www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
Design and Implementation of Single-Stage Grid-Connected Flyback
Microinverter Operates in DCM for Photovoltaic Applications
Turki K. Hassan1 and Mustafa A. Fadel
2
1PhD, Electrical Engineering Department, Faculty of Engineering, Al-Mustansiriya University, Iraq.
2 MSc, Electrical Engineering Department, Faculty of Engineering, Al-Mustansiriya
University, Iraq, Baghdad.
Abstract
In this paper, a single-stage grid-connected flyback microinverter is proposed. The proposed
flyback microinverter has some advantages such as high voltage gain, high efficiency, low cost, small
size, simple control and high power factor. The proposed system is used to connect the PV panel to the
grid with achieving maximum Power Point Tracking (MPPT) control. The converter operates in DCM to
inject a sinusoidal current into the grid with unity power factor. A complete system has been simulated
using PSIM program and the hardware is build using analog and digital devices. The simulation and
experimental results are obtained to validate the system.
Keywords: Single-Stage, Grid-Connected, Microinverter, Flyback, DCM, MPPT.
1. Introduction
In the last decades the fossil fuels have been widely used in order to cover the human needs of
energy. Moreover, extraction and transportation of fossil fuels cause environmental pollution along with
serious consequences such as air pollution, global warming, soil degradation and water deterioration.
Because of the risks of environmental contamination above, the searching for clean renewable sources of
energy are gaining more and more interest such as wind power, solar power, biomass, geothermal power,
wave and tidal power, and nuclear power. Now days the higher interest is concentrate in solar energy
exploitation, at present the power injection to the utility grid using photovoltaic panels (PV) is gaining more
attention [1, 2].
The photovoltaic panel is a device that converts luminous energy into electric energy through the
photoelectric effect. The electric energy is available at the terminals of the PV panel in the same instant that
the sunlight reaches it, most of the electric equipment of standard use cannot connected directly, this because
the generated current from the PV panel is continuous (dc) and at low voltage (generally between 12 and 68
volts, depending on the technology used in the panel construction) and the majority of the equipment
operates at alternating current (ac), at higher voltages [3]. This brings the need for power interface between
the PV panel and the grid through power electronic inverters. The latest technology for grid-connected PV
systems is the ac-PV module [4-6], where the inverter is integrated in the PV panel and both works as a
single unit that operates as an ac generator used to inject ac current to the grid.
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
The ac-PV module can be easily installed at any place such as rooftop and open areas without needs
to any special technical knowledge or extreme safety caution. The power converter unit of an ac-PV module
is usually a single-phase inverter, ranging from 50 to 400W. There are many single or multistage topologies
about grid-connected inverters for PV modules [2]. As shown in Figure (1) single stage inverters boost the
input voltage and convert it into ac voltage in the same stage. Multistage inverters consist of two cascaded
stages, the first stage is a boost dc-dc converter and the second one is an inverter. Single stage inverters have
some advantages over multistage inverters; such as low cost, high power density, small size, high efficiency
and high reliability. [7].
Figure (1): Single stage and multistage configurations.
The proposed inverter in this paper consists of flyback inverter with PWM modulation. The inverter
operates in the DCM to inject a naturally sinusoidal current into the grid with unity power factor.
2. The Proposed Inverter System
The flyback inverter shown in Figure (2) performs energy flow from the dc side (PV panel) to the ac
side (utility grid), by using transformer with two identical secondary windings. Each of them is able to
transfer energy to the ac side during a utility grid half cycle. For this reason, a semiconductor switches (S2
and S3) are placed in each secondary winding and they appropriately controlled to turn on and off to ensure
an ac output waveform synchronized with the grid. The output LC filter is used to filter the output produced
by the rest of the converter so that the appropriate final output current is produced and fed to the grid.
Figure (2):Single-Stage Flyback inverter.
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
While the main switch semiconductor S1 is modulated in high frequency (20–200 kHz), the switches
S2 and S3 are modulated in 50 Hz. The switching sequence of each semiconductor can be observed in Figure
(3).
Figure (3): Current waveforms and switching sequence diagram [8].
Figure (4) shows the operation of this converter during a line half cycle is as follows: When the
primary switch, S1, is on, the full PV panel input dc voltage is impressed across the transformer, thus putting
energy into its magnetizing inductance and making its magnetizing current rise. When S1 is off, the stored
energy in the transformer’s magnetizing inductance will transferred to the output, which is the grid. Since the
output is ac, which means it is either transferred through D1 and S2 when the voltage output is positive or
through D2 and S3 when the voltage output is negative.S1 duty cycle should be made to vary throughout the
ac voltage line cycle so that it is at its minimum when the ac voltage is at its minimum and it is at its
maximum when the ac voltage is at its peak.
S1 gate pulses
S2 gate pulses
S3 gate pulses
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
(a)
(b)
(c)
Figure (4): Equivalent circuit of the current source flyback inverter during a line half cycle. (a) Each line
half cycle. (b) During S1 on time. (c) During S1 off time.
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
In the following analysis, only discontinuous conduction mode (DCM) is considered due to its
simplicity of control. To ensure the inverter operates in DCM [9].
𝑡𝑜𝑓𝑓 _𝑝 ≤ 𝑇𝑠 − 𝑡𝑜𝑛 _𝑝 (1)
Where𝑡𝑜𝑓𝑓 _𝑝 is the off time of S1 in the switching cycle when the primary current reaches its peak value of
𝐼𝑝𝑟𝑖 _𝑝 and 𝑡𝑜𝑛 _𝑝 is the on time of S1 during the same switching cycle.
The on time can be expressed as:
𝑡𝑜𝑛 _𝑝 = 𝑑𝑝 𝑇𝑠 = 𝑑𝑝
𝑓𝑠(2)
Where 𝑓𝑠 is the switching frequency and 𝑑𝑝 is the duty cycle.
The current in Lm can drop to zero when S1 is turned off and the energy that is stored in it is transferred to the
output. When S1 is turned off, the voltage across the transformer is the output voltage that appears across the
secondary winding and is reflected to the primary. This voltage can be expressed as
𝑣𝑔𝑟𝑖𝑑 𝑡 = 𝑉𝑔𝑟𝑖𝑑 _𝑝 𝑠𝑖𝑛 𝜔𝑔𝑡 (3)
Where 𝑉𝑔𝑟𝑖𝑑 _𝑝 is the peak value of output voltage and 𝜔𝑔 is the grid frequency in rad/sec. Considering this
voltage reflected to the primary, the fall of current in Lm can be expressed as
𝑁 𝑣𝑔𝑟𝑖𝑑 𝑡 = 𝐿𝑚𝑑𝑖𝑝𝑟𝑖 (𝑡)
𝑑𝑡(4)
Where N is the turns ratio. So that 𝑡𝑜𝑓𝑓 can be expressed as:
𝑡𝑜𝑓𝑓 _𝑝 = 𝐿𝑚𝐼𝑝𝑟𝑖 _𝑝(𝑡)
𝑁 𝑉𝑔𝑟𝑖𝑑 _𝑝(5)
To determine the turn off time 𝑡𝑜𝑓𝑓 _𝑝 the peak primary current flowing through the flyback inverter 𝐼𝑝𝑟𝑖 _𝑝
needs to be determined. This can be done by considering the fact that the input dc voltage Vin is impressed on
the transformer primary when S1 is on. The rise in current when S1 is on can be expressed as:
𝑉𝑖𝑛 = 𝐿𝑚𝑑𝑖𝑝𝑟𝑖 (𝑡)
𝑑𝑡(6)
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
Substituting (2) into this equation gives the following expression for 𝐼𝑝𝑟𝑖 _𝑝
𝐼𝑝𝑟𝑖 _𝑝 =𝑉𝑖𝑛𝑑𝑝
𝑓𝑠𝐿𝑚(7)
Substituting this equation into equation (5) gives,
𝑡𝑜𝑓𝑓 _𝑝 =𝑉𝑖𝑛𝑑𝑝
𝑉𝑔𝑟𝑖𝑑 _𝑝 𝑓𝑠 𝑁(8)
It can be seen from equation (8) that 𝑡𝑜𝑓𝑓 _𝑝 dependent on various parameters. Assuming a fixed switching
frequency 𝑓𝑠 , these parameters are fixed except for peak duty cycle 𝑑𝑝 and turns ratio N. Values for 𝑑𝑝and N
need to be chosen so that the converter remains in DCM. This can be done by considering the expression for
DCM operation given in equation (1) and substituting equation (8) into this equation to get
𝑉𝑖𝑛𝑑𝑝
𝑉𝑔𝑟𝑖𝑑 _𝑝 𝑓𝑠 𝑁≤ 𝑇𝑠 − 𝑡𝑜𝑛 _𝑝 (9)
Equation (9) can be rearranged to give the following expression for peak duty cycle
𝑑𝑝 ≤ 𝑉𝑖𝑛
𝑁 𝑉𝑔𝑟𝑖𝑑 _𝑝+ 1
−1
(10)
The next step is to determine an appropriate value of magnetizing inductance Lm that can store sufficient
energy to be fed to the grid, for a rated output power Po. Once this has been determined, the final step is to
confirm that the converter can operate with DCM with this value of Lm. The value of magnetizing
inductance Lm can be calculated using the following equation:
𝐿𝑚 =1
2 𝑑𝑝
2𝑉𝑔𝑟𝑖𝑑 _𝑟𝑚𝑠2
𝑓𝑠𝑃𝑜
𝑉𝑖𝑛𝑉𝑔𝑟𝑖𝑑 _𝑝
2
(11)
The flyback inverter transferred power Po is expressed by the following equation [8]:
𝑃𝑜 =1
4
𝑉𝑖𝑛2 𝑑𝑝
2
𝐿𝑚𝑓𝑠 (12)
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
3. The Proposed Control
The proposed control is based on DCM operation. It requires the achievement of MPPT and unity
power factor for the output current of the inverter in addition to boosting the input voltage into its required
level. Figure (5) shows the schematic of the proposed control system, as shown in the figure, grid voltage
is sensed to provide control signal for the flyback inverter to operate in synchronization with grid voltage,
PV panel’s voltage and current (Vin and Iin) are provided to the MPPT controller to generate reference
signal (Eo). To provide sinusoidal modulation, grid voltage is rectified (S(t)) and then multiplied by the
output signal from the preoperational-integral controller (P-I controller), comparing its output with fixed
sawtooth signal to generate converter control signal (PWM signal for the main switch S1).
Figure (5): Proposed control circuit.
PV generation efficiency and power quality are the fundamental issues. PV power sources are
usually integrated with control algorithms that have the task of ensuring maximum power point (MPP)
operation. Many algorithms have been developed for tracking the maximum power point of a solar array
[10-12].
Most commonly used are perturb and observe (P&O) algorithm [13, 14] and the incremental
conductance algorithm [15]. The main advantages of these algorithms are easy to build and low cost
instruction. Consequently, researchers have been focused on the improvement of maximum power point
tracking (MPPT) control and the reduction of total harmonic distortion (THD). It is very important to
design the MPPT controller, so that the voltage ripple at the terminals of the PV panel is a minimum. The
Perturb and observe (P&O) method also called “Hill-Climbing” is the most widelytechnique used for
MPPT because of their simplicity and effectiveness. The perturbation in the operating voltage of the dc
link between the PV array and the power converter is repeatedly done. In this method, PV power P(k) is
measured and compared with the previous measured PV power P(k-1).
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
If the power increases, the same perturbation is applied in the same direction to get the next PV
powerotherwise perturbationis made in opposite direction. By this process, the operating point of the
system gradually moves towards the MPP and oscillates around it. Based on these facts, the algorithm is
implemented. The process is repeated until the MPP is reached [16]. P&O maximum power point tracking
algorithm is used in this paper. Figure (6) shows the flowchart of the used MPPT control technique.
Figure (6): P&O algorithm for MPPT.
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
4. Simulation Results
The proposed system as shown in Figure (7) is simulated using PSIM software. Table (1) shows the
simulated system specifications.
Figure (7): Proposed system simulation using PSIM program.
Table (1): System design specifications.
Parameters Symbol Value unit
Rated output power Po(max) 100 W
Switching frequency fs 20 kHz
Grid voltage Vgrid_rms 220 V
Input voltage Vin 22 ~ 33 V
Grid frequency fgrid 50 Hz
Total input capacitance Cdc 10000 μF
Turns ratio of transformer N 0.17 -
Output filter capacitance Cf 3 μF
Output filter inductance Lf 2 mH
Proportional constant gain kp 0.5 -
Integral constant gain ki 50 -
Figure (8) shows the input dc voltage from the PV panel, Vin=32.5 V, Which is not pure dc voltage
and it has a little value of ripple about Vripple=1V. However, any voltage ripple on the dc link will create
distortion on the output current waveform, and increase the total harmonic distortion (THD). In addition, the
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
increased voltage ripple on the dc link introduces utilization losses on PV power.
Therefore, a pure or low-ripple dc-link voltage is necessary. The main factor that causes the voltage
ripple in single phase grid-connected inverters is the instantaneous power fluctuation with a magnitude
twice that of the average power and a frequency twice that of the grid frequency. Employing a power
decoupling device is essential to filter this power fluctuation. Using a large electrolytic capacitor (10000μF)
at the input is a simple method for power decoupling in flyback type microinverters [17, 18]. Figure (9)
shows the PV output current, whose value Iin=3.09 A, and it has a little value of current ripple of
Iripple=0.048A. Figure (10) shows the output power from the PV panel Pin=100 W, for S=530 W/m2 sunlight
radiation and T=25 ̊C temperature.
Figure (8): The output voltage from the PV panel.
Figure (9): The output current from the PV panel.
(V)
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
Figure (10): PV output power.
Figure (11) shows the gate pulses sequence for the main switch S1(MOSFET) and switches pulses S2, S3
for the IGBTs.
Figure (11): (a) S1 gate pulses. (b) S2 gate pulses. (c) S3 gate pulses.
Figure (12) shows the drain-source voltage (Vds) for the MOSFET main switch S1, which has a
(a)
(b)
(c)
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
spike voltage of Vspike=78.73 V. The spike voltage appears due to the leakage inductance of the transformer.
As shown in Figure (13), the switch S1 current (IS1) and D1 current (ID1). Due to the spike’s high voltage, it
may damage the MOSFET and it should be reduced, this is done by adding a snubber circuit to the switch
between the drain and the source.
Figure (12): Drain-Source voltage (Vds) of S1.
Figure (13): Switch S1 current and diode D1 current.
The primary current can be seen in Figure (14), as shown, the current has a shape like a rectified sine due to
the sinusoidal modulation. The peak current value of the primary currentis Ipri.=19.43A.
Vspike
Vin
Vin+NVo
IS1
ID1
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
Figure (14): Primary current for flyback microinverter operates in DCM.
Figure (15) shows the voltage stress on the switches S1, S2 and S3. As shown in these figures, all
switches have lower stresses.
Figure (15):MOSFET Switch S1 voltage. (a) IGBT1 Switch S2 voltage. (b) IGBT2 Switch S3 voltage.
Figure (16-a) shows S2 output current Io1, Fig. (16-b) shows S3 output current Io2 and Fig. (16-c)
shows the output current Io before the output LC filter.
Ipri=19.43 A
(a)
(b)
(c)
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
Figure (16):(a) Switch S1 current. (b) Switch S2 current. (c) Output current before the output filter.
For flyback microinverter which operates in DCM. Figure (17) shows the simulation result for the output
current fed to grid after filtering, whose value of Io(rms)=0.44 A, and it almost in-phase with the grid voltage
by power factor of P.F=0.9811 and the output current has a low value of (THD), which is 3.916% for 530
W/m2 sunlight radiation and 25̊ C.
Figure (17):Current fed to grid multiplied by 100 and grid voltage.
5. Experimental Results
The experimental results are obtained based on the prototype setup illustrated in Figure (18). A
flyback microinverter operates in DCM scheme experimentally examined on a 100 W PV panel with 33
V dc input voltage. The prototype is tested to feed 100 W maximum power transferred to the network
with 220 Vrms, 50 Hz. Measurements are obtained by using the oscilloscope spectrum analyzer (RIGOL
digital oscilloscope DS1102E 100 MHz, 1 Gsa/s sampling, USB storage) and probes (Hantek 2 X
(a)
(b)
(c)
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
100MHz oscilloscope clip).
The sunlight radiation is measured using auto digitallux meter (victor 1010A), and the
temperature is measured by infrared thermometer (AR827D -50̊ C ~ 1050̊ C). The design parameters of
the implemented inverter are presented in Table (2).
v
Figure (18): Flyback microinverter prototype setup.
Table (2): Implemented inverter parameters.
MOSFET S1: APT5015BVR Core Material: 3F3
IGBT S2, S3: G40N150D N= 0.17
Diode D1,D2: RHRG75120 Cf =3 μF
fs=20 kHz Lf = 2 mH
Np=17 Turn, (Lm=50.5 μH) Standard aria wire gauge=19
lg= 0.3932 cm No. of primary strands=2
Core type: EE No. of primary strands=1
Figure (19) shows the output voltage from the PV panel (Vin) for S=530 W/m2 and T=25̊ C. As
MPPT Control
Circuit Current
Sensor
EMI filter
PIC
Microcontroller
Voltage
Sensor
Control Circuit Control Circuit
Power Circuit
HF Transformer
LC Filter S1
Cdc
S2
S3
G1
G2
G3
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
shown, the voltage carries a little value of voltage ripple Vripple=3.2 V, which discussed before how to
reduce its value.Figure (20) shows the output current from the PV panel (Iin) for S=530 W/m2 and T=25̊ C.
As shown, the current carries a little value of current ripple Iripple=29 mA. Figure (21) shows the triangular
wave signal, which is internally generated by the PWM IC. The triangular wave peak voltage Vtri.=3.2 V
and the frequency is fS=20 kHz . Figure (22) shows the rectified sine wave signal S(t), which is generated by
the precision diode rectifier circuit.
Figure (19): output voltage from PV panel(1V/div.).
Figure (20): output current from the PV panel.
Figure (21): The triangular wave signal for (1V/div.)
and 20 kHz switching frequency.
Figure (22): The rectified sine wave signal S(t)
(1V/div.).
Figure (23) shows the gate pulses sequence for the main switch S1, and Figure (24) shows the gate
pulse for both S2 and S3 switches. Figure (25) shows the primary current, whose shape like a rectified sine
wave. The peak value of the primary current is Ipri.=19.2 A. Figure (26) shows the drain-source voltage (Vds)
of the main switch S1, the value Vds=60.8 V, for S=109.5 W/m2 and T=25̊ C.
Vin=30 V
Vripple=3.2 V
Iin=3.09 A
Iripple=29 mA
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
Figure (23): Gate pulses sequence for the main
switch S1 (5V/div.).
Figure (24): Gate pulses sequence for switch S1 and
S2 (5V/div.).
Figure (25): The primary current Ipri (10A/div.).
Figure (26): drain-source voltage (Vds) of S1 switch.
The figures below shows experimental results for sinusoidal ac current fed to the grid by the single
stage flyback microinverter which operates in DCM with the grid voltage for different values of sunlight
radiation. Figure (27-a) shows the injected current to grid in phase with the grid voltage for S=515 W/m2,
T=25̊ C and the power generated from PV panel is Pin=93 W with respect to the given sunlight radiation.
Figure (27-b) shows the signals for S=357 W/m2, T=25̊ C and Pin=69 W. Figure (27-c) shows the signals for
S=257 W/m2, T=25̊ C and Pin=49 W. Figure (27-d) shows the signals for S=109 W/m
2, T=25̊ C and
Pin=16.5 W.
Ipri._p=19.2 A
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
(a)
(b)
(c)
(d)
Figure (27): The ac current fed to grid (0.2 A/div.), 50 Hz in phase with voltage grid (10 V/div.) (a)
Io=0.381 A, P.F= 0.98 (b) Io=0.294 A, P.F= 0.961 (c) Io=0.21 A, P.F= 0.93 (d) Io=0.105 A, P.F= 0.579
The figures below shows comparison between the simulation results from the PSIM software and
the experimental results measured from the hardware device, the comparison is made for the power factor,
efficiency and total harmonic distortion, as shown in Figure (28) the power factor between the current
injected to the grid and the grid voltage in both simulation and experimental measurements almost unity
power factor at high power level, but at low power levels the power factor is poor due to the capacitor of the
output filter.
Figure (29) shows very good efficiency for both simulation and experimental results about 94.5%
efficiency at 100 W input power from the PV panel.
Figure (30) shows small values of THD (below 5%) at high power levels for both simulated and
experimental results, the THD increases above 5% at low power levels.
Io=0.381 AVgrid/10 Io=0.294 A Vgrid/10
Io=0.21 AVgrid/10 Io=0.105 AVgrid/10
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
Figure (28):Calculated and measured P.F versus output power.
Figure (29): Calculated and measured efficiency versus output power.
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
15
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
Po
wer F
acto
r
Output Power Po (W)
Expreimental Power Factor
PSIM Power Factor
86
87
88
89
90
91
92
93
94
95
0 10 20 30 40 50 60 70 80 90 100
Eff
icie
ncy
(%
)
Output power Po (W)
PSIM Efficiency
Expreimental Efficiency
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
Figure (30): Calculated and measured THD versus output power.
6. Conclusion
In this paper a single phase current-source flyback microinverter for grid-connected PV systems has
been investigated and implemented to inject alternating current to the national grid via a 100 W
photovoltaic panel. A design strategy for the operation scheme has been proposed in order to achieve high-
power density. Moreover, this paper has highlighted, both experimentallyandsimulation, the optimum
inverter behavior when theDCM operation mode is used, leading to a global and high-efficiency solution
for wide power range “ac–PV module” applications.
The complete DCM system was verified and a hardware prototype is build using analogue devices
and microcontroller for the flyback microinverter control. Based on the simulation and experimental results
the following aspects can be concluded:
1. Sinusoidal output current injected into the grid with approximately unity power factor is
obtained at high sunlight radiation (high output power from PV panel).
2. The output power of the microinverter depends on the solar energy absorbed by photovoltaic
panel, which is converted to electric energy. The maximum power point tracking algorithm
(Perturb and Observe method) is used to extract the maximum power from the PV panel.
3. Low THD of the output current is obtained due to the efficient control method and low-pass
output filter (LC filter).
The suggested flyback microinverter has high efficiency, high reliability, small size and low cost due to
single-stage of dc/ac conversion.
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
0 20 40 60 80 100 120
Tota
l H
arm
on
ic D
isto
rtio
n (
%)
Output power Po (W)
Experimental THD
PSIM THD
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
References
[1] S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg,"A Review of Single-Phase Grid-Connected Inverters
for Photovoltaic Modules", IEEE Transactions on Industrial Application, vol. 41, no. 5, pp. 1292–
1306, Sep. 2005.
[2] J. Gow and C.Manning, “Photovoltaic converter system suitable for use in small scale stand-alone or
grid-connected applications,” IEE Proc. Electr. Power Appl., vol. 147, no. 6, pp. 535–543, Nov. 2000.
[3] L. J. Sheng, "Power conditioning systems for renewable energies", International Conference on
Electrical Machines and Systems, pp. 209 - 218,Seoul, Oct. (8-11), 2007.
[4] Y. Fang and X. Ma, “A novel PV microinverter with coupled inductors and double-boost topology,”
IEEE Trans. Power Electron., vol. 25, no. 12, pp. 3139–3147, Dec. 2010.
[5] Z. Liang, R. Guo, J. Li, and A. Q. Huang, “A high-efficiency PV module integrated DC/DC converter
for PV energy harvest in FREEDM systems,” IEEE Trans. Power Electron., vol. 26, no. 3, pp. 897–
909, Mar. 2011.
[6] A. Ch. Kyritsis, E. C. Tatakis, and N. P. Papanikolaou, “Optimum design of the current-source
flyback inverter for decentralized grid-connected photovoltaic systems,” IEEE Trans. Energy
Convers., vol. 23, no. 1, pp. 281–293, Mar. 2008.
[7] S. Jain and V. Agarwal,"A Single-Stage Grid Connected Inverter Topology for Solar PV Systems
with Maximum Power Point Tracking", IEEE Transaction on Power Electronics, vol. 22, no. 5, pp.
1928-1940, Sep. 2007.
[8] C. Nanakos, Emmanuel, C. Tatakis and N. P. Papanikolaou, "A Weighted-Efficiency-Oriented
Design Methodology of Flyback Inverter for AC Photovoltaic Modules", IEEE Transaction on Power
Electronics, vol. 27, no. 7, pp. 3221-3233, July. 2012.
[9] A. Ch. Kyritsis, E. C. Tatakis, and N. P. Papanikolaou, "Optimum Design of the Current-Source
FlybackInverter for Decentralized Grid-Connected Photovoltaic Systems", IEEE Transactions On
Energy Conversion, vol. 23, no. 1, pp. 281–293, Mar. 2008.
[10] J. S. C. M. Raj and A. E. Jeyakumar, "A Novel Maximum Power Point Tracking Technique for
Photovoltaic Module Based on Power Plane Analysis of I–V Characteristics", IEEE Transaction on
Industrial Electronics, vol. 61, no. 9, pp. 4734 - 4745, Sep. 2014.
www.saussurea.org
SAUSSUREA (ISSN: 0373-2525), 2016 Volume 6(3):PP. 219-240
RESEARCH ARTICLE
[11] C. Kalpana et al., "Design and Implementation of different MPPT Algorithms for PV System",
International Journal of Science, Engineering and Technology Research (IJSETR), vol. 2, no. 10, pp.
1926 - 1933, Oct. 2013.
[12] D. P. Hohm and M. E. Ropp, "Comparative study of maximum power point tracking algorithms using
an experimental, programmable, maximum power point tracking test bed", 28th Annual IEEE
Photovoltaic Specialists Conference, pp. 1699 - 1702,Anchorage, AK, Sep. (15-22), 2000.
[13] N. Femia et al., "Optimization of Perturb and Observe Maximum Power Point Tracking Method",
IEEE Transaction on Industrial Electronics, vol. 20, no. 4, pp. 963 - 973, Jul. 2005.
[14] A. M. Atallah et al., "Implementation of Perturb and Observe MPPT of PV System with Direct
Control Method Using Buck and Buck-Boost Converter", Emerging Trends in Electrical, Electronics
& Instrumentation Engineering: An international Journal, vol. 1, no. 1, pp. 31 - 44, Feb. 2014.
[15] A. Safari and S. Mekhilef,"Simulation and Hardware Implementation of Incremental Conductance
MPPT With Direct Control Method Using Cuk Converter", IEEE Transaction on Industrial
Electronics, vol. 58, no. 4, pp. 1154 - 1161, Apr. 2011.
[16] S. Jain, et al., "Comparative Analysis of MPPT Techniques for PV in Domestic Applications", 6th
IEEE Power India International Conference (PIICON), pp. 1 - 6, Delhi, Dec. (5-7), 2014.
[17] H. Hu, et al., "A Review of Power Decoupling Techniques for Microinverters With Three Different
Decoupling Capacitor Locations in PV Systems", IEEE Transactions on Power Electronics, vol. 28,
no. 6, pp. 2711–2726, Jun. 2013.
[18] H. Hu, et al. "A Three-port Flyback for PV Microinverter Applications With Power Pulsation
Decoupling Capability", IEEE Transactions on Power Electronics, vol. 27, no. 9, pp. 3953 - 3964,
Sep. 2012.
Top Related