Author
Rajiv K. Varma
Other affiliations: Indian Institutes of Technology, Indian Institute of Technology Kanpur
Bio: Rajiv K. Varma is an academic researcher from University of Western Ontario. The author has contributed to research in topics: Photovoltaic system & Electric power system. The author has an hindex of 31, co-authored 150 publications receiving 4995 citations. Previous affiliations of Rajiv K. Varma include Indian Institutes of Technology & Indian Institute of Technology Kanpur.
Papers published on a yearly basis
Papers
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27 Jul 2014TL;DR: In this article, the authors present two analytical frameworks to study the fault current contribution from inverter-based distributed generation (IB-DGs) in transient and steady state conditions.
Abstract: This paper presents two analytical frameworks to study the fault current contribution from inverter based distributed generation (IB-DGs) in transient and steady state conditions. The developed models can be used to analyze the fault response of IB-DGs in active distribution networks. The steady state analysis of fault current contribution from IB-DGs is calculated using the forward-backward sweep method, whereas the transient model for the IB-DGs is developed using the IB-DG differential equations. The results of the both models are validated by PSCAD simulations.
9 citations
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09 Nov 2020
TL;DR: In this article, a review of case studies and operational experiences of smart inverters in increasing hosting capacity in real distribution systems, worldwide is presented, and a comparative evaluation of different smart inverter functions such as constant power factor, volt-var, and volt-watt in improving hosting capacity is presented.
Abstract: This paper presents a review of case studies and operational experiences of smart inverters in increasing hosting capacity in real distribution systems, worldwide The phenomenal increase in penetration of solar PV systems has caused several grid integration challenges Overvoltage due to active power injection by solar PV systems is a prominent factor that restricts hosting capacity of PV systems in distribution networks Smart inverter functions on PV inverters have been shown to obviate this challenge and enhance hosting capacity This paper presents a comparative evaluation of different smart inverter functions such as constant power factor, volt-var, and volt-watt in improving hosting capacity Key takeaways from various simulation studies and operating experiences of smart inverters in actual distribution systems across the world are described This paper provides useful insights to utilities in understanding the impact of smart inverters for improving PV hosting capacity in their distribution systems
9 citations
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07 May 2012TL;DR: In this article, the maximum amount of PV solar generation that can be connected in a 27.6 kV feeder of a distribution utility - London Hydro -was investigated for various factors such as steady state voltage rise, Temporary Over Voltage (TOV), short circuit current and harmonic contributions, that could potentially constrain DG connectivity.
Abstract: This paper presents a study for determining the maximum amount of PV solar generation that can be connected in a 27.6 kV feeder of a distribution utility - London Hydro. Various factors such as steady state voltage rise, Temporary Over Voltage (TOV), short circuit current and harmonic contributions, that could potentially constrain DG connectivity are investigated. Load flow studies with PSS/E and electromagnetic transient simulation studies with EMTDC/PSCAD software are utilized for performing the above investigations. It is shown that harmonic amplification due to network resonance could potentially be the limiting factor for PV solar connectivity in this distribution feeder. This paper also makes a case that the conventional Connection Impact Assessment (CIA) studies for DG connections need to be made broader to include such harmonic aspects.
9 citations
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07 Nov 2011
TL;DR: It is shown that the proposed controller performs effectively by adapting the gains based on fuzzy supervision, it stabilizes the network faster than a conventional PI controller and the peak overshoot is also reduced significantly.
Abstract: This paper proposes a fuzzy supervised PI controller for the Voltage Source Converter (VSC) HVDC system connected to an Induction Generator based wind farm, in parallel with an AC transmission line. It is shown that the proposed controller performs effectively by adapting the gains based on fuzzy supervision. It stabilizes the network faster than a conventional PI controller and the peak overshoot is also reduced significantly. A nonlinear full-scale model is developed in MATLAB, which is linearized to obtain a state space model. Eigenvalues and participation factors are calculated from the state space model for small signal stability studies. Singular Value Decomposition (SVD) theory is also applied to test the controllability of the inputs with respect to specific oscillatory modes. For the fuzzy supervised PI controllers, a rule base is generated from several system simulations and then the proposed controller is implemented through the Fuzzy Inference System (FIS) in MATLAB. The aggregated wind farm model is validated through PSCAD/EMTDC simulation.
8 citations
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21 Jul 2013TL;DR: The Bibliography of FACTS technology for 2012-2013 as mentioned in this paper provides a listing of various journal and conference papers in this area, and includes papers published until November 2013, which is a very short time interval.
Abstract: This paper presents the Bibliography of FACTS technology for 2012–2013. It provides a listing of various journal and conference papers in this area. This Bibliography includes papers published until November 2013.
8 citations
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TL;DR: An overview of the recent advances in the area of voltage-source converter (VSC) HVdc technology is provided in this paper, where a list of VSC-based HVDC installations worldwide is included.
Abstract: The ever increasing progress of high-voltage high-power fully controlled semiconductor technology continues to have a significant impact on the development of advanced power electronic apparatus used to support optimized operations and efficient management of electrical grids, which, in many cases, are fully or partially deregulated networks. Developments advance both the HVDC power transmission and the flexible ac transmission system technologies. In this paper, an overview of the recent advances in the area of voltage-source converter (VSC) HVdc technology is provided. Selected key multilevel converter topologies are presented. Control and modeling methods are discussed. A list of VSC-based HVdc installations worldwide is included. It is confirmed that the continuous development of power electronics presents cost-effective opportunities for the utilities to exploit, and HVdc remains a key technology. In particular, VSC-HVdc can address not only conventional network issues such as bulk power transmission, asynchronous network interconnections, back-to-back ac system linking, and voltage/stability support to mention a few, but also niche markets such as the integration of large-scale renewable energy sources with the grid and most recently large onshore/offshore wind farms.
2,023 citations
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TL;DR: In this paper, the authors present an energy fundiment analysis for power system stability, focusing on the reliability of the power system and its reliability in terms of power system performance and reliability.
Abstract: (1990). ENERGY FUNCTION ANALYSIS FOR POWER SYSTEM STABILITY. Electric Machines & Power Systems: Vol. 18, No. 2, pp. 209-210.
1,080 citations
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27 Feb 2002
TL;DR: In this paper, the authors present a comparison of different SVC controllers for power transmission networks with respect to their performance in terms of the number of SVC inputs and outputs, as well as the frequency of the SVC outputs.
Abstract: 1. Introduction. 1.1 Background. 1.2 Electrical Transmission Networks. 1.3 Conventional Control Mechanisms. 1.4 Flexible ac Transmission Systems (FACTS). 1.5 Emerging Transmission Networks. 2. Reactor--Power Control in Electrical Power Transmission Systems. 2.1 Reacrive Power. 2.2 Uncompensated Transmission Lines. 2.3 Passive Compensation. 2.4 Summary. 3. Principles of Conventional Reactive--Power Compensators. 3.1 Introduction. 3.2 Synchronous Condensers. 3.3 The Saturated Reactor (SR). 3.4 The Thyristor--Controlled Reactor (TCR). 3.5 The Thyristor--Controlled Transformer (TCT). 3.6 The Fixed Capacitor--Thyristor--Controlled Reactor (FC--TCR). 3.7 The Mechanically Switched Capacitor--Thristor--Controlled Reactor (MSC--TCR). 3.8 The Thyristor--Switched capacitor and Reactor. 3.9 The Thyristor--Switched capacitor--Thyristor--Controlled Reactor (TSC--TCR). 3.10 A Comparison of Different SVCs. 3.11 Summary. 4. SVC Control Components and Models. 4.1 Introduction 4.2 Measurement Systems. 4.3 The Voltage Regulator. 4.4 Gate--Pulse Generation. 4.5 The Synchronizing System. 4.6 Additional Control and Protection Functions. 4.7 Modeling of SVC for Power--System Studies. 4.8 Summary. 5. Conceepts of SVC Voltage Control. 5.1 Introduction 5.2 Voltage Control. 5.3 Effect of Network Resonances on the Controller Response. 5.4 The 2nd Harmonic Interaction Between the SVC and ac Network. 5.5 Application of the SVC to Series--Compensated ac Systems. 5.6 3rd Harmonic Distortion. 5.7 Voltage--Controlled Design Studies. 5.8 Summary. 6. Applications. 6.1 Introduction. 6.2 Increase in Steady--State Power--Transfer Capacity. 6.3 Enhancement of Transient Stability. 6.4 Augmentation of Power--System Damping. 6.5 SVC Mitigation of Subsychronous Resonance (SSR). 6.6 Prevention of Voltage Instability. 6.7 Improvement of HVDC Link Performance. 6.8 Summary. 7. The Thyristor--Controlled SeriesCapacitor (TCSC). 7.1 Series Compensation. 7.2 The TCSC Controller. 7.3 Operation of the TCSC. 7.4 The TSSC. 7.5 Analysis of the TCSC. 7.6 Capability Characteristics. 7.7 Harmonic Performance. 7.8 Losses. 7.9 Response of the TCSC. 7.10 Modeling of the TCSC. 7.11 Summary. 8. TCSC Applications. 8.1 Introduction. 8.2 Open--Loop Control. 8.3 Closed--Loop Control. 8.4 Improvement of the System--Stability Limit. 8.5 Enhancement of System Damping. 8.6 Subsynchronous Resonanace (SSR) Mitigation. 8.7 Voltage--Collapse Prevention. 8.8 TCSC Installations. 8.9 Summary. 9. Coordination of FACTS Controllers. 9.1 Introduction 9.2 Controller Interactions. 9.3 SVC--SVC Interaction. 9.4 SVC--HVDC Interaction. 9.5 SVC--TCSC Interaction. 9.6 TCSC--TCSC Interaction. 9.7 Performance Criteria for Damping--Controller Design. 9.8 Coordination of Multiple Controllers Using Linear--Control Techniques. 9.9 Coordination of Multiple Controllers using Nonlinear--Control Techniques. 9.10 Summary. 10. Emerging FACTS Controllers. 10.1 Introduction. 10.2 The STATCOM. 10.3 THE SSSC. 10.4 The UPFC. 10.5 Comparative Evaluation of Different FACTS Controllers. 10.6 Future Direction of FACTS Technology. 10.7 Summary. Appendix A. Design of an SVC Voltage Regulator. A.1 Study System. A.2 Method of System Gain. A.3 Elgen Value Analysis. A.4 Simulator Studies. A.5 A Comparison of Physical Simulator results With Analytical and Digital Simulator Results Using Linearized Models. Appendix B. Transient--Stability Enhancement in a Midpoint SVC--Compensated SMIB System. Appendix C. Approximate Multimodal decomposition Method for the Design of FACTS Controllers. C.1 Introduction. C.2 Modal Analysis of the ith Swing Mode, C.3 Implications of Different Transfer Functions. C.4 Design of the Damping Controller. Appendix D. FACTS Terms and Definitions. Index.
954 citations
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TL;DR: In this article, the principle of modularity is used to derive the different multilevel voltage and current source converter topologies for high-power dc systems, where the derived converter cells are treated as building blocks and are contributing to the modularity of the system.
Abstract: In this paper, the principle of modularity is used to derive the different multilevel voltage and current source converter topologies. The paper is primarily focused on high-power applications and specifically on high-voltage dc systems. The derived converter cells are treated as building blocks and are contributing to the modularity of the system. By combining the different building blocks, i.e., the converter cells, a variety of voltage and current source modular multilevel converter topologies are derived and thoroughly discussed. Furthermore, by applying the modularity principle at the system level, various types of high-power converters are introduced. The modularity of the multilevel converters is studied in depth, and the challenges as well as the opportunities for high-power applications are illustrated.
883 citations
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01 May 1996TL;DR: In this paper, a new power system stabilizer (PSS) design for damping power system oscillations focusing on inter-area modes is described, and two global signals are suggested; the tie-line active power and speed difference signals.
Abstract: This paper describes a new power system stabilizer (PSS) design for damping power system oscillations focusing on interarea modes. The input to the PSS consists of two signals. The first signal is mainly to damp the local mode in the area where PSS is located using the generator rotor speed as an input signal. The second is an additional global signal for damping interarea modes. Two global signals are suggested; the tie-line active power and speed difference signals. The choice of PSS location, input signals and tuning is based on modal analysis and frequency response information. These two signals can also be used to enhance damping of interarea modes using SVC located in the middle of the transmission circuit connecting the two oscillating groups. The effectiveness and robustness of the new design are tested on a 19-generator system having characteristics and structure similar to the Western North American grid.
523 citations