F253f950 F9a9 11e8 8eb2 F2801f1b9fd1 [626976]

ACTA TECHNICA NAPOCENSIS
Electronics and Telecommunications
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Maximum power point tracking in solar panels

Faculty of E lectronics, Telecommunications and I nformati on Technology , Cluj-Napoca

Abstract—The electricity produces by solar panels is starting to win ground over conventional systems. The need for a
sustainable source of renewable energy has led to advancement s in the photovoltaic industry. The main goal of this paper is to
provide more information about the functionality of a photovoltaic system and maximizing the generated power.

I. INTRODUCTION
An MPPT, or maximum power point tracker is an electronic
DC to DC converter that optimizes the match between the
solar array (PV panels), and the battery bank or utility grid.
To put it simply, they convert the input DC voltage to lower
or higher voltage depending on the type of batteries used.
Solar cells are neat things. Unfortunately, they are not
very smart. Most PV panels are built to put out a nominal 12
volts. The catch is "nominal". In actual fact, almost all "12 –
volt" solar panels are designed to put out from 16 to 18
volts.
Generating higher efficiency solar panels is not the only
concern, the transfer between the solar panel and the load
provides certain efficiency. Solar panel s do not output a
constant voltage or current, the output voltage usually
depends on the number of cells connected in series and the
temperature of the cell, while the irradiance level has an
effect on the output current of the solar panel.
So what does optimizing the power transfer mean? Well,
if we look at the current -voltage chara cterisitc as shown in
figure 1 , we can observe that in a certain area the generated
power is higher than anywhere else.
Maximizing the transferred power is not as easy as
placing a load with an input resistance in the maximum
power area level because the maximum power point is
constantly changing based on the operating temperature and
solar irradiation .
In order to track the maximum power point, constant
measurement of the voltage and current is needed. Back in
the day analog maximum power point trackers were used.
But, because of the difficulty of the implementation and the
lower and lower microcontroller prices, a digital approach is
preferred now.
Between the solar panel and the load a switching mode
power supply is used. This way, the impedance can be
modified by modifying the PWM signal duty cycle.

What is Maximum Power Point Tracking?
There is some confusion about the term "trac king":
Panel tracking – this is where the panels are on a mount that
follows the sun. These optimize output by following the sun
across the sky for maximum sunlight.
Maximum Power Point Tracking is electronic tracking –
usually digital. The charge control ler looks at the output of
the panels and compares it to the battery voltage. It then figures out what is the best power that the panel can
put out to charge the battery. It takes this and converts it to
best voltage to get maximum AMPS into the battery.

Figure 1: I -V Curve of a photovoltaic cell
Figure 2: MPPT working principle

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Electronics and Telecommunications
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II. IMPLEMENTATION AND RESULTS
In order to simulate the functionality of a photovoltaic cell,
the equivalent circuit was used.

Figure 3: Solar cell equivalent circuit

In order t o track the maximum power, one tracking
algorithm must be used. One of the most used algorithm, and
the one presented in this paper is the “Perturb and Observe”
algorithm. This algorithm has the advantage of being
independent of the knowledge of the PV gen erator
characteristics, so that the MPP is tracked regardless of the
irradiance level, temperature, degradation, and aging, thus
ensuring high robustness and reliability. The algorithm uses
the current values of power and voltage and compares it
with the p revious values, adjusting the PWM on the DC -DC
converter in order to obtain higher input power compared to
the previous measured input power.
The most commonly used DC -DC converters are Boost,
Cuk or SEPIC converters because of the continuous current
on the inductor compared to the pulsed input current offered
by Buck or Buck -Boost converters.

Figure 4: Perturb and Observe tracking

Figure 5: Perturb and Observe flowchart

As shown in figure 5, the Perturb and Observe algorithm
keeps adjusting the PWM of th e DC -DC converter until the
input power begins to drop. When this happens, the
controller is oscillating around the MPPT until the
maximum power point moves down or up the I -V curve
(change caused by irradiance level or temperature).

Figure 6: Simulated s olar panel model

The model used in Figu re 6 is a typical 18V solar panel
with the output voltage varying between 24V and 16V.

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Electronics and Telecommunications
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Figure 7: Simulation schematic

In figure 6 we can see the schematic used for the solar
panel simulation. Multiple diodes are connected in series to
generate a high enough output, comparable with real solar
panels. A simple voltage divider is used to reduce the input
voltage to one accep ted by Arduino (under 5V).
For the current measurement was realized using a 10mΩ
schunt resistor and the INA168 current schunt monitor.
The gain was set to 100 with an external resistor, so
currents up to 5 Amps can be measured.
The DC -DC converter was mo deled using an Voltage
controlled voltage source, in order to reduce the simulation
time. A separate simulation of the DC -DC converter was
done using dedicated simulation tools.
Figure 8 : MPPT algorithm simulation

In figure 8 we can observe on channel A(yellow) the
input current on the simu lated PV array. On channel B(red)
we can see that the controll er is tracking the input power.

The converter used for this application was a boost
typology. The main reason was the continuous input current,
unlike the buck or buck -boost typology.
Figure 9: Boost converter
Unlike a typical boost converter, there are 2 major
differences. The output load is not a resistive one, a battery
is used instead. Also, because a battery is used, the output
capacitor was eliminated. Also, there is no feedback
regulation loop. The regulation is based on the input
parameters (Voltage, Current) instead out the output voltage.
Figure 10: Boost converter simulation

Because there was no feedback loop in this simulation,
the duty cycle is held constant. The output load is simulated
using an voltage source, therefore current spikes can be
observed across the diode when the inductor voltage is
higher than the battery voltage. Therefore the power is
transferred to the load.

Figure 1 1: Circuit schematic

Based on the presented simulations and the hardware
described in figure 10, a PCB was designed. In order to
retain the compatibility with the Arduino platform, it was
design ed to sit on top of it.

This is one important step considering the impact of
parasitic capacitances and inductances at those high
switching frequencies . Also, ground planes were used to
preserve the signal integrity.

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Electronics and Telecommunications
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Figure 12: PCB top and bottom view

Figure 13: Populated PCB

MPPT controllers tend to have a lower efficiency
compar ed to PWM controllers because they use more
components, but the overall efficien cy of the system greatly
increases. One particular area where boost based MPPT
controllers come in handy is when we are talking about a
partially shaded solar panel array. Panels include bypass
diodes to shunt current around them when they’re shaded.
This is primarily a safety mechanism (a panel could
conceivably burn up otherwise) but it also lets the array
continue to produce reduced power at a lower voltage. If this
volta ge is below the required output voltage with a PWM
controller, you’ll get essentially nothing. A MPPT will
adjust to the lower voltage and get as much power out of the
unshaded part of the array as possible.
Another advantage of the MPPT controll ers is the ability
to operate at higher voltages than PWM controllers.
When multiple cells are used in series, to provide a higher
voltage (in order to reduce the dimensions of the cable), a
differen t typology can be used to reduce the high input
voltage to battery level.

III.CONCLUSIONS
MPPT algorithms used in PV systems are one of the
most important factors affecting the elec trical efficiency of
the system. The paper proposes a simple MPPT method that
requires only the measurements of the input voltage and
current. However, by using this MPPT method we have
increase t he efficiency of the solar array module.

Figure 14: MPPT vs PWM charge controller

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