Solving the optimal power flow (OPF) problem on a large power system is computationally expensive. Network reduction and ac-to-dc network conversion can relieve this burden by simplifying the full system model to a smaller and mathematically simpler model. Traditional reduction methods, like Ward reduction, fractionalize generators when the buses they are attached to are removed, and scatters these fractions to topologically adjacent buses. In some OPF applications, this type of generator modeling is problematic. An improved approach is to keep generators intact by moving them whole to buses in reduced model and then redistributing loads to maintain base-case line flows. Determining generator placement using a traditional shortest electrical distance (SED) based method may result in cases where the OPF solution on reduced model is infeasible while the full model has a feasible solution. In this paper, an improved generator placement method is proposed. Tests show that the proposed method yields a better approximation to the full model OPF solutions and is more likely to produce a reduced model with a feasible solution if the unreduced model has a feasible solution.

%B 2014 North American Power Symposium (NAPS) %I IEEE %C Pullman, WA, USA %P 1 - 6 %8 09/2014 %R 10.1109/NAPS.2014.6965401 %0 Conference Paper %B 2012 North American Power Symposium (NAPS) %D 2012 %T Optimal generation investment planning: Pt. 1: network equivalents %A Di Shi %A Daniel L. Shawhan %A Li, Nan %A Daniel J. Tylavsky %A John T. Taber %A Ray D. Zimmerman %A William D. Schulze %K CERTS %K Eastern Interconnection %K investment planning %K optimal power flow (OPF) %K Power system modeling %K reliability and markets %K RM11-005 %XThe requirements of a network equivalent to be used in new planning tools are very different from those used in traditional equivalencing procedures. For example, in the classical Ward equivalent, each generator in the external system is broken up into fractions. For newer long-term investment applications that take into account such things as greenhouse gas (GHG) regulations and generator availability, it is computationally impractical to model fractions of generators located at many buses. To overcome this limitation, a modified- Ward equivalencing scheme is proposed in this paper. The proposed scheme is applied to the entire Eastern Interconnection (EI) to obtain several backbone equivalents and these equivalents are tested for accuracy under a range of operating conditions. In a companion paper, the application of an equivalent developed by this procedure is used to perform optimal generation investment planning.

%B 2012 North American Power Symposium (NAPS) %I IEEE %C Champaign, IL, USA %P 1 - 6 %8 09/2012 %@ 978-1-4673-2306-2 %R 10.1109/NAPS.2012.6336375 %0 Conference Paper %B 2012 North American Power Symposium (NAPS) %D 2012 %T Optimal generation investment planning: Pt. 2: Application to the ERCOT system %A Li, Nan %A Di Shi %A Daniel L. Shawhan %A Daniel J. Tylavsky %A John T. Taber %A Ray D. Zimmerman %A William D. Schulze %K CERTS %K investment planning %K Power system modeling %K power system planning %K reliability and markets %K RM11-005 %XPower system planning and market behavioral analysis using the full model of a large-scale network, such as the entire ERCOT system, are computationally expensive. Reducing the full network into a small equivalent is a practical way to reduce the computational burden. In a companion paper, a modified-Ward equivalencing procedure has been proposed. In this paper, the proposed scheme is applied to the ERCOT system to obtain several backbone equivalents, the accuracy of which are tested under a range of operating conditions. The ERCOT equivalent is used in a system planning tool to perform optimal generation investment studies with promising results observed.

%B 2012 North American Power Symposium (NAPS) %I IEEE %C Champaign, IL, USA %P 1 - 6 %8 09/2012 %@ 978-1-4673-2306-2 %R 10.1109/NAPS.2012.6336374