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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 1, February 2012)

158

Simulation and design of low cost single phase solarinverter

Nishit Kapadia1, Amit Patel2, Dinesh Kapadia3

1M.Tech student, Electrical engineering department, Institute of Technology, Nirma university, Ahmedabad2Assistant professor, Electrical engineering department, Institue of Technology,Nirma university, Ahmedabad

3Manager, R&D Department, Hitachi Hi-Rel Powerelectronics Pvt. Ltd., Gandhinagar

[email protected]

[email protected]

[email protected]

Abstract How solar energy is converted into electrical

energy in cost effective manner. The main components of this

solar system are solar cell, dc to dc boost converters, inverter.

Sine wave push pull inverter topology is used for inverter. In

this topology only two MOSFETs are used and isolation

requirement between control circuit and power circuit is also

less which helps to decrease the cost of solar inverter. In this

paper design of components for booster and inverter are done.

Simulation of solar inverter is done and simulation results for

different conditions are taken.

KeywordsLow cost solar inverter, Solar inverter, Single

phase solar inverter.

I.

INTRODUCTIONThere are two types of sources for electrical power

generation. One is conventional and other is non-

conventional. Today to generate most of electrical power

conventional sources like coal, gas, nuclear power

generators are used. Some of conventional source are

polluted the environment to generate the electricity. And

nuclear energy is not much preferable because of its

harmful radiation effect on the mankind. After some of ten

years conventional sources will not sufficient enough to

fulfill the requirements of the mankind. So some of the

electrical power should be generated by non-conventional

energy sources like solar, wind .With the continuously

reducing the cost of PV power generation and the further

intensification of energy crisis, PV power generation

technology obtains more and more application.

In this paper cost effective method is used to

implement single phase solar inverter. Solar cell/ PV cells

convert solar energy into electrical energy.

This electrical energy is in DC form. This dc voltage is

boosted using dc to dc boost converter. This boosted dcvoltage is fed to inverter. Inverter converts dc voltage into

ac voltage. Here sine coded PWM push-pull inverter is

used. The output of inverter is given to step-up transformer

and low-pass filter which will give 220V 50Hz sine wave

output. This output is given to the load.

Inverter topology is sine wave push pull inverter is

selected. This topology is used to decrease the cost of solar

inverter. In this topology only two MOSFETs are used.

And the isolation requirement between control and power

circuit is less.

II. BLOCK DIAGRAM

Block diagram of single phase solar inverter is

shown in Fig 1.1. Solar panel output is 24volt. Dc to dc

boost converter converts 24 volt dc voltage to 36 volt dc.

This dc voltage is converted to ac voltage using inverter.

Inverter output is sine coded PWM pulses. This sine coded

pulses are stepped up using step up transformer. These sine

coded PWM pulses are converted into sine wave using low-

pass filter. This sine wave ac voltage is fed to the load. The

ac output is 220volt 50Hz. For design the output power of

solar inverter is taken 250VA.

III.

DESIGN OF DC TO DC BOOST CONVERTER AND INVERTER

Inverter is designed for output power of 250 VA. Power

factor is taken 0.8. Therefore output power of inverter is

200 watt. Overall inverter efficiency of inverter is taken

97%. From this output power of booster is taken 206.18

watt. Overall booster efficiency is taken 97.5%. From this

input power of booster is 211.47 watt.
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Minimum input voltage to the booster is 21V. Maximum

input voltage of the booster is 27V. Output voltage of

booster is 36V. Relation between input voltage and output

voltage is given by equation 3.1.

Vo =

x Vin ..(3.1)

where Vo = output voltage,

Vin = input voltage,

= duty cycle

Duty cycle for minimum and maximum input voltage is

0.4167 and 0.25 respectively. Switching frequency of

MOSFET is taken 3.2 kHz. Switching period is 312.5 us.

From this on time of MOSFET for minimum and maximum

input voltage are 130.2 s and 78.125 s respectively.

From minimum input voltage and input power input current

is calculated 10.07A. Current ripple Iin is taken 20% of

input current. So current ripple Iin is 2.014A. In steady

state condition in on state of MOSFET the voltage equation

of booster is given by equation 3.2.

Vin = L x

..(3.2)

where L = inductance,

I = current ripple,

Ton = On time of MOSFET

From this formula inductance L is calculated 1357.67 H.

Maximum input current of booster with 150% overloading

is 16.61A. So inductor for booster should be designed for

value L = 1357.67 H and current I = 16.61A. Ripple

voltage is taken as 1% of output voltage which is

0.36V.Output current of booster is calculated from output

power and output voltage which is 5.7274A.Capacitance of

booster is given by equation 3.3. From equation 3.3 value

of capacitance C for dc to dc boost converter is 1357.67H.

C =

.(3.3)

where Io = Output current of MOSFET, Vo = Output

voltage ripple

Booster component values inductance L = 1357.67 Hand

Capacitance C = 2071.53 Hare found.

Booster output voltage Vob = 36V

Modulation index for inverter m = 0.97

Inverter transformer regulation r = 5%

Transformer primary voltage Vp = Vob *

=

23.419 V

Transformer efficiency t = 0.97

Safety factor SF = 1.1

Inverter MOSFET current or Transformer primary current

Ip =

= 25.679A

Low-pass

filter

230V AC

Solar Panel

LOAD

DC to DC Boost InverterTransformer

36 V DC

Figure 1.1 Block diagram of single phase solar

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MOSFETs of inverter have this current rating.

IV.

SCHEMATIC AND CONTROL STRATEGIES OF DC TO DC

BOOST CONVERTER AND INVERTER

Schematic and close loop control for dc to dc boost

converter is shown in the figure4.1(a). As the solar panel

voltage varies according to weather so to make the output

of dc to dc boost converter constant close loop control is

required. In the figure for close loop control PI

(Proportional and Integral) controller is used.

To control the output voltage of booster PI controller isused which is shown in Fig 4.1(b). As shown in Fig 1.2 (b)

reference voltage is compared with actual output voltage

and error in output voltage e is calculated. Error e is passed

through PI controller. The output of PI controller is given

by equation (4.1). The output of PI controller is compared

with triangular wave which will generate pulses which is

given to the MOSFET of the dc to dc boost converter. So

close loop control makes the output voltage of dc to dc

boost converter constant.

Output of PI controller = (Kp * e) +

(4.1)

Where Kp = Proportional gain, e = error and

Ti = Integration time

Output of dc to dc boost converter is given to inverter. The

schematic which contains inverter and booster is shown in

Fig 4.2 (a) and Fig 4.2 (b) shows the generation of PWM

pulses for inverter. To generate PWM pulses simple sinetriangular comparison is used. As shown in Fig 4.2(a) sine

wave push pull inverter topology is used. Main Advantages

of this topology are: (I) Only two switches/MOSFETs are

used (ii) Isolation requirement between control and power

circuit is less. These advantages help to decrease the cost.

A step up transformer is used in the output of inverter to

step up the ac voltage. A low pass filter is used to get the

sine wave at the output.

Figure 4.2(b)Fig 4.2 (a) Schematic of booster and inverter (b) Sine PWM generation

using sine triangular comparison

Figure 4.1(a)

Figure 4.1(b)

Figure 4.1(a) Close loop schematic of booster (b)Close loop controlsystem for booster

Figure 4.2(a)

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V. SIMULATION AND SIMULATION RESULTS

Simulation is carried out in PSIM software. Simulation

results for dc to dc boost converter are shown in Fig 5.1.

Fig 5.1(a) and (b) shows the results for input voltage 21V

and output voltage 36V at no load and full load

respectively.

Fig 5.1(c) shows the result for input voltage transition

from 27V to 21V. And it is shown in the figure though the

input voltage changes from 27 V to 21V output voltage

remains constant at 36V. PI controller is used to make

output voltage constant at 36 V volt level.

Fig 5.1(d) shows the simulation result for step load applied

and step load removed .It is shown in the figure thoughstep load is applied or removed the output voltage is

remains constant at 36 V voltage level. PI controller is used

to make output voltage constant at 36V volt level.

In FIG.5.2 (A) sine triangle comparison and generation of

sine PWM is shown. Here 50Hz sine wave is compared

with 3.2 kHz triangular wave which will generate sine

PWM. In figure 5.2 (B) inverter output without low pass

filter is shown.

In FIG.5.2 (C) the inverter output for full load condition for

simulation time 1.3 s to 1.5 s. FIG.5.2 (C) shows that RMS

value of output voltage and current of inverter are 220.09 V

and 0.905 A.

In FIG.5.2 (D) the inverter output for no load condition for

simulation time 1.3s to 1.5s. FIG.5.2 (D) shows that RMS

value of output voltage and current of inverter are 220 V

and 11 mA .

Figure 5.1(c)

Figure 5.1(d)

FIG.5.1 (A) Booster output at no load (B) Booster output at full load

(C) Booster output for input voltage transition from 37 volt to 21 volt(D)Booster output for step load applied and removed

Figure 5.1(b)

Figure5.1(a)

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VI.

CONCLUSION

Use of sine wave push pull inverter reduces the cost of

single phase solar inverter considerably. In this topology

only two switches are used and the isolation requirement

between control and power is less. Advantages of this

topology help to decrease the cost. Value of the

components for dc to dc boost converter and inverter is

calculated. This calculated value of components is used to

simulate dc to dc boost converter and inverter. Simulationfor different conditions viz. no load, full load, load

transition and input voltage transitions are carried out and

found satisfactory.

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Figure 5.2(c)

Figure 5.2(d)

FIG.5.2 (a) Sine Triangle comparison and PWM generation (b) Inverteroutput without low pass filter (c) Inverter output for full load condition (d)

Inverter output for no load condition

Figure 5.2(a)

Figure5.2(b)

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CONVERSION

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