Ashok kumar A - Academia.edu (original) (raw)

Teaching Documents by Ashok kumar A

This paper deals with improving the voltage quality of sensitive loads from voltage sags using dy... more This paper deals with improving the voltage quality of sensitive loads from voltage sags using dynamic voltage restorer (DVR). The higher active power requirement associated with voltage phase jump compensation has caused a substantial rise in size and cost of dc link energy storage system of DVR. The existing control strategies either mitigate the phase jump or improve the utilization of dc link energy by (i) reducing the amplitude of injected voltage, or (ii) optimizing the dc bus energy support. In this paper, an enhanced sag compensation strategy is proposed that mitigates the phase jump in the load voltage while improving the overall sag compensation time.

Effective photovoltaic power conditioning requires efficient power conversion and accurate maximu... more Effective photovoltaic power conditioning requires efficient power conversion and accurate maximum power point tracking to counteract the effects of panel mismatch, shading, and general variance in power output during a daily cycle. In this paper, the authors propose an integrated boost resonant converter with low component count, galvanic isolation, simple control, as well as high efficiency across a wide input and load range. Provided is a discussion of the converter synthesis, key operational features, converter design procedure, and loss analysis, as well as experimental verification by way of a 250-W prototype with a California Energy Commission efficiency of 96.8%. KEYWORDS

Papers by Ashok kumar A

Abstract—This paper proposes a three-phase nine switch ac/ac converter topology. This converter f... more Abstract—This paper proposes a three-phase nine switch ac/ac converter topology. This converter features sinusoidal inputs and outputs, unity input power factor, and more importantly, low manufacturing cost due to its reduced number of active switches... A suitable pulse width modulation (PWM) technique is employed to obtain the required output voltage. The different methods for PWM generation can be broadly classified into Triangle comparison based PWM (TCPWM) and Space Vector based PWM (SVPWM). In TCPWM methods such as sine-triangle PWM, three phase reference modulating signals are compared against a common triangular carrier to generate the PWM signals for the three phases. In SVPWM methods, a revolving reference voltage vector is provided as voltage reference instead of three phase modulating waves. The magnitude and frequency of the fundamental component in the line side are controlled by the magnitude and frequency, respectively, of the reference vector. The highest possible p...

ashok kumar

Voltage-source converters (VSCs) and half bridge Modular Multilevel Converters (MMCs) are among t... more Voltage-source converters (VSCs) and half bridge Modular Multilevel Converters (MMCs) are among the most popular types of HVDC converters. One of their serious drawbacks is their vulnerable nature to DC side faults, since the freewheeling diodes act as a rectifier bridge and feed the DC faults. The severity of DC side faults can be limited by connecting double thyristor switches across the semiconductor devices. By turning them on, the AC current contribution into the DC side is eliminated and the DC-link current will freely decay to zero. The main disadvantages of this method are: high dv/dt stresses across thyrsitors during normal conditions, and absence of bypassing for the freewheeling diodes during DC faults as they are sharing the fault current with thyristors. This paper proposes a new protection scheme for HVDC converters (VSCs as well as MMCs). In this scheme, the double thyristor switches are combined and connected across the AC output terminals of the HVDC converter. The proposed scheme provides advantages such as lower dv/dt stresses and lower voltage rating of thyristor switches, in addition to providing full separation between the converter semiconductor devices and AC grid during DC side faults. A simulation case study has been carried out to demonstrate the effectiveness of the proposed scheme.

An Improved Torque and Current Pulsation Suppression Method for Railway Traction Drives Under Fluctuating DC-Link Voltage

For railway traction drives, the active front end usually adopts a single-phase rectifier. Howeve... more For railway traction drives, the active front end usually
adopts a single-phase rectifier. However, the dc-link voltage of this single-phase rectifier contains a second-order fluctuating component due to the fluctuation of the instantaneous power at both the ac and dc sides. Fed by the fluctuating dc-link voltage, the traction motor suffers from severe torque and current pulsation. The hardware
solution with an additional LC resonant filter is simple, but
it will reduce the power density of the system. An alternative solution is to eliminate the beat component in the stator voltage/current through modulation ratio or frequency compensation. However, it is difficult to achieve high performance for the conventional feedforward
method. In this paper, an improved closed-loop torque and
current pulsation suppression method is proposed, which can eliminate the q-axis current pulsation component in the field-oriented control system through frequency compensation. The torque pulsation suppression is also achieved automatically. Simulation and
experimental results show that the proposed scheme can effectively reduce the torque and current pulsation in various operation modes compared with the conventional feedforward method.

POWЕR QUALITY IMPROVEMENT IN POWЕR SYSTЕM BY USING SVPWM BASED STATIC SYNCHRONOUS SЕRIЕS COMPЕNSATOR

Power quality improvement is an important issue in power system. Flexible AC Transmission (FACTS)... more Power quality improvement is an important issue in power system. Flexible AC Transmission (FACTS)
devices are commonly used for solving problems related to power quality and improving it. In this paper a
synchronous static series compensator (SSSC) is used for control and modulation of power flow in a transmission
line. The Pulse Width Modulation (PWM) and SVPWM control techniques are employed in SSSC. The active
performance of SSSC is evaluated using Matlab/Simulink environment. The simulation results validate that the power quality is enhanced properly using SSSC.

Power System Stability Enhancement Using Static Synchronous Series Compensator (SSSC)

In this study, a static synchronous series compensator (SSSC) is used to investigate the effect o... more In this study, a static synchronous series compensator (SSSC) is used to investigate the effect of this device in controlling active and reactive powers as well as damping power system oscillations in transient mode. The SSSC equipped with a source of energy in the DC link can supply or absorb the reactive and active power to or from the line. Simulations have been done in MATLAB/SIMULINK environment. Simulation results obtained for selected bus-2 in two machine power system shows the efficacy of this compensator as one of the FACTS devices member in controlling power flows, achieving the desired value for active and reactive powers, and damping oscillations appropriately.

Electric Spring for Voltage and Power Stability and Power Factor Correction, 2017

Electric Spring (ES), a new smart grid technology, has earlier been used for providing voltage an... more Electric Spring (ES), a new smart grid technology,
has earlier been used for providing voltage and power stability in a weakly regulated/stand-alone renewable energy source powered grid. It has been proposed as a demand side management technique to provide voltage and power regulation. In this paper, a new control scheme is presented for the implementation of the electric spring, in conjunction with non-critical building loads like
electric heaters, refrigerators and central air conditioning system.This control scheme would be able to provide power factor correction of the system, voltage support, and power balance for the critical loads, such as the building's security system, in addition to the existing characteristics of electric spring of voltage
and power stability. The proposed control scheme is compared with original ES’s control scheme where only reactive-power is injected. The improvised control scheme opens new avenues for the utilization of the electric spring to a greater extent by providing voltage and power stability and enhancing the power quality in the renewable energy powered microgrids.

Control of a Three-Phase Hybrid Converter for a PV Charging Station, 2018

Hybrid boost converter (HBC) has been proposed to replace a dc/dc boost converter and a dc/ac con... more Hybrid boost converter (HBC) has been proposed to
replace a dc/dc boost converter and a dc/ac converter to reduce conversion stages and switching loss. In this paper, control of a three-phase HBC in a PV charging station is designed and tested. This HBC interfaces a PV system, a dc system with a hybrid plugin electrical vehicles (HPEVs) and a three-phase ac grid. The control of the HBC is designed to realize maximum power point
tracking (MPPT) for PV, dc bus voltage regulation, and ac voltage or reactive power regulation. A testbed with power electronics switching details is built in MATLAB/SimPowersystems for validation. Simulation results demonstrate the feasibility of the designed control architecture. Finally, lab experimental testing is
conducted to demonstrate HBC’s control performance.

An Improved Beatless Control Method of AC Drives for Railway Traction Converters

The traction converter consists of a singlephase AC-DC rectifier and a three-phase DC-AC inverter... more The traction converter consists of a singlephase
AC-DC rectifier and a three-phase DC-AC inverter.
Due to special structural characteristics of single phase
rectifier, a fluctuating voltage component with the
frequency twice of the grid’s, exists in DC-link voltage. Fed
by fluctuating DC-link voltage, a beat phenomenon occurs
in traction motor, and harmonic components appear in both stator current and electromagnetic torque, especially when motor operates near the ripple frequency. In this paper, the mechanism and influence of fluctuating voltage are analyzed in detail. Based on modeling analysis of motor and switching function of inverter, a frequency compensation factor is derived in vector control of induction motor. Then an improved frequency compensation control method is proposed to suppress beat phenomenon without LC resonant circuit. Finally the modified scheme is verified by simulation and experiment.

Integrated Photovoltaic and Dynamic Voltage Restorer System Configuration, 2015

This paper presents a new system configuration for integrating a grid-connected photovoltaic (PV)... more This paper presents a new system configuration for integrating a grid-connected photovoltaic (PV) system together with a self-supported dynamic voltage restorer (DVR). The proposed system termed as a “six-port converter,” consists of nine semiconductor switches in total. The proposed configuration retains all the essential features of normal PV and DVR systems while reducing the overall switch count from twelve to nine. In addition, the dual functionality feature significantly enhances the system robustness against severe symmetrical/asymmetrical grid faults and voltage dips. A detailed study on all the possible operational modes of six-port converter is presented. An appropriate control algorithm is developed and the validity of the proposed configuration is verified through extensive simulation as well as experimental studies under different operating conditions.

Dynamic Modeling, Design, and Simulation of a Combined PEM Fuel Cell and Ultracapacitor System for Stand-Alone Residential Applications, 2006

The available power generated from a fuel cell (FC) power plant may not be sufficient to meet sus... more The available power generated from a fuel cell (FC) power plant may not be sufficient to meet sustained load demands, especially during peak demand or transient events encountered in stationary power plant applications. An ultracapacitor (UC) bank can supply a large burst of power, but it cannot store a significant amount of energy. The combined use of FC and UC has the potential for better energy efficiency, reducing the cost of FC technology, and improved fuel usage. In this paper, we present an FC that operates in parallel with a UC bank. A new dynamic model and design methodology for an FC- and UC based energy source for stand-alone residential applications has been developed. Simulation results are presented using MATLAB, Simulink, and Sim Power Systems environments based on the mathematical and dynamic electrical models developed for the proposed system.

Distributed Cooperative Control and Stability Analysis of Multiple DC Electric Springs in a DC Microgrid, 2018

Recently, dc electric springs (dc-ESs) have been proposed to realize voltage regulation and power... more Recently, dc electric springs (dc-ESs) have been proposed to realize voltage regulation and power quality improvement in dc microgrids. This paper establishes a distributed cooperative control framework for multiple dc- ESs in a dc microgrid and presents the small-signal stability analysis of the system. The primary level implements a droop control to coordinate the operations of multiple dc-ESs. The secondary control is based on a consensus algorithm to regulate the dc-bus voltage reference, incorporating the state-of-charge (SOC) balance among dc-ESs. With the design, the cooperative control can achieve average dc-bus voltage consensus and maintain SOC balance among different dc-ESs using only neighbor-to-neighbor information. Furthermore, a small-signal model of a four dc-ESs system with the primary and secondary controllers is developed. The eigenvalue analysis is presented to show the effect of the communication weight on system stability. Finally, the effectiveness of the proposed control scheme and the small-signal model is verified in an islanded dc microgrid under different scenarios through simulation and experimental studies.

Control of Induction Motor Drive using Space Vector PWM, 2016

In this paper speed of induction motor is controlled which is fed from three phase bridge inverte... more In this paper speed of induction motor is controlled which is fed from three phase bridge inverter. In this paper the speed of an induction motor can be varied by varying
input Voltage or frequency or both. Variable voltage and
variable frequency for Adjustable Speed Drives (ASD) is
invariably obtained from a three-phase Voltage Source Inverter (VSI). Voltage and frequency of inverter can be easily controlled by using PWM techniques, which is a very important aspect in the application of ASDs. A number of PWM techniques are there to obtain variable voltage and variable frequency supply such as PWM, SPWM, SVPWM to name a few, among the various
modulation strategies SVPWM is one of the most efficient
techniques as it has better performance and output voltage is similar to sinusoidal. In SVPWM the modulation index in linear region will also be high when compared to other

Backstepping Control of Smart Grid-Connected Distributed Photovoltaic Power Supplies for Telecom Equipment, 2015

Backstepping controllers are obtained for distributed hybrid photovoltaic (PV) power supplies of ... more Backstepping controllers are obtained for distributed hybrid photovoltaic (PV) power supplies of telecommunication equipment. Grid-connected PV-based power supply units may contain dc–dc buck–boost converters linked to single-phase inverters. This distributed energy resource operated within the self consumption concept can aid in the peak-shaving strategy of ac smart grids. New backstepping control laws are obtained for the single-phase inverter and for the buck–boost converter feeding a telecom equipment/battery while sourcing the PV excess power to the smart grid or to grid supply the telecom system. The backstepping approach is robust and able to cope with the grid nonlinearity and uncertainties providing dc input current and voltage controllers for the buck–boost converter to track the PV panel maximum power point, regulating the PV output dc voltage to extract maximum power; unity power factor sinusoidal ac smart grid inverter currents and constant dc-link voltages suited for telecom equipment; and inverter bidirectional power transfer. Experimental results are obtained from a lab setup controlled by one inexpensive dsPIC running the sampling, the backstepping and modulator algorithms. Results show the controllers guarantee maximum power transfer to the telecom equipment/ac grid, ensuring steady dc-link voltage while absorbing/injecting low harmonic distortion current into the smart grid.

Analysis and Implementation of a Novel Bidirectional DC–DC Converter, 2012

A novel bidirectional dc–dc converter is presented in this paper. The circuit configuration of th... more A novel bidirectional dc–dc converter is presented in this paper. The circuit configuration of the proposed converter is very simple. The proposed converter employs a coupled inductor with same winding turns in the primary and secondary sides. In step-up mode, the primary and secondary windings of the coupled inductor are operated in parallel charge and series discharge to achieve high step-up voltage gain. In step-down mode, the primary and secondary windings of the coupled inductor are operated in series charge and parallel discharge to achieve high step-down voltage gain. Thus, the proposed converter has higher step-up and step-down voltage gains than the conventional bidirectional dc–dc boost/buck converter. Under same electric specifications for the proposed converter and the conventional bidirectional boost/buck converter, the average value of the switch current in the proposed converter is less than the conventional bidirectional boost/buck converter. The operating principle and steady-state analysis are discussed in detail. Finally, a 14/42-V prototype circuit is implemented to verify the performance for the automobile dual-battery system.

An Improved Torque and Current Pulsation Suppression Method for Railway Traction Drives Under Fluctuating DC-Link Voltage, 2018

For railway traction drives, the active front end usually adopts a single-phase rectifier. Howeve... more For railway traction drives, the active front end usually adopts a single-phase rectifier. However, the dc-link voltage of this single-phase rectifier contains a second-order fluctuating component due to the fluctuation of the instantaneous power at both the ac and dc sides. Fed by the fluctuating dc-link voltage, the traction motor suffers from severe torque and current pulsation. The hardware solution with an additional LC resonant filter is simple, but it will reduce the power density of the system. An alternative solution is to eliminate the beat component in the stator voltage/current through modulation ratio or frequency compensation. However, it is difficult to achieve high performance for the conventional feedforward method. In this paper, an improved closed-loop torque and current pulsation suppression method is proposed, which can eliminate the q-axis current pulsation component in the field-oriented control system through frequency compensation. The torque pulsation suppression is also achieved automatically. Simulation and experimental results show that the proposed scheme can effectively reduce the torque and current pulsation in various operation modes compared with the conventional feedforward method.

Design of an Efficient Dynamic Voltage Restorer for Compensating Voltage Sags, Swells, and Phase Jumps, 2014

This paper presents a novel design of a dynamic voltage restorer (DVR) which mitigate voltage sag... more This paper presents a novel design of a dynamic voltage restorer (DVR) which mitigate voltage sags, swell, and phase jumps by injecting minimum active power in system and provides the constant power at load side without any disturbance. The design of this compensating device presented here includes the combination of PWM-based control scheme, dq0 transformation and PI controller in control part of its circuitry, which enables it to minimize the power rating and to response promptly to voltage quality problems faced by today’s electrical power industries. An immense knowledge of power electronics was applied in order to design and model of a complete test system solely for analyzing and studying the response of this efficient DVR. In order to realize this control scheme of DVR MATLAB/SIMULINK atmosphere was used. The results of proposed design of DVR’s control scheme are compared with the results of existing classical DVR which clearly demonstrate the successful compensation of voltage quality problems by injecting minimum active power.

Conventional power factor correction (PFC) single ended primary inductor converter (SEPIC) suffer... more Conventional power factor correction (PFC) single ended primary inductor converter (SEPIC) suffers from high conduction loss at the input bridge diode. To solve this problem, a bridgeless SEPIC converter with ripple-free input current is proposed. In the proposed converter, the input bridge diode is removed and the conduction loss is reduced. In addition, the input current ripple is significantly reduced by utilizing an additional winding of the input inductor and an auxiliary capacitor. Similar to the conventional PFC SEPIC converter, the input current in a switching period is proportional to the input voltage and near unity power is achieved. The operational principles, steady-state analysis, and design equations of the proposed converter are described in detail. Experimental results from a 130Wprototype at a constant switching frequency of 100 kHz are presented to verify the performance of the proposed converter. KEYWORDS