV module instead of

direct coupling.Fig. 13shows the air velocity and the air mass flow rate in the case of direct coupling

and with the MPPT in a sunny day. The figure shows clearly the great advantages of using

MPPT in increasing both the air velocity and the air mass flow rate.

Fig. 10. The daily percentage increase in the output energy of the PV system by the MPPT during 1 month.

Fig. 11. The PVP and NOP of the PV system measured in a cloudy day.



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8. Conclusions

A PC-based maximum power point tracker for a PV system using neural networks has

been developed and implemented. The system consists of a photovoltaic module with a

maximum power point tracker and a dc motor driving an air fan.

From the experimental results, the following conclusions can be deduced:

1. The PV system with the MPPT gives a good matching between the module and the dc

load under various operating conditions.2. The matching factor is about 97%, which means that about 97% of the actual maximum

power is drawn by the used MPPT.

Fig. 13. The air velocity and air mass flow rate in the case of direct coupling and with the MPPT in a sunny day.

Fig. 12. The PVP and NOP of the PV system measured in a cloudy day (second day).



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3. The radiation level or the module temperature does not affect the performance of the

MPPT.

4. The MPPT increases the system output energy by about 45.2% for clear sunny day. It

also maintains longer operating periods.5. The mechanical power is also increased due to the use of the proposed MPPT, where it

is related to the electrical power.

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4 Maximum Power Point Traking Controller for Pv