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Publications (9)3.19 Total impact

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    ABSTRACT: The protection of the sensitive unbalanced nonlinear loads from sag/swell, distortion, and unbalance in supply voltage is achieved economically using the dynamic voltage restorer (DVR). A simple generalized algorithm based on basic synchronous-reference-frame theory has been developed for the generation of instantaneous reference compensating voltages for controlling a DVR. This novel algorithm makes use of the fundamental positive-sequence phase voltages extracted by sensing only two unbalanced and/or distorted line voltages. The algorithm is general enough to handle linear as well as nonlinear loads. The compensating voltages when injected in series with a distribution feeder by three single-phase H-bridge voltage-source converters with a constant switching frequency hysteresis band voltage controller tightly regulate the voltage at the load terminals against any power quality problems on the source side. A capacitor-supported DVR does not need any active power during steady-state operation because the injected voltage is in quadrature with the feeder current. The proposed control strategy is validated through extensive simulation and real-time experimental studies.
    IEEE Transactions on Industry Applications 01/2013; 49(5):2330-2340. · 1.67 Impact Factor
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    ABSTRACT: The dynamic voltage restorer (DVR) is an attractive solution to protect sensitive loads from voltage sag, swell, unbalance and voltage harmonics. When the injected voltages by the DVR are in quadrature with line currents, the DVR can be supported by a capacitor on DC side. In this paper, a new and simple control algorithm based on reactive power estimation is proposed for a self-supported DVR. The DVR is controlled by tracking the load voltages to their reference values computed by the proposed control algorithm in the stationary reference frame. Furthermore, a proportional-resonant (PR) controller is utilized to avoid any reference frame transformation. Moreover, the PR controller has very high gain at both positive and negative sequence frequencies and thus it is used to achieve a better unbalance compensation without using two separate positive and negative sequence controllers. The proposed control strategy is validated by performing simulation studies in MATLAB environment. The simulation results for voltage sag, swell, harmonic and unbalance compensation using the proposed control algorithm are discussed.
    Harmonics and Quality of Power (ICHQP), 2012 IEEE 15th International Conference on; 01/2012
  • N. Adhikari, B. Singh, A.L. Vyas
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    ABSTRACT: This paper presents the design procedure and performance of a solar-PV (photovoltaic) energy generating system using an isolated zeta converter for meeting an energy demand of rural households. The solar-PV generating system consists of solar panels, a zeta dc-dc converter, a MPPT (maximum power point tracking) controller, energy storage system, VSI (voltage source inverter) and a filter. A feedback PID (Proportional-Integral-Derivative) controller is designed to regulate the output voltage under disturbances at the consumer loads. The system is designed and modelled in Matlab/Simulink and the simulation results are presented to demonstrate its performance in various atmospheric as well as consumer loads condition.
    Industrial and Information Systems (ICIIS), 2012 7th IEEE International Conference on; 01/2012
  • B. Singh, A.L. Vyas, N. Adhikari
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    ABSTRACT: This paper deals with the design, modeling and control of a variable speed Wind Energy Conversion System (WECS) consisting of a permanent magnet brushless DC (PMBLDC) generator, a rectifier, a push-pull converter and a voltage source inverter (VSI) and the maximum power point tracking (MPPT) controller. The proposed mechanical sensorless MPPT controller uses output voltage and current of the rectifier. The duty ratio of an isolated push-pull converter is controlled using a MPPT controller. The system is designed, modeled and its simulation is carried out in Matlab-Simulink environment for feeding an average consumer load of 1 kW, at 230 V, 50 Hz AC supply using a voltage source inverter (VSI). Simulated results are given to validate the performance of designed MPPT controller under varying wind speeds. The power quality at the output voltage across the loads is maintained using an output voltage controller, which regulates the output voltage under different types of consumer loads.
    Power Electronics, Drives and Energy Systems (PEDES), 2012 IEEE International Conference on; 01/2012
  • N. Adhikari, B. Singh, A.L. Vyas
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    ABSTRACT: This paper presents a design and modeling of a sensorless maximum power point tracking (MPPT) controller using a permanent magnet brush-less DC (PMBLDC) generator for a wind energy conversion system (WECS). A low power WECS is designed with an isolated flyback dc-dc converter, a battery and a voltage source inverter (VSI). The sensor-less MPPT control is based on the power-speed curve of a wind turbine for different wind speeds. The wind speed and the rotor speed are estimated for calculating the reference power generation. The standalone WECS is designed and the system is modeled in Matlab/Simulink. The response of the controller is illustrated in cases of sudden and random variations in the wind speed and the results are also presented to validate the system performance for variation in consumer loads.
    Sustainable Energy Technologies (ICSET), 2012 IEEE Third International Conference on; 01/2012
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    ABSTRACT: This paper deals with the design and modeling of a small scale stand-alone wind energy conversion system (WECS) using a maximum power point tracking (MPPT) controller and permanent magnet brushless dc (PMBLDC) generator. The WECS consists of a wind turbine, PMBLDC generator, MPPT controller, isolated half bridge dc-dc converter, battery, voltage source inverter (VSI) and output filter. The fuzzy logic based MPPT controller is designed for a stand-alone WECS for regulating the duty cycle of the dc-dc converter to extract maximum power. The power quality at the consumer load end is maintained using an output voltage controller, which regulates the output voltage and current of VSI. The designed system is modeled and its behavior is simulated in Matlab/Simulink using simpower system and fuzzy logic toolboxes.
    IECON 2012 - 38th Annual Conference on IEEE Industrial Electronics Society; 01/2012
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    ABSTRACT: In this paper a comprehensive study on the three-phase four-wire (3P4W) shunt active power filter (APF) is carried out on the basis of three system configurations. These three two-level voltage source inverter topologies are compared for 3P4W shunt APF, namely, split capacitor (2C), four-leg (4L) and three single-phase H-bridges (3HB). The performance of all three topologies, under an unbalanced non-linear load condition, is evaluated with a detailed digital signal processor (DSP)-based experimental investigation. The steady-state as well as dynamic performance of APF is studied to compensate for current harmonics, reactive power, current unbalance and neutral current. The advantages and limitations offered by each of the topologies are also discussed in brief.
    IET Power Electronics 05/2011; · 1.52 Impact Factor
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    ABSTRACT: This paper deals with the design, control and modeling of an isolated solar-PV (Photo-Voltaic) energy generating system. The proposed system is designed for supplying an average consumer load of 1.5 kW. A constant voltage method is applied to the PV array for MPPT (Maximum Power Point Tracking). A push-pull boost dc-dc converter is fed from the PV array for charging the battery. A VSI (Voltage Source Inverter) utilizing multi-loop feedback control technique with a BESS (Battery Energy Storage System) is used for power management of the proposed system. This solar-PV energy generating system is designed, modeled and its performance is simulated in the Matlab using the Simulink, Sim power system etc. toolboxes. Simulated results are presented for the linear, nonlinear and motor loads to demonstrate its performance.
    Industry Applications Society Annual Meeting (IAS), 2011 IEEE; 01/2011
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    ABSTRACT: Background Cesarean section has been identified as one of the commonest indication for blood transfusion in obstetric practice because it involves risk of major intra-operative blood loss. Different figures varying from less than 500 ml to more than 1000 ml have been quoted as estimated blood loss associated with caesarean section. There is also a wide variation in blood ordering practices for this surgery. Objective The objective of this study is to evaluate the blood ordering practice and transfusion for cesarean sections at our institute, to see post-operative drop in hemoglobin and hematocrit and to correlate those parameters with the duration between uterine incision and repair. Methods In this prospective observational study, non-randomised purposive sample was taken from 121 ladies who underwent elective and emergency cesarean section at the department of obstetrics of Dhulikhel Hospital-Kathmandu University Hospital. Post-cesarean drop in hemoglobin and hematocrit and their relation with duration of uterine manipulation was calculated. Cross-match to transfusion (C/T ratio) ratio, transfusion probability (%T) and transfusion index (Ti) were also calculated. Results Most frequent blood group was found to be O positive (38%) among those ladies. Average post-cesarean drop in hemoglobin was 1.52±1.27 gm/dl and drop in haematocrit was 5.49±4.1%. Post-operative drop in hemoglobin and haematocrit had weak and positive linear relation with duration between uterine incision and repair. Cross-match to transfusion ratio was 1, transfusion probability 100% and transfusion index was 2. Conclusion There is no need of routine cross-matching of blood for cesarean section. Only grouping with confirmation of availability should be done for emergency situation.
    Kathmandu University Medical Journal 11(42):144-146.