The example shows the application of an SSSC based on a two-level converter for EMT simulation. The grid is composed of two voltage sources and three 110 kV parallel lines. The SSSC is installed at the end of one of the lines and controls the current through the line. It is designed to inject a maximum voltage of ±10 kV.

The example shows the behavior of the SSSC during changes in the reference current and during a short-circuit on a parallel line. During the changes in the reference current, the injected voltage changes from capacitive to inductive. During the short-circuit the SSSC is bypassed, emulating the insertion of a thyristor bypass switch at its terminals. The short-circuit is cleared by disconnecting the affected line and the SSSC continues to control the current on to its initial value by varying the injected voltage.

The SSSC PWM converter control is implemented using a Modelica Model and is sourced from “CIGRE 371, STATIC SYNCHRONOUS SERIES COMPENSATOR (SSSC), WG B4.40, 2009”, Figure 8.4. The injected voltage is controlled by keeping a constant pulse modulation factor and varying the PWM DC capacitor voltage. The minimum absolute value of the injected voltage reference is limited to avoid complete discharge of the PWM DC capacitor voltage during changes from capacitive to inductive mode (or vice versa).

Sampling time for the controller is assumed to be 10 kHz. The sampling time can be changed in the Modelica model (ElmMdl) “SSSC control” (Clocked Model – Sampling period). The initial value of the injected voltage is entered as -5,4963 kV, which is also the voltage injected by the SSSC in the load flow calculation. If the load flow settings are changed, the new injected voltage has to be entered in kV as a parameter in the Modelica model (ElmMdl) “SSSC control” (Parameters - ictrl - piwithreset - integratorantiwindupreset  - y0).