Introduction

In the 1990s the development of high power semiconductor devices found application in power electronic equipment in power systems. Such transmission systems and associated devices are generally known as Flexible AC Transmission Systems (FACTS); a comprehensive description of the technology, the devices and references to the literature are given in [1] (published in 2000).

In this chapter the tuning of stabilizers is outlined for FACTS devices such as Static Var Compensators (SVCs), the converters at the ends of High Voltage Direct Current (HVDC) transmission lines, Thyristor-Controlled Series Capacitor (TCSC), and other similar FACTS devices. Such stabilizers are generally known as Power Oscillation Dampers (PODs), however, the role of PSSs is also to act as power oscillation dampers - hence we will refer to PODs as FACTS Device Stabilizers (FDSs) to emphasize the application to FACTS devices.

Consider the studies for Cases 1 to 6 presented in the previous chapter. Referring to Tables 10.11, 10.15 and 10.16 it is noted that, for all PSSs in service with the damping gain set to 20 pu on machine MVA rating, the real parts of the mode shifts for the local-area modes typically vary from -1.3 to -2.5 Np/s over the encompassing range of operating conditions covered by the six cases. However, the real parts of the mode shifts for the inter-area modes, modes K, L and M, roughly vary over a much smaller range, from -0.4 to -1.1 Np/s for the same operating conditions. The damping of all modes in these cases is good, the lowest damping ratio being about 15%. However, because the damping of some modes may be poor, stabilizers installed on FACTS devices can provide a significant improvement in the damping of targeted modes. By reducing PSS damping gains to 5 and/or 10 pu on machine MVA ratings, cases of poorer damping are also examined in which the damping ratios of the inter-area modes are in the range 2 to 8%.

The common configuration of the FACTS device and controllers is shown in Figure 11.1. In the case of a Static Var Compensator (SVC), for example, the controller regulates the voltage at its terminals or at an electrically close, high-voltage busbar where voltage support is required [1], [2]. The location of the SVC in the network may be such that a stabilizer installed on the SVC is effective in improving the damping of certain inter-area modes.