Control Circuit based Microcontroller Implementing a New

Sinusoidal Pulse with Modulation Technique for Solar Inverter

Abdennabi Brahmi

, Abdelouahed Abounada

, Zakaria Massaq

and Aumeur El Amrani

Faculty of Sciences and Techniques, Statistical Physics and Systems Modeling Laboratory, Errachidia, Morocco

Faculty of Sciences and Techniques, Automatics and Energy Conversion Laboratory, Beni-Mellal, Morocco

Keywords: Sinusoidal Pulse Width Modulation SPWM, DC/AC Inverter, Discretized Sinusoidal Signal, Look Up Table,

PIC16F876 Microcontroller.

Abstract: This paper presents a new technique to generate a digital Sinusoidal Pulse Width Modulation (SPWM) control

using PIC16F876 microcontroller. This technique is mainly used to control the DC/AC inverter output voltage

in many applications such as photovoltaic pumping system and motor drive. It reduces significantly low

harmonic components as well as distortion factor. The principle of this method is to transform the sampled

dc-biased sine wave signal to a repeating pulses train. The widths of these pulses vary sinusoidally and thus

as a digital SPWM. The different amplitude modulations index started from 0.5 until 1.3 (over modulation)

with 1 kHz switching frequency was implemented and tested. The literature review of the existing digital

SPWM techniques is presented firstly. Subsequently the proposed SPWM approach is briefly detailed.

Finally, experimental results are presented to demonstrate the validity of this SPWM method and the good

functionality of the realized control unit.

1 INTRODUCTION

Pulse width modulation PWM is widely used in

power electronics to digitize the power so that a

sequence of alternating voltage pulses can be

generated by the on and off of the inverter power

switches (Lucien, 2008), (Selvabharathi, Kamatchi,

Sathish, 2018.). Inverter is defined as a converter that

is used to change a DC input voltage to an AC output

voltage of desired magnitude and frequency

(Gavaskar, Maheswari, Adi, 2017), (Tarchanidis,

Lygouras, Botsaris, 2013). The output voltage of an

ideal inverter is the sinusoidal waveform which could

be fixed or variable at a fixed or variable frequency.

For the inverter, the harmonics spectrum exist at all

odd number of harmonics. The low-pass filter design

at the output of the inverter also can be quite difficult

(Gavaskar, Maheswari, Adi, 2017).

Sinusoidal PWM SPWM is as the alternative due

to the fewer harmonics introduced and it is widely

used method for major AC appliances. The analogue

method compares triangle wave which is used as

carrier with the sinusoidal wave as the reference

signal, whose frequency is the desired output

frequency. The fundamental component is useful for

any alternating current application. The digital

SPWM version is inspired from analogue SPWM

(Lucien, 2008).

With Field Programmable Gate Array FPG device

(Selvabharathi, Kamatchi, Sathish, 2018), Digital

Signal Processor DSP (Gavaskar, Maheswari, Adi,

2017), both the sine wave and triangle wave are

generated by a special intern controller. An internal

comparator is used to compare these signals. The

crossover points are used to determine the switching

instants such that if the sine wave is greater than

triangle wave then the output is high otherwise output

is low, thus a SPWM is created. These devices have

very high performance and density, more flexible but

present high cost.

With microcontrollers, there are three most

methods used to generate the SPWM. The first one

uses generally a counter (Abdel, Thomas, Ramadan,

2017). These counters have the task to create the sine

wave using a look up table of a pre-calculated sine

values. The triangle wave also is created with another

counter along with a control bit showing the slope

(positive – up, negative-down).

These two tasks are executed by the interrupt

service routine and are running in parallel with the

Brahmi, A., Abounada, A., Massaq, Z. and El Amrani, A.

Control Circuit based Microcontroller Implementing a New Sinusoidal Pulse with Modulation Technique for Solar Inverter.

DOI: 10.5220/0009775102710276

In Proceedings of the 1st International Conference of Computer Science and Renewable Energies (ICCSRE 2018), pages 271-276

ISBN: 978-989-758-431-2

271

main program routine. The computation time

consumed by the interrupt service routine is

negligible. The second task consists of an endless

loop that has the task to continuously compare the

current triangle and sine values. The comparison

result will be responsible to create the SPWM trigger

signals.

The second technique uses the simple software

modulation (multiplication) on microcontroller

(Tarchanidis, Lygouras, Botsaris, 2013). A sine wave

(with unity magnitude and low frequency) is

multiplied with the impulse train (with high

frequency and unity magnitude) in order to create a

train of SPWM pulses. Theses SPWM triggers can be

generated in such a manner that starting position of

pulse should be same as that of impulse and duty

cycle of the pulse must be equal to the product of unit

impulse and value of sine wave at that instant.

The third approach (Bilal, 2018) uses the output

compare modules in the DSPIC33FJ microcontroller.

This microcontroller contains two output compare

modules. Both these Outputs are used to generate

SPWM using two look up tables; sine look up table

and triangular look up table. Each module use two

sixteen bit timers that is Timer 2 and Timer 3. OCM

triangular values in each period time of the triangular

and write the comparison results to OCxR and OCxRS

registers of the output compare modules.

When both values become equal to each other,

state of output pin changes. It happens only once in

one period of PWM.

The simplicity without increasing resources,

programmability, the medium rapidity and the low

cost make the microcontroller device the most

favourable choice for prototyping digital control

circuit for our solar pumping inverter (Pattnaik,

Dash, Mukherjee, 2009), (Salam, 2001).

The new method we proposed in this work

consists on storing the different pulse widths (i.e. duty

cycles) of the desired SPWM signal in a look up table.

These duty cycles are obtained beforehand from

discrete values of a continuously dc-biased sinusoidal

function.

These results are stored in memory as a pulse

width table covering the entire period of the output

signal of the inverter.

This method offers several advantages in terms of

resolution and gain of the generated SPWM signal,

which remain constant regardless of the PWM output

frequency even at high frequency. The main feature

of this approach is the simplicity of the hardware;

only a very simple microcontroller with its associated

PWM output modules is required without using a test

of comparison. This results in a simple, low cost and

reliable control for a solar pumping system. The full

detail of this approach is given in the following

section.

2 PROPOSED DIGITAL SPWM

TECHNIQUE

2.1 Theory

The pulse widths (i.e. duty cycles) are constructed

from discrete values of a sinusoidal function (Ismail,

Taib, Isa, Daut, Mohd Saad, Fauzy, 2007). To

generate the repeating SPWM pulse train in complete

frequency F

ref

cycle of the sine reference wave cycle,

we first need a table whose values represent the

magnitude of this sine wave using the following

formula (Gavaskar, Maheswari, Adi, 2017):

sin













For i = 0…n-1

(1)

Since the PWM registers of the 16F876 accept

only positive values (PIC16F87X microcontrollers,

2001), (Ismail, Taib, Mohd Saad, Isa, Daut, 2006), we

can transform modulated sine wave in a dc-biased

sine wave to avoid the negative values. With this

transformation, the dc-biased sine wave samples S

can be written as:

dci





 )

sin(



For i = 0…n-

(2)

Where i is the sample number, and n is the number

of samples per complete F

ref

sine wave cycle. This

number is the equivalent parameter of the frequency

modulation index in the analogue SPWM control

(Ismail, Taib, Daut, Mohd Saad, Fauzy, 2007). It

depends on the desired switching frequency F

of the

SPWM patterns and the F

ref

sine wave cycle as:

ref

n 

(3)

A is the amplitude of the considered sine wave,

this parameter depends with the desired amplitude

modulation index m

like in

analogue SPWM control

(Ismail, Taib, Mohd Saad, Isa, Daut, 2006.) and with

ICCSRE 2018 - International Conference of Computer Science and Renewable Energies

272

PR2 register’s value (PIC16F87X microcontrollers,

2001):

2PR



(4)

PR2: period register of the PIC16F876.

B: the dc-biased value it depends with the value

that will be specified in PR2 register, this value is the

half of PR2 value that is expressed as follows:

B 

(5)

A table of n values (sample points) of a complete

ref

sine wave cycle with an angle resolution (2*π/n)

is obtained using equation (2). These samples values

represent the pulse width values or exactly the duty

cycles that can be sent periodically based Timer 2

interrupt mechanism to the PWM modules to generate

the desired SPWM switching signal. The period T

the SPWM signal is set by writing to the PR2 register

(PIC16F87X microcontrollers, 2001) using:

TpTPRTs

osc

 4)12(

(6)

Where T

osc

is the timer oscillator and T

is the

timer prescaler value.

The duty cycles d

are specified by writing S

dci

values to the CCPRxL registers (x=1, 2) using only

eight MSBs (PIC16F87X microcontrollers, 2001):

TpTCCPRxLd

oscw

 )(

(7)

Based on equation (7), the PWM module

transforms the S

dci

values to a duty cycles values d

When the CCP modules are used in the PWM

module (PIC16F87X microcontrollers, 2001), the

timer 2 register is used as the PWM time base. It

works by incrementing a counter at a user set

frequency F

, and when the value of this counter

equals the period programmed in PR2 register, an

interrupt is generated at each T

period.

The main idea to generating the repetitive pulse

train that varies sinusoidally is the use of the PWM

module based its Timer 2 interrupt, so in each

interrupt; the duty cycles d

values is read from the

sampled sine value in look up table and then sent to

CCPRxL registers. This approach is repeated for all

the n values in the created look up table in order to

generate SPWM patterns for complete T

ref

period.

To generate the SPWM in the sine wave cycle

ref

=50Hz), we noticed that only have to save a

quarter value of the calculate values d

in a look up

table array. This quarter allows creating the first

SPWM quarter using a p pointer and a i counter.

The remained three SPWM quarters were

deduced from this first SPWM1 quarter. Based only

this created look up table, the complementary

SPWM2 of the SPWM1 can be also deduced using

the same p pointer with a similar manner.

2.2 Numerical Application

For this implementation, the values of used

parameters are given in table 1 bellow.

Table 1: The values of used parameters.

ref

PR2 n B

1 kHz 50 Hz 104 60 52

Using the equation (6), to obtain F

equal to 1

kHz, we might use the timer prescaler with the value

16, and write 104 values to PR2 register. Based on

equation (3), at this frequency, the number n of pulses

per complete cycle of a reference frequency F

ref

of 50

Hz is n= 60.

From equation (4), the constant A depends on the

desired modulation index m

and the PR2 value.

Knowing that CCPR1L and CCPR2L are an 8-bit

registers, from equation (5), the constant B is equals

to 52, and i=0…59. The exact number that need to be

stored in look up table and thus be loaded into the

pulse width register PWM must therefore equal to S

dci

values obtained using equation(2) multiplied by the

amplitude modulation index m

The amplitude of the inverter output voltage is

controlled by m

. This is significant for using

photovoltaic panels to supply this inverter, because

the photovoltaic source produce a variable output

voltage according to the variations of the climatic

conditions. Thus producing constant amplitude

output voltage. If m

is greater than 1 (over

modulation), the amplitude of the output voltage

increase with m

, but not linearly. In order to work in

region, the m

must be lower than 1 to keep a linear

relationship between m

and the output voltage

amplitude in ordrer to control the solar inverter’s

output voltage.

Matlab Simulink software was used to generate

60 pulse widths train for i=0…59. And then we store

only its 15 first values in look up table array. This

trick allows optimizing the used of the

microcontroller memory program.

Control Circuit based Microcontroller Implementing a New Sinusoidal Pulse with Modulation Technique for Solar Inverter

273

3 SYSTEM DESIGN

The basic schematic diagram of the solar pumping

inverter to be designed and realized in our laboratory

is shown in the figure 1 below:

Figure 1: Control circuit of solar pumping inverter.

It consists of two parts: the power circuit and the

control circuit. In this work, we focused on the control

circuit. This last circuit is formed by many blocs; its

heart is a PIC16F876 that generate two

complementary SPWMs.

This section involves two parts: the Hardware and

the Software. Indeed, the Software development

involves the application of C language using CC5X

compiler integrated with MPLAB Software based

Bootloader technique (Beningo, 2015).

3.1 Hardware Design

The proposed technique deals with the use of a

PIC16F876 microcontroller for the implementation.

The use of this microcontroller brings more

reliable and resilient to change in software than

analogue devices. The advantage of this new method

is the use of a little calculation, and a discretized dc-

biased sinusoidal signal look up table values is

needed.

The schematic circuit for programming the

microcontroller was drawn as shown in figure 2.

There are two integrated circuits in this schematic

circuit. One is the PIC microcontroller, which does

almost everything. The other is a MAX232 chip

which converts TTL level (5V) signals to RS232

levels (12V) so that you can talk between a personal

computer's serial port and a TTL level UART device.

In order to ensure the microcontroller function, as

supply of 5 volts has to be provided to V

pin of the

PIC chip.

Figure 2: Schematic circuit for PIC programming using

Bootloader technique.

Therefore, High Speed crystal (HS) of 4 MHz is

chosen. The PWM pins were used to generate two

complementary 5 volts level SPWM patterns.

3.2 Software Design

The flowchart (figure 3) of the SWPM patterns

generation is composed into two parts: main function

and interrupt service routine (ISR) function.

Figure 3: SPWMs patterns flowchart generation.

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274

On reset, all hardware setting from the

microcontroller configuration is loaded into the

device and main function is executed firstly.

The figure 4 shows an infinite loop is entered,

when Timer 2 reaches the PR2 value (TMR2

overflow), the interrupt service routine (ISR) is

executed.

Figure 4: Interrupt Service Routine flowchart.

In this routine, the duty cycles values in look up

table are read and sent to CCPR1L and CCPR2L

registers every time when the TMR2 overflow. This

figure describes all the operations taking place in this

interrupt based p pointer and i counter.

This p pointer is incremented, to point the next

duty cycle value in the table, and the i counter is also

incremented in order to indicate the corresponding

SPWM quarter. In each T

, a new values are read and

sent to CCPR1L and CCPR2L registers. In this

interrupt mechanism, we have four tests to determine

the corresponding SPWM quarter.

The duty cycles values are read from the table and

then sent to the CCPRxL registers (x=1, 2) to generate

two complementary SPWM signals. The loop can be

terminated by resetting the reset switch of the

hardware bar. These SPWM signals will be used to

turn on and off the inverter’s power transistors in

order to create a sine wave output voltage with

reference frequency F

ref

4 EXPERIMENT RESULTS

The experimental setup is tested for different

amplitude modulation index m

for F

ref

=50Hz and

=1kHz. The selected results have been chosen to

illustrate some of main futures of microcontroller

SPWM control, which have been presented in this

paper. The control circuit is expected to output two

pulses with varying duty cycles that are 180° out of

phase with 1kHz switching frequency that depicted in

figure 5 to figure 8 below.

Figure 5: Complementary SPWMs for m

= 0.5.

Figure 6: Complementary SPWMs for m

= 0.7.

Figure 7: Complementary SPWMs for m

= 0.8.

Control Circuit based Microcontroller Implementing a New Sinusoidal Pulse with Modulation Technique for Solar Inverter

275

Figure 8: Complementary SPWMs for m

=1.3 (over

modulation).

These figures show the switching signal for

difference amplitude modulation index m

=0.5;

0.7; 0.8 and m

=1.3).

These results illustrate the amplitude modulation

index effect in the size of the pulses width. When the

is lower, the size of pulse is reduced and vice

versa. This allows implementing a very simple

adaptive voltage control for an inverter.

The results are very close to the expected values,

which certify that the SPWM control circuit is

functioning appropriately. For the reasons of safety

and to ensure better switching mechanism in the

power circuit, an opto-coupler and driver must be

inserted between the microcontroller output and the

power switches of the solar inverter.

5 CONCLUSION

The main task in this work was to develop a new

SPWM technique for the inverter control circuit for a

solar pumping system using look up table technique.

This proposed approach remains very simple and

allows eliminating the use of more electronic

components, thus a low price and minimum

occupation in the PCB board concept.

The investigated controller approach is able to

produce two complementary SPWMs with desired

switching frequency and amplitude modulation

index. The efficiency of this method is that the output

pulse width can be easily varied by changing PWM

index and thus a simple

adaptive control system can be implemented.

Also, this technique may be extended for a three-

phase solar inverter for pumping system.

The obtained experimental results were presented

and they were found to agree well with other

established work. In addition, we are working on the

practical realization of a new and compact solar Boost

pumping inverter.

REFERENCES

Lucien, N., Leary, M., 2008. Digital SPWM synthesis for

the design of single phase inverters, International

Journal of Electronics, Taylor & Francis Vol. 95, No. 5,

pp: 489–503.

Selvabharathi, P., Kamatchi K., V., Sathish, K., S., 2018.

SPWM based speed control of induction motor using

FPGA controller, International Journal of Pure and

Applied Mathematics; Vol. 119, No. 18, pp:2395-2403.

Gavaskar, R., B., Maheswari, L., Adi, G., K., 2017.

Performance improvement of single phase inverter

using SPWM. In ICMAEM’07, Conference Series

Materials Science and Engineering. India.

Tarchanidis, K., N., Lygouras, J., N., Botsaris, P., 2013.

Voltage stabilizer based on SPWM technique using

microcontroller, Journal of Engineering Science and

Technology Review, Vol. 6, No. 1, pp:38-43.

Abdel, S., S., Thomas, J., Ramadan M., 2017. Design and

Implementation of a Single Phase SPWM Inverter

Based Microcontroller for Wind Energy Conversion

Systems, International Journal of Systems Applications,

Engineering & Development, Vol. 11, pp: 291-296.

Bilal, 2018. DsPIC33F microcontroller based pure sine

wave inverter, microcontroller project,

microcontrollersLab.com.

Pattnaik, B., S., Dash, D., K., Mukherjee, J., 2009.

Implementation of PWM based firing scheme for

multilevel inverter using microcontroller, Department.

Electronic Engineering National Institue of

Technology, Rourkela-769008, Orissa.

Salam, Z., K., 2001. Generation of Pulse Width Modulation

PWM signals for three-phase inverter using a single

chip microcontroller, Jurnal Teknologi, 34(D),

Universiti Teknologi Malaysia, pp.1-12.

Ismail, B., Taib, S., Isa, M., Daut, I., Mohd Saad A., R.,

Fauzy, F., 2007. Microcontroller implementation of

single phase inverter switching strategies, In CIM’07,

International Conference On Control, Instrumentation

and Mechatronics Engineering. Johor Bahru, Malaysia,

pp: 104-107.

PIC16F87X microcontrollers, 2001. datasheet, DS30292C,

Microchip Technology, available:

www.microchip.com.

Ismail, B., Taib, S., Mohd Saad, A., R., Isa, M., Daut, I.,

2006. Development of control circuit for single phase

inverter using Atmel microcontroller. In ICMMS’06,

International Conference of Man-Machine System.

Langkawi.

Beningo, J., 2015. Bootloader Design for Microcontrollers

in Embedded Systems.

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276