Q13Power Quality and FACTS

STATCOM Overview

A STATCOM (Static Synchronous Compensator) is a shunt-connected FACTS device built around a voltage source converter (VSC) that generates a controllable AC voltage from a DC capacitor. It is connected to the power system bus through a coupling transformer and functionally behaves like an ideal synchronous condenser, exchanging reactive power (and, with storage, real power) with the network.

Principle of Operation

The STATCOM's VSC generates a fundamental-frequency voltage V_conv that is synchronized in phase with the system bus voltage V_sys but whose magnitude is controllable. Reactive power exchange between the STATCOM and the system is determined by the magnitude difference between V_conv and V_sys across the coupling transformer's leakage reactance. If V_conv is greater than V_sys, the STATCOM supplies (generates) reactive power to the system, acting as a capacitor. If V_conv is less than V_sys, the STATCOM absorbs reactive power from the system, acting as an inductor. When the two voltages are equal in magnitude, no reactive power flows.

Since the reactive current exchanged depends on the converter's own generated voltage rather than on the system voltage magnitude directly, the STATCOM can maintain its rated reactive current output even during low-voltage conditions, unlike a purely passive SVC. This gives it superior dynamic performance during faults and voltage sags, faster response time, and a smaller physical footprint compared to conventional synchronous condensers.

Applications

• Dynamic voltage regulation and support at transmission and distribution buses
• Power factor correction and reactive power compensation
• Damping of power system oscillations and improvement of transient stability
• Mitigation of voltage flicker from fluctuating loads such as arc furnaces