Operating Modes and Their Regulations of Voltage-sourced Converter Based Facts Controllers

Voltage-sourced converter (VSC) based FACTS controllers are capable of providing fast voltage support and active power flow control to improve the power transfer capability over congested transmission paths. In most published literature, a shunt VSC such as a Static Synchronous Compensator (STATCOM) is set to control the bus voltage and a series VSC such as a Static Synchronous Series Compensator (SSSC) is set to control the line power flow. In practical operations, however, there are other control modes that are more appropriate, such as fixed reactive power setpoint control for a shunt converter and fixed injected voltage control for a series converter. In this research work, we aim to investigate the modeling, simulation, and control of various operating modes and their regulations of VSC-based FACTS controllers embedded in transmission networks. The first major task of this research work is to study the impact of these FACTS controllers in both normal operation and rated-capacity operation. The second major task is to develop dynamic models so that the regulations of the various control modes can be properly investigated. The third major task is to design damping controllers supplemental to the regulations to improve small-signal stability. In this thesis work, an efficient control mode implementation has been proposed to implement steady-state dispatch of various operating modes of FACTS controllers, using an approach of separate models for a shunt VSC and for a series VSC. If the DC buses of the two converters are coupled, then an appropriate active power circulation constraint can be added to the VSC operating constraints. With this implementation, we only need to select and combine the appropriate equations of the shunt VSC, the series VSC, and the DC link coupling to form the specified FACTS controller and to operate it in the desired operating mode. Because the maximum dispatch benefit of an FACTS controller often occurs when it operates at its rated capacity, efficient dispatch strategies to optimize line power flow transfer have also been proposed when one or both VSCs of the FACTS controller are loaded