research article experimental learning of digital...

Research ArticleExperimental Learning of Digital Power Controller forPhotovoltaic Module Using Proteus VSM

Abhijit V. Padgavhankar and Sharad W. Mohod

Department of E & TC Engineering, PRMITR, Sant Gadge Baba Amravati University, Maharashtra 444602, India

Correspondence should be addressed to Abhijit V. Padgavhankar; [email protected]

Received 25 April 2014; Revised 29 May 2014; Accepted 6 June 2014; Published 15 September 2014

Academic Editor: Charles Michael Drain

Copyright © 2014 A. V. Padgavhankar and S. W. Mohod. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

The electric power supplied by photovoltaic module depends on light intensity and temperature. It is necessary to control theoperating point to draw the maximum power of photovoltaic module.This paper presents the design and implementation of digitalpower converters using Proteus software. Its aim is to enhance student’s learning for virtual system modeling and to simulate insoftware for PIC microcontroller along with the hardware design.The buck and boost converters are designed to interface with therenewable energy source that is PV module. PIC microcontroller is used as a digital controller, which senses the PV electric signalfor maximum power using sensors and output voltage of the dc-dc converter and according to that switching pulse is generatedfor the switching of MOSFET. The implementation of proposed system is based on learning platform of Proteus virtual systemmodeling (VSM) and the experimental results are presented.

1. Introduction

The growing market for renewable energy technologies hasresulted in a rapid growth in the need for power electronics.Due to the global concern about climate changes and sustain-able electrical power supply, renewable energy is increasinglybecoming more popular all over the world.

With the virtual system modeling (VSM) facility, it cantransform the product design cycle, in terms of reduced timeand cost. There are various tools that are available like NILabView, MATLAB/SIMULINK, Multisim, Orcad, and soforth. In looking to understand the best solution for gainingthe engineering knowledge practically, it is necessary to haveknowledge of simulation. Laboratories can be expensive andtime-consuming and difficult to understand [1]. The purposeis to use electronics simulation tool such as Proteus VSM forengineering education program. In many applications, dc-dcconverters are used to produce a regulated voltage or current[2, 3]. Inmany applications solar PVmodules were developedfor power satellites in space program, battery chargers, anddistributed power systems. In high power applications paral-lel connected converters are used to provide power [4–6].

The interfacing of PV modules with buck converterand boost converter was developed [7]. In closed loop, thefeedback signal to themicrocontroller is designed tomaintainthe output voltage level constant [8]. Inmany dc-dc convertercircuits, the power device selections are very important. Theparameters greatly affect the maximum switching frequencyof the converter and how much is the current; the convertercan be designed for these purposes [9].

Proteus VSM, developed by Labcenter Electronics Ltd.,was founded in 1988. The Proteus Design Suite is whollyunique in offering the ability to cosimulate both high andlow level microcontroller code in the context of a mixed-mode SPICE circuit simulation. Proteus’s VSM has micro-controller programming tool, environment, with its manysoftware features and hardware options. Many researchersand engineers use Proteus for testing and rapid prototypingin the product development process. In institutions of highereducation, Proteus can be useful for the electronics engineer-ing students to understand complex theories and connectthese to practical problems. Proteus VSM is now chosen asthe tool for the course projects due to its ability to providehands-on experiences for students, which is particularly

Hindawi Publishing CorporationJournal of Solar EnergyVolume 2014, Article ID 736273, 8 pageshttp://dx.doi.org/10.1155/2014/736273

2 Journal of Solar Energy

PV module

DC-DCconverter

Grid/battery

Feedbackcircuit

Modulator Controlalgorithm

PIC microcontroller

PSMsignal

Controlsignal

Setpoint

+−

Vi Vo

ΣVPV

IPV

Verr

Figure 1: Block diagram of DC-DC converter using PIC microcontroller as digital controller.

important for electronics engineering technology programs.This paper investigates the learning of software for utilizationand implementation of digital controller for maintainingthe maximum power due to variation in environmentalconditions for photovoltaic modules.

ProteusVSM is already unique in its capability to runnearreal-time simulations of complete microcontroller systems;its real power comes from its ability to perform these sim-ulations in single step mode. Proteus VSM is equipped withcomprehensive diagnostic or trace messaging. This allowsyou to specify which components or processor peripheralsare of interest at any given time and receive detailed textualreporting of all activity and system interaction. This isinvaluable as a debugging aid, allowing you to locate andfix problems in both software and hardware much fasterthan you could when working on a physical prototype.Proteus VSM also provides extensive debugging facilitiesincluding breakpoints, single stepping, and variable displayfor both assembly code and high level language source.Proteus VSM is uniquely suited to teach students about thedesign and operation of embedded systems solutions. Fullvirtual debugging interface is available in software, obviatingthe need for expensive hardware and facilitating freedom andflexibility to design and develop microcontroller solutionswithout the need for a physical prototype to the students.

The paper is organized as follows. Section 2 gives oper-ating configuration. Section 3 presents Proteus based imple-mentation. Section 4 presents simulation and experimentalresults, and Section 5 presents conclusion.

2. Operating Configuration

The proposed design configuration for photovoltaic moduleis mainly consisting of (i) buck converter and (ii) boostconverter and digital controller PIC16F628Amicrocontroller.The schematic blocks of the proposed system with dc-dcconverter with microcontroller are developed using ProteusVSMplatform.The real-timemicrocontroller is implemented

by using MikroC and MPLAB programming. The blockdiagram of proposed system is shown in Figure 1. Powerstage input which is the output of PV module is sensed byusing voltage and current sensor which sent to the digitalcontroller; the output voltage of power stage is applied todigital controller through feedback circuit as an error voltageby comparingwith set point voltage. According to this voltagedigital controller produces pulse skipping pulses (PSM) toswitch the MOSFET.

In the proposed scheme PIC16F628A microcontrollertakes the decision to generate the switching pulses to turnON and OFF the switches. MikroC orMPLAB programmingsoftware tool can be used to build source code and, aftercompiling, the hex file can be generated. Generated hex file isvery easy to burn in microcontroller memory using ProteusVSM. A wide range of microcontrollers is available in thesoftware, where as in this paper PIC16F628Amicrocontrolleris used in Proteus platform for switching the converters.

The solar PV module (𝑉PV) is connected to the dc-dc converter to maintain the generated dc voltage constantwhich is connected to dc grid or the battery or dc load.The output voltage (𝑉

𝑜) is sensed and sent to the digital

controller through feedback circuit. Feedback circuit con-tains the comparator which compares the 𝑉

𝑜and set point

voltage. Also PV module output and current which are theinputs to power stage are sensed by using voltage and currentsensors, respectively, to monitor the maximum power point.Generated error voltage by comparator is applied to thePIC microcontroller. The PIC16F628A has onboard voltagereference,𝑉ref, and comparators. In the proposed application,the 𝑉ref set point is at 2.5 V. According to set voltage, pulseskipping modulation is provided to the gate of MOSFET toturn ON and OFF.

2.1. Solar Cell Module. A solar PV module consists of anumber of 𝑁

𝑠solar cells in series and the equivalent circuit

of the physical model of the solar cell is given in Figure 2.

Journal of Solar Energy 3

+

+

−

−

�d

Rs i

id ir

iph �/Ns

Rsh

Figure 2: Equivalent circuit diagram of solar cell.

Table 1: Specifications of photovoltaic module.

Sr. number Electrical characteristics Value01 Product code SLP011-1202 Number of cells 3603 Standard light intensity 𝑆

𝑜1000

04 Ref. temperature 𝑇ref 25∘C05 Maximum power 𝑃max 11W06 Voltage at 𝑃max 17.6 V07 Current at 𝑃max 0.63A08 Open-circuit voltage 𝑉oc 21.1 V09 Short-circuit current 𝐼sc 0.68A10 Temperature coeff. of 𝑉oc −(80 ± 10) mv/∘C11 Temperature coeff. of 𝐼sc (0.065 ± 0.015%)/∘C12 Operating temperature −40∘C to 85∘C

The solar cells are made from semiconductors cells andare usually arranged in modules. There are different types ofsolar cells available in the market and are under developmentas sensitized nand-crystalline cells for high efficiency and lowcost. The datasheet parameters of physical PV module areshown in Table 1.

The solar cell describes the inverse relationship betweencurrent and voltage and the equations that describe a solarcell are as follows:

𝑖 = 𝑖ph − 𝑖𝑑 − 𝑖𝑟, (1)

𝑖ph = 𝐼sco ⋅𝑆

𝑆𝑜

+ 𝐶𝑡⋅ (𝑇 − 𝑇ref) , (2)

𝑖𝑑= 𝐼𝑜⋅ [𝑒 ⋅

𝑞 ⋅ V𝑑

𝐴𝑘

(1

𝑇ref−1

𝑇)] , (3)

𝑖𝑟=

V𝑑

𝑅sh, (4)

V𝑑= (

V𝑁𝑠

+ 𝑖 ⋅ 𝑅𝑠) (5)

𝑇 = 𝑇𝑎+ 𝑘𝑠⋅ 𝑆, (6)

where 𝑞 is the electron charge (𝑞 = 1.6 ∗ 10−19 C); 𝑘 is the

Boltzmann constant (𝑘 = 1.3806505 ∗ 10−23); 𝑆 is the light

intensity input; 𝑇𝑎is the ambient temperature input; V is the

0 10 20

V (V)

0 10 20

V (V)

I(A

)P

(W)

−2

0

2

4

6

8

10

12

−0.2

0

0.2

0.4

0.6

0.8

Figure 3: Characteristics of current versus voltage and power versusvoltage.

MOSFET

PWM pulses from PIC

+

L1

C1R1

Vin D1

Figure 4: Boost converter circuit diagram.

voltage across the entire solar module; and 𝑖 is the currentflowing out of the positive terminal of the solar module.

The photovoltaic module provides power to the loadwhich often operates away from the maximum operatingpoint of module. The characteristics curves for solar cellsimulated module are as shown in Figure 3.

2.2. DC-DC Boost Converter Configuration. The boost con-verter configuration by assuming continuous conductionmode of operation is shown in Figure 4.

The equations are consideredwhen themain switch isONand are shown in

𝑑𝑖𝐿

𝑑𝑡=1

𝐿(𝑉in) ,

𝑑V𝑜

𝑑𝑡=1

𝐶(−

V𝑜

𝑅) ,

0 < 𝑡 < 𝑑𝑇, 𝑄 : ON,

𝑑𝑖𝐿

𝑑𝑡=1

𝐿(𝑉in − V

𝑜) ,

𝑑V𝑜

𝑑𝑡=1

𝐶(𝑖𝐿−V𝑜

𝑅) ,

𝑑𝑇 < 𝑡 < 𝑇, 𝑄 : OFF.

(7)


Table 2: Designed parameters for boost converter.

Parameters ValueInductor, 𝐿 1mHCapacitor, 𝐶 47 uFDuty cycle,𝐷 5% to 95%Switching frequency, fsw 75KHzLoad resistance, RL 37.5ΩMOSFET IRF540

The following parameters are necessary for the powerstage: (i) input voltage range 𝑉min and 𝑉max and (ii) nominaloutput voltage 𝑉out and maximum output current 𝐼out. Thefirst step to calculate the switch current is to determine theduty cycle, for the minimum input voltage. The minimuminput voltage is used because this leads to the maximumswitch current. Consider the following:

𝐷 = 1 −𝑉in min × 𝜂

𝑉out, (8)

where 𝜂 is the efficiency of the converter.The efficiency is added to the duty cycle calculation,

because the converter has to deliver also the energy dissi-pated. Consider the following:

Δ𝐼𝐿=𝑉in min × 𝐷

𝑓𝑠× 𝐿

, (9)

where 𝑓𝑠is the switching frequency and 𝐿 is the selected

inductor value. Consider

𝐿 =𝑉in × (𝑉out − 𝑉in)

𝑓𝑠× Δ𝐿 × 𝑉out

. (10)

To reduce losses, Schottky diode is used. Consider thefollowing:

𝐼𝑓= 𝐼out max, (11)

𝐶out min =𝐼out max × 𝐷

𝑓𝑠× Δ𝑉out

. (12)

Table 2 shows the designed value of components for boostconverter as per above equations.

2.3. DC-DC Buck Converter Configuration. The state equa-tions corresponding to the converter in continuous conduc-tionmode are used by applying Kirchhoff ’s voltage law on theloop containing the inductor and Kirchhoff ’s current law onthe node with the capacitor branch connected to it.When theideal switch is ON, the dynamics of the inductor current 𝑖

𝐿(𝑡)

and the capacitor voltage V𝐶(𝑡) are given in (13) and (14).

The buck converter configuration with ideal switchingdevices is considered as shown in Figure 5. Consider thefollowing:

𝑑𝑖𝐿

𝑑𝑡=1

𝐿(𝑉in − V

𝑜) ,

𝑑V𝑜

𝑑𝑡=1


𝑅) ,

0 < 𝑡 < 𝑑𝑇, 𝑄 : ON(13)

MOSFET

PWM pulses from PIC

+

L1

C1R1

Vin

D1

Figure 5: Buck converter circuit diagram.

Figure 6: Block diagram of PIC microcontroller.

Table 3: Designed parameters for buck converter.

Parameters ValueInductor, 𝐿 1mHCapacitor, 𝐶 470 uFDuty cycle,𝐷 5% to 95%Switching frequency, fsw 75KHzLoad resistance, RL 3ΩMOSFET IRF540

and when the switch is OFF they are presented by

𝑑𝑖𝐿

𝑑𝑡=1

𝐿(−V𝑜) ,

𝑑V𝑜

𝑑𝑡=1


𝑅) ,

𝑑𝑇 < 𝑡 < 𝑇, 𝑄 : OFF.(14)

The critical inductor is calculated in (10). Consider thefollowing:

𝐿 =𝑅

2𝑓𝑠

(𝑉in − 𝑉𝑜) . (15)

The critical capacitor is calculated assuming change in voltageas in (11). Consider the following

𝐶 =𝐷

8𝐿𝑓2𝑠Δ𝑉𝑜

(𝑉in − 𝑉𝑜) . (16)

Table 3 shows the designed value of components for buckconverter as per above equations.

2.4. Pulse Skip Modulation (PSM) and Pulse Width Modu-lation (PWM). One of the simplest modulation techniques


PV moduleFeedback

circuit

PIC microcontroller

PSMsignal

Vi Vo

123

4

678910111213

1516 17

18RA0/AN0RA1/AN1

RA2/AN2/VREFRA3/AN3/CMP1

RA4/T0CKI/CMP2RA5/MCLR

RA6/OSC2/CLKOUTRA7/OSC1/CLKIN

RB0/INTRB1/RX/DTRB2/TX/CK

RB3/CCP1RB4RB5

RB6/T1OSO/T1CKIRB7/T1OSI

PIC16F628A

DC-DC converter Grid/battery

VPV

IPV

Figure 7: Digital power controller scheme in Proteus.

used for controlling a dc-dc converter is pulse skippingmodulation (PSM), which is also known as pulsed frequencymodulation (PFM). In a PSM system, the modulator gener-ates a train of pulses to turn the converter power switch ONand OFF. The pulses have a fixed pulse width and period.As long as the dc-dc converter output is below the desiredtarget, the PSM pulse continues to run the converter switch.This operation will result in decreasing pulse density as theconverter output reaches its target, or as the output loadingdecreases. When the converter output falls below the target,or as the output loading increases, the PSM pulse density willincrease. Similarly the PWM is used to maintain the constantoutput voltage by varying the ON and OFF period of thepulse.

3. Proteus Based Implementation

Proteus VSM includes a number of virtual instruments likean oscilloscope, logic analyzer, function generator, patterngenerator, counter timer, virtual terminal, and simple volt-meters and ammeters. In addition, it provides dedicatedmaster/slave/monitor mode protocols.

Proteus provides detailed measurements on graphs andperforms other analysis types such as frequency, distortion,noise, or sweep analyses of analogue circuits. It is capable ofsupporting schematic capture for both simulation and PCBdesign. The proposed designed prototype is implemented forbuck and boost converter. The PIC microcontroller blockdiagram is shown in Figure 6.

The controller tends to maximise the output power fromphotovoltaic module by adjusting the duty cycle so that thesolar cell module will always be at its maximum power at alltimes. Digital controller automatically increases or decreasesthe voltage applied to the pulse generator (PWM) in order to

change the duty cycle of the converter according to the PVmodule output voltage. The maximum power point loop isused to set the corresponding 𝑉ref to the input; the voltageregulator loop is used to regulate the solar output voltageaccording to reference, which is set as maximum operatingpoint and control scheme is shown in Figure 7.

This firmware modulator generates the PSM pulses onthe RB7 pin (port B, bit7), to drive the gate of MOSFETswitch of converter. When the dc-dc converter output isbelow the desired value, the firmware continuously sends outPSM pulses to increase the converter output. Once the dc-dcconverter output exceeds the target, the controller will skipthe PSMpulses until the output voltage, or current, falls belowthe threshold and the control cycle repeats.

The program is simulated in Proteus VSM and it has abil-ity of interaction between software running on a microcon-troller and analog or digital signal connected to it. It simulatesthe execution of object code (machine code), like a real chip.The programming logic using PIC is written with the help offlowchart. PIC performs themodulator function in firmware.To get the maximum power point, many methods have beenproposed.The program is developed using the flow chart andis shown in Figure 8.

Timer0 of the microcontroller is used to generate a timebase for the firmware modulator. Timer0 is enabled and theTMR0 register is loaded with a reload value. When Timer0overflows, an interrupt occurs. In the interrupt routine,TMR0 is again loaded with the reload value.The reload valuedetermines the time base of the PSM signal. In this program,the TMR0 reload value is chosen to produce a time base of 50microseconds when the microcontroller runs from a 16MHzcrystal. The comparator has several configurations, whichallow the comparators to compare external voltage to the𝑉refvoltage. To select this configuration, the comparator controlregister CMCON must be set. In it only C2 comparator of


Main

Initialize ports

Initialize comparatorsAN0 pin is input toC1 comparator

Enable VrefVref = VDD/2

Wait for

ISR

Reload TMR0

Flag = 1

VAN0 > Vref ? No

No

Yes

Yes

Flag = 0

Turn off pulse

interrupt flag

Flag = 1?

Turn on pulse

Return

Save W and status registers

Restore W and status registers

Initialize Timer0enable Timer0 interrupt

Timer0 interrupt

Clear Timer0

Figure 8: Flowcharts of program.

Figure 9: Generated PSM pulses on CRO screen1.

the PIC is used to compare the feedback voltage on theAN1 pin to the internal voltage reference 𝑉ref. If the dc-dcconverter output is lower than the desired value, then thefeedback voltage presented on AN1 is lower than 𝑉ref. Thevoltage control algorithm performed in firmware becomesvery simple; if the voltage on AN1 pin is lower than 𝑉ref, thenproduce PSM output pulse; else voltage on AN1 pin is higherthan 𝑉ref; then skip PSM output pulse shown in Figure 9where the duty cycle of PWM pulse varies approximately inbetween 5% and 30% and 30% and 95% as shown in Figure 10.

The actual implemented hardware is shown in Figure 11and its PWM output pulses on DSO are shown in Figures 12

Figure 10: Generated PSM pulses on CRO screen2.

Figure 11: Experimental setup.

and 13. Thus simulated result of digital power controller isexactly matched with actual hardware results.


Figure 12: Generated PSM pulses on DSO.

Figure 13: Generated PSM pulses on DSO.

4. Proteus Simulation andExperimental Results

The dc-dc converter with PIC16F628A is designed for com-patible load to achieve maximum power from photovoltaicmodules. The buck converter results are shown in Table 4.

Table 4 shows the input voltage𝑉in, output voltage𝑉𝑜, andoutput current 𝐼

𝑜, when considering load of 3Ω. From the

table, it is clear that change in 𝑉in, output voltage maintainconstant which approximately 1.5 V and 𝐼out is 0.39A whichare shown in Figure 14 by green and red colour, respectively.

Table 5 shows the boost converter result, in which inputvoltage changes to down from high value; the output voltage𝑉out ismaintained constant at approximately 24Vwith outputcurrent 𝐼out 0.63A.The response of digital controller for boostconverter is shown in Figure 15.

Here the design of buck converter is for obtaining theoutput voltage step down of 1.2 V, and output current is0.39A where the input voltage varies from 5V to 100V andboost converter is for obtaining the output voltage step upof 24V, and output current is 0.63A where the input voltagevaries from 17.6V to 6V. From responses of buck and boostconverter it is verified. Simulated and actual hardware resultsare approximately matched with each other. Therefore usingPIC16F628A microcontroller these dc-dc converters workefficiently for photovoltaic module.

5. Conclusion

The effectiveness of student learning becomes more easyand effective using Proteus software in the laboratory with-out implementing the physical prototype of a design. Therole of digital power controller in the renewable energysystem is important to maintain the output voltage andcurrent to a required suitable level. The purpose of proposedscheme is for maximum power operating point to adjustthe photovoltaic operating voltage close to maximum underchanging atmospheric condition. To realize the prototype

0.00 20.0 40.0 60.0 80.0 90.010.0 30.0 50.0 70.0 100.0

Time (ns)

Volta

ge (V

)

Vout

Iout

0.00

200n400n600n800n1.00

1.20

1.40

1.60

1.80

2.00

Step down 1.5V

Current 0.4A

Figure 14: Response of buck converter when 𝑉in = 5V.

0.00 20.0 40.0 60.0 80.0 90.010.0 30.0 50.0 70.0 100.0

Time (ns)

Volta

ge (V

)

Vout

Iout

Boosted output voltage 24V

Current 0.63A0.00

5.00

10.0

15.0

20.0

25.0

30.0

35.0

40.0

Figure 15: Response of boost converter when 𝑉in = 17.6V.

Table 4: Result of buck converter.

Sr. number 𝑉in (volts) 𝑉out (volts) 𝐼out (amp)01 5 1.189 0.3902 10 1.189 0.3903 15 1.199 0.3904 25 1.199 0.3905 50 1.199 0.3906 100 1.210 0.39

Table 5: Observation table for boost converter.

Sr. number 𝑉in (volts) 𝑉out (volts) 𝐼out (amp)01 17.6 23.9 0.6402 15 23.8 0.6303 12 23.8 0.6304 10 23.8 0.6305 8 23.8 0.6306 6 23.8 0.63

experience without implementing it, using Proteus VSM iseasy for implementation and execution. The desired logicaccording to flowchart can be programmed using MPLABor MikroC compiler and generate hex code file and burningin PIC16F628A microcontroller in Proteus VSM is simpleprocess. PICmicrocontroller is used as a digital controller fordc-dc converter where investigation for photovoltaic moduleapplication using Proteus VSM software and result are satis-factorily executed and verified with physical prototype.


Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper.

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