Converter with VSI · 2018. 6. 16. · Implementation of High Step -up Interleaved Converter with...

Implementation of High Step-up Interleaved

Converter with VSI Akshaya.S.R

1, R.Niranjan Kumar

2, D.Vinodini

3, M.Pradeep

4

1234Assistant professor, Department of Electrical and Electronics Engineering, Veltech, Chennai

[email protected] , [email protected]

2, [email protected]

3,

[email protected]

Abstract— The Interleaved converters are widely employed

in photovoltaic systems. The main advantage is low

conduction losses, low cost and high voltage gain. The high

step up interleaved converter with VSI proposed in this

project is used to boost the output power from the PV source

to the load with high step-up gain without operating at

extreme duty ratio. High voltage is obtained by the voltage

multiplier module of interleaved converter composed of

switched capacitors and coupled inductors. The boosted

output voltage is fed to the R load through single phase

voltage source inverter. The simulation of interleaved

converter is carried out in MATLAB/Simulink.

Keywords—PV system, Interleaved Converter, Voltage multiplier module, Voltage Source Inverter.

I. INTRODUCTION

The renewable energy is increasing demand that is collected from the various resources like solar, tides,

waves, wind and geothermal energy. These resources are

obtained naturally and can be considered to be

inexhaustible instead of using conventional resources. Renewable energy sources are known to be much cleaner

and produce energy without the harmful effects of

pollution unlike their conventional counterparts [3]. Renewable energy are clean sources of energy that have a

much lower environmental impact than conventional

energy technologies [1]. Each source of renewable energy

has unique benefits and cost. The major problem in solar PV is to track the maximum power from the solar PV cell.

To extract the maximum power from the solar panel

introduced MPPT technique (voltage feedback method).

The input supply get from sun light through solar panel

is fed to the integrated boost fly-back converter to

enhance the voltage [2]. The interleaved converter

operated with two switches, different phase shift can be

given to operate the converter. The two switches are

conduct parallel to each other to reduce the conduction

losses. The voltage stress across the switch will be

alleviated and reduction of conduction losses. Fig. 1

shows a typical block diagram for proposed system which

consists of solar photo voltaic system, a interleaved boost

fly-back converter and voltage source inverter for ac

application. The converter connected as two stage

converters with cascaded structure [5].

Figure 1. Block diagram for proposed system

Fig. 1 shows a typical block diagram for proposed

system which consists of solar photo voltaic system, a

interleaved boost fly-back converter and voltage source

inverter for ac application. The converter connected as

two stage converters with cascaded structure [5]. Now a day’s a conventional step up converters like

boost converter and fly-back converter cannot obtain high step-up conversion due to leakage inductance and high

stress on switch [6]. The step-up converters with single

switch are not suitable to obtain high voltage. The low

conduction losses will increases the lifetime of renewable

energy sources and suitable for high power applications.

The above mentioned disadvantages are limited by using

conventional interleaved boost converter to obtain high

power. Switched capacitors are integrated with interleaved

boost converter to make high voltage gain. A voltage

multiplier module in converter can be used in a converter

to multiple the output voltage [8]. The two switches

operated parallel, when one of the switch turn off then the

energy stored in the inductor will transfer to respective

paths and current distribution Voltage multiplier module

consist of switched capacitors and coupled inductors. For

ac power application single phase voltage source inverter

will be used.

International Journal of Pure and Applied MathematicsVolume 119 No. 15 2018, 3779-3784ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

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II. PV MODULE AND CONVERTER OPERATION

A. Mathematical Model of PV Module

The modeling techniques of PV array will represent the

photovoltaic array as an equivalent electrical circuit. Fig.1

represents the equivalent circuit of PV module [4].

The thermal voltage Vt of the module for Ns cells connected

in series is given as NskT/q. RS and Rsh are the equivalent

series resistance and shunt resistance of the photovoltaic cell. v,cell is the current generated by the incident light (it is directly proportional to the Sun irradiation).

Figure 3. Block diagram for proposed system

All PV array datasheets bring basically the following

information: the nominal open-circuit voltage (Voc,n ), the

nominal short-circuit current (Isc,n ), the voltage at the

MPP (Vmp), the current at the MPP (Imp), the open-circuit

voltage/temperature coefficient (Kv), the short circuit

current/temperature coefficient (Ki) and the maximum

experimental peak output power (Pmax,e). This information is always provided with reference to the nominal condition or Standard Test Condition (STC),

where the temperature is 25oC and solar irradiation is

1000 W/m2.

B. Converter Operating Principles

The interleaved converter with voltage multiplier module is composed of switched capacitor and coupled inductor connected with boost converter to form a boost fly-back converter with interleaved structure [5]. The step-up interleaved converter with interleaved structure is shown in Fig. 3. The fly-back converter has primary

windings of coupled inductors with Np turns and

secondary winding of coupled inductors with Ns turns are connected to increase voltage [6]. The interleaved fly-back converter consists of two MOSFETs. When one switch get turn OFF then it performs as a fly-back converter, and other switch will be turned off to perform as a forward converter [5]-[8]. Different phase shift can be given to control both the switches.

Mode I: The power switch S2 in ON condition then S1 begin to turn on. All the diodes are reverse biased and stored energy is quickly released to output terminal via

Df2.

Mode II: The power switches S1 and S2 are in ON state

and all the diodes are reverse biased.

Mode III: The switch S1 will be in On state where S2

will be in OFF state. The energy released to output

terminal and Vc1 obtain double output voltage of the

boost converter.

Figure 3. Interleaved boost fly-back converter

Mode IV: In this mode the operating condition will be

same as that of the previous condition. Mode V: The power switch S1 remains in ON state, and

the other power switch S2 begins to turn on. The store

energy is released through the output terminal via fly-back

– forward diode Df1. Mode VI: Both of the power switches S1 and S2 remain

in ON state, and all diodes are reversed biased. Current through both the leakage inductor will increase linearly.

Mode VII: The power switch S2 remains in ON state, and

the other power switch S1 begins to turn off. The current through series leakage inductors flow through the output

capacitor C2 via fly-back–forward diode Df2. Here Vc1 obtains double times the output voltage of the boost

converter. Mode VIII: In this mode the operating condition will be

same as that of the previous condition except the clamped

diode Dc1.

III. CONVERTER CONFIGURATION AND

SIMULATION DIAGRAM

A. Step-up Voltage gain

The voltage on clamp capacitor can be regarded as an output voltage of the boost converter; thus, voltage VCc can be derived from

VCc =

𝑣𝑖𝑛

(1 −𝐷)

(2)

When one of the switch get turned off then Vc1

obtains double output voltage of the boost converter and

derived from

VCc = 𝑣𝑖𝑛

(1−𝐷)+ Vcc (3)

International Journal of Pure and Applied Mathematics Special Issue

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The output filter capacitors C2 and C3 are charged by energy transformation from the primary side. When S2 is in ON state and S1 is in OFF state, Vc2 is equal to the

induced voltage of Ns1 plus the induced voltage of Ns2, and when S1 is in ON state and S2 is in OFF state, Vc3 is

also equal to the induced voltage of Ns1 plus the induced

voltage of Ns2.

Vc1 =

𝑣𝑖𝑛

(1 − 𝐷)

+ + 𝑣𝑖𝑛

(1−𝐷) (4)

Vc1 =

2𝑣𝑖𝑛

(1 − 𝐷)

(5)

Thus the voltages Vc2 and Vc2 can be derived from

Vc2 = Vc3 =

𝑛 𝑣𝑖𝑛

(1 − 𝐷)

(6)

The output voltage can be derived from

V0 = Vc1 + Vc2 + Vc3

V0 = 2𝑣𝑖𝑛

(1−𝐷) +

𝑛 𝑣𝑖𝑛

(1−𝐷) +

𝑛 𝑣𝑖𝑛

(1−𝐷)

V0 = 𝑣𝑖𝑛

(1−𝐷) (2 + 2n)

V0 =

2 + 2𝑛 𝑣𝑖𝑛

(1 − 𝐷)

(7)

The step-up voltage of interleaved boost converter

is derived it as

as to be always capable of defining the ac output voltage [16]. It can be observed that the ac output voltage can take

values up to the dc link value Vi, which is twice that

obtained with half-bridge VSI topologies. Several modulating techniques have been developed that are applicable to full-bridge VSI.

Figure 4. Simulation diagram for Interleaved boost fly-back converter

with VSI

IV. SIMULATION RESULTS

The Fig. 5 represent the voltage and current waveforms

for interleaved boost fly-back converter. The output

voltage obtained is 220V and output current obtained is

0.42A.

TABLE I POWER SPECIFICATIONS

𝑣0

𝑣𝑖𝑛 =

(2+2𝑛)

(1−𝐷) (8)

B. Simulation Diagram for Interleaved Converter

The boost converter with interleaved structure is shown

in Fig. 3. The switches are controlled by sinusoidal pulse

width modulation technique. A high step-up interleaved

converter, which is suitable for renewable energy system,

is proposed in this paper [9]. Through a voltage multiplier

module composed of switched capacitors and coupled

inductors, a conventional interleaved boost converter

obtains high step-up gain without operating at extreme

duty ratio [10]-[13]. The converter not only reduces the

current stress but also constrains the input current ripple,

which decreases the conduction losses and lengthens the

lifetime of the input source [14]. By operating at less duty

cycle ratio the switching conduction losses will be

reduced which will be advantage for power electronics

circuits [15]. The voltage source inverter is similar to the half-bridge

inverter; however, a second leg provides the neutral point

to the load. As expected, both switches S3 and S6 (or S5

and S4) cannot be on simultaneously because a short

circuit across the dc link voltage source Vi would be produced. The undefined condition should be avoided so

System parameters Values

PV module rated power 100 W

Open circuit voltage 22.41 V

Short circuit current 6.2 A

Switching frequency of converter 50 KHz

Fly-back converter transforms N1/N2 = 1/1

turns ratio

Switching frequency of inverter 50 Hz

Output voltage 220 V

Input voltage 17 V

Inductor 500 µH

Capacitor 200 µH

Duty cycle ratio 0.7

The PV array has been assumed to be comprising a

combination of Ns cells in series and Np cells in parallel in order to achieve the required voltage, current and power

capacity. Vp, Vo and the internal resistance Rin for the array have been calculated from the values of the open

circuit voltage (Voc), maximum power voltage (Vpm) and

maximum power current (Ipm) of each cell [4]. The Fig. 6. represents the power waveform for interleaved boost fly-back converter. The output power obtained is 90W. All PV array datasheets bring basically the following

information: the nominal open-circuit voltage (Voc,n ), the

nominal short-circuit current (Isc,n ), the voltage at the

MPP (Vmp), the current at the MPP (Imp), the open-circuit


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voltage/temperature coefficient (Kv), the short circuit

current/temperature coefficient (Ki) and the maximum

experimental peak output power (Pmax,e). The amount of

incident light directly affects the generation of charge carriers, and consequently, the current generated by the device. The information is always provided with reference to the nominal condition or Standard Test Condition

(STC), where the temperature is 25oC and solar

irradiation is 1000 W/m2.

Figure 5. Output voltage and current for interleaved converter

Figure 6. Output power for interleaved converter

The modulation technique is multiple number of output

pulse per half cycle and pulses are of different width. The

width of each pulse is varying in proportion to the amplitude of a sine wave evaluated at the center of the

same pulse [14]. The gating signals are generated by

comparing a sinusoidal reference with a high frequency

triangular signal. Whenever the carrier wave greater than the reference wave switch pulse is generated [15]. The

single phase full bridge voltage source inverter is

connected with interleaved converter to get AC waveform. The inverter is operated by turning on the

cross switches to avoid short circuit. The Fig. 7.

Represents the switch pulse for inverter which has

sinusoidal in nature [16]. Analogy PWM control requires the generation of both

reference and carrier signals that are feed into the comparator and based on some logical output, the final

output is generated. The reference signal is the desired signal output maybe sinusoidal or square wave. There are

various types of PWM techniques and so it can get different output and the choice of the inverter depends on

cost, noise and efficiency.

Figure 7. Switch pulse for Inverter

The Fig. 8. represent the voltage and current waveform

for interleaved boost fly-back converter with VSI. The

output voltage obtained is 220V and output current obtained is 0.4A. The inverter power rating is 100W.

Figure 7. Output voltage and current waveforms for interleaved

converter with VSI in closed loop

The power output of the interleaved boost fly-back

converter is shown in Fig. 9.

Figure 8. Output power for interleaved converter with VSI

V. CONCLUSION

The Interleaved converter for solar photovoltaic system

is utilized in this project, in two different topologies such


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as interleaved converter without single phase full bridge

VSI and interleaved converter with single phase full bridge VSI for PV system. Typical features like high step-

up voltage and low conduction losses are obtained with the proposed system. The DC-DC converter consists of

boost converter connected in interleaved structure with fly-back rectifier, which boosts up the output of the solar

cell array. The single phase full bridge VSI generated the

sinusoidal output voltage that is smoothened with the R load.

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