Kailash Srivastava

AC Grid with Embedded VSC-HVDC for Secure and Efficient Power Delivery

Increased bulk power transactions in competitive energy markets together with large scale integration of renewable energy sources are posing challenges to high-voltage transmission systems. Environmental constraints and energy efficiency requirements also have significant effects on future transmission infrastructure development. This paper reviews the recent development in HVDC technologies and discusses the needs of the hybrid AC/DC grid structure for future power systems with focus on VSC-HVDC applications in meshed AC grid. It has also been recognized that hybrid AC/DC transmission system together with the wide area measurement system (WAMS) could effectively manage the overall power grid operation security and efficiency under uncertain supply and demand conditions.

Impacts of Stochastic Residential Plug-In Electric Vehicle Charging on Distribution Grid

In this paper, the impacts of residential Plug-In Electric Vehicles (PEVs) charging on a distribution grid are investigated. A stochastic charging model is developed and used to study the impacts on distribution transformer loading, hotspot temperature variation and Accelerated Aging Factor (AAF) of the transformer. Different penetration levels of PEVs are considered in a typical distribution system. Furthermore, distribution of State of Charge (SOC) is discussed which can be used to optimize battery capacity and required charging infrastructure. Distribution of parking time interval is also discussed which can be used to evaluate availability of PEVs for overnight charging. The merit of stochastic approach compared with deterministic approach is also illustrated. The main contribution of this paper is the stochastic approach to evaluate the impact of residential PEV charging on the distribution grid.

Transients in Wind Power Plants—Part II: Case Studies

This is the second part of a two-paper series. The first paper presented the transient modeling methodology for various components of wind power plants (WPPs). This paper presents a general methodology for transient analysis of WPPs and discusses case studies which investigate some of the most important high-frequency interactions between different components of the WPP. The focus has been on switching transients, and lighting transients have been excluded. Transient case studies conducted on a typical WPP are presented which discuss the impact of fast system surges on the performance of the circuit breaker and impact of fast surges caused by the circuit breaker on the adjacent power components. These case studies investigate the opening and closing of the collector grid vacuum circuit breaker for loaded and unloaded conditions. Simulation results provide a close match with the field measurements conducted on a laboratory prototype of a typical WPP. Differences caused by modeling assumptions or insufficient accuracy of measurement devices are highlighted. To understand the most onerous overvoltages that can be experienced in the test system, a couple of additional simulation case studies are reported. These case studies discuss the interruption of inrush current with an unloaded transformer and interruption of a small inductive current following the transformer energization.

Simulation of synchronous machines in phase coordinates including magnetic saturation

Abstract This paper describes a novel way to account for magnetic saturation for simulation of synchronous machines in phase coordinate for power system studies. A synchronous machine model in phase coordinates is presented and the effect of saturation along direct and quadrature axes are taken into account by identifying the flux linkages of individual phases in terms of the flux linkages of direct and quadrature axes. The proposed model was simulated using the high-level dynamic simulation language (DSL) and its performance was compared with the standard dqo model in SIMPOW™ for a sample round rotor machine.

Investigating the impact of wake effect on wind farm aggregation

Aggregation methodologies for creating equivalent wind farm models are needed for power system transient stability studies involving large wind farms. One strong argument in the literature suggests single machine equivalent representation of wind farm with the assumption that all wind turbines receive the same incoming wind speed and thus operate at the same loading condition. In this paper, we examine how the validity of such single machine equivalent is affected under different wind speeds across a feeder in a wind farm with many WTGs. In particular, we compare the total active power output from the WTGs which indicates significant difference between single machine equivalent and full wind farm model under certain wind speed ranges and distances between the WTGs. We then conclude the need to use multi-machine equivalent representation for large wind farm in order to achieve adequate accuracy under the full range of wind conditions.

Transients in Wind Power Plants - part II: Case studies

This is the second part of a two-paper series. The first paper presented the transient modeling methodology for various components of wind power plants (WPPs). This paper presents a general methodology for transient analysis of WPPs and discusses case studies which investigate some of the most important high-frequency interactions between different components of the WPP. The focus has been on switching transients, and lighting transients have been excluded. Transient case studies conducted on a typical WPP are presented which discuss the impact of fast system surges on the performance of the circuit breaker and impact of fast surges caused by the circuit breaker on the adjacent power components. These case studies investigate the opening and closing of the collector grid vacuum circuit breaker for loaded and unloaded conditions. Simulation results provide a close match with the field measurements conducted on a laboratory prototype of a typical WPP. Differences caused by modeling assumptions or insufficient accuracy of measurement devices are highlighted. To understand the most onerous overvoltages that can be experienced in the test system, a couple of additional simulation case studies are reported. These case studies discuss the interruption of inrush current with an unloaded transformer and interruption of a small inductive current following the transformer energization.