Wajiha Shireen - Profile on Academia.edu (original) (raw)

Papers by Wajiha Shireen

A DC voltage notching scheme for zero voltage switching (ZVS) of PWM inverters

This paper presents a DC voltage notching scheme for zero voltage switching (ZVS) of PWM inverter... more This paper presents a DC voltage notching scheme for zero voltage switching (ZVS) of PWM inverters. The proposed scheme permits programmed DC voltage notching, i.e. the DC voltage can be brought to zero on command to facilitate ZVS of the inverter switches. This is achieved without any over voltage excursion in the DC-link and with minimal additional components. The proposed

In this paper analysis of a three phase PWM inverter system, with harmonic assessment of the inve... more In this paper analysis of a three phase PWM inverter system, with harmonic assessment of the inverter input current and output voltage with balanced and unbalanced loads is presented. The analytical procedure and the simulation results presented show how MATLAB can be used as an effective tool to analyze a PWM inverter. Advantages of using MATLAB are: faster response, availability of various simulation tools and functional blocks and the absence of convergence problems. The analytical procedure and simulation outlined in this paper can be used as an educational tool to make the concepts of modern power conversion schemes comprehensible to students.

Electrolytic capacitors used in photovoltaic (PV) power conditioning units (PCU) for power decoup... more Electrolytic capacitors used in photovoltaic (PV) power conditioning units (PCU) for power decoupling purposes are less reliable in nature. Film capacitors can be adopted instead of electrolytic capacitors if the energy storage requirement of the PCU is reduced, since they offer better reliability and have a longer lifetime. The energy storage capacitor size reduction is facilitated by allowing DC-link voltage to have a specified amount of ripple. However, a high DC-link voltage ripple imposes a double-line frequency ripple in the PV panel voltage and current. This leads to oscillations in the extracted panel power and thereby results in power loss. In view of this, this thesis develops a locus line based maximum power point tracking (MPPT) control algorithm to mitigate this power loss. The proposed digital control algorithm was simulated in MATLAB Simulink and implemented in a laboratory prototype using the Digital Signal Processing

This paper presents the hardware and software aspects of a Digital Signal Processor (DSP) based c... more This paper presents the hardware and software aspects of a Digital Signal Processor (DSP) based controller for AC Induction motors. The hardware part of the setup consists of a DSP module, a three-phase inverter module and an interface module. The system implementation involves the use of different software modules to achieve the desired variable speed operation in open loop or closed loop. This setup can be effectively utilized to demonstrate to students the various motor control functions for variable speed operation and how it can be controlled in software by a DSP controller. DSP based systems have become an indispensable part of many modern equipment and industrial processes. Laboratory experience from the setup presented in this paper will familiarize the students to state of the art variable speed motor control methods that are being used in the industries. The setup can also be used as a research platform to test different motor control algorithms.

DSP-based control for reliable fuel cell power systems with input ripple current compensation

ABSTRACT Fuel cell power systems have increasingly become popular because of their inherent advan... more ABSTRACT Fuel cell power systems have increasingly become popular because of their inherent advantages over conventional energy systems. A fuel cell system typically requires some kind of power conditioning that usually includes a DC-DC converter and a DC-AC inverter. In a single phase system, the operation of a single phase inverter introduces a second harmonic (120 Hz) current ripple into the system. This ripple has been found to be detrimental to the performance, life and efficiency of the fuel cell if it is not adequately controlled. This paper proposes an active filtering method to cancel the second harmonic current ripple drawn from the fuel cell source in a single phase fuel cell system. This approach provides an alternate path for the 120 Hz current preventing it from flowing through the fuel cell. The conventional and the proposed systems have been simulated using PSpice and the results have been presented. Experimental results from a laboratory prototype are also included to validate the proposed approach. A major feature of this implementation is the use of a DSP TMS 320F2808 for the overall control and monitoring of the system.

Journal of Power Sources, Apr 1, 2007

This paper presents a DSP based algorithm to control inverters used in interfacing alternate ener... more This paper presents a DSP based algorithm to control inverters used in interfacing alternate energy systems with the electric utility. Since a constant and ripple free dc bus voltage is not ensured at the output of alternate energy sources, the main aim of the proposed algorithm is to make the output of the inverter immune to the fluctuations in the dc input voltage. In this paper a modified space vector pulse width modulation (SVPWM) technique is proposed which will maintain the quality of the ac output of the inverter, regardless of the ripple present at the inverter input. The principle is explained qualitatively and extensive experiments have been carried out to verify and validate the proposed algorithm. A 16-bit fixed-point C2000 family DSP from Texas Instruments was used as the controller to implement the proposed control algorithm.

IEEE Transactions on Industry Applications, Nov 1, 1994

Neutral current in three-phase power systems is often thought to be only the result of the imbala... more Neutral current in three-phase power systems is often thought to be only the result of the imbalance of the phase currents. With computer systems, very high neutral currents have been observed even when the phase currents are balanced. Recent surveys of 415V/230V three-phase four-wire electric systems, buildings and industrial plants with computers and nonlinear loads show excessive currents in the neutral. These neutral currents are fundamentally third harmonic and their presence is tied to wiring failures, elevating of neutral potentials, transformer overheating, etc. In response to these concerns, this paper proposes a active power filter scheme to cancel neutral current. The closed loop control of the active power filter guarantees cancellation of neutral current harmonics under varying load conditions. The neutral current In is sensed via a current sensor and is processed through a 50 Hz notch filter in order to remove any fundamental current component in In. The filtered current signal is then compared with Iref., which is set to zero. The resulting error signal is fed to the PWM control logic in order to inject an equal and opposite current In, thereby achieving cancellation in closed loop. This current injection technique neutralizes any harmonic current that is flowing in the neutral. The circuit is simulated and the result is verified with MATLAB7/SIMULINK.

Adaptive sensorless Maximum Power Point Tracking control for PMSG Wind Energy Conversion Systems

The major constraints encountered by a conventional Maximum Power Point Tracking (MPPT) control f... more The major constraints encountered by a conventional Maximum Power Point Tracking (MPPT) control for Wind Energy Conversion Systems (WECS) are perturbation speed versus control efficiency trade-off, use of mechanical sensors and system dependent characteristics. In view of these drawbacks, this paper presents a novel sensorless adaptive control for MPPT in WECS. The proposed control allows the generator to track the optimal operating point of the WECS under fluctuating wind conditions by an efficient two-step tracking process. The first step adapts an intelligent iterative approach to update the duty cycle of the boost converter to coordinate with the rapid changes in the wind conditions. A novel scanning process is initiated in succession with the iterative approach to counteract the non-constant efficiencies of the generator-converter subsystems in order to fine tune the obtained MPP. The performance of the proposed method is verified in simulation (PSCAD/EMTDC) and experimental results from a hardware prototype are also presented. The proposed method is compared with conventional perturb and observer (P&O) MPPT controller. The obtained results clearly demonstrates that the proposed control is more efficient than other conventional methods.

Active Filtering of Input Ripple Current to Obtain Efficient and Reliable Power from Fuel Cell Sources

ABSTRACT Fuel cells are one of the cleanest and most efficient technologies for generating electr... more ABSTRACT Fuel cells are one of the cleanest and most efficient technologies for generating electricity. In most cases, the fuel cell associated power conditioning system must include a DC-DC converter and a DC to AC inverter. Inverter input ripple current has been reported to possibly degrade fuel cell performance and reduce operating life if ripple currents are not adequately controlled. This paper proposes an active filtering method to cancel the 2nd harmonic current ripple drawn from the fuel cell source in a typical single phase fuel cell system. The proposed active harmonic filter provides an alternate path for the 120 Hz ripple, thereby, preventing the ripple from circulating through the source. The proposed system was simulated using PSpice and the results are presented. Experimental results from a laboratory prototype are also included to validate the proposed approach

IEEE Transactions on Energy Conversion, 1996

The foreseeable shortages in conventional sources of electric power has increased the emphasis on... more The foreseeable shortages in conventional sources of electric power has increased the emphasis on the research and development of alternate sources of energy. In order to make a noteworthy impact, the alternate sources of energy need to be utility interactive by means of a power electronic interface (a dc to ac converter). The inherent assumption in the control of dc to ac converters is, that the dc voltage available at the input of the converter is constant. However, when the input is an unregulated dc source such as: a battery, fuel cell, photovoltaic cells or any other form of alternate source, maintenance of the constant dc voltage at the input of the converter is often impossible. A modified inverter switching technique is proposed for the interface with the utility grid such that the ac output of the inverter becomes immune to fluctuations in the unregulated input dc obtained from alternate energy sources. I. INTRODUCTION: The threatened limitations on conventional sources of electric power, posed by future shortages of fossil and nuclear fission fuels and the reduced availability of Iiydroelectric power sites, has focused attention on "unconventional" sources or "alternate" sources of electric power. Renewable and nonpolluting sources of energy such as sun and wind have an enormous potential to supplement the fossil and nuclear based generation of electricity. Also, there has been 96 WM 043-0 EC A paper recommended and approved by the IEEE Energy Development and Power Generation Committee of the IEEE Power Engineering Society for presentation at the 1996 IEEEPES Winter Meeting,

An efficient robust MPPT control for grid-connected photovoltaic systems with reduced DC link capacitance

ABSTRACT

A DSP Based SVPWM Control for Utility Interactive Inverters used in Alternate Energy Systems

Implementation of a DSP based active power filter for electric power distribution systems supplying nonlinear loads

The use of nonlinear loads, which inject undesired harmonic currents into low voltage distributio... more The use of nonlinear loads, which inject undesired harmonic currents into low voltage distribution systems, is increasing rapidly. Active power filters are being considered as a potential candidate for solving harmonic problems in order to meet harmonic standards and guidelines. A new digital signal processor (DSP) based control method for a single phase active power filter (APF) is presented in this paper. Compared to conventional analog and microprocessor based methods the DSP based solution provides a flexible and cheaper method to control the APF. The proposed scheme employs a carrier based control that requires less feedback information compared to other reported solutions. Only one current sensor is used to sense the nonlinear load current and two voltage sensors to sense the input supply voltage and the DC bus voltage. It also reduces the total chip count of the system using on-chip power electronics peripherals of the DSP controller (TMS320F240). The proposed method provides both harmonic elimination and power factor correction. The PSpice simulation and experiments using the DSP controller are made to verify the feasibility of the method

Analysis and minimization of input ripple current in PWM inverters for designing reliable fuel cell power systems

Journal of Power Sources, Jun 1, 2006

This paper presents the implementation of a technique to minimize the input ripple current in thr... more This paper presents the implementation of a technique to minimize the input ripple current in three-phase voltage-source pulse width modulated (PWM) inverters when supplying unbalanced/nonlinear loads. This is achieved without increasing the KVA ratings of the dc ...

Energies, Nov 17, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Control and Design Aspects of Power Electronics Converters Using Pspice

Advanced Technology for Learning, 2006

In order to understand the functionality and design aspects of power converters, circuit simulati... more In order to understand the functionality and design aspects of power converters, circuit simulation software PSpice has become an industry standard. In a Power Electronics course the students are required to understand the operating principles of a variety of static power converters using different control techniques to achieve the desired input-output characteristics.This paper presents PSpice-based design projects that can be used as pre-Lab exercises in a Laboratory course accompanying a lecture course in Power Electronics. The students can be made to implement their design in the laboratory with actual hardware components. The transition from design to simulation and finally to experimental verification will aid to strengthen their understanding of the operation, control, and design aspects of power converters. The design projects are geared towards bringing out the importance of power quality and cost issues that are relevant to state of the art circuit design.The design examples in the paper will start with a set of design guidelines and input-output requirements of a given power converter system. The design will involve selection of the proper control algorithm, switching frequency, and input-output filter values to meet the design goals. The following are the basic converter systems that will be covered in the various design projects: single phase and three phase rectifier, single phase and three phase inverters, buck and boost converter.

Power Electronics is an important emerging technology and has become an integral part of power en... more Power Electronics is an important emerging technology and has become an integral part of power engineering education. This paper addresses the critical challenge of educating the future Electric Power Engineers in this rapidly developing multidisciplinary field. Special emphasis is placed on design aspects of power electronics by incorporating pre-Labs involving PSpice simulation. This allows the students to have a good understanding of the circuit design and operation before they get the hands on experience from the actual hardware experiments. This paper will disseminate the results of the newly developed laboratory experiments that have been implemented so far, along with the initial assessment data gathered by an independent evaluator.

Her current research interests are in the area of power electronics which includes advanced conve... more Her current research interests are in the area of power electronics which includes advanced converters for power supplies, power quality issues, active power filter development, utility interface issues, power conditioning systems for fuel cells, wind and solar energy systems. She holds one US patent with industry collaboration. She is an IEEE Senior member and is actively involved in funded research projects while engaged in teaching, research and consulting in the area of power electronics, motor drives, power quality and clean power utility interface issues.

A MCT-based zero voltage switching PWM inverter

ABSTRACT This paper presents a MOS-controlled thyristor (MCT) based zero voltage switching (ZVS) ... more ABSTRACT This paper presents a MOS-controlled thyristor (MCT) based zero voltage switching (ZVS) scheme for PWM inverters. The proposed scheme utilizes a front end DC voltage notching circuit consisting of auxiliary switches and resonant components. This allows the DC link voltage to be brought to zero on command. MCTs are used as auxiliary devices since MCTs were designed for enhanced dynamic performance under ZVS conditions. A detailed analysis of the circuit operation is presented. The feasibility of the proposed scheme is experimentally verified on an inverter

A soft switching inverter module with modified DC-link circuit for high frequency DC-AC power conversion

Page 1. A Soft Switching Inverter Module with Modified DC-Link Circuit for High Frequency DC-AC P... more Page 1. A Soft Switching Inverter Module with Modified DC-Link Circuit for High Frequency DC-AC Power Conversion Wajiha Shireen IEEE Senior Member 4800 Calhoun College of Technology University of Houston Houston, TX 77204-4022 ...