A GRID TIED MODIFIED SYMMETRICAL CASCADED H-BRIDGE BOOST

INVERTER WITH PV SYSTEM USING MPPT

S.Prakash1, N.P.Gopinath2, J.Suganthi3

Department of EEE, Aarupadai Veedu Institute of Technology,

Vinayaka Mission’s Research Foundation.

Paiyanoor, Chennai, India.

sprakash@avit.ac.in, gopinathnp@avit.ac.in, suganthi@avit.ac.in

Abstract:

With the fast entrance of photovoltaicassociated framework in modern and business

application, it is basic to enhance the effectiveness and upgrade the usage of PV power

control system. In this paper PV array with modified symmetrical cascaded H-bridge inverter

is developed.This work is based on integration and operation of a single phasemodified

symmetrical cascaded H-bridge with bidirectional switches.The boost converter with

maximum power point trackers (MPPT) technique is proposed to achieve the maximum

power output of the PV array. The proposed grid connected inverter with PV array is

simulated using MATLAB/SIMULINK and results are discussed in detail.

Keywords:Symmetrical Multilevel Inverter, Photovoltaic, Boost Converter, Maximum Power

Point Tracking

I. Introduction

Since energy assets and their usage have a noticeable issue of this century, the issues

of common asset consumption, natural effects, and the rising interest for new energy assets

has been talked about intensely as of late. Various forms of renewable energy sources are

available to make the environment as carbon-free pollution and the sources are solar, wind,

biomass, geothermal etc. are paid more attention to researchers and scientists.Amongst

different kinds of sustainable power sources, solar energy has turned out to be extremely

famous and requesting because of headway in control of power electronic techniques. Solar

technologies tap specifically into the unending energy of the sun and utilize that energy to

create heat, light, and control.

The energy created from solar cell transformation framework relies on the solar

illumination whereas the electrical lattice requires consistent voltage and recurrence. Hence

appropriate power electronic interface must be given between the sustainable power source

and the network for stable operation. Solar cell establishments include the utilization of

numerous solar boards or modules, which can be associated in arrangement or in parallel to

give the coveted voltage level to the inverter.

Keeping in mind the end goal to associate Renewable Energy Source to the

framework, two phases of energy change are utilized. The principal organize is to support up

the low voltage yield of Renewable Energy Source and to track its Maximum Power Point

(MPP), whereas the second stage is utilized to change over DC into AC wave as required by

the grid. To build the effectiveness of the network associated sustainable power source

International Journal of Pure and Applied MathematicsVolume 118 No. 5 2018, 833-843ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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frameworks single stage help inverters are proposed in the researcher. Single stage control

change technique decreases the losses, thereby expanding the proficiency, yet it experiences

disadvantages like higher Total Harmonic Distortion (THD) at the yield voltage which in the

long run builds the channel measure, thereby expanding the cost and size of the aggregate

framework.

To enhance the harmonic profile of the yield voltage of the inverter Multilevel

Inverters (MLIs) are recommended different researches. MLIs have almost sinusoidal yield

voltage and current waveforms with an enhanced harmonic profile, less voltage stress in

power electronic switches because of decreased voltages, bring down switching losses when

contrasted with regular three-level inverters, reduced the filter circuit, and lessened

electromagnetic interferences. As of late different MLIs are proposed in the researches and

the regularly utilized categories are diode-clamped, flying capacitor, cascaded H-bridge and

hybrid or modified H-bridge Multilevel Inverter . The cascaded H-bridge multilevel inverter

topology requires a different DC source for each H-bridge with the goal that high power or

potentially high voltage that can come about because of the blend of the various modules in a

multilevel inverter would support this topology. MLIs are further grouped into symmetrical

and asymmetrical types. This paper presents a Modified Symmetrical Cascaded H-Bridge

MLI (MS-CHBMLI) topology reasonable for sustainable power sources. The proposed

inverter is equipped for creating five levels with two bidirectional DC sources and six power

semiconductor controlled switches. From the six power semiconductor devices, two power

semiconductor devices are bi-directional and four devices are unidirectional devices. The

proposed inverter has many focal points like basic in structure, versatile for coordinating

Renewable Energy Source with the framework, bring down THD and the lesser number of

semiconductor switches.

II Proposed Modified Symmetrical Multilevel Inverter

In this proposed configuration comprises of two bidirectional switches along with

freewheeling diode added to the cascaded H-bridge circuit and the proposed concept diagram of solar

PV array with grid connected modified symmetrical multilevel inverter as shown in Fig.1. The

existing topology has been eight switches which is possible for creating the five levelsand it is or

asymmetrical or symmetrical kind. Hence In this topology proposed in has two bidirectional switches

which are equipped for producing five levels and the total number of switches is reduced from eight to

six.The traditional cascaded H-bridge inverter has the issue of capacitor voltage adjusting when

encouraged to high power loads. The modified symmetrical MLI proposed in this paper requires only

two bidirectional switches to generate five level output voltage or current waveform and also this

topologysmooth the progress of the issue of capacitor voltage balancing.

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Fig.1. Proposed PV connected Modified Symmetrical Cascaded H-Bridge Multilevel Inverter

(a) (b)

(c) (d)

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(e) (f)

Fig.2 Operating modes and current direction of proposed inverter a)& b) Mode-1 c) & d).Mode-2 e)

Mode-3 and f) Mode-4.

In order to generate the stepped waveform output wide range, the modified symmetrical

cascaded H-bridge multilevel inverter topology is proposed, shown in Fig. 1. The proposed topology

includesone H-bridge circuit along with connected auxiliary unit of bidirectional power

semiconductor switch A1 and A2through aline inductor and grid terminals. The operating mode of

proposed inverteris basically two groups.One is for with auxiliary circuit and the modes of operations

are Mode-1 & 2.The second group is without auxiliary circuit and their operating modes are Mode-3

& 4. The proposed topology operated as a traditional cascaded H-bridge inverter circuit when itsmode

of operation at Mode-3 and 4. The isolated d.c sources are symmetrical or equal value in the proposed

topology.

The fig.2 shows that the operating modes of proposed topology and their current direction in

the circuit are indicated as dark blue lines with arrow direction. The binary logic switching operation

of proposed MS-CHBMLI is as shown in table.1.The proposed concept can be extend any number of

level with same type of operating modes of operation.

Table 1. Binary Switching Table of proposed inverter

Inverter

Operation

Output

Voltage S1 S2 S3 S4 A1 A2

Mode-3 +2Vdc 1 1 0 0 0 0

Mode-2 +Vdc

1 0 0 0 1 0

0 1 0 0 0 1

Mode-0 0 0 0 0 0 0 0

Mode-2 -Vdc

0 0 1 0 0 1

0 0 0 1 1 0

Mode-4 -2Vdc 0 0 1 1 0 0

The output voltage generated at group one operating mode is

𝑣𝑜 = ∑ 𝑆𝑥4𝑥=0 = 𝑘𝑉𝑑𝑐 {

𝑓𝑜𝑟𝑘 = +1 if x <= 2𝑓𝑜𝑟𝑘 = −1 if x >= 3

(1)

where, S is the main H-bridge power semiconductor switches turn on / off condition

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x is the number power semiconductor switches

k is the polarity of output voltage at grid

III Maximum power point tracking with Grid

The proposed modified symmetrical cascaded H-bridge multilevel inverter can be a best

suitable for grid-connected green energy applications. The operating point of photovoltaic module is

determined by solar rays, the temperature of PV component and the amount of resistance added as a

load. For a given cell temperature and solar rays, there can be an exclusive operating point of the PV

array in its PV curve with maximum end result electricity. Henceforth Maximum Power Point

Tracking (MPPT) is important in PV arrays to be able to achieve maximum power from it regardless

of the load and environmental climatic conditions.Mostly, the DC-DC boost converter topology can

be used next to PV component for two primary reasons. The principal reason is to monitor the

maximum power point (MPP) and the supplementary reason is to improve up the lower result voltage

of PV component to ahigher level. Thus the DC-DCboost converters duty pattern would depend on

the MPPT algorithm. In this way when the environmental conditions shift MPPT algorithm changes

the duty cycle which thus increases or reduces the output generated voltage of the boost converter.

However the DC input voltage of the inverter must have a rigid value it is associated with the grid.

Consequently DC-DC boost converters are being used in cascade, some may be to track the MPP and

the other is to keep the DC-link voltage to a rigid value.

3.1 DC-DC Boost Converter

Open loop construction of DC-DC converter will most likely lead to poor efficiency. Hence

instantaneously the output of the converter is evaluated and with a given reference, and the duty cycle

of the switch should be altered. The boost converter is perfect for boost approach to treatment with

solar cell voltage as type source as shown in fig . For widely open loop simulation the input voltage to

the boost converter is extracted from the solar cell. The output of converter governed voltage will be

obtained. The duty cycle of the converter switch is determined by,

𝑑𝑏 = 𝑉𝑑𝑐−𝑉𝑝𝑣1

𝑉𝑑𝑐 (2)

Fig.3 DC-DC boost converter with MPPT

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The Perturbation and Observation(P&O) control algorithm is used in order to achieve

maximum power from PV solar panel. . In the event that the most extreme power level of a PV array

is higher than the power rating of an MPPT, the two MPPTs will be in parallel operation to function

as a single MPPT. Hencethese systems have need of an online arrangementfor ensure and to verify the

connection kinds of the two MPPTs, independentlyor in parallel. Additionally, if the two MPPTs are

in parallel operation, a uniform current control scheme is familiar with correspondingly flow the PV-

array output current to the two MPPTs. From the above relations, the P&O algorithm tracks maximum

power output through the controller based on the output of PV array.The maximum output current is

achieved when the solar array output current 𝑖𝑝𝑣 is equal to the inductor 1 output current 𝑖𝑚.Then the

expression for maximum power output of PV array output is

𝑃𝑚 = 𝑣𝑝𝑣𝑥𝑖𝑚 (3)

Where, 𝑣𝑝𝑣- PV array across the output voltage in volts

𝑖𝑚-maximum current through the inductor 1 of pv array circuit

3.2 Grid Interconnection

Solar PV array with MS-CHBMLI is interconnected with grid when achieving the amplitude

of voltage, frequency and phase angle are same.This ought to be conceivable disturbance affirmation

in regards to the system by identifying the grid voltage in a Phase Locked Loop (PLL).The grid

voltage angle position is determined from PLL output.The output of PLL signal is reference voltage

signal and it generates the gating signal to the MS-CHBMLI power semiconductor switches by multi

carrier sinusoidal pulse width modulation technique.The output voltage of inverter is generated based

on the grid voltage.The phase angle difference is calculated and this is controlled to make a zero for

faster interconnection between the grid and inverter.The power flow through the inverter to grid based

on delay angle is

𝑃 =𝑉𝑖𝑉𝑔

𝑋𝑙𝑠𝑖𝑛𝛿 (4)

where𝑉𝑖is the inverter output voltage,

𝑉𝑔is the interconnected grid voltage,

𝑋𝑙isthe medium impedance,

and δ is the angle between grid andinverter

IV Simulation Results

The proposed work is analyzed using Matlab simulation. It is shown in figure. The PV

modules output voltages are fed to the single phase inverter through boost converter. The

MPPT P&O algorithm extracts maximum power from the PV system.

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Fig 4. Simulation diagram of PV system

Fig 5. Input voltage from the PV system

The figure 5 shows the input voltage from the PV system. The PV output voltage is in

oscillatory nature due to temperature and irradiation variations. This voltage is given to the

boost converter. The MPPT algorithm extracts maximum power from the solar system.

Fig 6. Output voltage of the boost converter

The figure shows the output voltage of the boost converter. The MPPT algorithm

maintains constant voltage to the single phase five level inverter topology. The new topology

converter dc voltage into five level AC voltage.

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Fig 7. Output voltage of the five level inverter

The figure shows the five level inverter output voltage of the proposed topology. This

has reduce the THD. This voltage is given to the grid using synchronization technique.

Fig 8. Output voltage and current signal in the grid

The figure shows the synchronization of the voltage and current. Both voltage and

currents are in phase here.

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Fig 9. THD value of the proposed grid voltage

The figure shows the THD value of the grid voltage and its satisfies the harmonics

IEEE standard. The proposed five level inverter reduces the total harmonics distortion in the

output voltage.

V Conclusion

This projects develops single phase grid connected PV using reduced number of

switches with five level inverter. The MPPT algorithm extracts the constant ans maximum

power from the PV system. The five level inverter with reduced number of switches

minimize the THD. Switching losses also less in the proposed topology. The multi reference

PWM is used to control the output voltage of the inverter. The synchronization technique

reduce the THD and power quality issues. This paper THD result satisfied the THD

harmonics IEEE standard.

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