View
221
Download
0
Category
Preview:
Citation preview
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
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
2/25
A Wavelet-based Carrierless PWMScheme for dc-ac Converter
8/10/2019 14 Umakant Wavlenmt Power Electronics 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
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
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.
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
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)
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
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.
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
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.
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
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
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
9/25
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
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
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
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 = %
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
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
+
+
=
=
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
13/25
Wavelet Modulation (WM)
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
14/25
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
15/25
Switching Strategy Incorporated with Proposed WM
50% Reduction in Switching LossesWith proposed method
Basic WM
Proposed
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
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.
.
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
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
= = = =
= + % % % %
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
18/25
WM-Inverter and Load
WM-Pulse Generator WM-Simulink Block
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
19/25
WM-Simul ink Block
WM Embedded function
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
20/25
Basic WM Inverter Output Voltage
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
21/25
Proposed Wavelet PWM Inverter: Results
0.4 =
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
22/25
Proposed Wavelet PWM Inverter: Results
0.25 =
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
23/25
Fundamental Inverter Output Voltage Control
1 ve r su sV 1ver sus V
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
24/25
dSPACE Output of Developed WM-Simulink Block
8/10/2019 14 Umakant Wavlenmt Power Electronics Converter
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).
Recommended