Wajiha Shireen | University of Houston (original) (raw)

Papers by Wajiha Shireen

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

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

IEEE Transactions on Industry Applications, Nov 1, 1994

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.

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

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

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

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 ...

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.

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

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 ...

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

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

IEEE Transactions on Industry Applications, Nov 1, 1994

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.

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

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

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

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 ...

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.

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

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 ...