Selective harmonic elimination (she) for 3 phase voltage source inverter (vsi) (1)
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The Selective Harmonic Elimination (SHE) for 3-Phase Voltage Source Inverter (VSI) is presented here. The projected work investigates the Selective Harmonic Elimination (SHE) to eliminate harmonics produced by Pulse Width Modulation (PWM) inverter. The selective harmonic elimination method for three phase Voltage Source Inverter (VSI) is generally based on ideas of opposite harmonic injection. In this proposed scheme, the lower order harmonics (3rd, 5th, 7th, and 9th) are eliminated by the dominant harmonics of same order generated in opposite phase by Sinusoidal Pulse Width Modulation (SPWM) inverter and by using this scheme the Total Harmonic Distortion (THD) is reduced. Analysis of Sinusoidal Pulse Width Modulation (SPWM) technique and Selective Harmonic Elimination (SHE) is simulated using MATLAB/SIMULINK model.
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![ELECTRICAL PROJECTS USING MATLAB/SIMULINK
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CONCLUSION:
The paper presents a selective harmonic elimination technique for three phase voltage source
inverter with the RL load. A Three phase Voltage Source Inverter (VSI) changes DC input
voltage to a three phase variable frequency variable voltage output. The elimination of specific
low-order harmonics from a given voltage/current waveform achieved by Selective Harmonic
Elimination (SHE) technique. We unite the inductor filter with the capacitor the ripple aspect
will turn out to be more or less autonomous of the load filter. Finally Analysis and comparison of
Total Harmonic Distortion (THD) for sinusoidal Pulse Width Modulation (PWM) technique and
selective harmonic elimination technique has been done. From the comparison it is very apparent
that the Total Harmonic Distortion (THD) for selective harmonic technique is less than that of
sinusoidal Pulse Width Modulation (PWM) method.
REFERENCES:
[1] Ray, R.N., Chatterjee, and Goswami, S.K, “Reduction of voltage harmonic using
optimization – based combined approach on” proceeding on IET Power Electronics, 3 (3). 334-
344. 2008.
[2] Mohamed S.A.Dahidah and Vassilios G. Agelidis, “Selective harmonic elimination PWM
control for Cascaded multilevel voltage source converters: A generalized formula” IEEE Trans
on power electronics, 23(4). 1620-1630. Jul. 2008.
[3] Wells, Jason R. Xin Geng, Chapman, Patrick L. and Krein, Philip T. “Modulation based
harmonic elimination” IEEE Transactions on Power Electronics, 22(1). 2007.
[4] Fellow, Javier Napoles, Jose Ignacio Leon, and Aguirre, Miguel A. “A flexible selective
harmonic mitigation to meet grid codes in three level PWM converters” IEEE Transactions on
Industrial Electronics, 54(6).Dec.2007.
[5] Hadji, S. Touhami O. and C.J.Goodman, “Vector- optimized harmonic elimination for single-
phase pulse width modulation inverters/converters” IET Electr.Power Appl.,1(3). 423-432. 2007](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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ANALYSIS OF DISCRETE & SPACE VECTOR PWM CONTROLLED HYBRID ACTIVE FILTERS FOR ...
It is known from the fact that Harmonic Distortion is one of the main power quality problems frequently encountered by the utilities. The harmonic problems in the power supply are caused by the non-linear characteristic based loads. The presence of harmonics leads to transformer heating, electromagnetic interference and solid state device mal-functioning. Hence keeping in view of the above concern, research has been carried out to mitigate harmonics. This paper presents an analysis and control methods for hybrid active power filter using Discrete Pulse Width Modulation and Space Vector Pulse Width Modulation (SVPWM) for Power Conditioning in distribution systems. The Discrete PWM has the function of voltage stability, and harmonic suppression. The reference current can be calculated by ‘d-q’ transformation. In SVPWM technique, the Active Power Filter (APF) reference voltage vector is generated instead of the reference current, and the desired APF output voltage is generated by SVPWM. The THD will be decreased significantly by SVPWM technique than the Discrete PWM technique based Hybrid filters. Simulations are carried out for the two approaches by using MATLAB, it is observed that the %THD has been improved from 1.79 to 1.61 by the SVPWM technique.
Ei35761766
This document presents research on using a genetic algorithm to optimize switching angles in multilevel inverters in order to reduce total harmonic distortion. Specifically:
1) A genetic algorithm is developed and used to determine optimal switching angles for 7-level and 9-level cascaded inverters to eliminate low order harmonics and minimize total harmonic distortion, without needing to solve nonlinear equations.
2) Simulation results show the genetic algorithm approach produces switching angles that generate voltage waveforms with very low 5th, 7th, and 11th harmonics for the 9-level inverter and low 5th and 7th harmonics for the 7-level inverter.
3) The 9-level inverter achieves
G010334953
This document discusses methods for minimizing total harmonic distortion (THD) in pulse width modulation (PWM) inverters. It proposes using a phase compensation resonant controller (RSC) for a single-phase PWM inverter. The RSC uses multiple resonant controllers in parallel tuned to dominant harmonic frequencies to eliminate harmonic distortion. Simulation results for the RSC approach are compared to other controllers like state feedback and state vector PWM controllers. The RSC is able to achieve zero steady-state error control at resonant frequencies, improving tracking accuracy and eliminating dominant harmonics compared to other controllers.
Fuzzy Logic Controlled Harmonic Suppressor in Cascaded Multilevel Inverter
This paper presents an investigation of seven level cascaded H-bridge (CHB)
inverter in power system for compensation of harmonics. For power quality
control a Fuzzy Logic Control (FLC) giving comparatively better harmonic
reduction than the conventional controllers. Harmonic distortion is the most
important power quality problem stirring in multilevel inverter; the
harmonics can be eliminated by an optimal selection of switching angles. A
hybrid evaluation technique evaluates the obtained optimal switching angles
that are attained from the fuzzy inference system as well as neural network.
The proposed method will be implemented in MATLAB working platform
and the harmonic elimination performance will be evaluated.
Identification and minimization of Harmonics
In this ppt we will get to know about basic idea of harmonics, types of harmonics , measuring devices and minimizing techniques and also covering the there impact on power system and impact on consumer equipment's.
Inverter 2003
The document discusses DC to AC conversion using inverters. It describes the basic concept and components of inverters including single-phase, full-bridge, and three-phase inverter topologies. It also covers modulation techniques such as pulse width modulation (PWM) and discusses how they affect the output waveform harmonics.
PQ-1.ppt
This document discusses power system harmonics, including:
- Harmonics are integer multiples of the fundamental power frequency that distort voltage and current waveforms from nonlinear loads.
- Sustained harmonics can negatively impact equipment and power quality by causing overheating, capacitor failure, and interfering with protection devices.
- Standards like IEEE 519 provide limits on allowable harmonic distortion to mitigate these impacts.
- Solutions include improving power system design, adding filters, isolating loads, and using different transformer configurations to reduce harmonics.
Power System Harmonics Causes and Effect.ppt
Harmonics in power systems are integer multiples of the fundamental power frequency that distort the voltage and current waveforms. Nonlinear loads such as adjustable speed drives, electronic ballasts, and rectifiers are the primary sources of harmonics. Harmonics can cause overheating of equipment, false relay operations, capacitor failures, and reduced power quality. Standards like IEEE 519 provide limits on allowable harmonic distortion to mitigate its negative effects. Harmonic meters and oscilloscopes are used to measure harmonic levels and identify potential problems.
upqc
This document discusses a three-phase unified power quality conditioner (UPQC) for mitigating power quality issues like current harmonics, voltage sags, and reactive power. The UPQC consists of a series compensator to mitigate voltage sags between source and load, and a shunt compensator connected in parallel with the load to reduce harmonic currents and total harmonic distortion. An adaptive band-type hysteresis controller is used to control the voltage source inverters, with reference current signals generated using synchronous reference frame theory. Simulation results in Matlab/Simulink confirm the filter can compensate load current harmonics within IEEE 519 standards.
power quality
This document discusses a three-phase unified power quality conditioner (UPQC) for mitigating power quality issues like current harmonics, voltage sags, and reactive power. The UPQC consists of a series compensator to mitigate voltage sags between source and load, and a shunt compensator connected in parallel with the load to reduce harmonic currents and total harmonic distortion. An adaptive band hysteresis control is used with a voltage source inverter at the core of the active power filter. Simulation results in Matlab/Simulink confirm the filter can compensate load current harmonics within IEEE 519 standards.
7- 1st semester_BJT_AC_Analysis (re model)-1.pdf
The document discusses transistor AC modeling and analysis. It provides two common models used - the re equivalent model and h-parameter model. It then discusses important procedures for small signal AC analysis including replacing DC sources with shorts and capacitors with opens. Common configurations like common-emitter, common-base, and examples are analyzed. Input impedance, output impedance, and voltage gain are determined for different configurations both with and without bypassing the emitter resistor.
1 1 4
This document summarizes a research paper that proposes using artificial neural networks to generate optimal switching functions for voltage and harmonic control of three-phase inverters. Specifically:
1) A new training algorithm is developed for an artificial neural network to determine switching angles without using pre-computed desired angles. Instead, it uses the desired solution of harmonic elimination equations.
2) Theoretical analysis of the proposed solving algorithm with neural networks is provided. Simulation results show the high performance and advantages of the developed modulator.
3) An artificial neural network is trained using a backpropagation algorithm. Training data comes from optimal switching angles determined through selective harmonic elimination equations for different modulation indices.
1 1 4
This document discusses using artificial neural networks to solve the harmonics elimination problem in three-phase voltage-controlled inverters. It presents a new training algorithm for an ANN that does not use pre-computed switching angles from classical harmonic elimination methods. Instead, it trains the ANN by using the desired solution of the harmonic elimination equations, with the first harmonic equal to the modulation index and higher harmonics equal to zero. Theoretical analysis and simulation results show the high performance of using this ANN approach for generating optimal switching functions to control harmonics in inverters.
Harmonic reduction
The document presents information on harmonic reduction in inverter output voltage. It defines harmonics as integral multiples of a fundamental frequency that result in a distorted waveform when added together. Common sources of harmonics are identified as lighting ballasts, UPS systems, AC drives, and DC drives. Methods for attenuating harmonics discussed include inductive reactance, passive filters, active filters, 12-pulse and 18-pulse rectifiers, PWM, transformer connections, stepped wave inverters, and multilevel inverters. The document recommends limits on voltage and current distortion set by IEEE 519 and compares harmonic reduction performance of different converter and inverter configurations.
Harmonic estimation by lms algorithm
This document discusses harmonic estimation using the sliding window least mean square (SW-LMS) algorithm. It introduces harmonics and their effects, as well as traditional Fourier transform and LMS algorithms for analysis. The SW-LMS algorithm is presented as improving on LMS by using a sliding window to exclude oscillations and work better in noisy signals. Simulation results show the SW-LMS algorithm can effectively estimate harmonics even at high noise levels. In conclusion, SW-LMS provides an effective technique for harmonic estimation.
Efitra1006
This document summarizes research on pulse width modulation (PWM) techniques for three-phase inverters. It describes sinusoidal PWM switching schemes that allow control of output voltage magnitude and frequency. Simulation models of three-phase inverters using sawtooth and triangular carrier waveforms are presented and analyzed. The results show that a sawtooth carrier waveform produces a more appropriate three-phase voltage waveform compared to a triangular carrier waveform. In conclusion, sinusoidal PWM inverters can generate clean sinusoidal output voltages through comparison of reference and carrier signals to control switching.
A Tactical Chaos based PWM Technique for Distortion Restraint and Power Spect...
The pulse width modulated voltage source inverters (PWM-VSI) dominate in the modern industrial environment. The conventional PWM methods are designed to have higher fundamental voltage, easy filtering and reduced total harmonic distortion (THD). There are number of clustered harmonics around the multiples of switching frequency in the output of conventional sinusoidal pulse width modulation (SPWM) and space vector pulse width modulation (SVPWM) inverters. This is due to their fixed switching frequency while the variable switching frequency makes the filtering very complex. Random carrier PWM (RCPWM) methods are the host of PWM methods, which use randomized carrier frequency and result in a harmonic profile with well distributed harmonic power (no harmonic possesses significant magnitude and hence no filtering is required). This paper proposes a chaos-based PWM (CPWM) strategy, which utilizes a chaotically changing switching frequency to spread the harmonics continuously to a wideband and to reduce the peak harmonics to a great extent. This can be an effective way to suppress the current harmonics and torque ripple in induction motor drives. The proposed CPWM scheme is simulated using MATLAB / SIMULINK software and implemented in three phase voltage source inverter (VSI) using field programmable gate array (FPGA).
Simulation and Design of SRF based Control Algorithm for Three Phase Shunt Ac...
Active power filters are effective in mitigating line
current harmonics and compensating for the reactive power
in the line. There are basically two types of Active Power
Filters (APFs): shunt type and series type. Shunt active power
filters (SAPFs) represent the most important and most widely
used filters in industrial purposes, this is due not only to the
fact that eliminate the harmonic current but also they are
suitable for a wide range of power ratings. In this paper,
Synchronous Reference Frame (SRF) theory is employed to
calculate compensating currents while the three phase source
is feeding a highly non-linear load. The main objective is to
study and investigate the performance of Shunt active power
filter using SRF theory. The algorithm is simulated under
M ATLAB
7.8
environment
using
Simulinkand
SimPowerSystems toolbox. The results shown are within the
IEEE Standard 512-1992.
N1102018691
This document summarizes a research paper on minimizing total harmonic distortion (THD) in a three-phase, five-level cascaded H-bridge inverter. It first describes the configuration and operation of a cascaded H-bridge multilevel inverter. It then reviews the generalized formulation of selective harmonic elimination (SHE) for multilevel inverters. The document presents a MATLAB/Simulink model of a three-phase, five-level inverter that compares sinusoidal pulse width modulation to SHE for harmonic reduction. Simulation results show that SHE reduces THD from 71.2% to 4.66% by eliminating specific lower-order harmonics through optimization of the switching angles.
Similar to Selective harmonic elimination (she) for 3 phase voltage source inverter (vsi) (1) (20)
ANALYSIS OF DISCRETE & SPACE VECTOR PWM CONTROLLED HYBRID ACTIVE FILTERS FOR ...
ANALYSIS OF DISCRETE & SPACE VECTOR PWM CONTROLLED HYBRID ACTIVE FILTERS FOR ...
Fuzzy Logic Controlled Harmonic Suppressor in Cascaded Multilevel Inverter
Fuzzy Logic Controlled Harmonic Suppressor in Cascaded Multilevel Inverter
A Tactical Chaos based PWM Technique for Distortion Restraint and Power Spect...
A Tactical Chaos based PWM Technique for Distortion Restraint and Power Spect...
Simulation and Design of SRF based Control Algorithm for Three Phase Shunt Ac...
Simulation and Design of SRF based Control Algorithm for Three Phase Shunt Ac...
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Solar pv charging station for electric vehicles
This document describes a project to design and simulate a solar photovoltaic charging station for electric vehicles using MATLAB/Simulink. The charging station employs a multi-port design to provide constant voltage DC power from the solar panels to charge vehicle batteries using a constant current/constant voltage method. The performance of the charging system is validated through simulation and experimental results. The conclusion discusses opportunities to enhance such systems through optimization techniques, energy storage, intelligent controllers, and hybrid designs incorporating multiple renewable energy sources.
Generation of Higher Number of Voltage Levels by Stacking Inverters of Lower ...
This paper proposes a new method of generating higher number of levels in the voltage waveform by stacking multilevel converters with lower voltage space vector structures. An important feature of this stacked structure is the use of low voltage devices while attaining higher number of levels. This will find extensive applications in electric vehicles since direct battery drive is possible. The voltages of all the capacitors in the structure can be controlled within a switching cycle using the switching state redundancies (pole voltage redundancies). This helps in reducing the capacitor size. Also, the capacitor voltages can be balanced irrespective of modulation index and load power factor. To verify the concept experimentally, a 9-level inverter is developed by stacking two 5-level inverters and an induction motor is run using V/f control scheme. Both steady state and transient results are presented.
Novel symmetric modular hybrid multilevel inverter with reduced number of sem...
In this paper, by using a modular hybrid structure, a new topology for symmetric multilevel inverters (MLI) with a small number of semiconductors and low voltage stress across switches is proposed. Despite many other topologies, this topology can inherently produce negative levels and zero levels without using the H-bridge. The voltage stress across a particular switch of the proposed MLI is inversely proportional to the number of the switching of that switch in a voltage period. The proposed structure is based on two types of module, that is, the f-module and the e-module. The e-module uses a capacitive voltage divider to double the number of non-zero levels. The voltages of the capacitors are approximately balanced without complex control methods. The basic structure of the proposed topology is formed by connecting the f-module and the e-module in series with each other, and the cascaded topology is developed by cascading multiple f-modules with an e-module. To investigate the proposed topology and proving its practicability, simulation results with MATLAB/Simulink, investigation of the capacitor voltages, loss calculations and experimental results are presented. A comparative study is also performed to show the merit of the new multilevel inverter over other topologies.
A Variable DC Link based Novel Multilevel Inverter Topology for Low Voltage A...
In this paper; a variable dc link based novel multilevel inverter (MLI) topology is proposed. This proposed topology comprises two variable dc links and a modified H-bridge unit. This new single-phase topology offers advantages such as reduction in count of switches; gate drivers and dc sources while simultaneously improving the power quality. The proposed topology has been analyzed for both symmetric and asymmetric modes of operation. A comparative study of the proposed topology with some recent MLI topologies has been presented. The comparative study indicates that the proposed topology requires less number of dc sources; switches and driver circuits as compared to other topologies. The proposed topology has been simulated for 31- level asymmetric configuration in MATLAB/SIMULINK environment to verify the proper operation of proposed topology. Harmonic analysis was also performed for 31-level inverter which showed significant reduction in the total harmonic distortion (THD) for phase voltage and current waveforms. The proposed topology is suitable for low voltage applications such as standalone photovoltaic (PV) systems and hybrid electric vehicles (HEVs).
A Simplified Space Vector Pulse-Width Modulation Scheme for Three-Phase Casca...
This document presents a simplified space vector pulse-width modulation (SVPWM) scheme for three-phase cascaded H-bridge inverters. It treats each unit as a three-level inverter and uses three-level SVPWM to modulate each unit individually. Duty cycles from sector 1 are mapped to obtain duty cycles for other sectors. This simplifies the process compared to conventional multilevel SVPWM. Simulation and experimental results validate the presented SVPWM scheme, which provides a higher effective switching frequency while maintaining the same DC-link voltage utilization as conventional SVPWM, with significantly reduced FPGA resource utilization.
A New Family of Step-up Hybrid Switched- Capacitor Integrated Multilevel Inve...
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A multi cell 21-level hybrid multilevel inverter synthesizes a reduced number...
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Power Quality Improvement of Grid-Connected Photovoltaic Systems Using Trans-...
Voltage-source inverter has been used widely in traditional photovoltaic systems which have limitations. To overcome, Z-source inverter has been introduced. In spite of all the features introduced in Z-source inverter, its configuration has been improved over the years, like trans-Z-source inverter which has added advantages compared to traditional inverters, namely buck–boost feature, lesser passive elements, and higher voltage boost gain. In this paper, photovoltaic arrays are connected to the grid via the trans-Z-source inverter with the aim of improving its power quality. Moreover, the shoot through duty ratio is kept constant in the switching control method to add features like lower voltage stress (higher reliability), lower total harmonic distortion (lower maintenance cost), and higher voltage boost ratio. To evaluate the precision of the proposed system, the photovoltaic system is simulated on a standard grid and under partial shading condition which brings about voltage sag, and hence, a dynamic voltage restorer is used to mitigate voltage sag. Simulation results are presented to verify the validation of the proposed photovoltaic system in terms of voltage and current THD reducing 78.2% and 19.7%, respectively.
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Power flow control of hybrid micro grids using modified uipc
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Electricity generation from the wind and solar photovoltaic (PV) systems are highly dependent upon weather conditions. Their intermittent nature leads to fluctuations in their output. Therefore, the need for rapid compensation for energy transmission and distribution systems is increasingly important. Static Synchronous Compensator (STATCOM) can be adopted for reactive power compensation and for decreasing the voltage fluctuation caused by the system and renewable energy sources. This study presents modelling of a Solar PV-Wind Hybrid Micro-grid and the increase of the stable operating limit of the system in case of the incorporation of STATCOM is examined. The major contribution of this paper is the optimization of gain parameters of four PI controllers in STATCOM control circuit based on genetic algorithms (GA) and Bacteria Foraging Algorithm (BFA) and therefore obtaining better responses and voltage stability in terms of nonlinear nature of solar-wind hybrid micro-grid. The Simulink models of the system architecture include a wind turbine model, a solar PV power system model and a STATCOM. It is certified that the voltage fluctuation at the end of the bus bar is reduced by 8% using conventional PI controller, by 10% for GA-based PI controller, and by 15% for BFA based PI controller under variable load. The results obtained by GA and BFA-based optimization of PI controllers are compared with that of the conventional controller and better results attained.
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Implementation of solar pv battery and diesel generator based electric vehic...
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Selective harmonic elimination (she) for 3 phase voltage source inverter (vsi) (1)
- 1. ELECTRICAL PROJECTS USING MATLAB/SIMULINK Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245 For Simulation Results of the project Contact Us Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245 Selective Harmonic Elimination (SHE) for 3-Phase Voltage Source Inverter (VSI) ABSTRACT: The Selective Harmonic Elimination (SHE) for 3-Phase Voltage Source Inverter (VSI) is presented here. The projected work investigates the Selective Harmonic Elimination (SHE) to eliminate harmonics produced by Pulse Width Modulation (PWM) inverter. The selective harmonic elimination method for three phase Voltage Source Inverter (VSI) is generally based on ideas of opposite harmonic injection. In this proposed scheme, the lower order harmonics (3rd, 5th, 7th, and 9th) are eliminated by the dominant harmonics of same order generated in opposite phase by Sinusoidal Pulse Width Modulation (SPWM) inverter and by using this scheme the Total Harmonic Distortion (THD) is reduced. Analysis of Sinusoidal Pulse Width Modulation (SPWM) technique and Selective Harmonic Elimination (SHE) is simulated using MATLAB/SIMULINK model. KEYWORDS: 1. Selective Harmonic Elimination (SHE) 2. Pulse Width Modulation (PWM) e 3. Total Harmonic Distortion (THD) and Voltage Source Inverter (VSI) SOFTWARE: MATLAB/SIMULINK
- 2. ELECTRICAL PROJECTS USING MATLAB/SIMULINK Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245 For Simulation Results of the project Contact Us Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245 CONCLUSION: The paper presents a selective harmonic elimination technique for three phase voltage source inverter with the RL load. A Three phase Voltage Source Inverter (VSI) changes DC input voltage to a three phase variable frequency variable voltage output. The elimination of specific low-order harmonics from a given voltage/current waveform achieved by Selective Harmonic Elimination (SHE) technique. We unite the inductor filter with the capacitor the ripple aspect will turn out to be more or less autonomous of the load filter. Finally Analysis and comparison of Total Harmonic Distortion (THD) for sinusoidal Pulse Width Modulation (PWM) technique and selective harmonic elimination technique has been done. From the comparison it is very apparent that the Total Harmonic Distortion (THD) for selective harmonic technique is less than that of sinusoidal Pulse Width Modulation (PWM) method. REFERENCES: [1] Ray, R.N., Chatterjee, and Goswami, S.K, “Reduction of voltage harmonic using optimization – based combined approach on” proceeding on IET Power Electronics, 3 (3). 334- 344. 2008. [2] Mohamed S.A.Dahidah and Vassilios G. Agelidis, “Selective harmonic elimination PWM control for Cascaded multilevel voltage source converters: A generalized formula” IEEE Trans on power electronics, 23(4). 1620-1630. Jul. 2008. [3] Wells, Jason R. Xin Geng, Chapman, Patrick L. and Krein, Philip T. “Modulation based harmonic elimination” IEEE Transactions on Power Electronics, 22(1). 2007. [4] Fellow, Javier Napoles, Jose Ignacio Leon, and Aguirre, Miguel A. “A flexible selective harmonic mitigation to meet grid codes in three level PWM converters” IEEE Transactions on Industrial Electronics, 54(6).Dec.2007. [5] Hadji, S. Touhami O. and C.J.Goodman, “Vector- optimized harmonic elimination for single- phase pulse width modulation inverters/converters” IET Electr.Power Appl.,1(3). 423-432. 2007