Dynamics of a hydro-wind hybrid isolated power system

Implementation of Distributed Generation (DG) can improve power quality and reliability, and guarantee continuity of power supply. This paper addresses the issue of continuity of power supply especially for isolated communities. A part of a network can be electrically isolated from the main grid when the grid fails to supply power due to a fault in the network or unavailability of power generation. In this paper, a mini hydro-wind hybrid power system is considered, and operation and control of the hybrid system during connecting it with the grid as well as its operation in the isolated condition are investigated. The system behaviour and DG responses are also examined. Islanding operation is the most sensitive and problematic operation in power systems. Simulation has been conducted with PSCAD/EMTDC on a hypothetical test system for different scenarios and results are presented

Black start with DFIG based distributed generation after major emergencies

Grid connected distributed generation (DG) increases reliability and additional benefits for consumers as well as utilities. The stable and reliable operation of a power system is necessary after major emergencies (or blackouts) following a major system event. Distributed generation may be capable of black start and contribute to fast restoration process at medium to low voltage level. A large scale voltage and frequency excursions may occur during the process of black start with distributed generation due to low inertia and intermittency in power generation. Energy storage integrated with DG can absorb initial impact of central generation and ensure smooth load pickup during the restoration of a system. In this paper, the process of black start with a doubly fed induction generator (DFIG) based wind turbine is addressed and energy storage in DC link of DFIG is used for fast restoration after blackout. A control system has been developed for the process of black-start with DFIG. A sequence of actions for black start procedure is presented and tested

Control stabilisation of an Islanded system with DFIG wind turbine

Distributed Generation (DG) is often used to export power to the utility system. Loss of main supply can cause a severe loading mismatch between DG generation and load consumption. Consequently, the voltage and frequency of the islanded system will cross the allowable limit. Due to this fact, it is essential to control the voltage and frequency in the islanding mode of operation. In this paper, control stabilisation of an islanded system with a doubly-fed induction generator (DFIG) wind turbine has been addressed. Wind DG produces variable output and is not capable to produce enough reactive power. Hence, it is imperative to develop better control system for the islanding operation of wind system. Voltage and frequency control strategies of a doubly fed induction generator (DFIG) with energy storage for islanding operation have been developed. The investigation has been carried out through modeling of a doubly fed wind turbine and an energy storage system using SimPowerSystems tools of MATLAB. The simulations have been carried out in stand-alone operation of DFIG during various wind penetration

Energy storage system for reduction of mid-line voltage variation of a DFIG wnd turbine connected to a weak grid

Penetration of wind power into electricity system is constantly increasing. Wind resources are usually distant from existing transmission lines. Wind farms are often connected to weak grids far from central generation stations. Maximum wind power extraction causes the more irregular and unpredicted power output of wind turbine, which has same nature as wind speed variation. The voltage in such long line is vulnerable with the consumption and generation imbalance. In a long line, the mid-line voltage is largely affected by the variation and the penetration of the wind fluctuating power. Fluctuating nature of wind power output and long transmission line have led to concern that the voltage disturbances impressed on the weak system may become unacceptable. Fluctuating power and X/R ratio are key contributors for unnecessary voltage fluctuation and variation along the feeder. Control of the wind power fluctuation and variation can prevent the excessive voltage fluctuation and variation in the system. The weak grid with a doubly fed induction generator (DFIG) wind turbine has a higher probability of the voltage variation due to the fluctuations of the wind speed and load demands. To compensate the variation of power and voltage in a weak grid system, an energy storage system can be designed to provide fast controllable responses. In this paper, effect of energy storage system for reduction of voltage variations has been investigated. The investigation has been carried out through modelling of a doubly fed wind turbine and an energy storage system using SimPowerSystems tools of MATLAB. 1

Control Stabilization of Multiple Distributed Generation

Grid connected distributed generation (DG) increases reliability and additional benefits for consumers as well as utilities. Recently, different types of DG are connected into distribution networks. Different control phenomena are applied based on types of DG. The stable and reliable operation of such power system requires sophisticated control. This paper presents a small-signal analysis for investigating dynamic behaviours of the system with multiple DG and also investigating control interactions between different types of DG. Dynamic model of a synchronous generator (SG) based hydro generator and inverter based photovoltaic/ wind distributed resources are considered for case studies to investigate grid connected and islanding mode of operation

Impact of DFIG based wind generation on grid voltage and frequency support

Recent trends indicate replacement of fossil fuel drivenconventional synchronous generators from the existing power grid withinverter interfaced renewable energy sources in coming years. Asignificant portion of these renewable energy sources is predicted toinclude doubly fed induction generator (DFIG) based wind turbine. Thiswill cause a significant change in the grid dynamics, due to reduced systeminertia and the intermittent nature of wind power. The impact of gridintegration of DFIG-bases wind turbines on the grid voltage and frequencyhas been presented in this paper through rigorous simulation studiescarried out using the professional simulation software PSS/E. Thesimulation studies are carried out on a power grid network model thatincludes hydro, gas and wind generation under different voltage andfrequency contingencies or disturbances. Models of commercially availableDFIG-based variable speed wind turbines from top manufacturers havebeen used in the simulation studies. The effect of inertia, loss of generationsand loads on the system frequency, as well as the impact of different faultson system voltage are investigated and thoroughly analyzed. Furthermore,this study also includes the assessments of grid code requirements underfor high penetration of DFIG based wind turbines in the power grid.Critical analysis of the simulation studies reveal that DFIG-based windturbines are capable to contribute to system frequency and voltageregulation under different contingencies or network disturbances