Scherbius wind farm based fuzzy SSSC

Received Aug 24, 2019 Revised Feb 14, 2020 Accepted Mar 20, 2020 The wind is a clean, free, and readily available renewable energy source, it is cost-effective in several regions, it is a domestic source of energy and it is a sustainable source of energy. The SSSC system is a FACTS voltage compensator, it is inserted in series with the electrical transmission line through a coupling transformer, its role is to inject a voltage which allows to influence the active power transmitted. The goal of this paper is to examine the effect of using a wind farm SSSC to improve flexibility of a multimachine perturbed network.


INTRODUCTION
The world energy market wind turbine is growing faster than any other renewable energy source. Total worldwide, which did not exceed 4800 [1,2].
The synchronous series static compensator SSSC is a modern FACTS which provides voltage compensation, it is placed directly on the line [3]. Its presence translates into several advantages in terms of loss and planning and energy circulation [4,5].
The phenomena that impair the quality of electrical energy are of different natures: short circuit, voltage dips, breakdowns, harmonic pollution. Whatever the origin of these disturbances, it is essential to maintain or improve the quality of the electricity that passes through the transmission and distribution networks [6,7].
In this work we will study the advantage of the uses of wind-SSSC to increase transit power stability in the case of multi bus, multi machines perturbed network.

SCHERBIUS DFIG WIND SYSTEM
The Scherbius wind turbine system using a DFIM and an indirect matrix converter back-to-back converter, has many assets [8][9][10]. One of the advantages of this configuration is that the power elements used are dimensioned to pass part of the total power of the system, which makes it possible to reduce the power losses, illustrated in Figure 1 [11,12]. The dual feed induction machine is a powered rotor asynchronous machine with stator windings connected to the network through a power converter [13,14]. The simplified model is presented in Figure 2 [15]. The wind farm is an association of several wind turbines in series, each one is constitued of a double feed asynchronous machine, 850kW / 690V wound rotor sized for an air density of 1.225 kg / m 3 with a rotation speed between 14.6 and 30.8 rpm [16][17][18].

STATICS SYNCHRONOUS SERIES COMPENSATOR BASED WIND FARM
The composition of the synchronous static compensator in series of (SSSC) is based on three parts: the first is a continuous source or else the continuous storage element which is behaved from batteries, it will be determined according to the need for network, the second part is presented by the DC-AC converter and with the help of the command it can be used as an adjustable voltage source,the third part presents the output filter es the series coupling transformer, as described in Figure 3 [19,20].  Figure 4 shows the equivalent circuit of the network equipped with the synchronous series static compensator [21]. The r and L are parameters of including series transformer. The dynamic behavior of currents in Park coordinate system is given by:

Modelling and control of WSSSC
The active P and reactive powers Q to be controlled are given by equations (2) and (3) below: )

Fuzzy control
Some processes are inherently difficult to model because they vary over time or cannot be correctly represented by a linear model. In this case, the regulator setting parameters will not be optimal and the 1281 system may not be properly controlled. This is why we introduce the notion of fuzzy logic [22]. Figure 5 shows the decomposition into three main stages of a fuzzy controller [23]. a. Fuzzification of the inputs is the evaluation of the membership functions of the input variables. b. The inference engine: the evaluation of the output functions by the rules table c.
Dfuzzification: evaluation of the fuzzy controller output by calculating the center of gravity) [24].

STUDIED SYSTEM
Our objective is to examine the effect of the synchronic static serial compensator on the stability of an IEEE-14 node network, and demonstrate its feasibility. In a first section, the IEEE-14 bus network will be presented, and after that in a second section, a fault near a generator node will be applied under the simulation study; and finally, the WSSSC will be introduced to solve the problem of voltage drop propagation [25,26]. The WSSSC is installed in the most perturbed in the node 8 as shown in Figure 6.

Uses of WSSSC
In this case the WSSSC is connected to the bus 8, As in the previous section, we present the voltage curve in eache node of network in Figures 21 to 34, the voltage of WSSSC is mentioned in Figure.35, the impact of this voltage restore the network to its stability and cancela te the propagation of the disturbance caused by the fault.   Table 1 shows the voltage drop in the nodes. There is a deletion almost total voltage drop for all nodes except bus 8 (the default location).

Discussion of results
The WSSSC prevents the consequences of the fault (voltage drop, harmonics,...) from reaching the other regions of the electrical network.
The SSSC can't manage to eliminate the consequences of the defect totally, and this amounts to the maximum compensation capacity delivered by the WSSSC.

CONCLUSION
In this work, we examine the impact of a cascading wind farm as an SSSC which is a FACTS capable of compensating for voltage, faced with the propagation of voltage drops in the case of the IEEE 14 bus. The results obtained show that WSSSC provide a strong action in the voltage compensation and reduction of losses in power lines. Its uses make it possible to cancel the propagation of voltage drops in the network. However, in the case of a multi-machine network and loop lines, several compensators must be used to obtain perfect compensation.