Research article Maximum power extraction under different vector-control schemes and grid-synchronization strategy of a wind-driven Brushless Doubly-Fed Reluctance Generator Mohamed G. Mousa n , S.M. Allam, Essam M. Rashad Department of Electrical Power and Machines Engineering, Faculty of Engineering, Tanta University, Egypt article info Article history: Received 15 May 2017 Received in revised form 22 August 2017 Accepted 6 October 2017 Keywords: Brushless Doubly-Fed Reluctance Generator Wind energy conversion system Grid-synchronization strategy Vector control Soft starting Maximum wind-power extraction Unity power factor Minimum converter current abstract This paper proposes an advanced strategy to synchronize the wind-driven Brushless Doubly-Fed Re- luctance Generator (BDFRG) to the grid-side terminals. The proposed strategy depends mainly upon determining the electrical angle of the grid voltage, θ v and using the same transformation matrix of both the power winding and grid sides to ensure that the generated power-winding voltage has the same phase-sequence of the grid-side voltage. On the other hand, the paper proposes a vector-control (power- winding flux orientation) technique for maximum wind-power extraction under two schemes sum- marized as; unity power-factor operation and minimum converter-current. Moreover, a soft-starting method is suggested to avoid the employed converter over-current. The first control scheme is achieved by adjusting the command power-winding reactive power at zero for a unity power-factor operation. However, the second scheme depends on setting the command d-axis control-winding current at zero to maximize the ratio of the generator electromagnetic-torque per the converter current. This enables the system to get a certain command torque under minimum converter current. A sample of the obtained simulation and experimental results is presented to check the effectiveness of the proposed control strategies. & 2017 ISA. Published by Elsevier Ltd. All rights reserved. 1. Introduction Due to the cost increase, limited reserves, and adverse en- vironmental impact of fossil fuels [1,2], the development of renewable energy sources has been attracting a great attention from researchers [3,4]. Wind Energy Conversion System (WECS) is one of the top growing renewable energy technologies in the world [5]. The wind energy has proved to be a clean, abundant, and completely renewable source of power. Therefore, it is eco- nomical to use the wind energy in producing electric power especially in rural areas [5]. The wind turbine is a very effective component in WECS that converts the wind kinetic-energy into mechanical energy that can be used to drive an electrical generator. The wind-turbine generator converts the output mechanical energy of the wind turbine into electric power and can be connected either to stand-alone loads or connected to the utility grid. The squirrel-cage induction generator, doubly-fed induction generator and synchronous generator are the most common generators that have been used in WECS [1]. Wind turbines can be classified into fixed-speed and variable-speed tur- bines. The main drawback of fixed-speed turbines is that the max- imum power-conversion efficiency can be achieved only at a certain wind speed. However, variable-speed wind turbines can achieve maximum power-conversion efficiency over a wide range of wind speeds, since the turbine can continuously adjust its rotational speed according to the wind speed [1]. In order to make the turbine speed adjustable, the wind-turbine generator is normally connected to the utility grid through a power electronic converter. The power rating of the converter is normally the same as that of the generator. This results in increasing the overall system cost [6]. Brushless Doubly-Fed Machine (BDFM) is a special form of slip recovery machines that reduce the capacity of the required con- verter to be used if the required speed-control range is limited. This will lead to a significant reduction in the drive-system cost [7]. Therefore, the use of this type of machines would be a cost- effective one that should be used in variable-speed WECS. The Brushless Doubly-Fed Induction Machine (BDFIM) and the Brush- less Doubly-Fed Reluctance Machine (BDFRM) are the two main competitors attracting most of the attention from researchers [8]. The rotor design of both BDFIM and BDFRM ensures robustness, Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/isatrans ISA Transactions http://dx.doi.org/10.1016/j.isatra.2017.10.005 0019-0578/& 2017 ISA. Published by Elsevier Ltd. All rights reserved. n Corresponding author. E-mail addresses: mohamed.hussien3@f-eng.tanta.edu.eg (M.G. Mousa), sm_allam@f-eng.tanta.edu.eg (S.M. Allam), emrashad@ieee.org (E.M. Rashad). Please cite this article as: Mousa MG, et al. Maximum power extraction under different vector-control schemes and grid- synchronization strategy of a wind-driven Brushless Doubly-Fed.... ISA Transactions (2017), http://dx.doi.org/10.1016/j.isatra.2017.10.005i ISA Transactions ∎ (∎∎∎∎) ∎∎∎–∎∎∎