14 Umakant Wavlenmt Power Electronics Converter

8/10/2019 14 Umakant Wavlenmt Power Electronics Converter

1/25

Presentaion

Dr. U. D Dwivedi(Asst. Professor)

Rajiv Gandhi Institute of Petroleum Technology,

Raebareli


2/25

A Wavelet-based Carrierless PWMScheme for dc-ac Converter


3/25

OutlineIntroduction

1-Phase Inverter: Square-wave, Multi-pulse and PWM

Why A new modulation technique?

Wavelet Modulation (WM)

Generation of Switching Pulses using WM

Inverter Switching Scheme with WM Inverters

Simulation Results for a 1-pahse WM Inverter

Conclusions


4/25

DC to AC Conversion (INVERTER)DEFINITION: Converts DC to AC power by switching theDC input voltage (or current)in a pre-determined sequence soas to generate AC voltage (or current) output.

Uses power electronics switches

TYPICAL APPLICATIONS:

From small car adapter to large converters in solar and

wind powered systems.Industrial drives, Traction, HVDC, Un-interruptible powersupply (UPS), etc.


5/25

1-Phase Inverter: Square-wave, Multipulse and PWM

1-phase Inverter

(a) Square wave No control on output voltage

magnitude, No Harmonics control

(b) Multi-pulse Controllable output voltage

Magnitude, Limited degree of Harmonics

control

(a)

(b)

(c) Pulse Width Modulation (PWM) A better square wave notching is shown

this is known as PWM technique. Both amplitude and frequency can be controlled

independently.(c)


6/25

Sine-PWM Inverter

Switching Pulse Generation with SPWM

Output Voltage Control

A high freq. Carrier wave is compared with alow freq. sine wave to generate switching signal.


7/25

PWM Inverters

Main Objectives:1. To generate good quality controllable output ac voltage2. And to minimize harmonic distortion , filtering requirements, and

switching losses etc.

Higher switching freq. => less lower order harmonics and lowfiltering requirements, but higher switching losses

Sinusoidal PWM, Random PWM, Space Vector modulation, SelectiveHarmonics Elimination (SHE), etc.

Problem :the inverter can be modelled only as a lumped and averaged supply-

to-load elementlimited capabilities to effectively represent inverters, difficult tocorrelate them with modulation techniques.


8/25

Wavelet Based PWM Inverters

Motivation:A new PWM scheme based on non-uniform sampling andwavelet theory proposed in IEEE Transaction on Industrial

Electronics ( VOL. 56, NO. 7, JULY 2009 )Advantages:

Significant reduction in Harmonics compared to SPWM, RPWM, etc

Effective Inverter ModelProblem :

No output voltage magnitude control capability

Higher switching lossesProposed : ( Improved and generalization of basic WM scheme)

Full output voltage control capability50% Reduction in switching losses


9/25


10/25

From Wavelets to Wavelet Modulation (WM) Wavelets are defined by the wavelet function (t) ( also called the motherwavelet) and a scaling function (t).

Haar wavelet:

Dilation and translation of (t) generates a family of Haar scaling function:

where, j is scale parameterand k is translation parameter.

1, ( ) (2 ),

j j k H t t k

+=

1 0 1,( )

0 otherwise.

t t


11/25

Contnd.. In PWM, the output voltage is controlled by varying the width and position

of the pulses.

To generate variable width pulses, two Haar scaling functions arecombined to construct a new scaling function given as

where, j is scale parameter and is a constant.

Function , is subtracted from the original Haar scaling function to

obtain a synthesis function :

1 1 (. . 1).( ) (2 ) (2 ( 1 2 )), j j H j

j H t t t

+ + += + +

1,

j

( ) ( ) ( ). j H j jt t t = %


12/25

Contnd..

Function , is subtracted from theoriginal Haar scaling function toobtain a synthesis function :

creates two samples at eachdilation (scale) j at

( ) ( ) ( ). j H j jt t t = %

j

j %

( . 1)1

( . 1)2

2 ,

1 2

jd

jd

t

t

+

+

=

=


13/25

Wavelet Modulation (WM)


14/25


15/25

Switching Strategy Incorporated with Proposed WM

50% Reduction in Switching LossesWith proposed method

Basic WM

Proposed


16/25

Implementations Easy to implement as only two equations are required to generate the

switching signal

The proposed wavelet modulation scheme has been implemented using aMATLAB code and is finally converted to an equivalent SIMULINK model.

The developed WM simulink-block has been converted to a dSPACEmodel for hardware implementaion.

Extensive simulations have been carried out on single phase voltage sourceinverter using the developed simulink block to analyse the performance of the scheme.

.


17/25

Implementations Easy to implement as only two equations are required to generate the

switching signal

The proposed wavelet modulation scheme has been implemented using a

MATLAB code and is finally converted to an equivalent SIMULINK model.

Extensive simulations have been carried out on single phase voltage sourceinverter using the developed simulink block to analyse the performance of the scheme

The inverter output can be expressed as:

.

1 1

1 1 1 1

( ) ( ) ( ) ( /2) ( /2) J J J J

o dc j j J j m J j m j j j j

V t V t t t T t T

= = = =

= + % % % %


18/25

WM-Inverter and Load

WM-Pulse Generator WM-Simulink Block


19/25

WM-Simul ink Block

WM Embedded function


20/25

Basic WM Inverter Output Voltage


21/25

Proposed Wavelet PWM Inverter: Results

0.4 =


22/25

Proposed Wavelet PWM Inverter: Results

0.25 =


23/25

Fundamental Inverter Output Voltage Control

1 ve r su sV 1ver sus V


24/25

dSPACE Output of Developed WM-Simulink Block


25/25

Conclusions The main advantage of the WM scheme is that a single synthesis function,

derived using wavelet theory, can be used to generate the switching signalas well as to model the inverter output which is not possible with other modulation techniques.

Extensive simulations have been carried out on single phase VSI to analysethe performance of the proposed scheme for a wide range of frequency andoutput voltage magnitudes.

The proposed scheme provides a controllable output voltage with asignificant reduction in harmonics and switching losses.

The developed WM simulink-dSPACE model can be easily interfaced withexternal hardware (inverter).

Documents

14 Umakant Wavlenmt Power Electronics Converter