IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 08, 2016 | ISSN (online): 2321-0613
Analysis of Solar PV Inverter based on PIC Microcontroller and
Sinusoidal Pulse Width Modulation
Shamin Pandit1 Maulik Sanghvi2
1
B.E Student 2Project Guide
1
Department of Electronics & Communication Engineering
1
Kalol Institute of Technology, Kalol, Gujarat, India
Abstract— This paper focuses on design and development of
a solar PV inverter capable of delivering photovoltaic energy
to load in efficient and cost effective manner so that common
people can use it. The solar inverter in this paper is considered
for a stand-alone solar PV system, for operation of single
phase AC load at grid frequency and voltage. Interfacing the
solar inverter with AC load involves three major tasks. One
is providing regulated output of 230Vrms AC. Second is, it
should provide output at 50Hz frequency. Third is, it should
have sine wave output. The major challenges to be addressed
are, boosting the DC voltage of Solar Module and converting
it to regulated AC voltage. So this paper proposes a solution
by dividing the whole Inverter system into two major stages:
DC-DC Converter and DC-AC Inverter. In the DC-DC
Converter stage, Half-Bridge Push-Pull topology is used
which implements a high frequency transformer. In the DCAC inverter stage, full bridge topology is used implementing
SPWM switching technique using PIC controller. Based on
this design, a hardware prototype of Solar PV Inverter is
developed for 100VA.
Key words: DC-AC Inverter, DC-DC Converter, LC Filter,
Sinusoidal Pulse Width Modulation (SPWM), Solar PV
System.
voltage. DC-AC Inverter implementing full bridge inverter
topology is used to convert DC power into AC power. In DCAC Inverter digital method is used instead of analog method
to implement SPWM technique, to increase switching
efficiency and reliability. To remove the harmonics present
in the output voltage due to high switching frequency, low
pass LC filter is designed.
II. PROPOSED DESIGN
Figure 1 shows the basic block diagram of the proposed
system. The range of the inverter circuit is to obtain a desired
output voltage of 230Vrms AC and a frequency of 50Hz. The
contents of the designed system are:1) Inverter Topology Selection and design
2) Sine Wave Generation (SPWM)
3) LC Filter Design
4) Simulation (PSIM)
5) DC-DC Push-Pull converter design
6) Transformer design
7) DC-AC Full Bridge inverter design
8) SPWM Implementation using microcontroller
9) Simulation for SPWM in PROTEUS
I. INTRODUCTION
In the field of power sector these days, one of the major
concerns is day-by-day increase of power demand. But the
quantity and availability of conventional energy sources are
not enough to meet up the rising power demand. While
thinking about future availability of conventional sources of
power generation, it has become very important that the nonconventional energy sources must be utilized along
conventional energy sources to fulfill the rising demand of
energy. One of these non-conventional energy resources is
the solar energy, extracted from the sun radiation. With
continuously reducing cost of solar PV power generation and
the further increase of energy crisis, solar PV power
technology obtains more application. This paper is about to
convert solar energy into electrical energy with innovative,
efficient and cost effective method, making it suitable for
common people to use [1]. In this paper, a solar PV inverter
is introduced for operation of single phase AC load at grid
frequency and voltage. While incorporating a single solar PV
inverter with AC load, there are some issues to be addressed
like to boost the voltage of solar PV module upto grid voltage
level and Convert the DC power generated by solar PV
module into AC power. The paper leads to the solutions, DCDC Converter implementing push-pull topology will be used
to boost the voltage of solar PV module upto grid voltage
level. To regulate the voltage, feedback control system is
implemented using IC SG3525 in DC-DC Converter.
Transformer is used to provide galvanic isolation and boost
Fig. 1: Block diagram of the Solar PV Inverter
A. Inverter Topology Selection:
As we require dielectric isolation between input and output,
the non-isolated topologies can be ruled out. The Fly-back
and Forward topology have very simple circuit and are also
cheaper, but they are rated for lower power rating. Also they
operates transformer in only 1 domain which leads to underutilization of transformer core which increases the weight and
space taken by the device at higher rating. So we can rule
them out. In Full bridge topology, they are suitable for higher
power rating, because they cannot deliver higher efficiency at
lower power rating. For the considered power rating, only
Push-Pull and Half bridge topology are best suitable[4].
Compared to Push-Pull, output currents are much higher in
half bridge topology thereby making it less suited for high
current output. While in case of Push-Pull, the switch stresses
are very high (2∙VIN), so rating of switching device
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Analysis of Solar PV Inverter based on PIC Microcontroller and Sinusoidal Pulse Width Modulation
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(MOSFET/IGBT) should be carefully chosen. Figure 2 shows
the Push-Pull Converter.
Fig. 2: Push-Pull Converter
`Figure 3 shows Single Phase Full Bridge Inverter.
It consists of two arms with a two semiconductor switches on
both arms with anti-parallel freewheeling diodes for
discharging the reverse current. In case of resistive-inductive
load, the reverse load current flow through these diodes.
These diodes provide an alternate path to inductive current
which continue so flow during the Turn OFF condition [2].
Moreover, in this approach a True Sine Wave Inverter is used
because Most of the electrical and electronic equipment are
designed for the sine wave. Some appliances such as variable
motor, refrigerator, microwave will not be able to provide
rated output without sine wave. Electronic clocks are
designed for the sine wave and harmonic content is less [2].
harmonic is still present and there is relatively high amount
of higher level harmonics in the signal [2].
The modulating signal is a sinusoidal of amplitude
Am, and the amplitude of the triangular carrier is Ac, the ratio
m=Am/Ac is known as Modulation Index (MI). Note that
controlling the MI controls the amplitude of the applied
output voltage. A higher carrier frequency results in large
number of switching per cycle and hence increased power
loss [3].
C. LC Filter Design:
A low pass LC filter is required at the output terminal of full
bridge inverter to reduce harmonics generated by the
pulsating modulation waveform. While designing L-C filter,
the cut-off frequency is chosen such that most of the low
order harmonics is eliminated. The cut-off frequency can be
set by the formula below [4]:
FCUTOFF= 1 / 2*π* √LC
Fig. 4: SPWM comparison Signal and Unfiltered SPWM
output
Fig. 3: Single Phase Full Bridge Inverter
State Switches closed VAO
1
1 and 4
Vdc
2
2 and 3
-Vdc
Table 1:Switching States for single phase full bridge
inverter
B. Sine Wave Generation (SPWM):
The most common and popular technique for generating True
sine Wave is Pulse Width Modulation (PWM). This PWM
technique involves generation of a digital waveform, for
which the duty cycle can be modulated in such a way so that
the average voltage waveform corresponds to a pure sine
wave [4]. The simplest way of producing the SPWM signal is
through comparing a low power sine wave reference with a
high frequency triangular wave, as shown in fig 4. This
SPWM signal can be used to control switches. Through an
LC filter, the output of Full Wave Bridge Inverter with
SPWM signal will generate a wave approximately equal to a
sine wave, as shown in fig 5. This technique produces a much
more similar AC waveform than that of others. The primary
Fig. 5: Filtered SPWM Output
D. Simulation (PSIM):
Simulation and analysis for Sinusoidal Pulse Width
Modulation has been done on PSIM using Simulation
modeling and MATLAB (M-File) coding. To anticipate the
outcomes of the solar PV inverter, parts of the whole system
are simulated individually, then combined and justified the
desired output values in PSIM.
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Analysis of Solar PV Inverter based on PIC Microcontroller and Sinusoidal Pulse Width Modulation
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Fig. 11: Filtered Output Voltage of SPWM Inverter
Fig. 6: Circuit Diagram of PSIM Simulation
Observations of DC-DC converter, transformer,
Push-Pull converter and SPWM inverter are as per fig 7, fig.
8, fig. 9, fig. 10, fig. 11, fig. 12, fig. 13 and fig. 14:
Fig. 12: Harmonics Spectrum of Unfiltered Output of
SPWM Inverter
Fig. 7: Input pulses to DC-DC converter
Fig. 13: Filtered Output Current of SPWM Inverter
Fig. 8: Voltage on Secondary of Transformer
Fig. 14: Harmonics Spectrum of Filtered Output of SPWM
Inverter
Fig. 9: Push-Pull Converter Output
Fig. 10: Unfiltered Output of SPWM Inverter
E. DC-DC Push-Pull Converter Design:
In the design, the switching frequency is considered 50 KHz.
This will be the frequency at which the two MOSFET will be
driven by SG3525. Fig. 15 shows the pin diagram of pulse
width modulator IC SG3525. The source of power is
considered as DC Supply/ PV Panel, supply input voltage in
the range of 10.5 - 32V. For sample calculation, let’s consider
it to be 12V. This DC supply will be switched at 50 KHz, thus
producing square wave AC voltage of 12V. For operation of
such high frequency, a special type of transformer has to be
used, which is a ferrite core transformer. The transformer core
will be fed this 12V which will be stepped up to 325Vp
(peak). This 325Vp will be passed through a full bridge
rectifier having ultra-fast recovery diodes. As a result we will
obtain 325Vp DC power which will be passed through the
filter to decrease the amount of ripple in both, voltage and
current.
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Analysis of Solar PV Inverter based on PIC Microcontroller and Sinusoidal Pulse Width Modulation
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Observations for DC-DC Push-Pull Converter
without LC Filter and with LC Filter are shown in fig. 17 and
fig. 18:
Fig. 15: SG3525 Pin Diagram
The SG3525 is a pulse width modulator control
circuit that offer improved performance and lower external
parts count when implemented for controlling all types of
switching power supplies. The on–chip +5.1 V reference is
trimmed to ±1% and the error amplifier has an input
common–mode voltage range that includes the reference
voltage, thus eliminating the need for external divider
resistors. A wide range of dead time can be programmed by a
single resistor connected between the CT and Discharge pins
as shown in fig 15. These devices also feature built–in soft–
start circuitry, requiring only an external timing capacitor. A
shutdown pin controls both the soft–start circuitry and the
output stages, providing instantaneous turn off through the
PWM latch with pulsed shutdown, as well as soft–start
recycle with longer shutdown commands. The output stage of
the SG3525A features NOR logic resulting in a low output
for an off–state [6].
Fig. 17: DC-DC Output (Without LC Filter)
Fig. 18: DC-DC Output (With LC Filter)
F. Transformer Design:
The size of a power transformer is generally designed by a
parameter is called area product, Ap, as given by the
following equation [2],
Ap = cross sectional area of the core (Ac) * window
area (Aw)
Primary and secondary turns are given by
𝐸1
N1 =
4∗𝐾𝐹 ∗𝐴𝐶 ∗𝐵𝑀∗𝑓
N2 =
𝐸2
4∗𝐾𝐹 ∗𝐴𝐶 ∗𝐵𝑀∗𝑓
Current can be expressed in terms of current density
as follows:
I = J Awire
Where,
J = current density
Awire = area of the conductor cross section through which
current is flowing
Fig. 19: Center Tap Transformer Design
Fig. 16: Circuit Design of Push-Pull Converter
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Analysis of Solar PV Inverter based on PIC Microcontroller and Sinusoidal Pulse Width Modulation
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G. DC-AC Full Bridge Inverter Design:
Full-bridge inverter topology is used to design this stage.
The schematics diagram of the inverter design is shown in
fig. 20. It consists of 4 MOSFETs IRF840. It would be
operated through 4 switching pulses generated from
PIC18F4520 Microcontroller via IR2110 MOSFET driver.
The output of the DC-DC Converter will act as input for this
stage. The desirable input is 325V DC will be converted to
325 Vp AC, through controlled firing of these MOSFETs.
The resultant wave will not be sine wave due to harmonics
generated as a result of using high switching frequency of
20 kHz. So, low-pass LC filter will be introduced in the
system to obtain sine wave.
Fig. 20: DC-AC Inverter Design
Fig. 21: Pin Diagram of IR2110 MOSFET Driver
In many applications, floating circuit is required to
drive high side MOSFET. In H Bridge used in pure sine wave
inverter design, 2 MOSFET are used as high side MOSFET
and 2 MOSFET are used as low side MOSFET. IR2210 can
with stand voltage upto 500v (offset voltage). Its output pins
can provide peak current upto 2 ampere. It can also be used
to as IGBT driver. IR2210 floating circuit can drive high side
MOSFET upto 500 volt. Pin configuration and functionality
of each pin is given above fig. 21.
H. SPWM Implementation Using Microcontroller:
The SPWM program algorithm was developed based on
following flowchart as shown in fig. 22:
Fig. 22: Program Flowchart for SPWM generation
Implementation of SPWM with microcontroller is
associated with frequency of sine wave and therefore it
should be known first. The relationship of sin wave is known
with its phase angle and peak value,
y = A * sin (angle)
And also that half cycle of sine wave consist of 180
degree.
The calculation can be seen in table below:
Sine
X * Max
Sine lookup
Variable
function
Count
table
0.3090 *
sin (18)
309
1000
sin (36)
0.5877* 1000
587
sin (54)
0.8090* 1000
809
sin (72)
0.9511* 1000
951
Y
sin (90)
1* 1000
1000
sin (90)
1* 1000
1000
sin (72)
0.9511* 1000
951
sin (54)
0.8090* 1000
809
sin (36)
0.5877* 1000
587
sin (18)
0.3090* 1000
309
Table 2: SPWM Calculation
I. Simulation for SPWM in PROTEUS:
The program was first simulated in the PROTEUS software
and justified from the test results. Fig. 23 shows the circuit
diagram that was used to simulate the program of
PIC18F4520 controller. We have formed two waves: one is a
square wave of 50 Hz frequency and second is SPWM wave
of 20 kHz frequency. By using two AND gates and a Not gate,
a logic was formed to form four output pulses A, B, C, and D
as shown in fig. 24 .
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Analysis of Solar PV Inverter based on PIC Microcontroller and Sinusoidal Pulse Width Modulation
(IJSRD/Vol. 4/Issue 08/2016/004)
Fig. 23: Circuit Diagram for PROTEUS Simulation
These four pulses are gating the four MOSFETs of
the full bridge inverter through the MOSFET driver. During
the pulse A and C, MOSFET Q1 and Q4 will operate and
during pulse B and D, MOSFET Q2 and Q3 will operate. This
combination will produce SPWM voltage across the load of
50 Hz.
Fig. 24: Output of SPWM circuit (PROTEUS)
Fig. 26: Pulses A and C
2) The SPWM output voltage obtained across 40W load
without LC filter is shown in fig. 27.
Fig. 27: SPWM output voltage across the load
3) For the filtering purpose LC low-pass filter were
designed. The capacitor was of 0.01µF and the inductor
was of 98mH. The sine wave output voltage obtained
across 40W load after introducing LC filter is shown in
fig. 28.
III. RESULTS AND DISCUSSION
1) Fig. 25 shows the PWM train pulse generated at pin 17
of the PIC controller. In fig. 26 we can see pulse A and
C which fires the MOSFETs Q1 and Q4, shown in fig 20.
Similarly their inverting pulse will get us B and D, for
firing the MOSFETs Q2 and Q3, shown in fig 20. These
4 switching pulses obtained are identical to that of the
PROTEUS simulation, as shown in fig 24.
Fig. 28: Sine wave output after LC filter
Fig. 25: SPWM Pulse of 20 kHz
Fig. 29: Solar PV Micro-Inverter
The Solar PV inverter is tested with the Agilent DC
supply of rating upto 300V, 5A. The inverter is rated for 100
VA and fig. 29 shows the complete connection of both stages:
DC-DC Push-Pull Converter and DC-AC Full Bridge
Inverter along with the low pass LC filter connected via
breadboard. This inverter can work in the input voltage range
of 10.5 to 32 V DC.
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Analysis of Solar PV Inverter based on PIC Microcontroller and Sinusoidal Pulse Width Modulation
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IV. CONCLUSION
1) The simulation of the selected topology is simulated
successfully in PSIM software.
2) The feedback control system is successfully designed in
DC-DC Converter Stage using IC SG3525, to obtain
constant 325V DC output voltage with varying input
voltage, in the range of 10.5 - 32 V DC.
3) The program developed for SPWM technique is
successfully simulated in PROTEUS software and
implemented using PIC18F4520 Controller in DC-AC
Inverter stages.
4) Sine wave output of 50 Hz is successfully obtained
across the load.
5) Efficiency of 73.15 % was achieved at 40W load.
Output voltage of 230V AC is obtained only upto 40W
load. Still rectification is required to prevent the voltage
drop across the primary of the center tape transformer,
leading to under-voltage output at higher wattage of load.
V. ACKNOWLEDGMENT
I would like to thank the Mr. Nirav J. Chauhan, Assistant
Professor, Department of Electronics & Communications
Engineering, KIT for comments that greatly improved the
manuscript. I am also immensely grateful to the department
of Electrical Engineering, KIT for extending all the facilities
for caring out this work.
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[3] “Switch Mode Power Supply (SMPS) Topologies (Part
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[4] Lobaru, T. H., and Khosru M. Salim. “Design and
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[5] Haider, Rafid, et al. “Design and construction of single
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