IEEE Power Electronics Magazine - September 2021 - 49

voltage and current ratings needed. The larger resulting area
makes this system prone to non-uniform irradiation and partial
shading conditions. Partial shading is almost inevitable
in practical operation and must be considered for building
integrated SPV systems and SPV farms. Scenarios like partial
shading contribute to the occurrence of multiple peaks
in the photovoltaic I-V curve [4]. These peaks are known as
local maximum power points (LMPP). The single true MPP
in such cases is referred to as the global maximum power
point (GMPP). I-V and power-voltage (P-V) characteristics
of an SPV array under uniform and partial shading conditions
are shown in Figure 1.
The surrounding environmental conditions of an SPV
system are in a state of variable insolation, hence, the
GMPP must be tracked dynamically. As a result, identification
of GMPP and differentiating GMPP from LMPP
is another hurdle that MPPT solutions must tackle. Older
MPPT techniques such as incremental conductance (IC)
and perturbation and observation (P&O)
are particularly inadept at dealing with
partial shading conditions.
MPPT technologies can be broadly
divided into two categories: software solutions
and hardware solutions. Software
solutions require high-end microcontrollers
and usually exhibit algorithmic
complexity [4]. A few software MPPT techniques
include perturb and observe (P&O),
incremental conductance (IC), fuzzy logic
control, particle swarm optimization, and
neural network based techniques etc.
Hardware technologies can be integrated
into the SPV module for MPPT. This article
presents a hardware-based technique
that deploys periodic sweeps to trace the
dynamic I-V curve to determine GMPP.
SPV I-V Curve Tracing Technique
To obtain an accurate I-V curve, the current
and voltage of the system must be determined.
These values can be obtained by
logging the transition of the SPV array from
short circuit current to open circuit voltage.
To facilitate this transition, different
techniques are used for altering the load
fed by the SPV panels from minimal resistance
(~ 0 Ohm) to very high resistance
(~ ∞ Ohm) [5]. The different solutions may
be divided into variable dc load methods and
dynamic capacitor charging methods [6].
Among dc load solutions, the simplest
method to attain the load transition for
I-V curve tracing is achieved by employing
a variable load resistance. However, the
resultant I-V curve from variable resistance
loading is deficient in accuracy, uniformity,
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5
4
3
2
1
iMPP
and smoothness. Furthermore, this technique is a relatively
slow process.
Another solution utilizes power semiconductor devices
(PSD) as an electronic dc load. In this technique, the transistor
is operated in the linear region as a variable load.
This approach is very fast. However, as the transistors are
deployed at high temperatures for limited time periods, it is
mostly suited for low power SPV module measurement [7].
This leaves capacitor charging as a remaining suitable
solution for I-V curve tracing to determine GMPP.
Capacitor Charging Method for I-V Curve Tracing
The dynamic charging characteristics of a capacitor are suitable
for using a capacitor as a varying load for I-V curve tracing.
During this process, the SPV panel/array is disconnected
from its load and connected to a discharged capacitor.
Capacitor charging is a rapid and robust process. The SPV
array delivers short circuit current to the capacitor which
Maximum Power Point
Voltage-Current Curve
Voltage-Power Curve
vMPP
Voltage (V)
(a)
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3
2
1
GMPP
iMPP
Voltage-Current
Curve
Voltage-Power
Curve
1,000
1,200
1,400
1,600
1,800
LMPP
vMPP
Voltage (V)
(b)
FIG1 I-V and PV characteristics of a solar photovoltaic array. (a) under uniform
irradiance conditions. (b) under partial shading conditions.
September 2021 z IEEE POWER ELECTRONICS MAGAZINE 49
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800
050 100 150 200 250 300 350 400 450
2,600
2,400
2,200
2,000
1,800
1,600
1,400
1,200
1,000
800
600
400
200
Current (A)
Current (A)
Power (W)
Power (W)
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IEEE Power Electronics Magazine - September 2021

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