Volume 6, Issue 4, April – 2021 International Journal of Innovative Science and Research Technology

ISSN No:-2456-2165

Design of Low-Cost AC-Direct Driverless LED

Luminaries with Non – Perceptible Flicker
A.C.O. Azubogu 1, Obioma Peace C.2, Okwaraoka Chinedu P. A 3
1,2,3
Department of Electronic and Computer Engineering
Nnamdi Azikiwe University
Awka, Nigeria

Abstract:- Design considerations for a low cost and these other technologies when operating with the same power
efficient Light Emitting Diode (LED) luminaries involve rating.
numerous compromises. Factors such as efficiency,
power factor and flicker Index all present a compromise While LED’s present both an economical and efficient
against each other. It is conventional to employ suitable solution to lighting problems, the best way to power them
means that make for a low cost and efficient LED efficiently remains debateable. In the early stage, expensive
luminaire. In this paper, a driverless AC-Direct LED light engines and converters were mainly used for driving
luminaire with non-perceptible flicker, improved power LEDs. Most of these technologies depended on high voltage
factor, with acceptable total harmonic distortion (THD) Integrated Circuit (IC) switching chips for matching the
characteristics is designed. With a flicker index of 0.2, it number of LED strings during a power line cycle with the
outperforms most AC luminaires employing high voltage instantaneous power line voltage [8]. The major problem
switching chips, which have a typical flicker index associated with these LED drivers is that due to their poor
usually greater than 0.3. The efficiency is 88%, as against design and performance they greatly reduce the durability
80% achieved by most AC LED light engines. The design and cost of the lighting system.
has a THD of 18.79% and power factor of 0.92, this
meets Energy Star requirements for consumer products. Demands for higher efficiency, lower cost, and reduced
flicker content of the emitted light keeps increasing and
Keywords:- LED Luminaire, Flickerless LED, Driverless, spurring the implementation of improved techniques and
Low Cost, AC-Direct. products. By dividing the LED’s into sections, AC direct
driving techniques are employed to drive the LED’s without
I. INTRODUCTION need for a switching mode power supply (SMPS).

Globally, lighting forms a major part of energy In this paper, a driverless LED luminaire with non-
consumption worldwide. Lighting consumes about 25% of perceptible flicker, alongside improved power factor and
the world’s total electric energy [1]. Efficient lighting with total harmonic distortion (THD) characteristics is designed.
energy saving has become very vital. Consequently, current
light sources are expected to be designed to be highly II. CHARACTERIZING PHOTOMETRIC
efficient, environmentally friendly, energy saving, and should FLICKER
be able to deliver the required visual preference [2].
The Photometric flicker is a common phenomenon
Light Emitting Diode (LED) provides all the among light sources. Conventional light sources ranging
aforementioned properties, and with advancements in from incandescent lamps, High Intensity Discharge (HID),
technology, they are being deployed in mobile products and fluorescent, CFL, and LED’s all experience some degree of
backlighting of Liquid Crystal Display) LCD panels [3]-[4]. flicker. Photometric flicker is a characteristic of the light
Generally, LED lighting are majorly deployed in applications source resulting from power sources drawn from AC mains.
that require low-brightness illumination (e.g the screen According to the Illuminating Engineering Society of North
backlights of laptops and mobile phones), and high- America (IES) Lighting Handbook, flicker is defined as: “the
brightness illumination (which includes general lighting, rapid variation in light source intensity” [9]. The effect of
vehicle lighting, and backlighting of large television panels) light sources with flicker over a period of time on human
[5]-[6]. LED-based Solid State Lighting (SSL) is a promising observers can be very hazardous. This could lead to
energy saving technology to replace incandescent halogen, physiological effects and can have neurological
fluorescent tube, and Compact Fluorescent Light (CFL) in consequences. Light engines running on such rapid variations
the lighting industry. LED’s when compared to the are recognized as contributing to headaches and migraines
aforementioned technologies has a longer life span, about [10].
50,000 operational hours compared to 1000 – 2000 hours for
incandescent lamps and 5000 – 10,000 hours for CFL [7]. The adoption of driverless modules promising long life
LED’s also costs much less and has a higher luminosity than and quick return-on-investment in the market has been
greatly plagued by high flicker. The Illuminating Engineering

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Volume 6, Issue 4, April – 2021 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165
Society (IES) developed two metrics to quantify flicker as
described in RP-16-10 (Nomenclature and Definitions for
Illuminating Engineering) [11]. The more commonly utilized
metric is percent flicker. The percent flicker helps to indicate
the average amount of modulation in light output over a
single on–off cycle. A Percentage flicker of 100% indicates
that at some point in its cycle, no light is produced. A light
source that is completely steady is said to have zero percent
(0%) flicker.

The other metric is the flicker index. This ranges from

zero to one. It accounts for the shape of the light’s waveform
and the duty cycle. A low value of percent flicker and flicker
index is desirable for non-perceptible flicker. Note that recent
findings indicate a new metric called Compact Flicker
Degree (CFD). This helps in evaluating the performance of
light engines that use higher frequencies (up to and beyond
2000Hz) for modulation of light [12].
Fig.1 Figurative description of flicker Index [13].
Flicker is inherent in Conventional light sources.
Incandescent lamps have a percentage Flicker of around III. TOPOLOGIES FOR THE DESIGN OF LED
10~20% [13], while magnetically ballasted CFL lamps have LUMINAIRE WITH NON-PERCEPTIBLE FLICKER
a rather high flicker of 37 ~ 70%. Though modern
electronically ballasted CFL lamps have lower Percent flicker I. The Basic Offline LED Driver
of around 5% [13]. The operation of a mains fed LED driver is used to
illustrate the reason behind the 100Hz/120Hz perceptible
Presently, there is no clearly stipulated standard flicker in offline LED lamps.
regarding the maximum acceptable flicker in LED lamps.
The percent flicker specified by manufacturers stipulates that
the percent flicker should be less than 30% in the 100Hz -
120Hz frequency range [13]. A stable LED driving current is
required to achieve a flicker free operation. According to
[13], there are two kinds of light flicker observable in LED
lamps:
• AC line frequency related light fluctuation (usually at
double the line frequency (100Hz for 50Hz line frequency
and 120Hz for 60Hz line frequency).
• Random light intensity fluctuation (often caused by
incompatibility between lamp and peripheral lighting
components).

According to research, flicker above 75Hz is usually Fig. 2 Basic Offline LED Driver [13].
not noticeable by most individuals. Although, the
perceptibility of flicker is not only related to frequency: it is The converter for most single stage offline LED
also related to the intensity of the peaks and valleys of the drivers consists of a Buck-Boost or flyback converter to
light output (intensity modulation) and duration of these convert the rectified line voltage into a suitable output
variations [13]. voltage for driving the LED string.

In such a system shown in figure 2, flicker-free

operation is achieved if the LED current ILED is a stable DC
current, and the LED voltage VLED is fixed. Since the line
voltage is sinusoidal, the circuit must contain a voltage
buffer element that would help to transform the alternating
current into DC voltage. This achieved using either of C1 or
C2 as shown in figure 2. [13].

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ISSN No:-2456-2165
II. High Power Factor Applications
To control the flicker in a high PFC single stage LED
To design a system with high power factor that meets driver, the following procedure is followed [13]:
with the harmonic standards stipulated by IEC61000-3-2, the i. Characterize the maximum acceptable flicker
LED driver with an ac input incorporates Power Factor percentage requirement (about 30%)
Correction (PFC) control [14]. A unity power factor implies ii. Establish the maximum LED current peak to peak
that a pulsating power will be seen at the input side of the variation (IPP) from the Luminous Flux vs. forward
driver, while the output power is typically made constant to current curve.
drive the LEDs. To balance out the instantaneous power iii. Using the LED I/V curve, calculate the dynamic
difference between the pulsating input and the constant resistance (RD) of the LED at the operation point.
output an Electrolytic capacitor is usually employed for that. iv. Calculate the maximum peak to peak voltage ripple
(VPP) across all the LED string, mathematically, it is:
From figure 3, for good power factor with low input
harmonic current, the value of C1 must be kept small and the (𝑉𝑃𝑃 ) = (𝐼𝑃𝑃 ) ∗ (𝑅𝐷 ) (1)
converter must try to maintain a sine shaped input current as
well, requiring a low bandwidth control loop. The voltage v. Calculate the output capacitor value using equation (2):
buffer element (C2) is used to reduce the voltage ripple
across the LED string. A large value of C2 is required to
achieve very small LED voltage ripple. The LED current (IPP )
𝐶𝑂𝑈𝑇 = (V (2)
ripple and flicker is usually determined by the voltage ripple PP )∗2𝜋𝑓

along with the LED characteristics [13].

Where:
(IPP) is twice the average LED current and (VPP) is the
allowed peak to peak output voltage ripple across the LED
string

f is twice the line frequency.

IV. DESIGN PARAMETERS FOR THE AC –

DIRECT DRIVERLESS LED LUMINAIRE WITH
NON-PERCEPTIBLE FLICKER.

The design parameters for the LED luminaire are

chosen to match or exceed the photometric characteristics of
a two feet (2 feet) fluorescent light or a Compact Fluorescent
Light (CFL) down light luminaire at a reduced cost and
higher efficiency. Important photometric characteristics of
these light fixtures are compared in table 1.
Fig.3 High power factor converter [13].

TABLE 1
PHOTOMETRIC CHARACTERISTICS OF SOME LIGHT FIXTURES
*Source: Lamp manufacturers datasheet [15].
Characteristic CFL Value 2 ft. Fluorescent Value LED luminaire Value

Light Output (Lumen) 670* 950* 1026*

Power (Watts) 11 10 9
Efficacy (lm/W) 61 95 114
Correlated Colour Temperature 4000K 4000K 4000K
(CCT)

Two of the most important parameters in the design The LED used for this design is Cree XLAMP MX-6
process of any LED-based luminaire is the number of LED’s LED high brightness LED. Important parameters of the
required to meet the design goals and the effective XLAMP MX-6 LED are shown in Table 2.
capacitance of the circuit.

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TABLE 2
IMPORTANT PARAMETERS OF THE XLAMP MX-6 LED
Part Number Norminal CCT (K) Norminal Drive Typical Forward Typical Power Typical Efficacy
Current (mA) Voltage (V) (W) (lm/W)
XLAMP MX-6 4000 300 3.3 1 114

To effectively determine the number of LED’s needed, Thus a minimum of 12 LEDs of 114 lm @ 300mA
the inefficiencies contributed by the optical, thermal and operating current per LED wired in series are needed to
electrical systems is estimated as follows. satisfy the light output design goal.

 Optical Loss: Optical system efficacy is estimated by The effective capacitance Ceff represents the combined
examining light losses due to Secondary Optics and capacitance of the Power Factor Corrector (PFC) circuit
fixture Light loss. Fixture light loss arises when the light during the discharge period. The effective capacitance of the
source strikes the fixture housing before hiting the target. PFC circuit is given as:
The efficiency of the fixture depends on the placement of
the LED’s, the fixture shape and material. The structure 𝐶𝑒𝑓𝑓 = (𝐶1//𝐶3) + (𝐶2//𝐶4) (5)
for the designed LED luminaire is such that the LED’s
emit optical light directionally, removing the need for Different capacitor values yields different values of
reflectors; hence only secondary optical loss due to the power factor and THD %. According to [16], the best
diffuser placed over the LED’s is considered. The combination of capacitors that yields the highest PF and
generally accepted optical efficiency through the lowest THD is when 𝐶1 = 𝐶4 = 𝐶 and 𝐶2 = 𝐶3 = 𝐶/2.
secondary optical element lies within 85% and 90%. An Substituting this condition into equation () yields:
optical efficiency of 88% is assumed in this design.
 Thermal Loss: This is due to decrease in relative 𝐶𝑒𝑓𝑓 = 3𝐶/4. (6)
luminous flux output of the LED as junction temperature
(Tj) rises. Most LED data sheets list typical luminous The Output Power (Po), estimated Efficiency (ƞ),
flux at Tj = 25°C, while most LED applications use normal discharge period (tnormal), holdup time requirement
higher temperatures. A Junction temperature Tj = 80°C is (tholdup) and effective capacitance (Ceff) can be calculated
assumed which corresponds to a minimum relative flux from the following equation:
of 80% from the LED’s datasheet [15]. 85% relative
luminous flux is the thermal efficacy estimate used in the 2(𝑃𝑜 )(𝑡ℎ𝑜𝑙𝑑𝑢𝑝 + 𝑡𝑛𝑜𝑟𝑚𝑎𝑙 )
𝐶𝑒𝑓𝑓 = ƞ(𝑉𝑠2 −𝑉𝑓2 )
(7)
design.
 Electrical Loss: Electrical loss is inherent in electrical
devices, for the system designed; an efficiency of 88% is Where 𝑉𝑠 and 𝑉𝑓 are the designated initial and final voltage,
achieved. Most typical LED drivers has an efficiency respectively, in the entire discharge period.
between 80% and 90%.
The normal discharge period (tnormal) is 4ms for 50Hz
The exact number of LED lumens that is required to AC, while the holdup time requirement (tholdup) is 5ms. The
achieve the design goals is calculated considering only the circuit starts discharging at around two-third of input voltage
light efficiencies. Electrical efficiency does not affect the and assume 15% voltage ripple during discharge, thus:
amount of light produced by the luminaire. This is calculated
as shown below: 2
𝑉𝑠 = 3
√2 (𝑉𝑅𝑀𝑆 ) (8)
𝑇𝑎𝑟𝑔𝑒𝑡 𝐿𝑢𝑚𝑒𝑛𝑠
𝐴𝑐𝑡𝑢𝑎𝑙 𝐿𝑢𝑚𝑒𝑛𝑠 = (𝑂𝑝𝑡𝑖𝑐𝑎𝑙 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦)∗(𝑇ℎ𝑒𝑟𝑚𝑎𝑙 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦) 2
(3) 𝑉𝑠 = √2 (230) = 216.84𝑉
3
1026
𝐴𝑐𝑡𝑢𝑎𝑙 𝐿𝑢𝑚𝑒𝑛𝑠 = ≃ 1,372 𝑙𝑚
(88%) ∗ (85%) 𝑉𝑓 = (1 − 0.15)𝑉𝑠 (9)

The number of LED’s required to produce this amount 𝑉𝑓 = (1 − 0.15)(216.84) = 184.32V

of lumen depends on the operating current. For the LED
used (XLAMP MX-6 LED), the operating current is 300mA. 2(𝑃𝑜 )(𝑡ℎ𝑜𝑙𝑑𝑢𝑝 + 𝑡𝑛𝑜𝑟𝑚𝑎𝑙 )
𝐶𝑒𝑓𝑓 =
ƞ(𝑉𝑠2 − 𝑉𝑓2 )
Therefore:

𝐴𝑐𝑡𝑢𝑎𝑙 𝐿𝑢𝑚𝑒𝑛𝑠 𝑁𝑒𝑒𝑑𝑒𝑑 2(9)(0.004 + 0.005)

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝐿𝐸𝐷𝑠 = (4) 𝐶𝑒𝑓𝑓 = = 14.11𝜇𝑓
𝐿𝑢𝑚𝑒𝑛𝑠 𝑝𝑒𝑟 𝐿𝐸𝐷 0.88(216.842 − 184.322 )
1372 𝑙𝑚
= = 12.04 𝐿𝐸𝐷𝑠
114 𝑙𝑚

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4 diode is reverse-biased. At this point, the capacitor pairs
𝐶= 𝐶 = 18.81𝜇𝑓
3 𝑒𝑓𝑓 discharges in series to provide the output current.

In the actual design, 20 𝜇𝑓/250𝑉 electrolytic capacitor was At the zero crossing level, the Line voltage changes
used for C. direction but is lower than the valley fill voltage. Thus, the
input current still flows through the path R1-C10-D3. The
whole charging/discharging cycle repeats at the next half
V. CONTROL CIRCUITRY OF DRIVERLESS AC – line cycle when the input voltage is higher than the voltage
DIRECT LED LUMINAIRE WITH REDUCED sum of (VC1 +VC2), (VC3 +VC4) or (VC1 + VC4).
FLICKER.
Capacitors C9 and C10 are introduced to increase the
The harmonic input currents drawn from AC mains by conduction time of the input current, they provide an
the conventional bridge-diode rectifier with a large bulk alternate path for the input current to flow into the Valley fill
capacitor connected to its output led to the passive power circuit before the input line voltage rises above the Valley
factor correction approach adopted in this design. The circuit fill circuit voltage [16]. This helps to decrease the current
employed in this work is as shown in Fig.4. distortion. Their values are chosen to be smaller than that of
the capacitors in the PFC circuit. There are chosen after
deciding the value of the effective capacitance of the circuit.

Resistor’s R2 and R3 are introduced to reduce the

inrush current into the PFC circuit and to also suppress
current distortion by limiting and smoothing the peak diode
charging current. The power dissipated by these resistors is
only a fraction of the input power; therefore they wouldn’t
impact greatly on the efficiency of the system. For a hold up
time of 5mS at 0.92 power factor, 20Ω resistors were used.

According to Yanchao Method for Single-Phase

Rectifier [17], the distortion factor due to the waveform
distortion has a similar property to reactive power. The input
capacitor C11 was introduced to compensate this reactive
power. It absorbs the harmonic distortion power so as to
Fig.4 Circuit diagram for the driverless and flickerless LED yield higher power factor and lower THD. The distortion
Luminaire factor is related to the THD as shown below:

Considering the circuit diagram in fig. 4, an improved 1

𝐷𝑖𝑠𝑡𝑜𝑟𝑡𝑖𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟 = √1+ 𝑇𝐻𝐷 2 (10)
valley fill circuit is introduced to replace the bulk
electrolytic capacitor and hence make for better power factor
correction. When AC voltage is applied to the circuit, in the Where,
first instance, the line voltage would be slightly higher than 2
√∑𝑛 ≠1 𝐼𝑛_𝑅𝑀𝑆
the voltage across either of (VC1 +VC2), (VC3 +VC4) or (VC1 + 𝑇𝐻𝐷 = (11)
𝐼1_𝑅𝑀𝑆
VC4). Consequently, the bridge diode conducts and the Input
current flows to the output load directly. With time, the line
These all relate to the power factor in the expression
voltage rises slightly above the voltage sum, (VC1 + VC3 +
given below:
VC4) or (VC1 + VC2 + VC4) and starts charging the capacitor
pair with lower voltage first.
𝑃𝑜𝑤𝑒𝑟 𝐹𝑎𝑐𝑡𝑜𝑟 = 𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡 𝐹𝑎𝑐𝑡𝑜𝑟
× 𝐷𝑖𝑠𝑡𝑜𝑟𝑡𝑖𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟 (12)
In this design, C2 = C3, therefore they will all charge
up at the same time and the input current charges the
𝐷𝑖𝑠𝑡𝑜𝑟𝑡𝑖𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟 = 𝐶𝑜𝑠 (𝜃𝑣 − 𝜃𝑖 ) (13)
capacitors and flows to the load the same time.
Where, 𝜃𝑣 and 𝜃𝑖 are the phase of the voltage and current
Unlike the conventional large bulk capacitor, the input
current still flows to the load rather than remaining at the respectively.
peak input voltage and preventing the input current from
flowing as the input voltage decays. The PFC circuit allows VI. EXPERIMENTAL RESULT
the input current to still flow to the load because the valley-
fill voltage stays around two-third of the peak input voltage. The proposed circuit was simulated and tested at a
This lengthens the conduction time for bridge diodes power level of 9W and input voltage of 230V (RMS).
compared to the conventional rectifier. When the input Simulation and experimental results are presented in Table
3. The waveform of the input voltage, the input current and
voltage decreases and falls below two-third of the input peak
voltage, the input current stops flowing because the bridge

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ISSN No:-2456-2165
the output voltage of the experimental circuit are shown in
Figs. 5 and 7.

Fig. 8 Fourier analysis of the Conventional Circuit

Fig. 5 Operating Waveforms of the circuit

Fig. 9 Fourier analysis of the PFC Circuit

Fig. 6 Input current waveform of the conventional circuit TABLE 3

SIMULATION AND EXPERIMENTAL RESULTS
Parameter Simulation Measured
Value Value
Input Power 10W 10.18W
Input Voltage 170- 170- 230V(RMS)
Range 230V(RMS)
Output Power 9W 8.96W
Efficacy - 114lm/w
Efficiency 90% 88%
Power Factor 0.95 0.92
Flicker Index - 0.2

The LED strings are subdivided into four equal sub

segments as shown in Figure 4. From figure 5, the top sub
segment of the LED is shorted out during the positive half
cycles, while the bottom sub segment is shorted out during
the negative half cycles. When the input voltage turns
positive, C5 charges up through R5, and C6, which previously
was charged to the negative peak of the line voltage,
Fig. 7 Input current waveform of the PFC circuit receives current passing through the lower three strings. This
produces the first hump (of displacement current) seen in the
combined LED current waveform in Fig. 5. When C 5 is

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charged sufficiently, galvanic current starts passing through ACKNOWLEDGEMENTS
R4 leading to the second hump in the combined LED current
waveform of Figure. 5. A complementary series of the This project is being done under the Tertiary Education
described charging and discharging events happens during Trust Fund (TETFund) Institution Based Research Fund
negative half cycles. C5 and C6 stops about half of the LED (IBRF), Grant No.: 2014-2015-2016 TETFund Research
current from going through the resistors at all, which helps Projects Intervention (IRP). The support of TETFund is
to boost the system efficiency to over 90% without the immensely appreciated. The authors would like to thank all
protection circuitry. the staff of Electronics Lab, ECE department, Nnamdi
Azikiwe University.
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normal standard diodes, consequently reducing cost.

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https://www.cree.com/led-

AUTHORS’ INFORMATION
1
Lecturer, Department of Electronic and Computer Engineering, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria.
2
Lecturer, Department of Electronic and Computer Engineering, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria.
3
Lecturer, Electrical and Electronics Engineering Department of Federal, Polytechnic Nekede, Owerri, Imo State, Nigeria.

A.C.O. Azubogu hold B.Eng (Electronic Engineering) from the prestigious University of Nigeria, Nsukka;
M.Eng (Telecommunication) from University of Port Harcourt and Ph.D (Adaptive Signal Processing and
Wireless Communication) from Nnamdi Azikiwe University, Awka.
He has over 30 papers published in reputable international journals. He is presently a Professor in the
department of Electronic and Computer Engineering, Nnamdi Azikiwe University, Awka.
Mr. Azubogu is also a research associate with the Center for Sustainable Development (CSD) and the Center of
Excellence for Renewable Energy Development and Environmental Conservation (CEREDEC) at Nnamdi Azikiwe University.
He is married with two beautiful children. He can be reached by phone on +2348059626829 and through E-mail:
ac.azubogu@unizik.edu.ng or austinazu@yahoo.com.

Obioma Chibueze Peace received the B.Eng. degree in communication engineering from Nnamdi Azikiwe
University, Awka, Anambra state, Nigeria, in 2014. He is currently working toward the Master’s degree in the
department of Electronic and Computer Engineering, Nnamdi Azikiwe University. He has carried out research
on various LED lighting and display systems with focus on efficient and cost effective designs. He has
published works on Renewable Energy and Electric Vehicle Integration in Smart Grids, Overview of Internet
of Things technologies, etc. and has conference proceedings on Design of Low-Cost Driverless LED
Luminaries.
His research interests include Embedded System programming and design, Internet of Things technologies and LED based
intelligent lighting systems. He can be reached via email: obiomapeace2015@gmail.com.

Okwaraoka Chinedu P. A. Obtained his M.Eng in computer and control engineering, Nnamdi Azikiwe
University, Awka, Anambra State, Nigeria, in 2017. PGD in computer and control engineering, Nnamdi
Azikiwe University, Awka, Anambra State, Nigeria, 2014. HND in electrical and electronics engineering,
Federal Polytechnic Nekede, Owerri, Imo State, Nigeria, 2008.
He has published work on embedded fuzzy logic controller for battery charging systems, cost effective solar
charge controller for Li-ion batteries, LED light alternative for incandescent lighting systems, etc. He had
carried out research into various renewable energy generation, control and conversion techniques, and is
currently working on development of standalone self excited energy generation system suitable for rural environments.
Mr. Okwaraoka is currently teaching electrical electronics engineering technology at Electrical and Electronics Engineering
Department of Federal Polytechnic Nekede, Owerri, Imo State, Nigeria.
He can be reached via email: nodumbu@yahoo.com

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