Ashish Pandey - Academia.edu (original) (raw)

Papers by Ashish Pandey

Solar Energy Materials and Solar Cells, 2008

Maximum power point trackers (MPPTs) are used to track the peak output power of the solar photovo... more Maximum power point trackers (MPPTs) are used to track the peak output power of the solar photovoltaic sources. The maximum available power is tracked using specialized algorithms such as Perturb and Observe (P&O), which is an industry standard. The classical P&O algorithm requires the use of both voltage and current sensors. This algorithm has an inclination to drift away from desired operating point under rapidly changing atmospheric conditions. This classical algorithm also requires ad-hoc tuning measures at design time for selecting the right size of the search step. In most cost-and space-constrained systems, an algorithm with minimal sensing requirement, robust enough to cater to dynamic and steady-state requirements is desirable. The present work offers an algorithm involving simple computations and a single voltage sensor to arrive at and continuously track the maximum power point (MPP). In addition to eliminating drift during changing atmospheric conditions, the proposed method also provides self-tuning, variable search step that considerably improves dynamics and steady-state performance. A clear description and analysis of the algorithm is presented and verified experimentally on buck and boost converter topologies.

IEEE Transactions on Energy Conversion, 2008

The power available at the output of solar arrays keeps changing with solar insolation and ambien... more The power available at the output of solar arrays keeps changing with solar insolation and ambient temperature. Expensive and inefficient, the solar arrays must be operated at maximum power point (MPP) continuously for economic reasons. Of the numerous algorithms for this purpose, perturb and observe (P&O) is a standard. A derivative of gradient ascent method used in the optimization theory, this algorithm introduces a tradeoff between tracking and dynamic performance. This algorithm also has a tendency to drift the system away from the MPP as atmospheric conditions change. With continually changing atmospheric conditions, these inadequacies lead to poor utilization of solar arrays. This paper addresses both the issues. A variable-step-length algorithm is proposed to eliminate the tradeoff. The drift is minimized by evaluating the entire trend in a power versus voltage curve. Analytical results, validated on a prototype system show excellent performance.

IEEE Transactions on Power Electronics, 2007

Abstract—Maximum power point trackers (MPPTs) are used to ensure optimal utilization of solar cel... more Abstract—Maximum power point trackers (MPPTs) are used to ensure optimal utilization of solar cells. The implementation es-sentially involves sensing input current and voltage. An MPPT al-gorithm uses this information to maximize power drawn from the solar cells. ...

The focus of the present work is on introducing the power electronics community to the modelling ... more The focus of the present work is on introducing the power electronics community to the modelling and simulation of power factor corrected (PFC) converters. These techniques not only help to develop a deeper understanding of these converters but also to evaluate performance and feasibility of control strategies and topological features without fabrication of an actual system. Important PFC converter topologies

IEEE Transactions on Industrial Electronics, 2004

Three-phase ac-dc converters have been developed to a matured level with improved power quality i... more Three-phase ac-dc converters have been developed to a matured level with improved power quality in terms of power-factor correction, reduced total harmonic distortion at input ac mains, and regulated dc output in buck, boost, buck-boost, multilevel, and multipulse modes with unidirectional and bidirectional power flow. This paper presents an exhaustive review of three-phase improved power quality ac-dc converters (IPQCs) configurations, control strategies, selection of components, comparative factors, recent trends, their suitability, and selection for specific applications. It is aimed at presenting a state of the art on the IPQC technology to researchers, designers, and application engineers dealing with three-phase ac-dc converters. A classified list of around 450 research articles on IPQCs is also appended for a quick reference.

IEEE Transactions on Industrial Electronics, 2003

Solid-state switch-mode rectification converters have reached a matured level for improving power... more Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input ac mains and precisely regulated dc output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode ac-dc converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

Clinical Gastroenterology and Hepatology, 2002

In this work a simple and robust voltage controller is proposed to improve voltage dynamics in th... more In this work a simple and robust voltage controller is proposed to improve voltage dynamics in the power factor corrected (PFC) converters. The proposed controller eliminates twice the line frequency ripples from the voltage feedback path allowing large bandwidth design of voltage loop controller. As the voltage ripple is cancelled without any filtering, the controller action can be exercised at frequencies comparable to switching frequency. This eliminates large overshoots and undershoots during transients, which are common in conventionally designed PFC converters. The design of the proposed controller is described and simulation results are presented to demonstrate the feasibility of the proposed technique.

A novel DC bus voltage estimation algorithm with inherent cancellation of feedback voltage ripple... more A novel DC bus voltage estimation algorithm with inherent cancellation of feedback voltage ripple is presented in this work. Design issues are discussed and simulation results are presented. Apart from reduction of output voltage sensor, the proposed estimation algorithm also eliminates twice the line frequency ripple from the feedback path allowing a voltage controller bandwidth comparable to line frequency, suitable for most front-end power factor corrected (PFC) converter applications.

Analytica Chimica Acta, 2007

ABSTRACT

Bulletin of Materials Science, 2008

Ultrasonic mist chemical vapour deposition (UM-CVD) system has been developed to prepare ZnO nano... more Ultrasonic mist chemical vapour deposition (UM-CVD) system has been developed to prepare ZnO nanopowder. This is a promising method for large area deposition at low temperature inspite of being simple, inexpensive and safe. The particle size, lattice parameters and crystal structure of ZnO nanopowder are characterized by in situ high temperature X-ray diffraction (XRD). Surface morphology of powder was studied using transmission electron microscopy (TEM) and field emission electron microscope (FESEM). The optical properties are observed using UV-visible spectrophotometer. The influence of high temperature vacuum annealing on XRD pattern is systematically studied. Results of high temperature XRD showed prominent 100, 002 and 101 reflections among which 101 is of highest intensity. With increase in temperature, a systematic shift in peak positions towards lower 2θ values has been observed, which may be due to change in lattice parameters. Temperature dependence of lattice constants under vacuum shows linear increase in their values. Diffraction patterns obtained from TEM are also in agreement with the XRD data. The synthesized powder exhibited the estimated direct bandgap (E g ) of 3⋅43 eV. The optical bandgap calculated from Tauc's relation and the bandgap calculated from the particle size inferred from XRD were in agreement with each other.

Journal of Physics-condensed Matter, 2008

The Zn1-xCoxO thin films were prepared on a commercial glass substrate at 400 °C by ultrasonic sp... more The Zn1-xCoxO thin films were prepared on a commercial glass substrate at 400 °C by ultrasonic spray pyrolysis. The effect of doping concentration on the structural, optical and magnetic properties of these films has been studied. The structural and optical properties of these films reflect the fact that the Co2+ ions have substituted the Zn2+ ions without changing the wurtzite structure of ZnO. We have not observed any secondary phases even after doping the 10 at.% concentration of Co. All the films were highly oriented with preferred (002) direction. By increasing the Co content, a systematic change in both the c-axis lattice constant and the fundamental band gap energy was observed. Three absorption bands were found in the transmission spectra of the Co doped ZnO films at 657 nm (1.89 eV), 610 nm (2.03 eV) and 567 nm (2.20 eV). The absorption bands were attributed to d-d intraionic transitions of tetrahedrally coordinated high-spin Co2+ ions. Magnetic studies reveal the absence of room temperature ferromagnetic behaviour in these films. The values of coercivity (HC)~145 and 123 Oe and remanent magnetization (Mr)~4.32 × 10-5 and 7.28 emu cm-2 were observed at 5 K for Zn0.95Co0.05O and Zn0.93Co0.07O thin films.

Talanta, 2008

A new method for the determination of salbutamol has been developed using fullerene C 60 -modifie... more A new method for the determination of salbutamol has been developed using fullerene C 60 -modified glassy carbon electrode and validated using GC-MS. The presence of graphite and metallic impurities in C 60 are found to diminish the peak. The oxidation of salbutamol was observed in a single well-defined, diffusion-controlled process using square wave voltammetry. The peak potential of oxidation peak was dependent on pH and determination was carried out at physiological pH 7.4. The peak current versus concentration plot was linear in the range 100-2000 ng/ml of salbutamol. The detection limit was found to be 40 ng/ml. The determination of salbutamol was carried out in human blood and urine samples and common interferents such as dopamine, ascorbic acid and uric acid do not interfere. The method proved to be specific, rapid, and accurate and can be easily applied for detecting cases of doping. A cross-validation of the observed results with GC-MS indicated a good agreement. (R.N. Goyal).

Solar Energy Materials and Solar Cells, 2008

Maximum power point trackers (MPPTs) are used to track the peak output power of the solar photovo... more Maximum power point trackers (MPPTs) are used to track the peak output power of the solar photovoltaic sources. The maximum available power is tracked using specialized algorithms such as Perturb and Observe (P&O), which is an industry standard. The classical P&O algorithm requires the use of both voltage and current sensors. This algorithm has an inclination to drift away from desired operating point under rapidly changing atmospheric conditions. This classical algorithm also requires ad-hoc tuning measures at design time for selecting the right size of the search step. In most cost-and space-constrained systems, an algorithm with minimal sensing requirement, robust enough to cater to dynamic and steady-state requirements is desirable. The present work offers an algorithm involving simple computations and a single voltage sensor to arrive at and continuously track the maximum power point (MPP). In addition to eliminating drift during changing atmospheric conditions, the proposed method also provides self-tuning, variable search step that considerably improves dynamics and steady-state performance. A clear description and analysis of the algorithm is presented and verified experimentally on buck and boost converter topologies.

IEEE Transactions on Energy Conversion, 2008

The power available at the output of solar arrays keeps changing with solar insolation and ambien... more The power available at the output of solar arrays keeps changing with solar insolation and ambient temperature. Expensive and inefficient, the solar arrays must be operated at maximum power point (MPP) continuously for economic reasons. Of the numerous algorithms for this purpose, perturb and observe (P&O) is a standard. A derivative of gradient ascent method used in the optimization theory, this algorithm introduces a tradeoff between tracking and dynamic performance. This algorithm also has a tendency to drift the system away from the MPP as atmospheric conditions change. With continually changing atmospheric conditions, these inadequacies lead to poor utilization of solar arrays. This paper addresses both the issues. A variable-step-length algorithm is proposed to eliminate the tradeoff. The drift is minimized by evaluating the entire trend in a power versus voltage curve. Analytical results, validated on a prototype system show excellent performance.

IEEE Transactions on Power Electronics, 2007

Abstract—Maximum power point trackers (MPPTs) are used to ensure optimal utilization of solar cel... more Abstract—Maximum power point trackers (MPPTs) are used to ensure optimal utilization of solar cells. The implementation es-sentially involves sensing input current and voltage. An MPPT al-gorithm uses this information to maximize power drawn from the solar cells. ...

The focus of the present work is on introducing the power electronics community to the modelling ... more The focus of the present work is on introducing the power electronics community to the modelling and simulation of power factor corrected (PFC) converters. These techniques not only help to develop a deeper understanding of these converters but also to evaluate performance and feasibility of control strategies and topological features without fabrication of an actual system. Important PFC converter topologies

IEEE Transactions on Industrial Electronics, 2004

Three-phase ac-dc converters have been developed to a matured level with improved power quality i... more Three-phase ac-dc converters have been developed to a matured level with improved power quality in terms of power-factor correction, reduced total harmonic distortion at input ac mains, and regulated dc output in buck, boost, buck-boost, multilevel, and multipulse modes with unidirectional and bidirectional power flow. This paper presents an exhaustive review of three-phase improved power quality ac-dc converters (IPQCs) configurations, control strategies, selection of components, comparative factors, recent trends, their suitability, and selection for specific applications. It is aimed at presenting a state of the art on the IPQC technology to researchers, designers, and application engineers dealing with three-phase ac-dc converters. A classified list of around 450 research articles on IPQCs is also appended for a quick reference.

IEEE Transactions on Industrial Electronics, 2003

Solid-state switch-mode rectification converters have reached a matured level for improving power... more Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input ac mains and precisely regulated dc output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode ac-dc converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

Clinical Gastroenterology and Hepatology, 2002

In this work a simple and robust voltage controller is proposed to improve voltage dynamics in th... more In this work a simple and robust voltage controller is proposed to improve voltage dynamics in the power factor corrected (PFC) converters. The proposed controller eliminates twice the line frequency ripples from the voltage feedback path allowing large bandwidth design of voltage loop controller. As the voltage ripple is cancelled without any filtering, the controller action can be exercised at frequencies comparable to switching frequency. This eliminates large overshoots and undershoots during transients, which are common in conventionally designed PFC converters. The design of the proposed controller is described and simulation results are presented to demonstrate the feasibility of the proposed technique.

A novel DC bus voltage estimation algorithm with inherent cancellation of feedback voltage ripple... more A novel DC bus voltage estimation algorithm with inherent cancellation of feedback voltage ripple is presented in this work. Design issues are discussed and simulation results are presented. Apart from reduction of output voltage sensor, the proposed estimation algorithm also eliminates twice the line frequency ripple from the feedback path allowing a voltage controller bandwidth comparable to line frequency, suitable for most front-end power factor corrected (PFC) converter applications.

Analytica Chimica Acta, 2007

ABSTRACT

Bulletin of Materials Science, 2008

Ultrasonic mist chemical vapour deposition (UM-CVD) system has been developed to prepare ZnO nano... more Ultrasonic mist chemical vapour deposition (UM-CVD) system has been developed to prepare ZnO nanopowder. This is a promising method for large area deposition at low temperature inspite of being simple, inexpensive and safe. The particle size, lattice parameters and crystal structure of ZnO nanopowder are characterized by in situ high temperature X-ray diffraction (XRD). Surface morphology of powder was studied using transmission electron microscopy (TEM) and field emission electron microscope (FESEM). The optical properties are observed using UV-visible spectrophotometer. The influence of high temperature vacuum annealing on XRD pattern is systematically studied. Results of high temperature XRD showed prominent 100, 002 and 101 reflections among which 101 is of highest intensity. With increase in temperature, a systematic shift in peak positions towards lower 2θ values has been observed, which may be due to change in lattice parameters. Temperature dependence of lattice constants under vacuum shows linear increase in their values. Diffraction patterns obtained from TEM are also in agreement with the XRD data. The synthesized powder exhibited the estimated direct bandgap (E g ) of 3⋅43 eV. The optical bandgap calculated from Tauc's relation and the bandgap calculated from the particle size inferred from XRD were in agreement with each other.

Journal of Physics-condensed Matter, 2008

The Zn1-xCoxO thin films were prepared on a commercial glass substrate at 400 °C by ultrasonic sp... more The Zn1-xCoxO thin films were prepared on a commercial glass substrate at 400 °C by ultrasonic spray pyrolysis. The effect of doping concentration on the structural, optical and magnetic properties of these films has been studied. The structural and optical properties of these films reflect the fact that the Co2+ ions have substituted the Zn2+ ions without changing the wurtzite structure of ZnO. We have not observed any secondary phases even after doping the 10 at.% concentration of Co. All the films were highly oriented with preferred (002) direction. By increasing the Co content, a systematic change in both the c-axis lattice constant and the fundamental band gap energy was observed. Three absorption bands were found in the transmission spectra of the Co doped ZnO films at 657 nm (1.89 eV), 610 nm (2.03 eV) and 567 nm (2.20 eV). The absorption bands were attributed to d-d intraionic transitions of tetrahedrally coordinated high-spin Co2+ ions. Magnetic studies reveal the absence of room temperature ferromagnetic behaviour in these films. The values of coercivity (HC)~145 and 123 Oe and remanent magnetization (Mr)~4.32 × 10-5 and 7.28 emu cm-2 were observed at 5 K for Zn0.95Co0.05O and Zn0.93Co0.07O thin films.

Talanta, 2008

A new method for the determination of salbutamol has been developed using fullerene C 60 -modifie... more A new method for the determination of salbutamol has been developed using fullerene C 60 -modified glassy carbon electrode and validated using GC-MS. The presence of graphite and metallic impurities in C 60 are found to diminish the peak. The oxidation of salbutamol was observed in a single well-defined, diffusion-controlled process using square wave voltammetry. The peak potential of oxidation peak was dependent on pH and determination was carried out at physiological pH 7.4. The peak current versus concentration plot was linear in the range 100-2000 ng/ml of salbutamol. The detection limit was found to be 40 ng/ml. The determination of salbutamol was carried out in human blood and urine samples and common interferents such as dopamine, ascorbic acid and uric acid do not interfere. The method proved to be specific, rapid, and accurate and can be easily applied for detecting cases of doping. A cross-validation of the observed results with GC-MS indicated a good agreement. (R.N. Goyal).