Design and simulation of unified power flow controller with grid storage

Abstract

Power flow between two transmission systems across an uncontrolled interface can be problematic if there is unequal sharing between the tie lines. System configuration changes such as generation dispatch, or out of service elements can cause thermal overloads. In addition, some weaker areas of the system which may have insufficient transmission can have difficultly supporting the voltage at buses with high loading particularly after the loss of one element.

This thesis presents a real transmission system which has two problems: a thermal limitation caused by unequal tie-sharing across an uncontrolled interface, and a post-fault voltage stability concern. Various potential solutions are analyzed and shown to address one or the other of these two problems; none of which were capable of solving both. A Unified Power Flow Controller (UPFC) is proposed which can effectively address both problems and can provide additional benefit in the form of a grid storage interface.

The operational characteristics of a UPFC are analyzed and used to develop an electrical model and control system topology. The model with its control system is implemented in PSCAD. The UPFC is proven to be capable of effectively addressing the thermal limitation and voltage stability issues of the system. Further, a battery is added to the UPFC to provide grid energy storage. Cost saving measures through controller design are also proposed and implemented.

This work demonstrates that a UPFC can be an effective solution to typical problems (such as thermal and voltage constraints) faced by a transmission system. A UPFC with grid storage can also provide an alternative to building costly transmission lines or generation by enhancing reliability, reducing demand on generation cause by system peaks, smoothing intermittent generation, etc.