Showing papers by "Rajiv K. Varma published in 2011"

Grid Interconnection of Renewable Energy Sources at the Distribution Level With Power-Quality Improvement Features

Abstract: Renewable energy resources (RES) are being increasingly connected in distribution systems utilizing power electronic converters. This paper presents a novel control strategy for achieving maximum benefits from these grid-interfacing inverters when installed in 3-phase 4-wire distribution systems. The inverter is controlled to perform as a multi-function device by incorporating active power filter functionality. The inverter can thus be utilized as: 1) power converter to inject power generated from RES to the grid, and 2) shunt APF to compensate current unbalance, load current harmonics, load reactive power demand and load neutral current. All of these functions may be accomplished either individually or simultaneously. With such a control, the combination of grid-interfacing inverter and the 3-phase 4-wire linear/non-linear unbalanced load at point of common coupling appears as balanced linear load to the grid. This new control concept is demonstrated with extensive MATLAB/Simulink simulation studies and validated through digital signal processor-based laboratory experimental results.

Optimal 24-hr utilization of a PV solar system as STATCOM (PV-STATCOM) in a distribution network

Abstract: This paper presents a novel optimal utilization of photovoltaic solar system as STATCOM for voltage regulation and power factor correction during both nighttime and daytime. The PV solar system conventionally generates real power during the day but the entire asset remains idle at night. This novel PV solar system operated as STATCOM is termed PV-STATCOM which utilizes the entire inverter capacity in the night and that remaining after real power generation during the day for accomplishing various STATCOM functionalities. Bluewater Power Corporation in Sarnia, Canada, is going to showcase this new concept of optimal utilization of PV solar system on a 10kW PV system in its network. The controller for the PV-STATCOM is being developed in the university lab and will be installed in the distribution utility network. A simulation model for the 10kW PV-STATCOM and the Bluewater Power distribution system network is developed in PSCAD software. This paper presents the steady state and transient performance of the PV-STATCOM controller for voltage regulation and power factor control both during nighttime and daytime. This proposed PV-STATCOM if connected at the terminals of an industrial customer having induction motor loads can help improve power factor and avoid potential penal tariffs over a 24-hour period, in addition to generating revenues due to sale of real power during the day.

Novel application of a PV solar plant as STATCOM during night and day in a distribution utility network

Abstract: PV solar farms produce power during the day and are completely idle in the nights. This paper presents a novel utilization of a PV solar plant as STATCOM in the night for load reactive power compensation and voltage control. This STATCOM functionality will also be available to a substantial degree during the daytime with the inverter capacity remaining after real power production. The local distribution company London Hydro is implementing this new technology, for the first time in Canada, on a 10 kW solar system to be installed on the rooftop of their headquarters building. The PV solar plant inverter controller will be designed, developed and tested in the university Lab and will then be installed in field by Spring 2011. This paper presents the EMTDC/PSCAD simulation studies of the performance of the 10 kW PV solar plant as a STATCOM. The benefits of employing such a new control of the PV solar system as a Flexible AC Transmission System (FACTS) device are presented.

Subsynchronous resonance in single-cage self-excited-induction-generator-based wind farm connected to series-compensated lines

Abstract: Integration of large wind farms may get constrained owing to the available transfer capacity of existing transmission networks. This transmission capacity may be enhanced by incorporating series compensation. However, series capacitors are known to cause subsynchronous resonance (SSR) oscillations in synchronous generators. In this study, the potential of SSR is investigated with series-compensated lines connected to wind farms based on single-cage self-excited induction generators. A small-signal mathematical model is developed for the prediction of SSR oscillations in such a wind farm for a study system similar to the IEEE First SSR benchmark system. Eigenvalue analysis is performed through MATLAB at various operating points. This is validated by detailed time-domain simulation through electromagnetic transient simulation software EMTDC/PSCAD for a three-phase-to-ground (LLLG) fault at the remote end of the compensated line. An equivalent circuit analysis is performed to examine the impact of a similar fault at the terminals of the wind farm. It is shown from detailed non-linear simulation that even at a realistic level of series compensation a three-phase fault at generator terminals for low levels of wind farm power generation may subject the generator shafts to potentially dangerous magnitudes.

Bibliography of FACTS applications for grid integration of wind and PV solar power systems: 1995–2010 IEEE working group report

Abstract: This paper presents the Bibliography of Flexible AC Transmission System (FACTS) applications for grid integration of wind power systems and PV solar power systems during the period 1995 to 2010. It provides a listing of various journal and conference papers in this area.

PSCAD/EMTDC model of a 3-phase grid connected photovoltaic solar system

Abstract: Photovoltaic (PV) solar farms are being increasingly utilized for producing energy, worldwide. To integrate such solar farms with the grid, a thorough technical study is required in terms of their impact on system voltage, power quality, response to faults and short circuit contributions, etc. These studies require a complete modeling of the PV solar system in an electromagnetic transient software environment like PSCAD/EMTDC. This paper presents a PSCAD/EMTDC model of PV solar panels, the grid connected three phase voltage sourced inverter (VSI) and its controller system. The VSI control is implemented with current control loops. A maximum power point tracking (MPPT) algorithm is implemented to get the maximum output power for any given solar irradiation and temperature. This is integrated with the inverter control in such a way that the requirement of DC-DC converter is eliminated to harvest the maximum power. The inverter model also maintains near unity power factor regardless of the level of power output and maintains an acceptable level of current harmonics. Finally, the developed model is validated with the output of a commercially used PV module.

Global PV incentive policies and recommendations for utilities

Abstract: The photovoltaic (PV) energy industry has been making significant strides in its development over the past couple of decades. This paper makes a brief presentation of the government incentive policies of countries around the globe who are leading in Photovoltaic (PV) development. Feed-In Tariffs and government subsidies are discussed in the context of their specific implementations as well as some strengths and weakness of each country's PV programs. Aside from government incentives policies, which cannot be controlled by local distribution companies, some recommendations are made for utilities to help overcome the non-technical and technical challenges and help increase interest in PV development in their jurisdictions.

Laboratory validation of the relationship between Geomagnetically Induced Current (GIC) and transformer absorbed reactive power

Abstract: This paper presents the theory and simulation work to establish a relationship between Geomagnetically Induced Current (GIC) flowing through a transformer's windings and the reactive power absorbed by that transformer's core. This relationship is determined in laboratory for various levels of GICs injected under different loading conditions of a transformer. This obtained relationship validates the results obtained through electromagnetic transients simulation using PSCAD/EMTDC and also correlates well with actual field data. This study is one of the first laboratory simulation studies of the effect of GIC, reported in literature.

Modeling and mitigation of Geomagnetically Induced Currents on a realistic power system network

Abstract: This paper utilizes a novel technique developed to correlate the magnitude of Geomagnetically Induced Current (GIC) with the reactive power absorbed by the transformer's magnetizing reactance to model the impacts of GIC in load flow studies. A portion of an actual 500 kV power system segment is modeled and the impacts of a GIC event are considered on the voltage profile of the segment. Different what-if scenarios are considered and a potential operational mitigation strategy is proposed. It is shown that an improved visibility of GIC within the network can help the system operator take more informed and effective measures to protect the system during GIC events.

Concepts of FACTS controllers

Abstract: This paper provides a summary of one of the presentations planned under the Panel Session on “Dynamic Reactive Compensation” sponsored by the DC and FACTS Subcommittee. A brief description of the operating characteristics and control applications of different Flexible AC Transmission System (FACTS) Controllers is presented in this paper.

Fuzzy supervised PI controller for VSC HVDC system connected to Induction Generator based wind farm

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.

Determination of the spectrum of frequencies generated by a saturated transformer

Abstract: This paper develops a technique to model the frequency response of a saturated transformer. This technique is used to determine the range of frequencies that will be generated when a transformer experiences saturation due to an injection of typically low frequency currents. This paper examines the case when a power transformer is saturated due to geomagnetically induced currents (GIC) caused by solar storms. The proposed technique is validated for a study system utilizing EMTDC/PSCAD simulations. The results from this technique are also correlated with those from a Hydro Quebec study. This technique will be useful in understanding the impact of transformer saturation on neighbouring equipment and as well as on FACTS controllers, and help design appropriate mitigation strategies.

Bibliography of FACTS 2009–2010: Part IV IEEE working group report

Abstract: This paper presents the fourth part of the Bibliography of FACTS technology for 2009 and 2010. It provides a listing of various journal and conference papers in this area.

Instability in induction generator based wind farms connected to series compensated transmission lines

Abstract: This paper presents a study of subsynchronous mode instability in Induction Generator (IG) based wind farm connected to a series compensated transmission line. The IEEE First SSR benchmark system is modified by replacing the synchronous generator with an aggregated wind farm. A small signal stability analysis is carried out to detect the instability analytically and then results are validated through a detailed electromagnetic transient simulation using PSCAD/EMTDC. Two types of studies are performed for the small signal analysis. First, a linearized state space model is developed for the eigenvalue calculation. Then, a simple equivalent circuit model is developed for the resonant speed analysis. From the equivalent circuit model, two resonant speeds - upper resonant speed (URS) and lower resonant speed (LRS), are obtained. If the post fault speed of the aggregated generator comes close or enters in the band within these two resonant speeds, the induction generator may become unstable. The performance of the aggregated wind farm model is validated with a distributed wind farm model. It is shown that the wind generator may experience SSR if the fault occurs at the terminals of the wind farm even at a realistic level of series compensation.

Bibliography of FACTS: 2000 — Part II IEEE working group report

Abstract: This paper presents the second part of the Bibliography of FACTS technology mainly for the year 2000. Papers published/presented in Conferences in later part of 1999, which appeared on search engines only in the year 2000 are also included in this Bibliography. It provides a listing of various journal and conference papers in this area.

Bibliography of HVDC transmission 2009–2010: Part-II IEEE working group report

Abstract: This paper presents the second part of the Bibliography of High Voltage Direct Current (HVDC) transmission technology for 2009–2010. It provides a listing of various journal and conference papers in this area.

Bibliography of FACTS: 1998 IEEE working group report

Abstract: This paper presents a Bibliography of FACTS technology mainly for the year 1998. Papers published/presented in Journals and Conferences in later part of 1997, which appeared on search engines only in the year 1998, are also included in this Bibliography. It provides a listing of various journal and conference papers in this area.

Bibliography of FACTS 2009/2010 — Part II IEEE working group report

Abstract: This paper presents a Bibliography of FACTS technology for 2009 and 2010 It provides a listing of various journal and conference papers in this area

Bibliography of FACTS 2009–2010: Part I IEEE working group report

Abstract: This paper presents a Bibliography of FACTS technology for 2009 and 2010. It provides a listing of various journal and conference papers in this area.

Bibliography of FACTS: 1999 IEEE working group report

Abstract: This paper presents a Bibliography of FACTS technology mainly for the year 1999. Papers published/presented in Conferences in later part of 1998, which appeared on search engines only in the year 1999 are also included in this Bibliography. It provides a listing of various journal and conference papers in this area.