ROLE AND APPLICATION OF SINGLE PHASE MULTILEVEL INVERTER IN GRID CONNECTED PHOTOVOLTAIC SYSTEMS

7/27/2019 ROLE AND APPLICATION OF SINGLE PHASE MULTILEVEL INVERTER IN GRID CONNECTED PHOTOVOLTAIC SYSTEMS

1/30

Dissertation

On

ROLE AND APPLICATION OF SINGLE PHASE

MULTILEVEL INVERTER IN GRIDCONNECTED PHOTOVOLTAIC SYSTEMS.


2/30

Literature Review

Photovoltaic System

The multilevel inverter

Pulse Width Modulation Technique

Technical Issues

References


3/30

Literature Review

The multilevel inverter has been proven to be one of theimportant enabling technologies in photovoltaic (PV)utilization.

Hydro, photovoltaic (PV) and wind energy conversion have

advantages such as reliability

reasonable installation and energy production costs

low environmental impact

capability to support microgrid systems and to connect to theelectric grid

Among these energy sources the PV is pointed out as one of

the most modular and environmentally friendly technologies.


4/30

Photovoltaic System

Photovoltaic (PV) power supplied to the utility grid is gainingmore and more visibility, while the worlds power demand isincreasing.


5/30

Photovoltaic Technology

PV systems as an alternative energy resource

complimentary energy-resource in hybrid systems.

Necessary:

high reliability

reasonable cost

user-friendly design


6/30

Islanding

Islanding is the continued operation of the inverter when the grid hasbeen removed on purpose, by accident, or by damage

Detection schemes - active and passive.

1. The passive methods -monitor grid parameters.

2. The active schemes introduce a disturbance into the grid and monitorthe effect.


7/30

Small stand-alone DC or AC system

The PV array charges the battery during daylight hours and the batterysupplies power to the loads as needed. The charge regulator terminatesthe charging when the battery reaches full charge. The load center maycontain meters to monitor system operation and fuses to protect wiringin the event of malfunction or short circuit in the house.


8/30

Grid connected systems

Grid-connected photovoltaic powersystems are powersystems energized by photovoltaic panels which areconnected to the utility grid.


9/30


10/30

Applications of PV

Water Pumping: PV powered pumping systems are excellent ,

simple ,reliable

life 20 yrs Commercial Lighting: PV powered lighting systems are reliable and low

cost alternative. Security, billboard sign, area, and outdoor lighting areall viable applications for PV

Consumer electronics: Solar powered watches, calculators, and camerasare all everyday applications for PV technologies.

Telecommunications

Residential Power: A residence located more than a mile from the electricgrid can install a PV system more inexpensively than extending theelectric grid

source of)


11/30

PV TechnologyThe key to successful solar energy installation is to use quality components

that have long lifetimes and require minimal maintenance.

The future is bright for continued PV technology dissemination.

PV technology fills a significant need in supplying electricity, creating local

jobs and promoting economic development in rural areas, avoiding the

external environmental costs associated with traditional electrical generation

technologies.

Major power policy reforms and tax incentives will play a major role if all the

above said is to be effectively realized.


12/30

Multi level inverter The elementary concept of a multilevel converter is to achieve

higher power to use a series of power semiconductor switcheswith several lower voltage dc sources to perform the powerconversion by synthesizing a staircase voltage waveform.

Multilevel inverters, in case of n-level, can increase the power by(n-1) times than that of two-level inverter through the seriesconnection of power semi conductor devices without additionalcircuit to have uniform voltage sharing.

Three types of multilevel inverter have been proposed in ourdissertation.1. Diode Clamped multilevel inverters2. Flying Capacitor multilevel inverters3. Cascaded H-bridge multilevel inverters


13/30

As the levels increases, the voltage that can be spanned by summing multiplevoltage levels also increases.In high power and high voltage application multilevel inverters are used toavoid limitations of 2- level inverters at high frequency


14/30

Generalized waveform of cascaded multilevel inverter


15/30

1. Diode Clamped multilevel inverters

One leg of 3-level diode clamped inverter topology

The diode clamped inverter uses half bridge version in each level. The diodeclamped multilevel inverter is most commonly used. However, it is difficult tocontrol voltage of each capacitor constituted DC-link beyond four level.


16/30

2. Flying Capacitor multilevel inverters

One leg of 3-level flying capacitor inverter topology

The flying capacitor multilevel inverter does not require separatelyisolated dc sides and additional clamping diode.


17/30

3. Cascaded H-bridge multilevel inverters

One leg of cascaded H-bridge inverter topology

A cascaded multilevel inverter consists of a series of H-bridge(single-phase, full bridge) inverter units. The cascaded multilevel has

no voltage sharing problem except for series connected devices and

capacitors but it has separately isolated dc power supplies, which

requires special input transformer.


18/30

Features Of Multilevel Inverter

The key features of a multilevel structure follow:

The output voltage and power increase with the number oflevels.

The harmonic content decreases as the number of levelsincreases and filtering requirements are reduced.

With additional voltage levels, the voltage waveform has morefree switching angles, which can be preselected elimination.

In the absence of any techniques, the switching losses can beavoided.

Increasing output voltage and power does not require anincrease in rating of individual device.

The switching devices do not encounter any voltage sharing

problems.


19/30

Advantages Of Multilevel Inverter It is easier to produce a high power and high voltage with the multilevel structure.

High power ratings and reduced cost.

No transformers are needed to produce these high voltages, whereas traditional 12, 24,and 48-pulse inverters require transformers.

If a component fails on a multilevel inverter, most of the time the inverter will still beusable, at a reduced power level [14].So it is reliable.

Multilevel inverters allow for the utilization of smaller, more reliable components.

Increasing the number of voltages levels in the inverter without requiring higher ratingson individual devices can increase the power rating.

The structure of multilevel voltage source inverters allow them to reach high voltageswith low harmonics.

By using multilevel structure, the stress on each switching device can be reduce in

proportional to the number of levels and thus the inverter can handle higher voltages. Consequently in some application, it is possible to avoid expensive and bulky step up

transformer.

The multilevel inverter can also be used to provide ride-through capability underemergency conditions.


20/30

Applications OfMultilevel Inverters-

Multilevel inverters utilize several dc voltages to synthesize a desiredac voltage. For this reason, multilevel inverters can be implementedusing distributed energy resources such as photovoltaic and fuelcells.

The application of multilevel inverters being considered is

connecting the fore mentioned energy resources with an ac powergrid.

Using a multilevel inverter as a reactive power compensator can helpto improve the power factor of a load.

If the dc sources of the multilevel inverter are banks of batteries or

capacitors, the multilevel inverter can also be used to provide ride-through capability under emergency conditions. Another possible application of multilevel inverters is their use in

Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs).Multilevel inverters generally allow for smaller components, thusreducing weight[14].


21/30

PULSE WIDTH MODULATION TECHNIQUE

The energy that a switching power converter delivers to a motor is controlled by PulseWidth Modulated (PWM) signals applied to the gates of the power transistors.

PWM signals are pulse trains with fixed frequency and magnitude and variable pulse

width. There is one pulse of fixed magnitude in every PWM period. However, thewidth of pulses changes from pulse to pulse according to a modulating signal.

When a PWM signal is applied to the gate of a transistor, it causes the turn on andturn off intervals of the transistor to change from one PWM period to other PWMperiod according to the same modulating signal [12]

The frequency of a PWM signal must be much higher than that of the modulatingsignal, the fundamental frequency such that the energy delivered to the motor and itsload depends mostly on the modulating signal.


22/30

Pulse-Width Modulation Objective of PWM

Control of inverter output voltage Reduction of harmonics

Disadvantages of PWM Increase of switching losses due to high PWM frequency

Reduction of available voltage EMI problems due to high-order harmonics


23/30


24/30

Disadvantages Of PWM Drastically increased switching frequencies

Attenuation of the wanted fundamental component ofthe PWM waveform.

Generation of high frequency harmonic components.

It is susceptible to EMI (electromagnetic interference)

and sometimes even produces audible noises.


25/30

Technical Issues

The main grid interface criteria which should bechecked with the utility are the following:Voltage regulation Frequency regulation Harmonic distortion in the operating load range:

Total of all current harmonics (usually 5% maximum) Any single current harmonic (usually 3% maximum) Total of all voltage harmonics (usually 5% maximum)

Power factor and reactive power consumption

Protection and operation criteria Inverter disconnect criteria in the event of a grid failure. Inverter reconnect criteria. Adequate safeguard against islanding.


26/30

Total harmonic distortionOne of the leading problems in inverter is theharmonic contents. The harmonics can be classifiedinto

voltage harmonics

current harmonics.

Current harmonics is usually generated by harmonics

contained in voltage supply and depends on the typeof load such as resistive load, capacitive load andinductive loads. Harmonic distortion can havedetrimental effects on electrical equipment.


27/30

How harmonic distortion can affect the operation?

Equipment responds to harmonics differently depending ontheir method of operation. For example incandescent lightsand most types of household electric heaters and stoves are

not affected adversely at all. On the other hand, induction motor windings are overheated

by harmonics, causing accelerated degradation of insulationand loss of life. Harmonic voltages can give correspondingly

higher currents than do 50 Hz voltages and one can easilyunderestimate the degree of additional heating in the motor.The operation of some equipment depends on an accurate

voltage wave shape and they can malfunction when harmonicsare present.


28/30

REFERENCES

[1] Key world energy statistics - 2009, International Energy Agency (IEA), 2009. Available at:http://www.iea.org.

[2] F. Kininger, Photovoltaic systems technology. Kassel, Germany: Universitt Kassel, Institut fr RationelleEnergiewandlung, 2003. Available at:www.uni-kassel.de/re.

[3] M. Liserre, T. Sauter, J.Y. Hung, Future energy systems: integrating renewable energy sources into the smartpower grid through industrial electronics, IEEE IndustrialElectronics Magazine, vol.4, no. 1, pp. 18-37, Mar.

2010.

[4] Global Market Outlook for Photovoltaics Until 2014, European Photovoltaic Industry Association (EPIA).Available at: http://www.epia.org.

[5] Energy poverty: how to make modern energy access universal, World Energy Outlook 2010, InternationalEnergy Agency (IEA). Available at: http://www.iea.org.

[6] Management of storage batteries used in stand-alone photovoltaic power systems report, IEA PVPS T3-10:2002, International Energy Agency (IEA), 2002. Available at: http://www.iea.org.

7] J. P. Benner and L. Kazmerski, Photovoltaics gaining greater visibility, IEEE Spectr., vol. 29, no. 9, pp. 3442,Sep. 1999.
http://www.iea.org/http://www.iea.org/http://www.uni-kassel.de/rehttp://www.uni-kassel.de/rehttp://www.epia.org/http://www.epia.org/http://www.epia.org/http://www.iea.org/http://www.iea.org/http://www.iea.org/http://www.iea.org/http://www.iea.org/http://www.iea.org/http://www.epia.org/http://www.uni-kassel.de/rehttp://www.uni-kassel.de/rehttp://www.uni-kassel.de/rehttp://www.iea.org/


29/30

8] Limits for Harmonic Current Emission (Equipment Input Current


30/30

Thank You.

Documents

ROLE AND APPLICATION OF SINGLE PHASE MULTILEVEL INVERTER IN GRID CONNECTED PHOTOVOLTAIC SYSTEMS