The principle of a STATCOM (Static Synchronous Compensator) is to provide reactive power compensation and voltage control in an electrical power system. It is a type of power electronics-based device used in power systems to improve the stability and quality of electrical power.

The STATCOM operates by regulating the flow of reactive power in the power system. Reactive power is required for magnetizing electric devices and maintaining voltage levels. By injecting or absorbing reactive power as needed, the STATCOM helps to compensate for reactive power imbalances and voltage fluctuations.

The key principle behind the STATCOM is its ability to generate or absorb reactive power rapidly and continuously. It achieves this through the use of power electronics, including voltage source converters (VSCs) and insulated-gate bipolar transistors (IGBTs). The VSCs convert the DC power from a capacitive energy storage element (such as a capacitor) into AC power and inject it into the power system to provide reactive power support. The IGBTs control the switching of the VSCs to regulate the magnitude and phase of the injected or absorbed reactive power.

The control system of a STATCOM continuously monitors the voltage and current signals in the power system. It calculates the required amount of reactive power compensation based on the system conditions and adjusts the operation of the STATCOM accordingly. This control mechanism enables the STATCOM to respond rapidly to voltage fluctuations and variations in reactive power demand.

In summary, the principle of a STATCOM revolves around the rapid and precise control of reactive power injection or absorption to maintain voltage stability and improve power system performance. It is a flexible and dynamic solution for mitigating power quality issues and enhancing the overall efficiency and reliability of electrical power networks.

We usually call high voltage Static var generator SVG in China.