ABSTRACT: Power quality is one of the major area of concern in recent

40 years both in transmission and distribution system. The major fault occur in

the system are voltage sag, voltage swell, harmonics, voltage fluctuation etc.

There are various custom power devices are used to compensate such problems. In

this paper we have discuss on the Multilevel inverter based DVR which is used

to protect the sensitive equipment such as computer, printer from line fault

such as voltage sag. The implementation of the DVR in the distribution system is based on the

multilevel inverter topology against voltage sag by using microcontroller.

KEYWORDS: Multilevel inverter, Dynamic voltage restorer,

voltage sag

I.INTRODUCTION

The common characteristics in

most of the electronics apparatus is they are very sensitive to the voltage

variation. Now a days the use of power electronics devices, computer, printer

etc. can create power quality issue. Among those power quality issue the most

of them is related to the voltage such as voltage sag, voltage swell etc. As

there are many custom power devices has been used to compensate such problems.

Dynamic voltage restorer is one of the device that can be capable of generating

and absorbing active and reactive power in distribution system against the

voltage sag. In this paper the multilevel inverter based DVR is used. The

multilevel inverter provide much attention in recent year because they can

operate with PWM techniques also with amplitude modulation. It can also provide

the improve output voltage waveform. Multilevel inverter have number of

topologies such as 1. Cascade multilevel inverter 2. Diode clamped 3. Flying Capacitor

diode

From using Multilevel inverter,

the output voltage waveform obtained is in staircase waveform but at the same

time increased in voltage levels can create circuit complexity. Multilevel

inverter based DVR provide the compensation of the voltage sag with less

voltage stress.

II.LITERATURE SURVEY

Voltage

sag/swell is one of the challenging power quality problem in utility industry

can be compensated by injecting power in distribution system.DVR is the series

compensation device which inject the voltage in distribution system via

insertion transformer. A typical DVR system is show in fig1.The purpose of

improvement of the voltage quality depend on the magnitude, phase shift, wave

shape. The system can be designed for based on the dc-dc converter where dc

link voltage adjusted according to voltage sag. It offers variable dc voltage as

output that given to the dc-dc converter as an input voltage. H bridge topology

has used so that dv/dt stress are to be reduce 1.The implementation of the

single phase DVR is presented 2.Analysis and implementation of the Five level

cascaded H Bridge inverter is presented, the configuration is useful in the

constant frequency applications and reactive power compensation 3.There are

different topologies are used in the case of multilevel inverter that have been

discussed 4.The MATLAB modal have been invented for the system. The simulink

is developed for the POD control technique of 5 level diode clamp MLI

presented5.Interline dynamic voltage restorer can be used to mitigate voltage

sag, its performance is based on the load power factor, simulation modal

presented in PSCAD6.Simulation modal has been done for the closed loop and

open loop system, where the PQ theory has been used to to generate reference

voltage7. Z source converter has been implemented for the various power

conversions for that impedance circuit presented8. The simulink is done to

show its effectiveness.

Fig

1. Typical DVR system

III.MULTI LEVEL INVERTER TOPOLOGY

Multi level inverter

basically used of number of electronics switches such as MOSFET, GTO etc.

Sometimes capacitor, flying clamp diode can be used to obtain higher number of

stepped waveform. By introducing the concept of Multilevel inverter the output

voltage stress become reduce also harmonic profile improved.

Following are the

types of multilevel inverter:

1)

Cascade multilevel inverter

2)

Multilevel inverter using flying

capacitor

3)

Diode clamp multilevel inverter.

1)

Cascade

multilevel inverter

Cascade

multilevel topology often used. It is always have separate dc source so it is

efficient because it does not require any capacitor or diode clamp. In this

method the soft switching could be used to avoid bulky and losses due to

capacitor diode switching snubber circuit.

Fig 2. Cascade multilevel inverter

2) Multilevel inverter using flying

capacitor

The

building block of capacitor clamp circuit is known as the flying capacitor

multilevel inverter. By applying the suitable combination of capacitor the

balancing of capacitor is possible. For this method the number of bulky

capacitor clamp are required.

Fig 3. Multilevel inverter using flying capacitor

3) Diode

clamp multilevel inverter

This type of inverter

uses the diode to produce the different voltage levels. It is having disadvantage

of the real power flow control is difficult to do also for higher number of

voltage levels diode clamp required in

large number.

IV.PROPOSED SYSTEM

Fig 1.Block diagram of MLI based DVR system.

In this project we are

designing multi stage dynamic voltage restorer system (DVR) to protect

sensitive devices such as computer etc. from line faults such as voltage sag,

voltage swell etc. here we constantly monitor the input line voltage using

voltage reading circuit. This input is given to microcontroller unit. The ADC

of microcontroller reads real time voltage. If the voltage is less than 10% of

nominal voltage (Voltage Sag) then accordingly microcontroller triggers the

MOSFET driver and hence the MOSFET Bridge to produce constant voltage of 230V

to protect the load device from voltage sag condition. When voltage is normal

then microcontroller turns off triggering to the bridge. Step up transformers

are connected in series with the line source and load.

In this we are designing

the voltage reading circuit by using capacitor, diode and resistor.PIC

microcontroller is capable of sensing the line voltage directly. The operating

frequency of PIC is very high (20 MHz), so any small change in line voltage is

sensed quickly and action is taken in fraction of second. Microcontroller unit

i.e. PIC16F877A is used which is having operating voltage of 3.3 to 5 volt and

also it has 33input output pin. In MOSFET bridge circuit, All

four MOSFETs are triggered in Chris-Cross way i.e. ‘S1’ & ‘S3’ are

triggered ON simultaneously keeping ‘S2’ & ‘S4’ OFF while ‘S2’ & ‘S4’

are triggered ON simultaneously keeping ‘S1′ &’S3’ OFF. The

MOSFET IRF540 is used as switch for triggering purpose, it has fast switching

& it has simple drive requirement.

VI.CONCLUSION

The multilevel inverter emerged

as one of the effective techniques due to its advantages it can be used for

many applications. The implementation of MLI based DVR system using

microcontroller has been presented. DVR is an effective custom power device for

voltage sag mitigation. The impact of voltage sag/swell on sensitive equipment

is severe. Therefore, DVR is considered to be an efficient solution due to its

small size and fast response.

References

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