INTRODUCTION · H 6 TRANSFORMERLESS FULL -BRIDGE PV GRID -TIED INVERTERS S. Sherine 1,G.Hemavathi 2 1,2 Assistant professor Department of EEE BIHER, BIST, Bharath University Chennai

1

H6 TRANSFORMERLESS FULL-BRIDGE PV GRID-TIED INVERTERS

S. Sherine1,G.Hemavathi

2

1,2Assistant professor

Department of EEE

BIHER, BIST, Bharath University

Chennai- 600073. [email protected]

ABSTRACT

Transformer less inverters are widely used

in grid-tied photovoltaic (PV) generation

systems, due to the benefits of achieving

high efficiency and low cost. Various

Transformerless inverter topologies have

been proposed to meet the safety

requirement of leakage currents, In this

project, a family of H6 Transformerless

inverter topologies with low leakage

currents is proposed, and the intrinsic

relationship between H5 topology, highly

efficient and reliable inverter

concept(HERIC) topology, and the

proposed H6 topology has been discussed

as well. One of the proposed H6 inverter

topologies is taken as an example for detail

analysis with operation modes and

modulation strategy. The power losses and

power device costs are compared among

the H5, the HERIC, and the proposed H6

topologie

INTRODUCTION

The applications of distributed

photovoltaic (PV) generation systems in

both commercial and residential structures

have rapidly increased during recent years.

Although the price of PV panel has been

declined largely, the overall cost of both

the investment and generation of PV grid-

tied system are still too high, comparing

with other renewable energy sources.

Therefore, the grid-tied inverters need to

be carefully designed for achieving the

purposes of high efficiency, low cost,

small size, and low weight, especially in

the low-power single-phase systems(less

than 5 kW). From the safety point of view,

most of the PV grid-tied inverters employ

line-frequency transformers to provide

galvanic isolation in commercial structures

in the past. However,[1-4] line-frequency

transformers are large and heavy, making

the whole system bulky and hard to install.

Compared with line-frequency isolation,

inverters with high-frequency isolation

transformers have lower cost, smaller size

and weight. However, the inverters with

high-frequency transformers have several

power stages, which increase the system

complexity and reduce the system

efficiency. As a result, the Transformerless

PV grid-tied inverters, as shown in Fig. 1,

are widelyInstalled in the low-power

distributed PV generation systems.

International Journal of Pure and Applied MathematicsVolume 119 No. 12 2018, 8691-8702ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

8691

2

Unfortunately, when the transformer is

removed, the common mode (CM) leakage

currents (ileakage) may appear in the

system and flow through the parasitic

capacitances between the PV panels and

the ground. Moreover, the leakage currents

lead to serious safety and radiated

interference issues.[5-9] Therefore, they

must be limited within a reasonable range.

Fig. 1. Leakage current path for

Transformerless PV inverters.

As shown in Fig. 1, the leakage

current iLeakage is flowing through the

loop consisting of the parasitic

capacitances (CPV1and CPV2), bridge,

filters (L1 and L2), utility grid, and ground

impedance Zg. The leakage current path is

equivalent to an LC resonant circuit in

series with the CM voltage [11], and the

CM voltage vCM is defined as

Where vAN is the voltage difference

between points A and N,vBN is the

voltage difference between points B and

N. L1 andL2 are the output filter inductors.

In order to eliminate leakage

currents, the CM voltage must be kept

constant or only varied at low frequency,

such as50 Hz/60 Hz. The conventional

solution employs the half-bridge inverter.

The filter inductor L2 is zero in the half

bridge inverters. Therefore, (1) is

simplified as

The CM voltage vCM is constant

due to the neutral line of the utility grid

connecting to the midpoint of the split dc-

link capacitors directly. However, a

drawback of half-bridge inverters is that,

the dc voltage utilization of half-bridge

type topologies is half of the full-bridge

topologies. As a result, either large

numbers of PV panels in series are

involved or a boost dc/dc converter with

extremely high voltage transfer ratio is

required as the first power conditioning

stage, which could decrease the system

efficiency.[10-12]

The full-bridge inverters only need half of

the input voltage value demanded by the

half-bridge topology, and the filter

inductors L1 and L2 are usually with the

same value. As a result, (1) is simplified as

Existing Limitation

In the traditional grid-connected PV

inverters, either a line frequency or a high-

frequency transformer is utilized to

provide a galvanic isolation between the

International Journal of Pure and Applied Mathematics Special Issue

8692

3

grid and the PV panels. In half bridge

inverter the voltage across the parasitic

capacitor is clamped to be constant by the

dc bus capacitor. However, this method

has an important disadvantage that the

required dc bus voltage should be doubled

compared with the full-bridge topologies.

[13-14]

Proposed Merits

Removing the isolation transformer can be

an effective solution to increase the

efficiency and reduce the size and cost.

Current stress is reduced, Switching losses

get reduced.

BLOCK DIAGRAM

Proposed H6 Transformerless Full-

Bridge PV Grid-Tied Inverters

Many solutions have been proposed to

realize CM voltage constant in the full

bridge transformerless inverters . A

traditional method is to apply the full-

bridge inverter with the bipolar

sinusoidal pulsewidth modulation

(SPWM).

The CM voltage of this inverter is kept

constant during all operating modes. Thus,

it features excellent leakage currents

characteristic. However, the current ripples

across the filter inductors and the

switching losses are likely to be large.

The full-bridge inverters with uniploar

SPWM control are attractive due to the

excellent differential-mode (DM)

characteristics such as smaller inductor

current ripple, and higher conversion

efficiency.

However, the CM voltage of conventional

unipolar SPWM fullbridge inverter varies

at switching frequency, which leads to

high leakage currents. [16-19]

Two solutions could be applied to solve

this problem. One solution is to connect

the PV negative terminal with the neutral

line of the utility grid directly, such as the

Karschny inverter derived from buck–

boost converter, and the inverters derived

from virtual dc-bus concept. The CM

voltage is kept constant by these full-

bridge topologies with unipolar

modulation methods. Another solution is

to disconnect the dc and ac sides of the

full-bridge inverter in the freewheeling

modes. Various topologies have been

developed and researched based on this

method for keeping the CM voltage


8693

4

constant, such as the H5 topology , the

highly efficient and reliable inverter

concept , (HERIC) topology, the H6-type

topology, [20-24]the hybrid-bridge

topology, etc,

Passive Components Design

(a) Capacitor Design

Based on the energy storage the input

capacitance could be calculated as

The middle capacitor CL impacts Q factor

and double-pole frequency. Large CL

leads to small Q but low frequency double-

pole, which is analyzed in 3.2. And also

from the power decoupling point of view,

as shown in Figure 2.18, large CL also

leads to large pulsating input power that

means large Cin is needed to decouple the

power, which is not expected. In our case,

2 F is chosen for CL.[25-29]

2.13.Leakage Current Analysis

the capacitance between the point of

contact and a single

PV module has been calculated to range

between 100 – 400 pF. The capacitance

depends on weather conditions, and in the

worst case as rainy days, the capacitance

can be as high as 80 nF/kW [55]. Because

of there is no isolation between the input

and output without a transformer, the

transformerless inverter needs to consider

the leakage current issue as shown in

Figure 23. The Maximum current which

can flow through the human body is 0.2

mA. And the German standard [56] lists

the disconnection time for different levels

of leakage currents as shown in Table 2.2.

Figure23.Leakage current path

for transformer less PV inverters.

Table C. Leakage current and

corresponding disconnection time

[56] .

Because of this safety issue, the leakage

current should be as small as possible for

transformerless inverter. Many literatures

[57]-[59] analyzed the leakage current in

transformerless grid-connected inverter.


8694

5

For the proposed topology, the negative

terminal “O” of solar modules is set as the

reference point, and the middle points of

the bridge legs are set as “P” and “N” for

the output terminals as shown in Figure

24.

Figure 24

III SIMULATION RESULTS

Simulation Circuit and Results

Pulse pattern

Current


8695

6

waveform

OutputWaveform

IV Hardware Circuit and Results

Input waveform


8696

7

Pulse pattern

Output waveform

CONCLUSION

In this paper, from the topological

relationship point of view,the intrinsic

relationship between H5 topology and

HERICtopology is revealed. The HERIC

topology can be derived fromH5, H6-type,

and hybrid-bridge topologies by the idea of

reducing conduction loss. Moreover, based

on the H5 topology, a new current path is

formed by inserting a power device

between the terminals of PV array and the

midpoint of one of bridge legs. As a result,

a family of single-phase transformerless

full-bridgeH6 inverter topologies with low

leakage currents is derived. The proposed


8697

8

H6 topologies have the following

advantages and evaluated by experimental

results:

The conversion efficiency of the novel H6

topology is betterthan that of the H5

topology, and its thermal stressdistribution

is better than that of the H5 topology; The

leakage current is almost the same as

HERIC topology,and meets the safety

standard; [30-45]The

excellentDMperformance is achieved like

the isolatedfull-bridge inverter with

unipolar SPWM. Therefore, theproposed

H6 topologies are good solutions for the

singlephasetransformerless PV grid-tied

inverters.

REFERENCES

1. Nimal, R.J.G.R., Hussain, J.H.,

Effect of deep cryogenic treatment

on EN24 steel, International

Journal of Pure and Applied

Mathematics, V-116, I-17 Special

Issue, PP-113-116, 2017

2. Parameswari, D., Khanaa, V.,

Deploying lamport clocks and

linked lists, International Journal of

Pharmacy and Technology, V-8, I-

3, PP-17039-17044, 2016

3. Parameswari, D., Khanaa, V., Case

for massive multiplayer online

role-playing games, International

Journal of Pharmacy and

Technology, V-8, I-3, PP-17404-

17409, 2016

4. Parameswari, D., Khanaa, V.,

Deconstructing model checking

with hueddot, International Journal

of Pharmacy and Technology, V-8,

I-3, PP-17370-17375, 2016

5. Parameswari, D., Khanaa, V., The

effect of self-learning

epistemologies on theory,

International Journal of Pharmacy

and Technology, V-8, I-3, PP-

17314-17320, 2016

6. Pavithra, J., Peter, M.,

GowthamAashirwad, K., A study

on business process in IT and

systems through extranet,

International Journal of Pure and

Applied Mathematics, V-116, I-19

Special Issue, PP-571-576, 2017

7. Pavithra, J., Ramamoorthy, R.,

Satyapira Das, S., A report on

evaluating the effectiveness of

working capital management in

googolsoft technologies, Chennai,




8. Pavithra, J., Thooyamani, K.P., A

cram on consumer behaviour on

Mahindra two wheelers in Chennai,




9. Pavithra, J., Thooyamani, K.P.,

Dkhar, K., A study on the air

freight customer satisfaction,





Dkhar, K., A study on the working

capital management of TVS credit

services limited, International



Issue, PP-185-187, 2017


Dkhar, K., A study on the analysis

of financial performance with

reference to Jeppiaar Cements Pvt


8698

9

Ltd, International Journal of Pure

and Applied Mathematics, V-116,

I-14 Special Issue, PP-189-194,

2017

12. Peter, M., Dayakar, P., Gupta, C.,

A study on employee motivation at

Banalari World Cars Pvt Ltd

Shillong, International Journal of

Pure and Applied Mathematics, V-

116, I-18 Special Issue, PP-291-

294, 2017

13. Peter, M., Kausalya, R., A study on

capital budgeting with reference to

signware technologies,




14. Peter, M., Kausalya, R., Akash, R.,

A study on career development

with reference to

premheerasurgicals, International



Issue, PP-415-420, 2017

15. Peter, M., Kausalya, R., Mohanta,

S., A study on awareness about the

cost reduction and elimination of

waste among employees in life line

multispeciality hospital,




16. Peter, M., Srinivasan, V., Vignesh,

A., A study on working capital

management at deccan Finance Pvt

Limited Chennai, International



Issue, PP-255-260, 2017

17. Peter, M., Thooyamani, K.P.,

Srinivasan, V., A study on

performance of the commodity

market based on technicalanalysis,




18. Philomina, S., Karthik, B., Wi-Fi

energy meter implementation using

embedded linux in ARM 9, Middle

- East Journal of Scientific

Research, V-20, I-12, PP-2434-

2438, 2014

19. Philomina, S., Subbulakshmi, K.,

Efficient wireless message transfer

system, International Journal of



293, 2017


Ignition system for vechiles on the

basis of GSM, International Journal

of Pure and Applied Mathematics,

V-116, I-20 Special Issue, PP-283-

286, 2017


Avoidance of fire accident by

wireless sensor network,




22. Pothumani, S., Anuradha, C.,

Monitoring android mobiles in an

industry, International Journal of



540, 2017


Decoy method on various

environments - A survey,





Priya, N., Study on apple iCloud,




25. Pothumani, S., Hameed Hussain,

J., A novel economic framework

for cloud and grid computing,



8699

10



26. Pothumani, S., Hameed Hussain,

J., A novel method to manage

network requirements,




27. Pradeep, R., Vikram, C.J.,

Naveenchandra, P., Experimental

evaluation and finite element

analysis of composite leaf spring

for automotive vehicle, Middle -

East Journal of Scientific Research,

V-12, I-12, PP-1750-1753, 2012

28. Prakash, S., Jayalakshmi, V.,

Power quality improvement using

matrix converter, International



Issue, PP-95-98, 2017

29. Prakash, S., Jayalakshmi, V.,

Power quality analysis &

power system study in high voltage

systems, International Journal of


116, I-19 Special Issue, PP-47-52,

2017

30. Prakash, S., Sherine, S., Control of

BLDC motor powered electric

vehicle using indirect vector

control and sliding mode observer,




31. Prakesh, S., Sherine, S.,

Forecasting methodologies of solar

resource and PV power for smart

grid energy management,




32. Prasanna, D., Arulselvi, S.,

Decoupling smalltalk from rpcs in

access points, International Journal

of Pure and Applied Mathematics,

V-116, I-16 Special Issue, PP-1-4,

2017


Exploring gigabit switches and

journaling file systems,





Collaborative configurations for

wireless sensor networks systems,




35. Priya, N., Anuradha, C., Kavitha,

R., Li-Fi science transmission of

knowledge by way of light,




36. Priya, N., Pothumani, S., Kavitha,

R., Merging of e-commerce and e-

market-a novel approach,




37. Raj, R.M., Karthik, B., Effective

demining based on statistical

modeling for detecting thermal

infrared, International Journal of



276, 2017

38. Raj, R.M., Karthik, B., Energy sag

mitigation for chopper,




39. Raj, R.M., Karthik, B., Efficient

survey in CDMA system on the

basis of error revealing,




40. Rajasulochana, P.,

Krishnamoorthy, P., Ramesh Babu,


8700

11

P., Datta, R., Innovative business

modeling towards sustainable E-

Health applications, International



4904, 2012

41. Rama, A., Nalini, C., Shanthi, E.,

An iris based authentication system

by eye localization, International



23980, 2016

42. Rama, A., Nalini, C., Shanthi, E.,

Effective collaborative target

tracking in wireless sensor

networks, International Journal of

Pharmacy and Technology, V-8, I-

4, PP-23981-23986, 2016

43. Ramamoorthy, R., Kanagasabai,

V., Irshad Khan, S., Budget and

budgetary control, International



Issue, PP-189-191, 2017

44. Ramamoorthy, R., Kanagasabai,

V., Jivandan, S., A study on

training and development process

at Vantec Logistics India Pvt Ltd,




45. Pradeep, R., Vikram, C.J.,

Naveenchandran, P., Experimental

evaluation and finite element

analysis of composite leaf spring

for automotive vehicle, Middle -

East Journal of Scientific Research,

V-17, I-12, PP-1760-1763, 2013


8701

8702

Documents

INTRODUCTION · H 6 TRANSFORMERLESS FULL -BRIDGE PV GRID -TIED INVERTERS S. Sherine 1,G.Hemavathi 2 1,2 Assistant professor Department of EEE BIHER, BIST, Bharath University Chennai