Page 1 of 6
European Journal of Business &
Social Sciences
Available at https://ejbss.org/
ISSN: 2235-767X
Volume 07 Issue 04
April 2019
DEVELOPMENT AND IMPLEMENTATION OF MPPT AND INVERTER CONTROL
ALGORITHM FOR SOLAR PHOTOVOLTAIC SYSTEM
BALAKRISHNAN .A
PG Student
PRIST Deemed to be University, Thanjavur
Abstract
This paper presents a single-phase five-level PV inverter
topology with dual reference modulation technique. Two
reference signals identical to each other with an offset
equivalent to the amplitude of the triangular carrier signals
were used to generate PWM signals. Maximum Power Point
Tracking (MPPT) is implementation in solar array power
system with direct control method. The incremental
conductance algorithm is used to track the MPP, as it
performs better control under rapidly changing atmospheric
condition. The Total Harmonic Distortion (THD) produced
by the inverter is reduced. The proposed system is verified
through simulation.
Keywords: Photovoltaic system, Maximum power point
tracking (MPPT), Incremental Conductance (IncCond),
PWM Multilevel Inverter
1. Introduction
The demand for renewable energy has increased
significantly over the years because of shortage of fossil fuels
and greenhouse effect. Among various types of renewable
energy sources, solar energy and wind energy have become
very popular and demanding due to advancement in power
electronics techniques. Photovoltaic (PV) sources are used
today in many applications as they have the advantages of
being maintenance and pollution free. Solar-electric-energy
demand has grown consistently by 20%–25% per annum over
the past 20 years, which is mainly due to the decreasing costs
and prices [1].
PV Inverter is used to convert dc power obtained from
PV modules into ac power to be fed into the load. Improving
the output waveform and performance of the inverter reduces
its respective harmonic content and, hence the size of the
filter used and the level of electromagnetic interference (EMI)
generated by switching operation of the inverter [2]. In recent
years, multilevel inverters have become more attractive for
researchers and manufacturers due to their advantages over
conventional three-level pulse width-modulated (PWM)
inverters. They offer improved output waveforms, smaller
filter size, lower EMI, lower total harmonic distortion (THD)
[3]–[4].
The three common topologies for multilevel inverters are
1) Diode clamped (neutral clamped)
2) Capacitor clamped (flying capacitors) and
3) Cascaded H-bridge inverter
Several modulation and control strategies have been
developed for multilevel inverters like multilevel sinusoidal
(PWM), multilevel selective harmonic elimination, and
space-vector modulation [3]. A typical single-phase three- level inverter adopts full-bridge configuration by using
approximate sinusoidal modulation technique as the power
circuits. The output voltage has zero, positive (+Vdc), and
negative (−Vdc) supply dc voltage. The harmonic
components of the output voltage are determined by the
carrier frequency and switching functions. Therefore, their
harmonic reduction is limited to a certain degree [4].
To overcome this limitation, this paper presents a five- level PWM inverter whose output voltage can be represented
in the following five levels: zero, +Vdc/2, Vdc, −Vdc/2,
and−Vdc. As the number of output levels increases, the
harmonic content can be reduced. This inverter topology uses
two reference signals, instead of one reference signal, to
generate PWM signals for the switches. Both the reference
signals Vref1 andVref2 are identical to each other, except for
an offset value equivalent to the amplitude of the carrier
signal Vcarrier. Because the inverter is used in a PV system,
a proportional–integral (PI) current control scheme is
employed to keep the output current sinusoidal and to have
high dynamic performance under rapidly changing
atmospheric conditions and to maintain the power factor at
near unity. Simulation results are presented to validate the
proposed inverter configuration.
2. Methodology
PV Model
The use of equivalent electric circuits makes it
possible to model characteristics of a PV cell. The
equations are implemented in MATLAB programs for
simulations. The below fig 1.1 shows mathematical model
of solar cell. It is used to vary the input voltage according to
variation in temperature. The Mathematical model of solar
cell is design based on the following equations.
Short circuit current at working conditions,
Isc=Isck*(1+(a*(Tak-Tref))
Reverse saturation current at reference temperature,
Page 2 of 6
European Journal of Business &
Social Sciences
Available at https://ejbss.org/
ISSN: 2235-767X
Volume 07 Issue 04
April 2019
Iok=Isck/(exp(Vock/Vt)-1)
Fig 1.1 Mathematical model of Solar cell
Output current of the cell,
Ia=Iph-Io*(exp((Vc+Ia*Rs)/Vtc)-1)
Output power of the cell,
P=Va*Ia
Where,
Isc = short circuit current
Isck = short circuit current at reference temperature
Tak = Cell temperature in Kelvin
Tref = Reference Temperature(25 C) in Kelvin
Iok = Reverse saturation current at
reference temperature
Vt = Thermal potential at reference temperature
Iph = photo current of the solar cell
Io = Reverse saturation current at working
temperature
Vc = cell voltage per cell
Ia = output current of the cell
Rs = Series Resistance of the cell
Vtc = Thermal potential at working temperature
Five-level inverterTopology
The proposed inverter topology consists of a PV array,
five-level H-bridge inverter and load as shown in fig1.2
The PV array generates DC supply through solar energy.
The DC supply is applied to the five-level inverter through
DC bus capacitor. The five-level inverter is used for
conversion of DC to AC voltage. The AC voltage is
connected to the load through the filtering inductor. The
injected current must be sinusoidal with low harmonic
distortion.
1. MPPT
Tracking the maximum power point of a photovoltaic
array is usually an essential part of a PV system. As such
many MPP tracking (MPPT) methods have been developed
and implemented. Fig. 1.3 shows the characteristic power
curve for a PV array. The problem considered by MPPT
techniques is to automatically find the voltage VMPP or
current IMPP at which a PV array should operate to obtain the
maximum power output PMPP under a given temperature and
irradiance.
The various MPP tracking (MPPT) methods are
1. Hill climbing method
2. Perturb and observe (P&O) method
3. Incremental conductance method
4. Constant voltage method
5. Short-Circuit Current method
Fig 1.3 Characteristic PV array power curve
Incremental Conductance Algorithm
The incremental conductance method is based on the
fact that the slope of the PV array power curve is zero at the
MPP, positive on the left of the MPP, and negative on the right,
as given by
dp/dv=0 at MPP
dp/dv>0 left of MPP
dp/dv<0 right of MPP
fig 1.2 single phase five level inverter
where,
dp=change in power ; dv=change in voltage
As power (P) =IV,
dp/dv=d(IV)/dv
dp/dv=I+v dI/dv
dp/dv=I+v ∆I/∆V
above equation can be written as,
∆I/∆V= -I/V, at MPP
∆I/∆V>-I/V, left of MPP
∆I/∆V< -I/V, right of MPP
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European Journal of Business &
Social Sciences
Available at https://ejbss.org/
ISSN: 2235-767X
Volume 07 Issue 04
April 2019
The MPP can thus be tracked by comparing the
instantaneous conductance (I/V) as shown in the flowchart.
Vref is the reference voltage at which the PV array is forced
to operate. At the MPP, Vref equals to Vmpp. Once the MPP
is reached, the operation of the PV array is maintained at this
point unless a change in ∆I is noted, indicating a change in
atmospheric conditions and the MPP. The algorithm
decrements or increments Vref to track the new MPP.
The increment size determines how fast the MPP is
tracked. Fast tracking can be achieved with bigger increments
but the system might not operate exactly at the MPP and
oscillate about it instead; so there is a tradeoff. In [5] and [6],
a method is proposed that brings the operating point of the
PV array close to the MPP in a first stage and then uses
IncCond to exactly track the MPP in a second stage. By
proper control of the power converter, the initial operating
point is set to match a load resistance proportional to the ratio
of the open-circuit voltage (Voc) to the short-circuit current
(Isc) of the pv array. This two stage alternative also ensures
that the real mpp is tracked in case of multiple local maxima.
In [7], a linear function is used to divide the I-V plane into
two areas, one containing all the possible MPPs under
changing atmospheric conditions. The operating point is
brought into this area and the Incremental Conductance is
used to reach the MPP. Incremental Conductance technique is
to use the instantaneous conductance and the incremental
conductance to generate an error signal
e=I/V + dI/dV
From above equation, e goes to zero at the MPP. A simple
proportional integral (PI) control can then be used to drive e
to zero
Fig 1.4 Incremental Conductance algorithm with direct
control
4. Operational Principle of Proposed Inverter
A. Single phase five level inverter with control
algorithm is implemented:
The principle of operation of the proposed inverter is
shown in fig 1.5. to generate five-level output voltage, i.e., (0,
+Vdc/2, +Vdc, -Vdc/2 and –Vdc). An auxiliary circuit which
consists of four diodes and a switch S1 is used between the
dc-bus capacitors and the full-bridge inverter. Proper
switching control of the auxiliary circuit can generate half
level of PV supply voltage, i.e., (+Vdc/2, -Vdc/2) [4]. Two
reference signals Vref1 and vref2 will take turns to be
compared with the carrier signal at a time. If Vref1 exceeds
the peak amplitude of the carrier signal Vcarrier, Vref2 will
be compared with the carrier signal until it reaches zero. At
this point onward, Vref1 takes over the comparison process
until it exceeds Vcarrier. This will lead to a switching pattern,
as shown in fig 1.7 and 1.8. Switches s1-s3 will be switching
at the rate of the carrier signal frequency, whereas s4 and s5
will operate at a frequency equivalent to the fundamental
frequency. Following table 1 illustrates the level of Vinv
during s1-s5 switch on and off.
S1 S2 S3 S4 S5 Vinv
ON OFF OFF OFF ON Vpv/2
(positive)
OFF ON OFF OFF ON Vpv
(positive)
OFF OFF
(or)
ON
OFF
(or)
ON
ON
(or)
OFF
ON
(or)
OFF
zero
ON OFF OFF ON OFF Vpv/2
(negative)
OFF OFF ON ON OFF Vpv
(negative)
Table 1 (Inverter output voltage during S1-S5)
The proposed single-phase five-level inverter involves
various steps of operation. The configuration and the
principle of operation of the proposed inverter is given
below. voltage produced by the arrays is known as Varrays.
The voltage across the dc-bus capacitors is known as
photovoltaic voltage.
B. Modes of operation:
The proposed single-phase five-level inverter
involves steps of operation. The five level PWM inverter is
shown in fig 1.6.
Maximum positive output (+vdc):
Switch 1 is ON, connecting the load positive terminal to Vdc,
