ABSTRACT: Power quality is one of the major area of concern in recent40 years both in transmission and distribution system. The major fault occur inthe system are voltage sag, voltage swell, harmonics, voltage fluctuation etc.There are various custom power devices are used to compensate such problems.
Inthis paper we have discuss on the Multilevel inverter based DVR which is usedto protect the sensitive equipment such as computer, printer from line faultsuch as voltage sag. The implementation of the DVR in the distribution system is based on themultilevel inverter topology against voltage sag by using microcontroller. KEYWORDS: Multilevel inverter, Dynamic voltage restorer,voltage sag I.INTRODUCTIONThe common characteristics inmost of the electronics apparatus is they are very sensitive to the voltagevariation. Now a days the use of power electronics devices, computer, printeretc.
can create power quality issue. Among those power quality issue the mostof them is related to the voltage such as voltage sag, voltage swell etc. Asthere 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 generatingand absorbing active and reactive power in distribution system against thevoltage sag. In this paper the multilevel inverter based DVR is used. Themultilevel inverter provide much attention in recent year because they canoperate with PWM techniques also with amplitude modulation.
It can also providethe improve output voltage waveform. Multilevel inverter have number oftopologies such as 1. Cascade multilevel inverter 2. Diode clamped 3.
Flying CapacitordiodeFrom using Multilevel inverter,the output voltage waveform obtained is in staircase waveform but at the sametime increased in voltage levels can create circuit complexity. Multilevelinverter based DVR provide the compensation of the voltage sag with lessvoltage stress. II.LITERATURE SURVEYVoltagesag/swell is one of the challenging power quality problem in utility industrycan be compensated by injecting power in distribution system.DVR is the seriescompensation device which inject the voltage in distribution system viainsertion transformer. A typical DVR system is show in fig1.
The purpose ofimprovement of the voltage quality depend on the magnitude, phase shift, waveshape. The system can be designed for based on the dc-dc converter where dclink voltage adjusted according to voltage sag. It offers variable dc voltage asoutput that given to the dc-dc converter as an input voltage. H bridge topologyhas used so that dv/dt stress are to be reduce 1.The implementation of thesingle phase DVR is presented 2.Analysis and implementation of the Five levelcascaded H Bridge inverter is presented, the configuration is useful in theconstant frequency applications and reactive power compensation 3.There aredifferent topologies are used in the case of multilevel inverter that have beendiscussed 4.
The MATLAB modal have been invented for the system. The simulinkis developed for the POD control technique of 5 level diode clamp MLIpresented5.Interline dynamic voltage restorer can be used to mitigate voltagesag, its performance is based on the load power factor, simulation modalpresented in PSCAD6.Simulation modal has been done for the closed loop andopen loop system, where the PQ theory has been used to to generate referencevoltage7.
Z source converter has been implemented for the various powerconversions for that impedance circuit presented8. The simulink is done toshow its effectiveness. Fig1. Typical DVR system III.
MULTI LEVEL INVERTER TOPOLOGYMulti level inverterbasically used of number of electronics switches such as MOSFET, GTO etc.Sometimes capacitor, flying clamp diode can be used to obtain higher number ofstepped waveform. By introducing the concept of Multilevel inverter the outputvoltage stress become reduce also harmonic profile improved.Following are thetypes of multilevel inverter:1) Cascade multilevel inverter2) Multilevel inverter using flyingcapacitor3) Diode clamp multilevel inverter. 1) Cascademultilevel inverterCascademultilevel topology often used. It is always have separate dc source so it isefficient because it does not require any capacitor or diode clamp. In thismethod the soft switching could be used to avoid bulky and losses due tocapacitor diode switching snubber circuit.
Fig 2. Cascade multilevel inverter 2) Multilevel inverter using flyingcapacitorThebuilding block of capacitor clamp circuit is known as the flying capacitormultilevel inverter. By applying the suitable combination of capacitor thebalancing of capacitor is possible. For this method the number of bulkycapacitor clamp are required. Fig 3. Multilevel inverter using flying capacitor 3) Diodeclamp multilevel inverter This type of inverteruses the diode to produce the different voltage levels. It is having disadvantageof the real power flow control is difficult to do also for higher number ofvoltage levels diode clamp required inlarge number. IV.
PROPOSED SYSTEM Fig 1.Block diagram of MLI based DVR system. In this project we aredesigning multi stage dynamic voltage restorer system (DVR) to protectsensitive devices such as computer etc. from line faults such as voltage sag,voltage swell etc. here we constantly monitor the input line voltage usingvoltage reading circuit. This input is given to microcontroller unit.
The ADCof microcontroller reads real time voltage. If the voltage is less than 10% ofnominal voltage (Voltage Sag) then accordingly microcontroller triggers theMOSFET driver and hence the MOSFET Bridge to produce constant voltage of 230Vto protect the load device from voltage sag condition. When voltage is normalthen microcontroller turns off triggering to the bridge. Step up transformersare connected in series with the line source and load.In this we are designingthe voltage reading circuit by using capacitor, diode and resistor.PICmicrocontroller is capable of sensing the line voltage directly. The operatingfrequency of PIC is very high (20 MHz), so any small change in line voltage issensed quickly and action is taken in fraction of second.
Microcontroller uniti.e. PIC16F877A is used which is having operating voltage of 3.3 to 5 volt andalso it has 33input output pin. In MOSFET bridge circuit, Allfour MOSFETs are triggered in Chris-Cross way i.
e. ‘S1’ & ‘S3’ aretriggered ON simultaneously keeping ‘S2’ & ‘S4’ OFF while ‘S2’ & ‘S4’are triggered ON simultaneously keeping ‘S1′ &’S3’ OFF. TheMOSFET IRF540 is used as switch for triggering purpose, it has fast switching& it has simple drive requirement. VI.CONCLUSIONThe multilevel inverter emergedas one of the effective techniques due to its advantages it can be used formany applications. The implementation of MLI based DVR system usingmicrocontroller has been presented.
DVR is an effective custom power device forvoltage sag mitigation. The impact of voltage sag/swell on sensitive equipmentis severe. Therefore, DVR is considered to be an efficient solution due to itssmall size and fast response. References1 SmithaSethumadhavan, “Hardware Implementation of MLI BasedDynamic Voltage Restorer”InternationalJournal of Science and Research (IJSR) ISSN (Online): 2319-7064.2 Dr.
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