| 1. |
- Dolguntseva, Irina, et al.
(author)
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Contour-Based Dead-Time Harmonic Analysis in a Three-Level Neutral-Point-Clamped Inverter
- 2015
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In: IEEE Transactions on Industrial Electronics. - : IEEE. - 0278-0046 .- 1557-9948. ; 62:1, s. 203-210
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Journal article (peer-reviewed)abstract
- The term dead time refers to a prime safety factor for most power electronic converter topologies, and it is included either in the control software or in the gate/base driver hardware, depending on the application as well as the control requirements. In this paper, the authors present a comprehensive numerical analysis of dead-time effects on the output voltage of a three-level neutral-pointclamped (NPC) inverter. To incorporate the dead-time effect in the output voltage, 3-D models of three-level carrier pulse width modulation (PWM) methods are modified for two dead-time implementations. Closed-form expressions of inverter phase voltage harmonics for phase opposition disposition (POD) PWM are derived based on the double Fourier series approach and modified contour plots. The harmonic spectra from numerical evaluations, simulations, and experiments for natural sampling (NS), symmetrical regular sampling (SRS), and asymmetrical regular sampling (ARS) are compared to validate the mathematical models. In addition, the fundamental voltage with respect to the dead time and the load phase angle is presented based on analytical results and simulation.
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| 2. |
- Elamalayil Soman, Deepak, et al.
(author)
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Discontinuous conduction mode of a three-level boost DC-DC converter and its merits and limits for voltage cross regulation applications
- 2014
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In: Proceedings, IECON 2014 - 40th Annual Conference of the IEEE Industrial Electronics Society. - : IEEE conference proceedings. - 9781479940325 ; , s. 4268-4272
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Conference paper (peer-reviewed)abstract
- Distributed generation and smart grid integration of renewable energy sources introduce a lot of challenges for the enabling power electronic converter technology. Some of these challenges include wide controllability range, high power handling and good reliability. Three-level boost converter is one of the attractive solution for applications requiring voltage cross regulation such as three-level neutral point clamped inverter based grid integration of renewable sources. The present work shows the advantages and disadvantages of using discontinuous conduction mode of a Three-level boost converter for voltage cross regulation. The converter working principle, modes of operation and operating cases are listed briefly. The simulation results compare the DCM and CCM cross regulation effects. Based on these results, the controllability range of the converter is analyzed to understand the suitability of the converter for various applications.
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| 3. |
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| 4. |
- Krishna, Remya, 1985-, et al.
(author)
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Analysis of linear wave power generator model with real sea experimental results
- 2013
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In: IET Renewable Power Generation. - : Institution of Engineering and Technology (IET). - 1752-1416 .- 1752-1424. ; 7:5, s. 574-581
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Journal article (peer-reviewed)abstract
- This study presents the dynamic modelling of a linear permanent magnet generator for extracting energy from ocean waves. Translator position, calculated from measured generator voltage, is used as input for the simulation model. Instantaneous power from the simulation model has been compared with the measurements from the Lysekil research site. The power output from the model considering the air gap flux variation is precisely matching with the measured values before core saturation. The generator dynamic model is modified by including the saturation effect. Although a simple mathematical expression is considered for representing the saturation, the model gives accurate power spectrum close to the experimental results. The presented model is a first step towards the system model that can simulate the entire electric system including electric grid. As such, the generator model can be used for further analysis of the wave energy conversion system.
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| 5. |
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| 6. |
- Krishna, Remya, 1985-
(author)
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Grid Connected Three-Level Converters : Studies for Wave Energy Conversion
- 2014
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Doctoral thesis (other academic/artistic)abstract
- This thesis presents an electrical system analysis of a wave energy converter (WEC) for the objective of grid connection. To transfer the enormous amount of power from waves to the load centers, efficient power electronic systems are essential. This thesis includes the modeling of a buoy–translator dynamics and the modeling of a linear permanent magnet generator along with simulation and experimental validation. Diode bridge rectifiers are considered for rectification to avoid the complex linear generator control at the input side. To reduce the size and the cost of energy storage elements, DC voltage regulation is done using a DC/DC converter.To achieve smooth and high power, many WECs need to be connected to a common DC link. A neutral point clamped inverter is considered for the DC/AC conversion due to its advantages over conventional topologies. Various pulse width modulation schemes are tested for the inverter to choose the optimum PWM method. The harmonics in the inverter output voltage is derived numerically and compared with simulation and experiment to understand the effect of dead-time in the inverter operation.Depending on the load current drawn from the inverter, the voltages in the two input capacitors of a three-level neutral point clamped inverter deviates from equilibrium unless the neutral point is grounded. To avoid this voltage imbalance as well as to regulate the DC link voltage a dual output boost converter with pulse delay control is proposed. The modeling, simulation and experiments show an improvement in the compensation voltage using pulse delay control compared to the previously proposed methods in the literature. The synchronous current control and the grid connection of the three-level converter have been accomplished in the laboratory. Finally, the three-level power converter system has been tested with a linear permanent magnet generator at Lysekil to analyze the controller requirements.
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| 7. |
- Krishna, Remya
(author)
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Multilevel Inverter for Wave Power Conversion
- 2011
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Licentiate thesis (other academic/artistic)abstract
- This thesis deals with the electrical system analysis of a Wave Energy Converter (WEC) for the objective of grid connection. The Linear Permanent Magnet Generator (LPMG) is modeled and validated with experimental results. The comparison studies establish that this model is useful for the subsequent system modeling and performance analysis. To simplify the generator side control, diode bridge rectifiers are used for rectification. To reduce the size and cost of energy storage elements, DC voltage regulation is done using a DC/DC converter. Since the buoy has limited control, the electrical system needs additional design requirements. Moreover, to achieve smooth and high power, many WEC are connected to a common DC link. As a result, the inverter for the DC/AC conversion should be capable to withstand the low frequency instantaneous power peaks. Conventional multilevel inverters are considered for the initial analysis. The Neutral Point Clamped (NPC) inverter is chosen for the detailed analysis due to its advantages over other topologies. Voltage balancing technique and current control method are examined. The experimental performance of NPC converter for the WEC will be the focus in future.
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| 8. |
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| 9. |
- Krishna, Remya, 1985-, et al.
(author)
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Pulse delay Control for Capacitor VoltageBalancing in a Three Level Boost Neutral PointClamped Inverter
- 2015
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In: IET Power Electronics. - : Institution of Engineering and Technology (IET). - 1755-4535 .- 1755-4543. ; 8:2, s. 268-277
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Journal article (peer-reviewed)abstract
- The cross regulation effect in multi-output DC/DC converters offers a reliable support for the grid integration of multilevel inverters by balancing the capacitor voltages. The capacitor voltage balancing by single input dual output boost converter is often realised by conventional three-level switching scheme. The three-level operation benefits lower inductor ripple current, but it limits the maximum possible compensation voltages. In this study, the entire operating modes of the boost converter is presented and all the possible cases which contribute to the voltage balancing are employed for balancing the capacitor voltages in a three-level neutral point clamped inverter. A proportional-integral controller based duty ratio control and pulse delay control are used for DC link voltage regulation and capacitor voltage balancing. Since the classical state-space averaging technique is not suitable for SIDO converters, inductor current ripple averaging technique is utilised for controller design. The circuit simulation is performed in Matlab/Simulink. The digital controller is realised using the Virtex-5FPGA in Labview/CompactRIO module. Both simulation and experimental results are presented to validate the controller performance.
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| 10. |
- Krishna, Remya, 1985-, et al.
(author)
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Space vector modulation method to balance the neutral point voltage for a three-level inverter
- 2010
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In: Power Electronics, Drives and Energy Systems (PEDES) & 2010 Power India, 2010 Joint International Conference on. - : IEEE conference proceedings. - 9781424477821 ; , s. 1-6
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Conference paper (peer-reviewed)abstract
- This paper investigates the capacitor voltage balance scheme for a neutral point clamped inverter. A symmetrical space vector modulation is used to analyze the imbalance in neutral point voltage. This method overcomes the drawbacks of Nearest Three Vector modulation method. The redundancies of different switch configurations for the generation of the same output voltage are used to limit the voltage drift when modulation index is less than half. The deviation in the neutral voltage is further reduced by adjusting the duty cycle distribution variable. The voltage balance scheme is analyzed for linear and non linear loads. The performance of control strategy is also examined for a grid connected inverter.
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