TCCC model

The TCCC is composed of two bidirectional Graetz bridges, a coupling transformer with three windings, harmonic filters, and passive elements, as shown in Figure 4. The model of the thyristor is composed of an inductor Ltyr, a resistor Rtyr, and a DC voltage source that represents the forward voltage Vft. These components are connected in series. A logical signal that depends on the gate signal g, the current IAK, and the voltage VAK controls the switch. A series Rsnub-Csnub snubber circuit is connected in parallel with the thyristor model. Figure 11(b) shows the static VI characteristic of the model. The thyristor and TCCC parameters are shown in Tables 1 and 2.

#### Steam turbine model

According to Figure 12, the steam turbine model is composed of a four-stage steam turbine, a shaft with up to four masses, a speed governing system, and an automatic generation control (AGC) system. The speed governing system is composed of a servomotor that regulates the

Figure 11. (a) Thyristor model and (b) static VI characteristic of the thyristor.


Table 2. TCCC parameters.

Figure 12. Steam turbine model.

turbine valve, a proportional regulator, and a speed relay. A PI regulator performs the secondary frequency control at the AGC subsystem. In this work, the load variations of the steam turbine are less than 4%; therefore, the boiler pressure is assumed constant during the simulation time [39].
