**3. System models**

The wind turbine operated in the OWF could be the doubly fed induction generator (DFIG) or full converter (FC). Both wind turbine models are briefly summarized in this section.

The onshore VSC-HVDC converter applies the conventional DC voltage and AC voltage (or reactive power compensation) controller. The DRU model is also introduced in this section.

#### **3.1 DFIG wind turbine model**

The basic configuration of a DFIG wind turbine is shown in **Figure 4** [1–3].

**Figure 4.** *Structure of DFIG.*

The stator of the induction machine is connected directly to the grid, and the rotor is connected to the grid through two converters: line-side converter (LSC) and rotorside converter (RSC). The LSC and RSC consist of two three-phase pulse-width modulated (PWM) converters, and they have a common DC bus. Conventionally, both converters are of three-phase two-level type having three legs, each of which consists of two IGBTs and two anti-parallel diodes as illustrated in **Figure 5**. Voltage control in these converters is done by the PWM using a carrier frequency in the order of kHz [1–3]. In this chapter, the general DFIG controllers introduced in [1–3] are applied.
