88 PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 90 NR 7/2014 A. L. L. Murari 1 , H. G. Tabares 1 , G. A. L. Vargas 1 , E. A. Belati 1 , V. A. de Sousa 2 , M. B. C. Salles 3 and A. J. Sguarezi Filho 1 UFABC (1), UFSCar (2), USP - PEA (3) Study of Transmission System with Wind Power Control and Optimal Reactive Power Flow Abstract. This paper presents a methodology of controlling the power injected into system by wind generators and the use of Optimal Reactive Power Flow (ORPF). The methodology used two stages: in the first one scheme for Doubly-Fed Induction Generator (DFIG) is realized to control the active and reactive powers, in the second stage, the ORPF based in the Modified Barrier Lagrangian Function approach (MBLF) is used to optimize reactive power dispatch aiming to minimize active power losses system. Case studies on the modified IEEE 14 bus "modified" clearly shows the benefits of using the associated generator control whit ORPF. Streszczenie. Artykuł przedstawia metodologię sterowania dołączaniem energii z elektrowni wiatorwych do systemu energetycznego oraz użytkowania algorytmu RRPF – Optimal Reactive Energy Flow. W pierwszym etapie analizowano sterowanie generatorem typu DFIG w celu kontroli mocy biernej i czynnej, w drugim etapie wykorzystano metodę MBLF (Modified Barrier Lagrangian Function) do optymalizowania mocy biernekj w systemie. Analiza systemu energetycznego ze sterowaną mocą elektrowni wiatrowych i optymalnym przesyłem mocy Keywords: Optimal Reactive Power Flow; Wind Power Control; Transmission System Słowa kluczowe: optymalizacja mocy biernej, sterowanie mocą, system energetyczny. doi:10.12915/pe.2014.07.17 1. Introduction Year after year technology and society´s “eco-thoughts” evolved together, bringing out new concepts such as sustainability and green corporative compliances. The human development and the access of technology makes energy demands continuously grows while natural sources like: oil, coal and gas becomes low . World consumption of electrical energy will increase by 84% between 2008-2035 [1], while in Brazil the increase will be 4.6% between 2010- 2020 [2]. At this scenario smart grids involving hybrids power generation systems into distributed power generation created a new era for energy distribution. These systems are usually composed by parallel connection of photovoltaic solar panels and wind generators. Although the most advantageous solution for standalone use is the wind generator [3], where the energy produced by wind is considered technically usable when at a height of 50m the winds have speeds of at least 7 m/s [4]. The doubly fed induction generator (DFIG) is a generator type commonly employed in this type of application [5]. The techniques for independent control of active and reactive powers of DFIG are traditionally performed by the technique of the stator flux orientation or grid voltage by controlling the rotor currents [6]. Initially the aero generators were designed to operate with unity power factor, however, some studies [7] [8] presents techniques for controls reactive power of DFIG, that enable the operation of the generator supplying reactive to the network. With the reactive power control of the DFIG, the optimal reactive power injection can be evaluated respecting the DFIG´s constraints for wind speed, specified load/generation and constraints of the power system. This optimal can be evaluated via optimal reactive power flow (ORPF), which promotes management efficiencies, as improvements in voltage profile and lower losses in active power. The ORPF is a non convex static nonlinear programming problem; it is one of the most powerful tools to analyses static systems of electrical energy. The ORPF used has the objective of minimizing a function and, at the same time, of satisfying a set of physical and operational constraints in power systems, e.g. reactive power injection constraint. As a solution, it provides the optimal operation point for the electrical network for a given load and generation configuration of the system satisfying all system constraints. It was proposed by Carpentier in the early 60's based on the economic dispatch problem [9]. Since then, many papers have been written in an attempt to solve the problem [10-13]. This work considers the reactive power injection capacity of a wind farm using DFIG to optimize the active power losses in a power system. In this way is proposed to use an ORPF for a system with DFIG. The DFIG´s power control is achieved by using stator flux orientation and proportional plus integral controller. The dynamic machine model was used to obtain the steady state output of active and reactive power to be supplied to the ORFP algorithm. The ORPF algorithm uses the Modified Barrier Lagrangian Function (MBLF) [14] in the process solution. In the section 3 the ORPF problem and MBLF is displayed. Thus, the contribution of this paper is the analyzes of the benefits of the reactive power injection, by an wind farm with reactive power control, to the power system provided by optimal reactive power injecting control performed via ORPF. This paper is organized as follows: Section 2 presents the machine model and rotor current vector control. Section 3 describes the ORPF approach used. The simulation results, which demonstrate the effectiveness of the analyses, are shown and discussed in Section 4. Finally, in Section 5 some concluding remarks are made. 2. Wind Generator Control 2.1. Rotor side converter: For decoupled control of active and reactive power, it is necessary the induction machine dynamics model, also assuming stator flux, where the flux vector is aligned with the direct axis sdq sd s       , and sdq sq s v v v    [5]. The DFIG power control is achieved by rotor current control. Hence the independent stator active P and reactive Q power control. In this case, P and Q are computed by each individual rotor current. The active and reactive power are done by [5], (1) rq s M s i L L v P 2 3   (2)           rd s M s s s i L L L v Q  2 3