Optimal Control of a Doubly Fed Induction Generator of a Wind Turbine in Island Grid Operation

Great significance is given to the use of energy from renewable sources, especially in industrial and municipal applications. The present article is devoted to the optimal control of a DFIG generator with the help of a rotor-side converter (RSC). Its aim is to ensure the delivery of the voltage of a three-phase network with appropriate parameters while operating in an islanded grid. Such a grid is usually characterized by an uneven loading of each phase. Additionally, the load of these phases changes randomly in time. In order to ensure the assumed parameters of line voltages, the optimal control is applied with a square cost function. This ensures the shape of voltage that is in accordance with the referential voltage. Moreover, higher harmonics with a given number are detected and reduced. The simulations that were executed confirm compliance with the conditions of the parameters of the output voltage in the islanded grid. Attention was paid to oscillations in the power flowing through the rotor-side converter (RSC). The methods to accelerate the suppression of these oscillations are presented.

Islanding Detection Using a Micro-Synchrophasor for Distribution Systems with Distributed Generation

Distributed Generation (DG) has changed the power generation system to small-scale instead of large-scale generation. The demanding issue with the interconnection of DG is the detection of unintended islanding in a network. Several methods proposed in the literature show drawbacks such as high non-detection zones (NDZ) and higher tripping time. In this paper, the IEEE 13 bus distribution network with DGs like wind and solar power plants is integrated at two buses. Islanding is detected by utilizing data from a micro-synchrophasor located at the distribution grid and the DG. The micro-synchrophasor-based unintended islanding detection algorithm is based on parameters such as voltage, rate of change of voltage, frequency, rate of change of frequency, voltage phase angle difference and the rate of change of the voltage phase angle difference between the utility and the islanded grid. The proposed islanding detection algorithm discriminates between islanding and non-islanding conditions and is highly efficient under zero power mismatch conditions. The proposed method has null NDZ and satisfies the IEEE 1547 standard for DG tripping time. The effectiveness of the proposed IDM was verified when there are multiple DGs in the islanded grid. Also, the proposed method does not require additional hardware as it can be incorporated in digital relays with synchrophasor functionality.

Adaptive Command-Filtered Backstepping Control for Virtual Synchronous Generators

Distributed energy sources are usually interfaced to the grid using power electronic converters, and lack of inertia in inverter dominated microgrids can affect the system stability. This paper presents a new method for virtual synchronous generator (VSG) control in order to solve the low system inertia and support the grid frequency problem. In this paper, the VSG based on electromagnetic transient characteristics is improved and an adaptive command filter back-stepping controller is designed. Firstly, the rotor swing equation and power part are modeled to complete the controller design for achieving system stability in the islanded, grid-connected and transition modes. In addition, a limited-amplitude command filter is used to deal with computational complexity and nonlinear saturation problems in the design process. Secondly, projection operator, and adaptive inertia and damping control are introduced to reduce the modeling error and disturbance caused by changing parameters. This ensures the boundedness of the estimated value and further improves the frequency response, especially in the transition mode. Finally, simulation results show that the proposed controller is more effective than the traditional control method for achieving power stability and frequency improvement.