**2.3 Basic types of FACTS controllers**

In general, FACTS Controllers can be classified into three categories (Hingorani, NG., and Gyugyi L, 1999) :

• Series Controllers

214 Electrical Generation and Distribution Systems and Power Quality Disturbances

If the dynamic series FACTS Controller (type inductive) installed at line 2-3 adjusted dynamically to deliver an inductive reactance, it increase the line's impedance from 5 Ω to 12.1Ω, so that power flows through the lines 1-2, 1-3, and 2-3 will be 248.22 MW, 1751.78

248.22 MW

**G2** 

XL=7.1 Ω

**G2** 

XL=8.1 Ω

*Series FACTS Controller*

*Series FACTS Controller*

1248.22 MW

210.33 MW

1210.33 MW

96.83%

99.86%

**1 2** 

24.82%

2000MW 1000MW

*Load*  3000MW

Load *3000MW* 

It is clear from Fig. 9 and Fig. 10, that if the series inductance is adjustable, then other power flow levels may be realized in accordance with the ownership, contract, thermal limitations,

**3** 

Fig. 11. Load flow solution with consideration of dynamic compensators: Case2

transmission losses, and wide range of load and generation schedules.

**3** 

**1 2** 

2000MW 1000MW

Fig. 10. Load flow solution with consideration of dynamic compensators: Case2

21.03%

**Case 2: Inductive Series Compensation at line 2-3** 

1751.78 MW

87.59%

MW and 1248.22 MW, respectively.

**G1** 

**G1** 

1789.67 MW

89.48%


#### **a. Series Controllers**

In Fig. 12 the series controllers could be variable impedance, such as capacitor, reactor, etc., in principle; all series controllers inject voltage in series with the line. Even variable impedance multiplied by the current flow through it, represents an injected series voltage in the line. As long as the voltage is in phase quadrature with the line current, the series Controller only supplies or consumes variable reactive.

Fig. 12. Series Controller

#### **b. Shunt Controllers**

In Fig. 13 as in the case of series Controllers, the shunt controllers may be variable impedance, variable source, or a combinaison of these.

Fig. 13. Shunt Controller

In principle, all shunt controllers inject current into the system at the point of connection. Even a variable of shunt impedance connected to the line voltage causes a variable current flow and hence represents injection of current into the line (Mahdad, 2010).

#### **c. Hybrid Controllers (Combined series-shunt)**

This could be a combination of separate shunt and series compensators, which are controlled in coordinated manner, or a unified power flow with series and shunt elements.

Understanding Power Quality Based FACTS

*Vr* **O**

α min

Fig. 16. Two SVC models representation

**3.2 Unified Power Flow Controller (UPFC)** 

*YvR*

*Vk*

sources:

*kI*

voltage. Fig. 16 shows the two SVC models basic representation.

α max

principle of the UPFC (Achat et al., 2004) , (Mahdad et al., 2005).

**~** *EvR*

Fig. 17. Equivalent circuit based on solid state voltages sources

Where *VvR* and *VcR* are the controllable magnitude,

*IvR*

1*I*

Using Interactive Educational GUI Matlab Package 217

model is based on representing the controller as a variable impedance, assuming an SVC configuration with a fixed capacitor (FC) and Thyristor-controlled reactor (TCR) as depicted in Fig. 15, the controlling element is the Thyristor valve. The thyristors are fired symmetrically, in an angle control range of 90 to 180 with respect to the capacitor (inductor)

**Power Flow** 

b) Susceptance Model a) Firing angle Model

An equivalent circuit of the UPFC as shown in Fig. 17 can be derived based on the operation

*Bus k Bus m* 

The UPFC equivalent circuit described in Fig. 17 is represented by the following voltage

*EV j vR vR* ( ) cos sin () () *vR vR* = + δ

*EV j cR cR* ( ) cos sin () () *cR cR* = + δ

*Vr* **O**

*B*max

*Vm*

(10)

(11)

*mI*

*B*min

*YcR EcR*

Re{ } <sup>0</sup> \* \* *EvRIvR* <sup>+</sup> *EcRIm* <sup>=</sup>

 δ

 δ

In Fig. 14 combined shunt and series controllers inject current into the system with the shunt part of the controller and voltage in series in the line with the series part of the controller. However, when shunt and series controllers are unified, there can be a real power exchange between the series and shunt controllers via the power link (Achat et al., 2004).

Fig. 14. Unified series-shunt Controller
