Multi-Band Subsynchronous Damping Controller for Type III DFIG Wind Turbines with Single Mass and Multi-Mass Rotor Models

Abstract

Sub-Synchronous Interactions (SSI), are a family of issues involving the exchange of energy between the generation system and the transmission system, most often found in situations involving series compensated transmission lines. These sub-synchronous oscillations present a hazard to generation systems, transmission systems, and connected equipment that can result and have resulted in catastrophic failure. A subset of SSI are known as Sub-Synchronous Control Interactions (SSCI). SSCI involves the interaction between the power electronic based excitation control of a Type III wind generator and the transmission system. A key feature of SSCI is the fact that they are a completely electrical interaction and as a result, large oscillations can develop much more quickly than with an electro-mechanical oscillation such as the well-studied Sub-Synchronous Resonance (SSR). Because of the speed with which SSCI's develop, quick corrective action must be taken to eliminate these incidents. Doubly Fed Induction Generators (DFIG) have been observed to have experienced SSCI's when connected radially through a series compensated transmission line. This thesis develops a Multi-Band Sub-Synchronous Damping Controller (MBSSDC), which will leave the existing generator protection and control system in place while adding protection against SSCI. The MBSSDC is run in parallel with the main control loop of the generator. The solution envisioned uses a two band controller. This represents a simple and elegant solution to the problem of sub-synchronous control interactions between Type III wind generators and series compensated transmission lines. A solution to a problem of particular interest to North American utilities, due to the influx of wind power to their systems and the prevalence of long transmission lines in their systems.