Since large scale unscheduled tripping of wind power generation could lead to power system stability problem. Thus network interconnection regulations become more rigid when the wind power penetration reaches a non-neglible portion of the total power generation. This thesis presents a comparison of five different low voltage ride through (LVRT) capability enhancement technologies, i.e., additional rotor resistance, DC bus chopper, crowbar on rotor, the combination of above schemes, and grid voltage support by controlling grid side converter. System simulations are performed under Digsilent environment with model and control blocks provided by the package. Additional models are developed to implement the LVRT enhancement schemes studied. A Doubly-Fed Induction Generator (DFIG) with pitch control is used to simulate different system fault scenarios with different voltage sag magnitude and duration time. Simulation results indicate that different enhancement schemes provide various levels in relieving DC bus overvoltage, rotor winding overcurrent, and overspeed problems, and the method combines all tested schemes seems to provide the best result.

Large off-shore wind farms raise the concern of widespread tripping of off-shore wind generator in the presence of system faults and corresponding voltage dips that could potentially cause system wide blackout. In this thesis an offshore wind farm and three different types of power transmission are modeled and studied using simulation software. Off-shore wind farm composed of fixed speed induction generators and HVAC interconnection, HVAC interconnection plus STATCOM and HVDC interconnections are studied. Onshore grid faults are simulated for each interconnection. Voltage tolerance curves are established to assess fault ride through capability of each interconnection and compared with different grid transmission ride through capacity required by grid operator.

When more induction generator based wind farms are integrated into the power system, the system voltage dips and stability problems may arise due to the draw of reactive power by induction generators. The power system short-circuit event induced wind turbine trips could result in power imbalance and lead to power system instability. This thesis studies the influence of two compensation techniques on the wind turbine low voltage ride-through (LVRT) capability. One of which is based on a parallel compensation by a static synchronous compensator (STATCOM), and the other one is a series compensation by a dynamic voltage restorer (DVR). In this study, Matlab tools and models are used to simulate an active-stall controlled fixed-speed induction generator connected to a power system. Two system configurations are used to simulate three phase faults and compare the improvement of wind turbine LVRT capability due to the two studied compensation techniques. Simulation results indicate that wind turbine compensated by DVR would have better LVRT performance than that by STATCOM in dealing with the low voltage situations due to system faults.

Attempts to reduce greenhouse gas emissions are promising with the recent dramatic increase of installed renewable energy sources (RES) capacity. Integration of large intermittent renewable resources affects smart grid systems in several significant ways, such as transient and voltage stability, existing protection scheme, and power leveling and energy balancing. To protect the grid from threats related to these issues, utilities impose rigorous technical requirements, more importantly, focusing on fault ride through requirements and active/reactive power responses following disturbances. This dissertation is aimed at developing and verifying the advanced and algorithmic methods for specification of protection schemes, reactive power capability and power control requirements for interconnection of the RESs to the smart grid systems. The first findings of this dissertation verified that the integration of large RESs become more promising from the energy-saving, and downsizing perspective by introducing a resistive superconducting fault current limiter (SFCL) as a self-healing equipment. The proposed SFCL decreased the activation of the conventional control scheme for the wind power plant (WPP), such as dc braking chopper and fast pitch angle control systems, thereby increased the reliability of the system. A static synchronous compensator (STATCOM) has been proposed to assist with the uninterrupted operation of the doubly-fed induction generators (DFIGs)-based WTs during grid disturbances. The key motivation of this study was to design a new computational intelligence technique based on a multi-objective optimization problem (MOP), for the online coordinated reactive power control between the DFIG and the STATCOM in order to improve the low voltage ride-through (LVRT) capability of the WT during the fault, and to smooth low-frequency oscillations of the active power during the recovery. Furthermore, the application of a three-phase single-stage module-integrated converter (MIC) incorporated into a grid-tied photovoltaic (PV) system was investigated in this dissertation. A new current control scheme based on multivariable PI controller, with a faster dynamic and superior axis decoupling capability compared with the conventional PI control method, was developed and experimentally evaluated for three-phase PV MIC system. Finally, a study was conducted based on the framework of stochastic game theory to enable a power system to dynamically survive concurrent severe multi-failure events, before such failures turn into a full blown cascading failure. This effort provides reliable strategies in the form of insightful guidelines on how to deploy limited budgets for protecting critical components of the smart grid systems.