Transfer capacity estimation using extended DC-model for systems with phase shifting transformers

An interconnected power system is made of several areas that can exchange power through tie lines. Some or all of these tie lines are equipped with Phase Shifting Transformers (PSTs). These transformers are widely used for active power flow control and increasing the transfer capacity of that area. In a multi-area power system operation, an operator within a control area should know the maximum power that can be imported to the area for the best possible operation of the system. Various optimization techniques are mentioned in power system literature. The AC power flow algorithm if opted for optimization does not result in linear equations and makes the problem more complicated due to the nonlinear nature.;The objective of this research is to optimally evaluate the maximum power that can be imported to a particular area and to obtain optimum settings for the PSTs. This research work suggests an Extended DC power flow model for estimation of transfer capacity of a system. Instead of using AC Power Flow algorithm which leads to complex mathematical expressions and complicates the optimization problem, a DC Power Flow model is used for the systems involving PSTs. The suggested model makes use of Bus Incidence and Loop incidence matrices to derive simple linear expressions that relate the line flows to the phase shifts introduced by the PSTs. Linear Programming is used for the optimization process. The proposed technique is tested for the IEEE standard systems using MATLAB.