An investigation on AC loss reduction for permanent-magnet wind power generator with superconducting windings

High temperature superconducting (HTS) tapes could be introduced into large scale wind power generators in order to improve the power density. However, the alternating current (AC) loss of HTS tapes will cause the reduction of efficiency. On the basis of analytical and numerical model calculations, this paper presents an optimal design of the HTS armature winding aiming at lower AC loss. The main contribution of this work is that the relationship between the installation parameters and the AC loss of such HTS armature windings has been figured out based on the analysis of the shape feature of the HTS tape and the external magnetic field. When the tape is placed along a particular direction where the perpendicular component of external magnetic field has the lowest amplitude, the AC loss is the smallest. The modified installation location and angle are found based on the proposed generator. These results are verified using finite element method (FEM).

Event-Based Under-Frequency Load Shedding Scheme in a Standalone Power System

Under-frequency load shedding (UFLS) prevents a power grid from a blackout when a severe contingency occurs. UFLS schemes can be classified into two categories—event-based and response-driven. A response-driven scheme utilizes 81L relays with pre-determined settings while an event-based scheme develops a pre-specified look-up table. In this work, an event-based UFLS scheme is presented for use in an offshore standalone power grid with renewables to avoid cascading outages due to low frequency protection of wind power generators and photovoltaic arrays. Possible “N-1” and “N-2” forced outages for peak and off-peak load scenarios in summer and winter are investigated. For each forced outage event, the total shed load is minimized and the frequency nadir is maximized using particle swarm optimization (PSO). In order to reduce the computation time, initialization and parallel computing are implemented using MATLAB/Simulink because all forced outage events and all particles in PSO are mutually independent. A standalone 38-bus power grid with two wind turbines of 2 × 2 MW and photovoltaics of 7.563 MW was studied. For each event, the proposed method generally obtains a result with a smaller shed load and a smaller overshoot frequency than the utility and existing methods. These simulation results verify that the proposed method is practically applicable in a standalone power system with penetration of renewables.

Airflow Characteristics According to the Change in the Height and Porous Rate of Building Roofs for Efficient Installation of Small Wind Power Generators

In this paper, the air flow characteristics and the impact of wind power generators were analyzed according to the porosity and height of the parapet installed in the rooftop layer. The wind speed at the top was decreasing as the parapet was installed. However, the wind speed reduction effect was decreasing as the porosity rate increased. In addition, the increase in porosity significantly reduced turbulence intensity and reduced it by up to 40% compared to no railing. In the case of parapets with sufficient porosity, the effect of reducing turbulence intensity was also increased as the height increased. Therefore, it was confirmed that sufficient parapet height and high porosity reduce the effect of reducing wind speed by parapets and significantly reducing the turbulence intensity, which can provide homogeneous wind speed during installation of wind power generators.

Prospects for Increasing the Dynamic Efficiency of Asynchronous Double-Feed Machines and Wind Power Generators Using Structural Methods and Solutions

The chapter proposes to consider the problems of control of asynchronous machines with dual power supply, as a nonlinear structure, the transfer functions of which depend on the frequency of the stator voltage and the relative slip. The authors cite the results of research confirming the high efficiency of control of asynchronous electric motors, using cross-dynamic connections on the developed torque or a signal close to it (active component of the motor stator current). The proposed correction operates in a wide range of changes in the rotation and sliding speeds of the asynchronous electric generator. This is especially important for wind turbines that need to remain efficient at different speeds. As a justification, the results of experiments, modeling and industrial application of control algorithms with positive torque coupling are presented. Research results suggest that such algorithms will improve the efficiency of wind power by 5–10%.