Oruganti,Ramesh

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eleramsh@nus.edu.sg


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Now showing 1 - 10 of 76
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    Evaluation of power losses in a boost PFC unit by temperature measurements
    (2006) Viswanathan, K.; Oruganti, R.; ELECTRICAL & COMPUTER ENGINEERING
    High power conversion efficiency is an important requirement of the front-end power-factor corrected (PFC) boost rectifier used in shaping the ac input current in a typical modern off-line power supply. A reasonably accurate estimate of the power losses in individual components is essential in order to improve the efficiency of the PFC rectifier. In this paper, difficulties in the measurement of individual component power losses with particular reference to an ac-dc converter are brought out. A method of loss evaluation by measurement of temperatures of individual components and surrounding ambient is presented. Experimental results carried out on the front-end boost PFC rectifier of a commercial ac-dc converter are presented to validate the loss estimation method. © 2006 IEEE.
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    Small signal analysis and closed loop control design of L-L type active-clamped ZVS current-fed isolated DC-DC converter
    (2009) Rathore, A.K.; Bhat, A.K.S.; Oruganti, R.; ELECTRICAL & COMPUTER ENGINEERING
    This paper presents the small signal model and closed loop control design using average current control for an L-L type active-clamped zero-voltage switching (ZVS) current-fed isolated DC-DC converter. State-space averaging technique is used to derive the small signal model. The controller is designed for fixed-frequency duty cycle modulation and works for wide input voltage and load variation. A complete design procedure is presented. Frequency response curves are obtained at different input voltage and load conditions to verify the stability and design, and to evaluate the performance of the controller. Simulation results for step changes in input voltage and load are given to check the transient response of the converter. ©2009 IEEE.
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    Novel PFC scheme for AC to DC converter with reduced losses
    (1994) Oruganti, Ramesh; Thean, Cham Yew; ELECTRICAL ENGINEERING
    A novel single phase ac to dc power factor correction (PFC) scheme named boost bypass control (BBC) is presented. Here, the conventional boost PFC circuit drawing a sinewave input current is bypassed during input ac voltage peaks by a rectifier resulting in lower rated power components and acceptable power factor. The proposed control scheme controls directly the power shared between the boost path and the bypass path. The viability of such a scheme is established theoretically and experimentally. Practical implementation of the BBC scheme as well as experimental results are presented.
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    Modeling of hysteresis loops of ferrite cores excited by a transient magnetic field
    (1998) Mi, N.L.; Oruganti, R.; ELECTRICAL ENGINEERING
    This paper presents a modified Jiles-Atherton model for calculating the transient magnetization trajectory of a ferrite core. It is an integrated model without calculating the irreversible and reversible magnetization components and their volume fractions separately. With the loop by loop technique proposed by authors, the magnetization trajectory with asymmetric minor loop excursion under arbitrary waveform magnetic field excitation can be easily obtained. The modified model and the proposed technique are verified experimentally using a toroidal inductor. The agreement between simulation and experimental result is good. © 1998 IEEE.
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    An asymmetrical half bridge DC-DC converter : Close loop design in frequency domain
    (2004) Xu, X.; Khambadkone, A.M.; Oruganti, R.; ELECTRICAL & COMPUTER ENGINEERING
    In this paper, the small signal model analysis of an Asymmetrical Half-Bridge DC-DC Converter (AHBC) operating in the continuous conduction mode (CCM) is presented. The influence of the non-ideal components to the system performance is discussed. Based on the small signal model, the close loop feedback is designed in the frequency domain for a PI controller and a lead-lag controller. The design criteria for the close loop feedback is described and a clear design process for the feedback compensator is presented. How to achieve the optimum bandwidth and phase margin under the influence of the complicated system structure is investigated. The close loop system load dynamic response from a 12V/4A experiment circuit is obtained.
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    A low cost high efficiency inverter for photovoltaic AC module application
    (2010) Li, Y.; Oruganti, R.; ELECTRICAL & COMPUTER ENGINEERING
    The unfolding-type flyback inverter operating in Discontinuous Conduction Mode (DCM) has been previously investigated as a low cost solution for a photovoltaic AC module application. The aim of the present work is to improve the efficiency of the scheme by adopting Continuous Conduction Mode (CCM) operation. The paper presents the control modeling and analysis of the flyback-CCM inverter and discusses its control challenges. These include 1) the presence of a right-half plane (RHP) zero in the direct output current control transfer function, 2) the inevitable DCM operation when the instantaneous AC voltage is low, and 3) issues associated with the large variation in the power level. An indirect average current control scheme to avoid the problem of the RHP zero has been proposed and its effectiveness verified experimentally. The results show an improvement of 7.4% in the weighted California efficiency over the benchmark flyback-DCM scheme for a 200W PV panel. The total harmonics distortion and output power factor satisfy IEC61727. Practical implementation problems faced in the sensing of current are also addressed. © 2010 IEEE.
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    Closed loop control design of two inductor current-fed isolated DC-DC converter for fuel cells to utility interface application
    (2008) Rathore, A.K.; Bhat, A.K.S.; Nandi, S.; Oruganti, R.; ELECTRICAL & COMPUTER ENGINEERING
    This paper presents a closed loop control design for a two inductor active-clamped ZVS current-fed isolated DC-DC converter using two-loop average current control. State-space averaging technique is used to derive the small signal model. The controller is designed for fixed frequency duty cycle modulation and works for wide input voltage and load variation. A complete design procedure is presented. Experimental results for step-change in load are presented at different input voltage conditions. © 2008 IEEE.
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    High-performance control of a UPS inverter through iterative learning based on zero-phase filtering
    (2004) Deng, H.; Oruganti, R.; Srinivasan, D.; ELECTRICAL & COMPUTER ENGINEERING
    The purpose of a voltage controller for UPS inverters is to produce stable and regulated output voltage with low distortion under all loading conditions, especially under nonlinear loads. Since the loads which cause the tracking errors in the output voltage are typically periodic, iterative learning control is an obvious and excellent intuitive choice for achieving this close voltage tracking. In this paper, an iterative learning controller based on zero-phase filtering is directly combined with the open-loop UPS inverter. Due to the feedforward involved in the open-loop inverter operation, the overall dynamic response can be expected to be reasonably satisfactory. A zero-phase filter designed in frequency domain is applied to compensate the open-loop inverter so as to ensure error convergence. This acts to compensate the poor dynamics of the inverter owing to the presence of the L-C circuit. Furthermore, a 'forgetting factor' is introduced in this control algorithm to increase the robustness of the scheme against measurement noise, initialization error and/or variation of system dynamics due to parameter drift. The experimental results show that the proposed controller can achieve very low total harmonic distortion and fast error convergence under different loads even with only one sensor. The proposed method can be an effective solution for UPS products where high-quality output voltage is more important than fast dynamic response. © 2004 IEEE.
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    Soft-switched DC/DC converter with PWM control
    (1998) Oruganti, R.; Heng, P.C.; Guan, J.T.K.; Choy, L.A.; ELECTRICAL ENGINEERING
    In this paper, a new converter with two variations is proposed. A novel asymmetrical pulse-width-modulation (PWM) control scheme is used to control the converter under constant switching frequency operation. The modes of operation for both variations are discussed. The dc characteristics, which can be used in the design of the converters, are also presented. Two 50-W converters were built to verify the characteristics of the converters. Due to the zero-voltage-switching (ZVS) operation of the switches and low device voltage and current stresses, the converter has high full- and partial-load efficiencies. They are potential candidates for high-efficiency high-density power supplies application.
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    A unity power factor converter using half-bridge boost topology
    (1998) Srinivasan, R.; Oruganti, R.; ELECTRICAL ENGINEERING
    A single-phase high-efficiency near-unity power-factor (PF) half-bridge boost converter circuit, which has been proposed earlier by other researchers, is presented with detailed analysis. This converter is capable of operating under variable PF. However, the focus of this paper is in achieving unity PF operation only. The efficiency of this circuit is high because there is only one series semiconductor on-state voltage drop at any instant. The existence of an imbalance in the voltages of the two dc-link capacitors, which was noted before, is confirmed here. The cause for the imbalance is analyzed using appropriate models, and a control method to eliminate it is discussed in detail. Analysis and design considerations for the power circuit using the fixed-band hysteresis current control (HCC) technique are provided. The analytical results are verified through simulation using switched and averaged circuit models of the scheme and also through experimental work. At 90-V ac input and 300-W 300-V output, the experimental prototype demonstrates an efficiency of 96.23% and a PF of 0.998. This converter, with its relatively high dc-output voltage, is well suited for the 110-V utility supply system. A circuit modification for universal input voltage range operation is also suggested. © 1998 IEEE.