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This paper deals with the integration and control of the doubly fed induction generatorbased wind turbine (DFIG-WT) in a DC grid. In this way, the stator of the DFIG-WT is integrated with the DC grid via an uncontrolled diode-bridge rectifier as well as a buck converter to provide a flexible connection path. In addition, the rotor of the DFIG-WT exchanges power with the DC grid through a rotor-side converter (RSC). By considering the DFIG-WT system topology, three control strategies based on the stator flux-oriented vector control are developed for the RSC and buck converter. The control schemes consist of the outer and the inner control loops with the proportional-integral (PI) controllers. Additionally, the stability of control strategies and their dependence on the generator parameters are evaluated and compared using modal analysis and numerical simulations in the MATLAB/SIMULINK environment. Finally, a real-time hardware-inthe-loop emulation-based OPAL-RT 5600 is accomplished to assess the performance of the superior control method from a practical perspective.

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Single-phase voltage source inverters (SP-VSIs) are widely used in grid connected solar photovoltaic (PV) systems. This paper deals with the dynamic modeling and stability analysis of single-phase grid connected PV inverters taking the PLL dynamics into account. The PLL structure employed in this paper includes two control branches; the main branch, known as phase estimation loop, extracts the phase and frequency of the grid voltage and the other branch, known as voltage peak estimation loop, determines the grid voltage amplitude. In this way, the paper first proposes design considerations for the dc-link voltage control and PLL control loops. Then, unified dynamic modeling of the SP-VSI system comprising PLL, dclink dynamics and grid is presented and linearized block diagram of the whole system is extracted. The linearized block diagram depicts the interaction between the control loops of the PLL and dc-link system, where the PLL control loops consist of phase/frequency and amplitude estimation loops of the grid voltage. Next, the small signal stability of the full system is presented, and impacts of grid strength, operating point, and PLL closed loop bandwidth on the performance of SP-VSI are investigated by the modal analysis and time domain simulations.

Commonly, a simple topology consisting of a single diode‐rectifier and pulse‐width‐modulation (PWM) converter is used for the connection of the doubly‐fed induction generator‐based wind turbines (DFIG‐WTs) to the DC grid, in which the rotor‐side converter (RSC) and the stator diode‐rectifier are linked to the common DC bus. But, this topology suffers from less flexibility due to the requirement of matching the stator nominal voltage with the DC grid. Hence, in this paper, a buck converter is added to the DFIG‐WT topology and two methods are proposed to control the power converters, where in the first one, the RSC regulates the active power and stator flux linkage, and in the second one, the RSC regulates the DC bus voltage and stator flux linkage. Then, the small‐signal stability and the performance of the DFIG‐WT system with the mentioned control strategies are compared analytically and through the off‐line simulations. At last, a real‐time hardware‐in‐the‐loop (HIL) emulation‐based OPAL‐RT is carried out to investigate the performance of the proposed control methods from a practical perspective.