Nowadays, the doubly-fed induction generators (DFIGs) based wind turbines (WTs) are the dominant type of WTs. Traditionally, the back-to-back converters are used to excite the rotor circuit of DFIG. In this paper, an indirect matrix converter (IMC) is proposed to control the generator. Compared with back-to-back converters, IMCs have numerous advantages such as higher level of robustness, reliability, and reduced size and weight due to the absence of bulky electrolytic capacitor. According to the recent grid codes wind turbines must have low voltage ride-through (LVRT) capability. In this paper a new crowbar system is proposed so that along with the control system it protects the IMC from large fault currents and supports the grid voltage dips during grid faults. This crowbar system is provided using the existing converter switches to establish a short circuit mode without any extra circuitry. Even in severe fault conditions, the duration of short circuit mode is quite small so the control system will be activated shortly after the fault to inject reactive power as required by new LVRT standards. Therefore, the new LVRT standards are well satisfied without any extra costs. PSIM simulation results confirm the efficiency of the proposed method. 1. Introduction Wind energy has been found as the fastest growing renewable power generation resources over the world. Government support and advancement in technology of WT have accelerated this rapid growth. Based on estimation the wind power capacity becomes double every three years [1]. Due to their superior characteristics, most of the grid-connected WTs operate at a variable speed. Among the different variable speed types, the DFIG is the most promising one. The stator winding of DFIG is directly connected to the grid, while the rotor winding is connected to the grid through an ac-ac power electronic converter having bidirectional switches. Traditionally the back-to-back converters are used to excite the rotors of DFIGs. The presence of the dc-link capacitor in this arrangement is a serious drawback as it increases the costs and reduces the overall lifetime of the system and also makes the system bulky [2]. In this paper, the back-to-back converter arrangement is replaced by an indirect matrix converter (IMC) to control the generator as shown in Figure 1. The main advantages of a matrix converter are robustness, reliability with less size and weight due to the absence of the bulky electrolytic capacitor, controllable input power factor, nearly sinusoidal input current, and output voltage with only switching
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