power quality improvement in grid connected

8/19/2019 Power Quality Improvement in Grid Connected..

1/23

Power Quality Improvement in Grid connectedsystem using Four leg VSI


2/23

Abstract This project presents a new method thatconsists of a four leg inverter that is capableof simultaneously compensating problems likepower factor, current imbalance and current

harmonics, and also of injecting the energygenerated by renewable energy powersources. The fourth leg of inverter is used tocompensate the neutral current of load. The

grid interfacing inverter can thus be utilizedas: 1) power converter to inject powergenerated from !" to the grid, and #) shunt$%& to compensate current unbalance, loadcurrent harmonics and load reactive powerdemand. The inverter is actively controlled in


3/23

Existing method The e(isting method describespassive lters have been used toeliminate line current harmonics.*owever, they introduce resonance inthe power system and tend to be bulky."o active power line conditionershave become popular than passivelters as it compensates the harmonics

and reactive power simultaneously. The active power lter topology canbe connected in series or shunt andcombinations of both. "hunt active

lter is more popular than series activelter because most of the industrial


4/23

raw bac!s existing%ower factor, currentimbalance and current

harmonics, The injecting the energygenerated by renewableenergy power sources with avery high T*.

ecreasing the power +ualityof the electric grid.


5/23

Proposed method The proposed method describes newmethod that consists of four leg -"that is capable of simultaneously

compensating problems like powerfactor, current imbalance and currentharmonics, and also of injecting theenergy generated by renewable energy

power sources with a very low T*.!ven when there is no energy availablefrom the power source the -oltagesource inverter can still operate,increasing the power +uality of the

electric grid.


6/23

Schematic o" Proposed istributed

Generation system


7/23

t is assumed that a non/linearunbalanced load consisting of athree phase and single phasediode rectier is connected to a

three/phase balanced sourcevoltages. The voltage source inverter isa key element of a 0 system asit interfaces the renewableenergy source to the grid anddelivers the generated power.

The !" may be a source oran $ source with rectier

coupled to dc/link.


8/23

Active power "ilter #APF$

n a modern power system, increasing of loads

and non/linear e+uipment2s have been

demanding the compensation of the disturbances

caused for them.

These nonlinear loads may cause poor power

factor and high degree of harmonics.

$%& have the ability to adjust the amplitude of

the synthesized ac voltage of the inverters by

means of pulse width modulation or by control of

the dc/link voltage, thus drawing either leading or

lagging reactive power from the supply.


9/23

istributed generation #G$

istributed energy, also on/site generation

45"0) or district'decentralized energy isgenerated or stored by a variety of small,grid/connected devices referred to asdistributed energy resources 4!) or

distributed energy resource systems.onventional power stations, such as coal/red, gas and nuclear powered plants, aswell as hydroelectric dams and large/scalesolar power stations, are centralized andoften re+uire electricity to be transmittedover long distances. 6y contrast, !systems are decentralized, modular andmore 7e(ible technologies, that are located

close to the load they serve, albeit having


10/23

Power %uality #PQ$

%ower +uality determines the tnessof electric power to consumer devices."ynchronization of the voltage fre+uencyand phase allows electrical systems to

function in their intended manner withoutsignicant loss of performance or life. The term is used to describe electricpower that drives an electrical load and theload2s ability to function properly. ithoutthe proper power, an electrical device maymalfunction, fail prematurely or not operateat all. There are many ways in whichelectric power can be of poor +uality and

many more causes of such poor +uality


11/23

The +uality of electrical powermay be described as a set ofvalues of parameters, such as:ontinuity of service

-ariation in voltage magnitude Transient voltages and currents*armonic content in thewaveforms for $ power


12/23

&enewable energy #&E$

enewable energy is generally denedas energy that is collected fromresources which are naturallyreplenished on a human timescale, such

as sunlight, wind, rain, tides, waves, andgeothermal heat.enewable energy often providesenergy in four important areas:

electricity generation, air and waterheating'cooling, transportation, and rural4o


13/23

ontd=enewable energy resources e(ist overwide geographical areas, in contrast toother energy sources, which areconcentrated in a limited number of

countries. apid deployment of renewable energyand energy e>ciency is resulting insignicant energy security, climate change

mitigation, and economic benets. The results of a recent review of theliterature concluded that as greenhousegas40*0) emitters begin to be held liablefor damages resulting from 0*0 emissionsresulting in climate change, a high value


14/23

Voltage source Inverter #VSI$$ variable/speed wind power conversionsystem is used for illustration, where the-"/based interface needs to convert avariable voltage to a nearly constant $

voltage with high/+uality power. The powercontrol principles of -" are described.t is shown that better utilization ofsemiconductors and more 7e(ible control

may be achieved by using a separatelycontrolled link, rather than a directlyconnected -" that has to operate at alower modulation ratio at higher power.n some cases, multiples inverterstructures may be preferred, despite higher


15/23

Advantages

%ower factor, current imbalance andcurrent harmonics, The injecting the energy generated byrenewable energy power sources with avery low T*.ncreasing the power +uality of theelectric grid.

?sually there is a fast internal currentcontrol loop, which regulates the gridcurrent.an e(ternal voltage loop which

controls the /link voltage


16/23

Applications"hunt active lter is morepopular than series active lterbecause most of the industrialapplications re+uire currentharmonics compensation. The electrical grid will include avery large

@umber of small producers thatuse renewable energy sources,like solar panels or windgenerators.


17/23

link model of representation of designed sys


18/23

!(pected results of grid voltages and current


19/23

0rid, Aoad and nverter @eutral urrents


20/23


21/23


22/23

'()'*+SI()S

This project presented a control of an Three phase &our leg grid interfacinginverter improve the +uality of power at% for a B phase C wire system to injectpower generated from !" to % and toimprove the +uality of power at %. Thusthe proposed controller precisely managesany variation in real power at dc link ande


23/23

power quality improvement in grid connected

Documents