Faculty Publications

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Publications by NITK Faculty

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Author: search.filters.author.Sandeep, N.

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    A comparison of seven-level inverter topologies for multilevel DC-AC power conversion
    (Institute of Electrical and Electronics Engineers Inc., 2014) Salodkar, P.; Sandeep, N.; Kulkarni, P.S.; Yaragatti, R.Y.
    Multilevel inverter (MLI) performance is high compared to the conventional two level inverters since they offer high power capability, associated with lower output harmonics and lower commutation losses. However the main drawback of MLI is their increased number of power devices, passive components, complex pulse width modulation control and balancing of capacitor voltages. In this paper the most popular topologies like diode-clamped inverter (neutral-point clamped), cascaded multicell with separate dc sources, and transistor clamped H-Bridge inverter are discussed. A simplified multilevel inverter (Switched Transistor MLI) is proposed and its performance is compared with the above said topologies. Component count and the % total harmonic distortion (THD) of the output voltage are considered as the indexes of the comparative performance. The operating principle of each topology, the most relevant modulation method of all the topologies and the detailed analysis of the proposed Switched Transistor MLI is included. The selection of topology and control techniques depends and varies according to power demands of inverter. Simulation study of all the topologies considered is carried out on MATLAB/SIMULINK platform and the performance of the proposed topology is verified experimentally by the tests performed on a scaled laboratory prototype. © 2014 IEEE.
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    A single-stage active damped LCL-filter-based grid-connected photovoltaic inverter with maximum power point tracking
    (Institute of Electrical and Electronics Engineers Inc., 2015) Sandeep, N.; Kulkarni, P.S.; Yaragatti, R.Y.
    In this paper, a simple single-phase grid-connected photovoltaic (PV) inverter topology consisting of a three-level inverter, an LCL filter, and a new current feedback method for active damping is considered. A dynamically rapid method is used for tracking the maximum power point (MPP) of photovoltaic arrays, known as ripple correlation control. The algorithm uses the current and voltage low-frequency oscillations as the perturbation signals, which are introduced in the output of PV array due to the sinusoidal power being injected into the single-phase utility grid, to enable operation at MPP. The capacitor of the conventional LCL filter is split into two parts and the current flowing between these two parts is used as the feedback for regulation of grid current being injected. By doing so the V - I transfer function of the grid connected inverter system degrades to first-order one from third order function. Due to which, wide control-loop bandwidth can be achieved with a large proportional control-loop gain ensuring good stability. Proportional-resonant (PR) current controller is suggested to provide power to the line with unity power factor and the PV inverter offers much less total harmonic distortion. The entire system has been numerically simulated in MATLAB/SIMULINK platform and the performance results are presented for variation in insolation levels and grid voltage profile showing the effectiveness of the proposed system. © 2014 IEEE.
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    Novel asymmetrical multilevel inverter topology with reduced number of switches for photovoltaic applications
    (Institute of Electrical and Electronics Engineers Inc., 2015) Dhananjaya, D.; Sandeep, N.; Rao, G.R.
    The performance of multilevel inverter is high compared to the classical two level inverters owing to their reduced total harmonic distortion, and lower electromagnetic interference. However the setbacks of multilevel inverter are increased number of power devices, complex PWM and gating circuitry. In this paper, a new multilevel inverter topology, capable of generating large number of levels with fewer number of power switches, gating circuits and power diodes is proposed. In contrast to classical multilevel topologies, the presented topology consequences in reduction of the number of power devices and conduction losses. The proposed topology is asymmetrical, employing isolated dc sources of voltage ratio 421 (Binary fashion). Staircase control PWM at fundamental frequency is employed for the gating of power switches makes it suitable in applications like flexible alternative current transmission systems (FACTS), renewable energy sources, drives control and vehicle propulsion system. The structure of the proposed inverter is modular and thus best suited for PV applications. Detailed simulation is carried out using MATLAB/SIMULINK platform and simulation results are presented. © 2015 IEEE.
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    Single-phase modular multilevel inverter based grid-connected photovoltaic system
    (Institute of Electrical and Electronics Engineers Inc., 2016) Sandeep, N.; Yaragatti, R.Y.
    This paper presents a control scheme for single-phase grid-connected modular five-level inverter applied to photovoltaic (PV) system. The five-level topology considered consists of two series connected H-bridge cells popularly known as cascaded H-bridge inverter. The reason that it requires an isolated dc sources makes it very attractive and its inherent modularity, easy scalability makes the system more reliable. One of the main challenges associated with multilevel converter is to control the drift in dc-link voltage caused by the power imbalance of the cells. A two loop control scheme is proposed to combat this issue; it consists of an asynchronous frame or proportional resonant (PR) for regulating the grid current and a proportional integral (PI) controller for regulating dc-link voltage. The proposed scheme regulates the dc-link voltage independently, in accordance with the reference value generated by the maximum power point tracking (MPPT) algorithm enabling the extraction of maximum power from each module. The inverter injects current which is in phase with the grid voltage ensures the unitary power factor operation with zero reactive power and less total harmonic distortion. The proposed control scheme can be extended to any number of cells connected in series for increasing the number of level in output voltage. Simulation results are presented to validate the analytical expectations and the control scheme developed. © 2015 IEEE.
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    Transformer-Based seven-level inverter with single-dc supply for renewable energy applications
    (IEEE Computer Society help@computer.org, 2016) Behara, S.; Sandeep, N.; Yaragatti, R.Y.
    This paper puts forward a single-DC source based seven-level inverter for harvesting energy from renewable sources. Three single-phase transformers with cascaded outputs are powered from the switching power circuit resulting in then generation of multilevel at the output of the inverter. The proposed configuration can generate output voltage having levels of magnitude (-3VDC, -2VDC, -VDC, 0, VDC, 2VDC, 3VDC) from the DC supply (VDC). Structurally this topology exhibits the advantage of fewer power devices in comparison to conventional inverter for the generation of same number of output voltage levels. Simple logic gate based gating pulse generation scheme is suggested obviating the need for complex pulsewidth-modulation (PWM) scheme. Simulation results confirming the viability and effectiveness of the proposed inverter are presented. © 2016 IEEE.
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    A new nine-level single-DC source-based inverter topology for distributed generation
    (Institute of Electrical and Electronics Engineers Inc., 2017) Sandeep, N.; Yaragatti, U.R.
    Multilevel inverter enables to completely remove the passive filtering requirement at the grid interfacing end, resulting in improved efficiency and reduced cost. These features have led to increasing attention towards their application to medium and high-power arena. In this paper, investigation of a hybrid 9-level inverter topology for grid integration of renewable energy sources is presented. The structural details, operating principle, capacitor voltage balancing control and the main features of the proposed inverter are presented. The proposed topology is compared with other similar 9-level converters to emphasize its superior characteristics and performance. Simulation results demonstrating the grid connected operation of the converter for two test cases are presented. The results affirm the effectiveness of the capacitor voltage balancing control in maintaining capacitor voltages at set values, under steady state and transient operation of the converter. © 2016 IEEE.
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    Simplified hybrid nine-level stacked multiceli converter with reduced part count for grid-connected applications
    (IEEE Computer Society, 2017) Sandeep, N.; Yaragatti, U.R.
    Increasing demand for high-efficiency inverters with improved output waveform quality has enhanced the research in the area of multilevel inverters (MLIs). A dc-ac hybrid inverter formed by cascading a five-level (5L) stacked multicell converter (SMC) and floating capacitor (FC) H-bridge is proposed. It requires only 12 switches and three FCs for nine-level (9L) operation. The most important advantage of the proposed inverter lies in the fact that it requires minimum topological alteration for extending 5L SMC to 9L. FC voltage control strategy and results confirming the effectiveness and operability of the proposed inverter is presented. © 2017 IEEE.
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    Architectural framework of on-board integrator: An interface for grid connected EV
    (Institute of Electrical and Electronics Engineers Inc., 2017) Hampannavar, S.; Likassa, K.; Ayenew, E.; Sandeep, N.; Yaragatti, U.R.
    Vehicle to Grid (V2G) is the concept of connecting a group of electric vehicles (EV) to the grid for power transaction. EVs can be connected to the grid through the home interface or through the chargers available at charging stations. In this paper, a single phase on-board charger with low complexity control scheme is proposed for EV power transaction. The power flow from and to the grid is processed using two stage cascaded converters consisting of a bidirectional DC-DC and DC-AC converters. The LCL filter is used as an interface between DC-AC converter and the grid to attenuate the grid current harmonics. A proportional resonant (PR) controller is employed for the control of grid current and to enable the unity power factor operation of the DC-AC converter. The setbacks associated with the conventional proportional-integral (PI) controller for single phase system is elevated by employing PR controller. Filter design guidelines and the control strategy developed for the proposed system is numerically simulated and verified with extensive simulation carried using MATLAB/SIMULINK. The results demonstrating the feasibility and viability of the proposed system are presented. © 2017 IEEE.
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    Switched-Capacitor-Based Three-Phase Five-Level Inverter Topology with Reduced Components
    (IEEE Computer Society help@computer.org, 2018) Sandeep, N.; Jagabar Sathik, J.S.M.; Yaragatti, U.R.; Krishnasamy, K.
    This paper presents a new five-level multilevel inverter (MLI) based on retrofitting of the conventional two-level (2L) three-phase inverter modules with minimum structural reconfigurations for low-voltage and high-power-quality demanding applications. It comprises two such inverter modules connected in series with 2L switched-capacitor units (SCUs). It requires only two isolated dc sources which are shared by all inverter output phases and thus eliminates the chances of output phase unbalance. Further, the voltage across the floating capacitors of the SCUs are naturally regulated without any sensors, thus makes the proposed topology more elegant for industrial applications. Further, an extensive comparison with the recent other MLI topologies attests the reduced requirement of the components in devising the proposed topology. Finally, experimental results from a low-power hardware prototype are presented to validate the feasibility of the proposed configuration. © 2018 IEEE.
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    Development of a microcontroller based PV emulator with current controlled DC-DC buck converter
    (International Journal of Renewable Energy Research icolak@gazi.edu.tr, 2014) Balakishan, C.H.; Sandeep, N.
    Testing and validation of Photovoltaic based energy conversion systems requires Photovoltaic (PV) panels in laboratory environment. A flexible testing system, which eliminates these panels and emulating the dynamic characteristics of PV sources in real time are gaining importance. This paper presents a new algorithm for emulation of PV characteristics using a DC-DC buck converter in current control mode. The algorithm tracks the point on the V-I characteristics of the PV under varying loads by generating the corresponding current reference. This reference current is used for the generation of gate pulses for the DC-DC converter, which acts like a constant current source to emulate the PV panel. In the proposed system, real time variation of irradiance and temperature are incorporated as a time varying input parameters to the PV emulator. The proposed algorithm has been simulated numerically using MATLAB/SIMULINK platform and is experimentally verified on a laboratory test bench consisting of a DC-DC buck converter of 50 W rating with AT'mega328 as a core controller. Both simulation and hardware results are presented showing the effectiveness of the proposed system under dynamic loading and environmental conditions.