Comparison of H-Bridge Single-phase
Transformerless PV String Inverters
Jacson R. Dreher1, Filipe Marangoni2, Luciano
Schuch3, Mário L. da S. Martins2,3
Leandro Della Flora4
4
1
Federal Institute of Santa Catarina, IFSC
2
Federal University of Technology – Parana, UTFPR
3
Federal University of Santa Maria, UFSM
fi.marangoni@gmail.com, mariolsm@gmail.com
Abstract— This paper presents a detailed comparison among
single-phase transformerless string inverters for grid-connected
PV systems. The characteristics of the PV modules and their nonidealities are taking into the account for the design and the
performance of the inverter with respect to the IEEE 1547
Standard. Simulated and experimental results for the inverter
topologies are carried out.
Keywords- Grid connected PV System; String Inverter;
Transformerless Inverter.
I.
INTRODUCTION
II.
GRID-CONNECTED INVERTER TOPOLOGIES
PV systems are modular by nature, increasing the power by
adding PV modules, [1]. These PV modules are gathered in a
set of series and parallel connections by an array. Depending
on the type of the array the system can be classified in different
categories, [1]. If there is only one inverter for the entire set of
series and parallel connections of the PV modules, the power
converter system is called central inverter. Otherwise, it is
named decentralized inverter. Further classification of
decentralized inverters is given according to the number of
modules and series strings of modules, Fig. 1. As the name
implies, the module-integrated (or AC-module) concerns the
inverter that operates from a single PV module. As the power
converter is dedicate to only one PV module, it can be designed
and optimized for the module characteristics, enhancing its
performance and power generation. On the other hand, the
string inverter is a system that comprises a single string of PV
modules of about ten to twenty series connected PV modules.
This way, higher power is achieved. Nevertheless, the total
power is proportional to the system DC bus voltage and,
consequently, to the number of PV modules of the string.
When more power is needed, the alternative is to use multistring inverters. In this system, each string has a dedicated DCDC stage that is connected with its output in series with other
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...
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On the other hand, H-bridge family of inverters requires
half of the input voltage demanded by the half-bridge topology,
that is, around 350 VDC. To avoid a varying common-mode
voltage, the H-bridge has to be modulated with bipolar PWM,
leading to high current ripple levels that should be handled by
the output filter [2]. Intending to overcome these limitations
several topologies have been proposed. This paper proposes a
comparative analysis among the most popular single-phase Hbridge transformerless topologies.
...
Domestic PV systems are mostly low-power single-phase
systems (up to 10 kW) and are becoming more important
worldwide. These systems are usually private where the owner
aims the maximum system profitability. In this grown lowpower PV market there has an increased concern for the need
of power processing systems characterized by high efficiency,
small size and weight, and chiefly low cost. To achieve such
characteristics, it is mandatory to eliminate the output line
frequency transformer. Nevertheless, in order to avoid leakage
currents and the injection of dc current into the grid, it is
necessary for transformerless inverter to be modified with
respect their circuit and switching strategy when compared to
standard H-bridge topologies. These modifications intend to
make the inverter operates with no variable common-mode
voltage [1]. An interesting alternative is found in the halfbridge family of inverters, because of the natural ground of
their DC bus mid-point. With two or more voltage levels the
half-bridge inverters could be a simple choice to implement
transformerless good quality grid-connected PV systems. The
main drawback of this alternative is the need of high input
voltages, which involves either the use of a large PV string or a
step-up stage, offsetting the low component count advantage of
the transformerless inverters.
Danfoss Power Electronics
Loves Park, Illinois, USA
ldellaflora@gmail.com
...
(a)
(b)
(c)
(d)
Fig. 1. Grid connected PV systems concepts. (a) module-integrated,
(b) string, (c) multistring and (d) central inverter concept.
DC-DC stages to the input of a single inverter stage. This way,
the multi-string inverter has the advantages of both string and
central inverters, i.e., it has decentralized MPPT for a small
group of PV modules, but a single standard inverter.
A. H-bridge inverter
The H-bridge topology with standard unipolar modulation
cannot be used in transformerless PV systems, due to leakage
currents problem aforementioned. Fig. 2(a) shows the main
voltages of a H-bridge with unipolar PWM. The grid voltage is
the blue trace, the H-bridge pulsating voltage is shown in red
and the common voltage (VCM) is shown in gray. It can be
observed that VCM swings at the switching frequency around
the half of the bus voltage value. This voltage variation
discharges the parasitic capacitances, injecting the leakage
current through the circuit into the grid. To reduce the leakage
current, the VCM must be kept constant. Fig. 2(b) shows the
main voltages of a H-bridge with bipolar PWM. It can be
observed that VCM remains still at half of the bus voltage value.
In spite of solute the leakage current problem, the bipolar
PWM impose twice the dv/dt (Fig. 3) to the inverter output
filter compared to the unipolar PWM, causing the increase of
inductor value, size and, consequently cost. As can be seen in
Fig. 3, to keep Imax the same the value of the inductance must
be the double.
In order to keep VCM constant with a three level voltage
applied to the output filter, some modifications of the H-bridge
will be present in the next sections.
B. HERIC inverter
This topology, shown in Fig. 4, is comprised by a standard
H-bridge circuit that is modulated in a bipolar PWM mode.
However, the switches at the same branch do not operate
complementarily, instead of, they operate only for a half-cycle
of the grid voltage and are hold inactivate in the other one [3].
To implement the freewheeling stage, an additional branch is
VDC
0
vagv
VDC
2
vagv
t
VAB
vagv
0
i
t
-VDC
2
i
Imax
i
Imax
ipp
ipp
t
t
Imax
d
Imax
d
TAB
TAB
(a)
(b)
Fig. 3. Output voltage and current waveform of (a) unipolar PWM
and (b) bipolar PWM.
used. It is placed in parallel with the load, before the output
filter and comprises two switches in opposite direction, which
provides an alternative path for the load current in each halfcycle of the grid voltage waveform. This AC-bypass provides a
zero voltage level to the output voltage waveform, reducing the
occurrence of leakage currents, since the PV array is decoupled
from the grid during the freewheeling stage. The operating
stages during the positive output voltage half-cycle are shown
in Fig. 3. It can be observed that during the free-wheeling stage
the DC bus is disconnected off. The AC switch S5 could stay
on during the entire positive output voltage half-cycle, or to be
modulated complementarily to S1/S4.
In practice voltage at the middle point of both inverter legs
is equal during free-wheeling interval, however it is at a
potential is not clamped and thus it can vary between VDC and
zero, as will be demonstrated later.
C. H5 inverter
This inverter, shown in Fig. 5, basically consists of a
standard H-bridge with two high-frequency switches and two
low-frequency switches per cycle. Likewise the HERIC
+VDC
S3
S1
Vcm
+VDC/2
PV
0
C
VDC
S6
-VDC/2
B
-VDC
PV
0
4.16
8.33
12.50
16.67
20.83
25.00
29.17
Time (ms)
S4
S1
Vcm
PV
C
0
VDC
S3
S6
B
PV
-VDC
4.16
8.33
12.50
16.67
20.83
25.00
29.17
33.34
Time (ms)
(b)
Fig. 2. Main voltage of H-bridge inverter. (a) With unipolar
PWM modulation (b) With bipolar PWM modulation.
0
igrid
A
-VDC/2
0
vgrid
VAB
(a)
(a)
+VDC
+VDC/2
S5
S2
0
33.34
igrid
A
S2
S5
vgrid
VAB
S4
(b)
Fig. 4. HERIC inverter operating stages during positive output
voltage half-cycle. (a) Power transfer stage (b) Free-wheeling
stage.
topology, the H-bridge switches are not complementary
operated. To implement the PWM modulation, a DC-bypass
approach is introduced, which consists of the switch (S5) that is
activated every time the high-frequency switches are on [3]. It
can be seen that besides to modulate the PWM, the switch S5
also decouple the PV array from the grid. The main advantage
of H5 is that only five switches are required, instead of six, like
the HERIC inverter.
The main difference in the operation of the inverter is that
three devices are on during the power transfer stage, which
augments the conduction losses. The free-wheeling stage is
accomplished by the H-bridge devices. During this stage, it can
be seen in Fig. 5(b) that voltage VDC is applied across switches
S5 and S2 and hence, the middle point of the inverter legs is
effectively in the half potential. Nevertheless, to make the freewheeling always with switches S3 on, it will present high
conduction and switching efforts than the other H-bridge
devices.
D. H6 inverter
In the H6 inverter topology, there is the addition of the S6
switch (Fig. 6) that is placed in series connections with the
negative DC-rail. It operates in a very similar way as the H5
topology, nevertheless, the free-wheeling stage can be
accomplished keeping S1 and S4 on (for the positive half
cycle) or S2 and S3 on (for the negative half cycle). It
distributes equally the device efforts and balances the thermal
distribution.
Voltage VDC will appear across the switches S5 and S6
during the free-wheeling stages.
The disadvantage of the H6 is that four devices are on
during the power transfer stages. On the other hand, all
switches anti-parallel diodes are put on conduction during the
free-wheeling stages, which requires that they present low
reverse recovery losses. It implies that IGBT is preferable for
the H6 inverter.
E. H6D1 inverter
To implement the H-bridge switches with high speed
MOSFETs, it is required to give an alternative path to the freewheeling current to flow. It is accomplished by an extra diode
placed across the H-bridge, as shown in Fig. 7.
In this topology the extra disadvantage is that the freewheeling stage presents three devices on that enlarge the
PV
C
PV
C
S3
S1
VDC
0
S6
S2
C
igrid
0
S2
PV
C
B
PV
0
S3
PV
C
igrid
VDC
PV
C
VDC
0
S3
A
PV
C
igrid
S2
S4
S2
S1
S4
(c)
Fig. 5. H5 inverter operating stages. (a) Power transfer stage for
positive output voltage half-cycle; (b) Power transfer stage for
negative output voltage half-cycle; (c) Free-wheeling stage.
S3
A
VDC
igrid
vgrid
VAB
vgrid
VAB
0
S6
(c)
B
PV
vgrid
B
PV
S5
S1
igrid
VAB
(b)
S5
S3
A
S4
S2
S4
S1
vgrid
VAB
0
S2
S5
B
PV
S6
(b)
A
VDC
vgrid
VAB
S4
S1
igrid
A
VDC
(a)
S5
S3
S1
vgrid
VAB
S4
(a)
B
PV
vgrid
VAB
B
PV
PV
A
VDC
igrid
A
S5
S5
S3
S1
S5
B
PV
0
S6
S2
S4
(d)
Fig. 6. H6 inverter operating stages. (a) Power transfer stage for
positive output voltage half-cycle; (b) Free-wheeling stage for
positive output voltage half-cycle; (c) Power transfer stage for
negative output voltage half-cycle; (c) Free-wheeling stage for
negative output voltage half-cycle.
S5
PV
VDC
C
S3
S1
TABLE I.
igrid
A
CURRENT
vgrid
D
VAB
0
S2
S6
S4
S5
VDC
C
S3
S1
igrid
A
vgrid
D
VAB
B
PV
0
S6
S4
S2
(b)
Fig. 8. H6D1 free-wheeling stages. (a) For positive output
voltage half-cycle; (b) For negative output voltage half-cycle.
conduction losses.
F. H6D2 inverter
The high conduction losses of H6 and H6D1 can be
reduced if the DC bus MOSFETs and free-wheeling diodes
could be rated for low voltages, which are possible using the
approach shown in Fig. 8. It can be noticed that only half of the
bus voltage is applied across the DC bus MOSFETs and freewheeling diodes.
Aiming to summarize the main features of the
abovementioned topologies Table I presents concise
information about all inverters described in this section.
III.
PV STRING AND GRID SPECIFICATIONS
Intending to analyze practical aspects of the previously
S5
C1 VDC
PV
2
C
VDC
C2 2
PV
S6
0
S3
S1
D1
PV
S5
C1 VDC
2
C
C2
VDC
2
S6
0
1.5
0.6
0.3
5.0
discussed inverters this section presents a brief discussion
about some key design and implementation characteristics that
may benefit or offset a specific topology in detriment of the
others.
A. Grid connection and Standards
Most of standards dealing with utility interconnection
regard for the level of the DC current injected to the grid (see
IEEE 929-2000, IEC 61727, IEEE 1547, EN 61000-3-2) and
this varies between 0.5 and 1% of the rated current. They also
concern about the harmonic content that is always limited.
Table II show the limits for the IEEE 1547.
In addition, some standards, like the German DIN VDE
0126-1-1, in case of transformerless PV inverters connected to
the grid, impose the need for a Residual Current Monitoring
Unit (RCMU), which is sensitive for DC and AC currents and
can sense DC fault currents. In case the leakage current to
ground (peak value) is greater than 300mA, then disconnection
is necessary within 0.3s.
Hence, the design of the inverter filter must cope with the
requirements impose by the Standard. Furthermore, the leakage
current also has an important role in the filter specification as
will be discussed later.
In buck derived inverter topologies, the DC-bus must be at
a voltage slightly higher than the peak of the grid voltage, so
that the current flows only from the inverter to the grid. This
way, the number of PV modules in the string and the
irradiation/temperature conditions that guaranty such
conditions must be taken into account in the design of the PV
vgrid
VAB
D2
TABLE II.
COMPARATIVE OF H-BRIDGE STRING INVERTERS
B
S2
S1
D1
2.0
igrid
A
Inverter Features
S4
Topology
S3
Bipolar Hbridge
Unipolar Hbridge
(a)
PV
4.0
* Even harmonics are limited to 25% of the odd harmonic limits above.
(a)
PV
Harmonic order h H < 11 ≤ h 17 ≤ h 23 ≤ h 35 ≤ Total Harmonic
(odd)*
11 < 17
< 23
< 35
h Distortion (THD)
Percent (%)
B
PV
MAXIMUM HARMONIC CURRENT DISTORTION IN PERCENT OF
A
igrid
vgrid
VAB
D2
B
S2
S4
(b)
Fig. 7. H6D2 inverter operating stages during positive output
voltage half-cycle. (a) Power transfer stage; (b) Free-wheeling
stage.
HERIC
N. of
switches /
diodes
Output
voltage
Switches on
(diodes on)
4/4
2 levels
2 (0) / 0 (2)
4/4
3 levels
2 (0) / 1 (1)
6/2
3 levels
2 (0) / 1 (1)
H5
5/4
3 levels
3 (0) / 1 (1)
H6
6/4
3 levels
4 (0) / 2 (2)
H6D1
6/5
3 levels
4 (0) / 2 (1)
H6D2
6/6
3 levels
4 (0) / 2 (2)
Freewheeling
diodes of
the bridge
diodes of
the bridge
AC bypass
(a)
diodes of
the bridge
diodes of
the bridge
DC bypass
(b)
DC bypass
(c)
a) 1 switch and 1 diode on; b) 1 diode on; c) 2 diodes on.
system.
2000
1800
1600
1400
1200
1000
800
600
400
200
0
Expression (1) can be used to determine the minimum
voltage to the DC-bus and further the number of PV modules
in the string (expression (2)).
 1
2t 
    VS 
VDC  min   Vgrid max 
 ma max Ts 


Where, VΔS represents the total voltage drop of all on
semiconductors in conduction; tΔ is the defined as blanking
time or dead time; Vgrid is the peak of grid voltage; mamax is the
modulation index.

N mod 
VDC  min 
VPV  min 
, N mod  Z 

Where, Nmod is the number of the modules, VDC(min) is the
minimum voltage required for the DC-bus and VPV(min) is the
minimum voltage of a single PV module under the worst
irradiation/temperature conditions.
Figure 9 show the VDC(min) in function of the switching
frequency. The curve is plotted for a grid voltage of 127 V and
also takes into account the data for a standard PV module given
in Table III.
B. PV characteristics and DC-bus voltage
As the PV modules have a characteristic curve that is
modified with temperature and solar irradiation, during the day,
the voltage and the current at the maximum power point of the
PV array will vary in a large range of values. The least
irradiation value (100 W/m2), at 25°C, produces a voltage of
21.7V and a current of 0.757A per PV module. At this
operation point the produced power is the lower and the DCbus voltage is at VPV(min). The high irradiation condition (1000
W/m2) at 25° produces a voltage of 26.2V and a current of
7.637A per PV module. The DC-bus voltage achieves the
VDC(max). Hence, during the PV system operation the DC-bus
TABLE III.
PV MODULE PARAMETERS FROM KC200GT
Parameter
Irradiation
Temp.
VPV (IPV)
100 W/m²
25°C
VPV (IPV)
1000 W/m²
25°C
215
210
205
200
195
190
185
180
Value
21.7 [V]
(0.757 [A])
26.2 [V]
(7.637 [A])
11 modules
40
60
0
50
100
150
200
250
VDC(min)VPV(min) VDC(max)
300 Voltage (V)
VPV(max)
Fig. 10. PV String power versus voltage.
voltage variation can be defined as Vop. Analogously, the
power of the PV string also varies as determined by PPV.
Nevertheless, when the PV string is disconnected, the voltage
of each PV module reaches its highest value that is the open
circuit voltage. At this point, the PV string is at VPV(max).
From the inverter design perspective, the power stage must
be designed to support the open circuit voltage of the PV string
(VPV(max)) and the maximum PV module current IPV at 1000
W/m2. On the other hand, the controller design should be able
to handle the inverter operation with a DC-bus disturbance of
Vop.
C. Inverter output voltage and ripple of the grid current
For bipolar modulation the output voltage assumes two
values, VDC or -VDC. The frequency fAB of the output voltage is
the same as the switching frequency, i.e., fAB = fs. For the
HERIC, H5 and H6*, the bypass switches clip the voltage
waveforms at the zero voltage level, yielding a three level
PWM, due to additional switches used during the freewheeling
stage, thus the voltage levels are VDC, 0 (zero) and -VDC. Thus,
the current ripple can be determined by means of Fig. 3(a).
From the inverter circuit it can be observed that,

i pp  VDC  vgrid  t  
d  t  .TAB
L


Where VDC is the bus voltage; vgrid (t) is grid voltage during
a period TAB; and d(t) is the duty-cycle of the PWM at a
switching period.
Since the vgrid and d(t) varies in during the output voltage
period, an average ripple should be determined in order to
define L. This way, the ripple factor (RFsw) was proposed by
[5] and it stands for the ratio between the current ripple and its
fundamental component. It can be seen as a quality factor of
the total current injected in the grid and is given by (4),


20
Vop
RFsw 
IR
 100  %  
I o1

Expression (3) can be expressed in terms of output voltage
angle (θ) as follows,
10 modules
0
PPV
80
100 120 140 160 180
Switching frequency [kHz]
Fig. 9. Minimum DC-bus voltage versus the switching frequency.
i pp   
VDC TAB
1  ma sin    ma sin   
L

Where θ varies in the interval 0 < θ < π of the output
voltage.
Thus, the switching ripple factor of grid-connected singlephase inverters (RFsw) can be found dividing expression (8) by
expression (9). Reversely, the filter inductor can be given by
16
14
Bipolar
12
10 f = f
AB
sw
8
6
f = 2fsw
4 AB

2
0
100 200 300 400 500 600
Irradiation (W/m²)
0
700 800 900 1000
Fig. 12. Filter inductor versus PV string irradiation.
The ripple current waveform for a grid period is shown in
Fig. 11(a) and Fig. 11(b), describes the distribution of the filter
inductor current (triangle waveforms), where the magnitude of
any k-th triangle waveform can be calculated as (6).
In analogy, the peak-to-peak value of the filter inductor
current Δipp that results
imax k  

VDCTAB
1  ma sin k   ma sin k  
2L

where,  k   2k  1 4m f , k  1, 2,..., m f .
Since the RMS value of each triangle wave is Δimax(θk)/√3, the
RMS value of IR is,

IR 
2
imax  k 
mf


k 1
k
2
3

2
3

 /2
0
2
imax
  d 

L
1 TAB
4    3ma2
Lgrid
 1 
RFsw T
3  4 
4
 4ma

3


 


Figure 12 shows the expression (10) versus the solar
irradiation for three conditions of VAB, bipolar PWM, unipolar
PWM, and double frequency unipolar PWM. It can be seen that
the inductor size is inversely proportional to the irradiation. It
also is observed that inductor value reduces with the reduction
of dv/dt and also with the increasing of frequency.
D. Synchronism and Current Control
In grid-connected applications, the current control is the
key to the inverter performance. For a single-phase inverter to
use PI controllers in D-Q frame, it is required an additional
imaginary or orthogonal signal to move to D-Q frame. At
synchronous frame the PI controllers provide zero steady state
error. The block diagram of the inverter and the current
controller in D-Q frame is shown in Fig. 13(a) and Fig. 13(b),
respectively. The construction of the synchronous frame
consists in measure the grid current and passes it through a
Kalman filter to get its orthogonal value. The complete
diagram of the system is shown in Fig. 14. The Kalman blocks
are applied to generate the orthogonal signals for the PLL and
to estimate the current in quadrature to the synchronous frame
for the current controller.
The system performance can be evaluated with respect of
By calculating the integral, the RMS value of the switching
ripple current, it can be found that

IR 
VDC TAB
2L
2ma2    3ma2
 1 
3  4 
4
 4 
  ma  
 3 

And the fundamental component is given by,

I o (1) 
VDC ma
2 Z grid

VDC maT
2 2 Lgrid


(a)
IR
Imax|
ipp|
 t
/2
0
k
IR
ir
(a)
max(k)
Imax(k)|
ipp(k)|
Ir(k)
k = 
2mf
t
(b)
Fig. 11. Ripple current. (a) RMS value and (b) detail of RMS ripple
current.
(b)
Fig. 13. Block diagrams in D-Q frame. (a) Inverter model; (b)
Current controller.
Fig. 15. Block diagrams for the whole system.
sudden shadowing that can change rapidly the reference for the
D-Q frame current controller. The current Id response for a step
change of 100% is shown in Fig. 15(a). The system reaches the
steady-state in 48.12 ms. On the other hand, grid disturbance
can also affect the current controller. The current Id response
for a step change of 10% in the grid voltage is shown in Fig.
15(b). It can be seen that the system respond quickly ensuring a
good performance.
Figure 16 show the experimental waveforms for the grid
voltage and current of the HERIC inverter for an emulated
irradiation of 500 W/m2. It can be observed that the
synchronism is achieved and the current is of good quality.
IV.
COMPARATIVE ANALYSIS
Besides the HERIC inverter to provide the AC decoupling
of the grid, the common mode voltage of the inverter is not
30
48.12 ms
48.12 ms
20
10
0
0.3
0.35
0.4
Time (s)
Aiming to compare the impact of the leakage current in the
grid current, Table V, VI, VII and VIII show the comparison of
the grid current harmonics for the HERIC, H5, H6 and H6D2.
The simulation results take into account a parasitic PV
capacitance of 200 nF.
It can be seen for the HERIC inverter that for irradiation
below 400 W/m2, the THD is larger than the permit by IEEE
1547 Standard. It means that the leakage current degraded the
harmonic performance of the HERIC inverter in such way that,
in spite of the design consider its operation for irradiation as
low as 100 W/m2, the HERIC inverter should be turned off at
four times high due to Standard compliance.
In Table VI, the simulated results for the H5 inverter show
a slightly better numbers. The THD for H5 inverter do not
reach the requirements for irradiation lower than 300 W/m2.
-10
-20
-30
0.25
kept constant. It presents a variation at high frequency as
shown in Fig. 17. These voltage variations reach almost 100V
of peak, which can increase the leakage current and degrade the
grid current harmonic performance, mainly for low irradiation
conditions, as can be seen in Table IV. The experimental
current measured THD for irradiations below 400 W/m2 do not
comply with IEEE 1547 Standard.
The H6 inverter presented results comparable to the HERIC
inverter and also do not comply with the IEEE Standard for
irradiation lower than 400 W/m2.
0.45
0.5
Table VIII show the results for the H6D2 inverter.
(a)
30
20
10
0
Vgrid(d)
10
-10
-20
-30
Vgrid(d) - 10%
10
Overshoot
Settling time
0.25
0.3
0.35
Time (s)
0.4
0.45
(b)
Fig. 14. System response for Id and Igrid. (a) Id step of 100%; (b)
Vgrid step of 10%.
Fig. 16. Grid voltage and current for the HERIC inverter.
[3]
[4]
[5]
F. Schimpf, L. E. Norum, “Grid Connected Converters for Photovoltaic,
State of the Art, Ideas for Improvement of Transformerless Inverters.”
Nordic Workshop on Power and Industrial Electronics.
B. Yang, W. LI and Y. DENG, “A novel single-phase transformerless
photovoltaic inverter connected to grid.” Power Electronics, Machines
and Drives, p.1-6.
H. Kim, K.H. Kim, “Filter design for grid connected PV inverters,”
IEEE ICSET 2008, p. 1070-1075.
HERIC INVERTER SIMULATED THD
TABLE V.
Fig. 17. Measured common mode voltage for the HERIC inverter.
TABLE IV.
Irradiation
[W/m²]
500
400
300
200
100
HERIC INVERTER EXPERIMENTAL THD
Pin [W]
Pout [W]
950.2
746.8
537.8
341.3
151.1
η [%]
THD
913
96.063
4.373
718
96.186
5.781 *
519
96.421
6.101 *
331
97.018
8.302 *
148
97.923
14.571 *
* Do not comply with IEEE 1547 Standard
Compared to the other topologies, it presented the worst
performance and it complies with the IEEE 1547 Standard for
irradiation higher than 700 W/m2.
V.
CONCLUSION
This paper presented a comparison among single-phase
transformerless inverters for grid-connection applications. It
demonstrate that in spited of the design of the output filter to
allow the inverter operation for low irradiation conditions, the
leakage current injected to the grid due to the absence of the of
the line transformer, degrades the THD, limiting the operation
of most of String inverters to irradiations of 300 W/m2, 400
W/m2 and even 600 W/m2. This limitation in the range of
operation of the inverters quite reduces the power generated by
the inverters.
ACKNOWLEDGMENT
The authors would like to express their gratitude to
‘Conselho Nacional de Desenvolvimento Científico e
Tecnológico–CNPq’ (proc. 554103/2010-9 and proc.
481432/2011-6) for financial support and Xilinx for material
support.
REFERENCES
[1]
[2]
M. Calais, and V. G. Agilidis, “Multilevel converters for single-phase
grid connected photovoltaic systems-an overview.” IEEE International
Symposium on Industrial Electronics, p.224-229.
G. Spagnuolo, G. Petrone, S.V. ARAUJO, et al, “Renewable Energy
Operation and Conversion Schemes: A Summary of Discussions During
the Seminar on Renewable Energy Systems,” IEEE Industrial
Electronics Magazine, v.4, n.1, p.38-51.
Irradiation [W/m²]
1000
900
800
700
600
500
400
300
200
100
igrid [A]
14.273
12.726
11.195
9.682
8.187
6.716
5.270
3.856
2.485
1.174
TABLE VI.
Irradiation [W/m²]
1000
900
800
700
600
500
400
300
200
100
H5 INVERTER SIMULATED THD
igrid [A]
14.287
12.741
11.209
9.697
8.202
6.730
5.280
3.869
2.497
1.190
TABLE VII.
Irradiation [W/m²]
1000
900
800
700
600
500
400
300
200
100
Irradiation [W/m²]
1000
900
800
700
600
500
400
300
200
100
ileakage [mA]
% ileakage
THD %
26.578
0.19
4.977
24.372
0.19
4.527
21.958
0.20
3.928
19.055
0.20
3.652
17.627
0.21
3.514
14.738
0.22
3.744
12.093
0.23
4.287
10.291
0.24
5.438 *
10.162
0.41
7.861 *
9.677
0.81
14.665 *
* Do not comply with IEEE 1547 Standard
H6 INVERTER SIMULATED THD
igrid [A]
14.262
12715
11.183
9.670
8.174
6.702
5.255
3.840
2.469
1.151
TABLE VIII.
ileakage [mA]
% ileakage
THD %
12.967
0.09
4.901
13.218
0.10
4.641
13.675
0.12
3.986
15.037
0.16
3.896
11.802
0.14
3.743
10.555
0.16
4.421
9.93
0.19
5.326 *
9.668
0.25
6.792 *
9.602
0.39
9.521 *
9.738
0.83
16.177 *
* Do not comply with IEEE 1547 Standard
ileakage [mA]
% ileakage
THD %
12.361
0.09
4.932
12.289
0.10
4.639
13.051
0.12
3.988
13.055
0.14
4.007
15.611
0.19
3.725
10.332
0.15
4.294
9.657
0.18
5.220 *
9.843
0.26
6.610 *
9.801
0.40
9.367 *
9.689
0.84
15.636 *
* Do not comply with IEEE 1547 Standard
H6D2 INVERTER SIMULATED THD
igrid [A]
14.258
12.714
11.186
9.673
8.180
6.710
5.266
3.855
2.446
1.161
ileakage [mA]
% ileakage
THD %
48.753
0.34
3.892
48.195
0.38
3.821
47.450
0.42
3.993
46.469
0.48
4.439
45.282
0.55
5.202 *
44.125
0.66
6.069 *
42.652
0.81
7.290 *
40.334
1.05
9.430 *
37.307
1.53
12.949 *
32.214
2.44
17.845 *
* Do not comply with IEEE 1547 Standard