Application of UPFC on stabilizing torsional oscillations and improving transient stability

This paper investigates the application of Unified Power Flow Controller (UPFC) to stabilize multi-mode torsional oscillations of sub-synchronous resonance (SSR), and to improve the transient stability during a three phase short circuit fault that may result in oscillatory torques on the generator rotor shaft causing serious damages to the system and may call for the disconnection of a wind farm to avoid any possible damages. Simulation is carried out using MATLAB/Simulink software. Results show that the proposed UPFC controller is very effective in damping all SSR modes of the system under study and in minimizing the potential for the wind farm disconnection during the studied faults. The proposed controller is simple and easy to be implemented

Effect of intermittent voltage source converter faults on the overall performance of wind energy conversion system

The doubly fed induction generator (DFIG) is interfaced to the AC network through voltage source converters (VSCs) which are considered to be the core of the DFIG system. This paper investigates the impact of different intermittent VSC faults on the overall performance of a DFIG-based wind energy conversion system (WECS). The fault ride through capability of the DFIG under various VSC faults is also investigated. Faults such as open circuit and short circuit across the switches, when they occur within the grid side converter (GSC) and rotor side converter (RSC), are considered and compared in this paper. Short circuit and open circuit across the DC-link capacitor are also considered in this study as common VSC problems. Simulation results indicate that the short circuit faults have a severe impact on the overall performance of the DFIG, especially when they occur within the GSC. This is attributed to the fact that the GSC directly regulates the point of common coupling voltage. The open circuit faults have less impact on the performance of the DFIG-based WECS. A proper controller along with flexible AC transmission device should be available to compensate the required active and reactive power during these faults. A protection technique is necessary to detect these faults in advance to protect the VSC switches and the machine winding from any catastrophic failure

DFIG fault ride through improvement during VSC faults

The sensitivity of the doubly fed induction generator (DFIG) to external faults has motivated researchers to investigate the impact of various grid disturbances such as voltage sag and short circuit faults on the fault ride through (FRT) capability of the DFIG. However, no attention has been given to the impact of internal faults within voltage source converters (VSCs) that interface the DFIG with the grid, on the dynamic performance of the machine. This paper investigates the impact of various VSC faults on the dynamic performance and the FRT capability of the DFIG. Faults such as fire-through and flashover within the VSC switches are considered in this paper. Moreover, faults across the DC-link capacitor are included in this study as a common problem in the VSCs. The impact of these faults when they occur within the grid side converter (GSC) and rotor side converter (RSC) are investigated. A proper STATCOM controller to mitigate the effects of these faults on the FRT is proposed. The DFIG compliance with numerous and recently released FRT grid codes under these faults with and without the STATCOM are examined and compared. Furthermore, the capability of a proposed controller to bring the voltage profile at the point of common coupling (PCC) to the nominal steady-state level under five possible VSC faults cases is examined. The proposed controller is efficient, simple, and easy to implement

Application of SMES unit to improve the performance of wind turbine conversion system

The amount of wind turbine connected to the power grid has significantly increased during the last decade. This has resulted in essential need to establish grid codes. Previously, wind turbine generators (WTGs) were allowed to be disconnected from the network during any disturbance at the grid side to avoid WTGs from being damaged. However, lately, the transmission system operators (TSOs) require WTGs to be stayed connected to provide support to the grid during fault. This new requirement has been regulated in the new grid codes. In this paper, the super conducting magnetic energy storage (SMES) unit is used to enhance the high voltage ride through (HVRT) capability of DFIG based WTG during voltage swell events at the grid side. Two new grid codes are used to verify the ability of the SMES unit to avoid the WTG from being disconnected from the grid

Combined ANFIS–wavelet technique to improve the estimation accuracy of the power output of neighboring PV systems during cloud events

The short-term variability of photovoltaic (PV) system-generated power due to ambient conditions, such as passing clouds, represents a key challenge for network planners and operators. Such variability can be reduced using a geographical smoothing technique based on installing multiple PV systems over certain locations at distances of meters to kilometers. To accurately estimate the PV system’s generated power during cloud events, a variability reduction index (VRI), which is a function of several parameters, should be calculated precisely. In this paper, the Wavelet Transform Technique (WTT) along with Adaptive Neuro Fuzzy Inference System (ANFIS) are used to develop new models to estimate the PV system’s power output during cloud events. In this context, irradiance data collected from one PV system along with other parameters, including ambient conditions, were used to develop the proposed models. Ultimately, the models were validated through their application on a 0.7 km2 PV plant with 16 rooftop PV systems in Brisbane, Australia

Impact of DC-link fault on the dynamic performance of DFIG

The number of doubly fed induction generators (DFIG) connected to the existing network has increased significantly worldwide during the last two decades. This triggers off manufactures to improve the performance of DFIG through robust and reliable design. The stator in DFIG is directly connected to the grid whereas the rotor is interfaced to the grid through two voltage source converters; rotor side converter (RSC) and grid side converter (GSC), which are considered as the crux of the DFIG system. The converter stations determine the ability of wind turbine to operate optimally during wind speed fluctuation and it can provide reactive power support to the grid during grid disturbance events. The DC capacitor link between the two converters allows optimum and smooth power exchange between DFIG and the grid. Therefore, any faults within the DC link will affect the overall performance of the DFIG. This paper investigates the impact of open circuit and short circuit faults in the DC link capacitor on the dynamic performance of the DFIG. The compliance of the wind energy conversion (WEC) system with different grid codes such as those of Denmark, Spain, Nordic and Sweden under such faults is also investigated

A heuristic approach for coordination of plug-in electric vehicles charging in smart grid

In this paper, a heuristic load management algorithm (H-LMA) is proposed for Plug-in Electric Vehicles (PEVs) charging coordination. The proposed approach is aimed to minimize system losses over a period T (e.g., 24 hours) through re-optimizing the system at time intervals (e.g., 15 minutes) while regulating bus voltages through future smart grid communication system by exchanging signals with individual PEV chargers. Scheduling is performed based on the allowable substation transformer loading level and taking into account PEV owner preference/priority within three designated charging time zones. Starting with the highest priority consumers, H-LMA will distribute charging of PEVs within the selected priority time zones to minimize total system losses over a period T while maintaining network operation criteria such as power generation and bus voltages within their permissible limits. Simulation results are presented for different charging scenarios and are compared to demonstrate the performance of H-LMA for the modified IEEE 23 kV distribution system connected to several low voltage residential networks populated with PEVs. The main contribution of this paper lies in the detailed simulations / analyses of the smart grid under study and highlighting the impacts of and T values on the performance of the proposed coordination approach in terms of accuracy and coordination execution time

Impact of intermittent misfire and fire-through on the performance of full converter based WECS

The integration of wind turbines into modern power grids has significantly increased during the last decade. The wind turbine equipped with full converter based wind energy Conversion System (FCWECS) represented about 20.3% of the worldwide total wind capacity in 2003. Since FCWECS is equipped with a voltage source inverter (VSI), it is vulnerable that misfire and fire-through may occur within the VSI switches. In this paper, impact of these switching malfunctions on FCWECS performance is investigated and discussed. Detailed simulations of the system under study are carried out using Matlab/Simulink to highlight the influence of these converter internal faults on PCC voltage, DC link voltage and shaft speed, as well as generator active and reactive power. Furthermore, compliance of the FCWECS with Spain fault ride through (FRT) grid codes is also investigated

Performance of heuristic optimization in coordination of plug-in electric vehicles charging

A heuristic load management (H-LMA) algorithm is presented for coordination of Plug-in Electric Vehicles (PEVs) in distribution networks to minimize system losses and regulate bus voltages. The impacts of optimization period T (varied from 15 minutes to 24 hours) and optimization time interval (varied 15 minutes to one hour) on the performance, accuracy and speed of the H-LMA is investigated through detailed simulations considering enormous scenarios. PEV coordination is performed by considering substation transformer loading while taking PEV owner priorities into consideration. Starting with the highest priority consumers, HLMA will use time intervals to distribute PEV charging within three designated high, medium and low priority time zones to minimize total system losses over period T while maintaining network operation criteria such as power generation and bus voltages within their permissible limits. Simulation results generated in MATLAB are presented for a 449 node distribution network populated with PEVs in residential feeders