Penetration Of Wind Turbine Generators Research Articles

Impact of installing renewable energy sources on a small-scale power network in the Caribbean

Many small island states in the Caribbean like Antigua and Barbuda depend heavily on petroleum-based products for power generation. Given the fluctuating oil prices, there is now an urgent push for increased energy security. Antigua is one of the fastest-growing islands for grid-connected Renewable Energy Sources (RES). Whilst the increase in grid-connected RES improves the islands’ energy security, and it is equally important to understand the impact that RES have on the network’s reliability and security. Thus, a base case model of the power network was built, and the following areas were analysed: load flow, contingency analysis, and fault analysis. The Antigua Public Utilities Authority (APUA) 69kV power network is used as a case study for this project. PowerWorld and Homer Energy software have been used to simulate and model the grid. Results from the project show that RES changes the power flow and could help to improve the system voltage profile if placed correctly. Whilst increased penetration of Wind Turbine Generators (WTG) on the grid increases the system fault levels, they also play a key role in active and reactive power control. This means that the APUA network must be more flexible, and system operators must have network visibility to react to changes on the network. The aim of this paper is to investigate the impact that RES (in particular, wind and solar PV) has on the operational, security, or reliability of a small-scale power network.

Damping sensitivity analysis and optimized battery controller for small-signal stability enhancement in wind penetrated networks

Alarming greenhouse gaseous emissions is one of the key factors for meeting future energy demand from sustainable eco-friendly resources like wind and solar. These resources use power electronic converters for the interconnection with the grid resulting in their zero/low inertia response. This can lead to non-deterministic damping of low-frequency oscillations in the power system. Moreover, this may impose Small-Signal Stability (SSS) challenges for the secure operation & control of power systems. A two-stage method is proposed in this paper to enhance the damping of multiple critical modes in large interconnected networks with high penetration of wind turbine generators (WTGs). Damping Ratio Sensitivity Index (DRSI) at a candidate location is the summation of sensitivities of damping ratios (DRs) of critical electromechanical modes (EMs) against inertia. But, the sensitivities of DRs of various EMs w.r.t inertia at a specific candidate location can be equal and opposite. This can lead to their mutual cancellation and hence DRSI may not be sufficient to identify the impact of WTGs in networks with multiple critical EMs. Thus, stage-1 of the proposed method introduces an improved Weighted Damping Sensitivity Ratio (WDSR) for identifying the locations for integrating WTGs with beneficial impacts on SSS. It assigns weight to the sensitivity factors of DRs and hence annihilates the problem with their amalgamation which exists in the case of DRSI. The modified WDSR performs the sequential computation of DR sensitivity analysis. This ensures that the variations in the DR sensitivities of critical modes against inertia due to WTG integration are not ignored. A multiband Optimized Battery Damping Controller (OBDC) is proposed in stage-2 for improving the damping of critical inter-area (IA) modes in networks with high WTG penetration. The location of the battery energy storage system (BESS) is determined based on a stability index. The proposed multiband controller is implemented using a single BESS and is optimally tuned for the most vulnerable operating scenarios identified for the critical modes. The performance of the proposed two-stage method is evaluated using the modified IEEE 68 bus system for a wide range of operating conditions and it is observed that damping of all the critical modes has improved to more than 5% in each operating scenario.

Assessing the Use of Reinforcement Learning for Integrated Voltage/Frequency Control in AC Microgrids

The main purpose of this paper is to present a novel algorithmic reinforcement learning (RL) method for damping the voltage and frequency oscillations in a micro-grid (MG) with penetration of wind turbine generators (WTG). First, the continuous-time environment of the system is discretized to a definite number of states to form the Markov decision process (MDP). To solve the modeled discrete RL-based problem, Q-learning method, which is a model-free and simple iterative solution mechanism is used. Therefore, the presented control strategy is adaptive and it is suitable for the realistic power systems with high nonlinearities. The proposed adaptive RL controller has a supervisory nature that can improve the performance of any kind of controllers by adding an offset signal to the output control signal of them. Here, a part of Denmark distribution system is considered and the dynamic performance of the suggested control mechanism is evaluated and compared with fuzzy-proportional integral derivative (PID) and classical PID controllers. Simulations are carried out in two realistic and challenging scenarios considering system parameters changing. Results indicate that the proposed control strategy has an excellent dynamic response compared to fuzzy-PID and traditional PID controllers for damping the voltage and frequency oscillations.

Automated Dispatch of Wind Power On Microgrid For Voltage Regulation

The variability of wind power generation adversely affects the grid conditions and the utilities find it challenging to accommodate variations in the injected wind power. To resolve this issue utilities impose curtailment of wind power generation. Demand side management (DSM) strategies have gained popularity among utilities in recent years. An advanced Demand Response (DR) scheme known as Demand Dispatch (DD) enable utilities to reshape demand curve to closely follow generation. An automated DD strategy is proposed as a solution to the issues related to high penetration of wind turbine generators (WTG) on micro grid. It basically balances the WTG power injection with real time controlled dispatchable loads. DD adopts smart communication for real time data collection as well as for dispatchable load management. A field implementation of DD in maintaining voltage stability in a DC microgrid with micro-WTG (m-WTG) is studied. The experiment results presented validate the scheme.

Application of a Superconducting Fault Current Limiter to Enhance the Low-Voltage Ride-Through Capability of Wind Turbine Generators

The penetration of wind turbine generators onto the grid has grown worldwide at unprecedented rates in recent years. This raises the concern that the tripping of wind turbine generators could potentially cause system collapses. To alleviate these concerns, wind turbine generators need to maintain connection with the grid when a grid fault occurs. This has provoked many countries to adopt low-voltage ride-through (LVRT) for wind turbine generators. The LVRT is the capability of wind turbine generators to maintain connectivity during certain periods of voltage sag. The wind turbine generators should be connected to the grid to support fault recovery. Also, wind turbine generators must provide reactive power according to the grid voltage sag. Therefore, much research has been focused on enhancing LVRT capability. To enhance LVRT capability, this paper proposes the application of a superconducting fault current limiter (SFCL) in the system. The fault current was suppressed and the voltage sag was improved through the application of the SFCL. By improving the voltage sag, the wind turbine generator and the grid were able to maintain a connection. However, suppression of the fault current can cause a problem in the overcurrent relay (OCR) trip time delay. The trip time delay was solved by OCR resetting. Through a power system computer-aided design/electromagnetic transients including DC (PSCAD/EMTDC), the enhancement of LVRT capability and improvement of the trip delay was confirmed.

Set Theory-Based Safety Supervisory Control for Wind Turbines to Ensure Adequate Frequency Response

Inadequate frequency response can arise due to a high penetration of wind turbine generators (WTGs) and requires a frequency support function to be integrated in the WTG. The appropriate design for these controllers to ensure adequate response has not been investigated thoroughly. In this paper, a safety supervisory control (SSC) is proposed to synthesize the supportive modes in WTGs to guarantee performance. The concept, region of safety (ROS), is stated for safe switching synthesis. An optimization formula is proposed to calculate the largest ROS. By assuming a polynomial structure, the problem can be solved by a sum of squares program. A feasible result will generate a polynomial, the zero sublevel set of which represents the ROS and is employed as the safety supervisor. A decentralized communication architecture is proposed for small-scale systems. Moreover, a scheduling loop is suggested so that the supervisor updates its boundary with respect to the renewable penetration level to be robust with respect to variations in system inertia. The proposed controller is first verified on a single-machine three-phase nonlinear microgrid, and then implemented on the IEEE 39-bus system. Both results indicate that the proposed framework and control configuration can guarantee adequate response without excessive conservativeness.

Reliability assessment of distribution system with the integration of renewable distributed generation

Recent studies have shown that renewable energy resources will contribute substantially to future energy generation owing to the rapid depletion of fossil fuels. Wind and solar energy resources are major sources of renewable energy that have the ability to reduce the energy crisis and the greenhouse gases emitted by the conventional power plants. Reliability assessment is one of the key indicators to measure the impact of the renewable distributed generation (DG) units in the distribution networks and to minimize the cost that is associated with power outage. This paper presents a comprehensive reliability assessment of the distribution system that satisfies the consumer load requirements with the penetration of wind turbine generator (WTG), electric storage system (ESS) and photovoltaic (PV). A Markov model is proposed to access the stochastic characteristics of the major components of the renewable DG resources as well as their influence on the reliability of a conventional distribution system. The results obtained from the case studies have demonstrated the effectiveness of using WTG, ESS and PV to enhance the reliability of the conventional distribution system.

에너지저장장치와 결합한 WTG를 포함하는 전력계통의 Capacity Credit 평가 및 ESS 적정규모 평가방안

This paper proposes a new method for evaluating Effective Load Carrying Capability(ELCC) and capacity credit(C.C.) of power system including Wind Turbine Generator(WTG) combined with Battery Energy Storage System(BESS). WTG can only generate electricity power when the fuel(wind) is available. Because of fluctuation of wind speed, WTG generates intermittent power. In view point of reliability of power system, intermittent power of WTG is similar with probabilistic characteristics based on power on-off due to mechanical availability of conventional generator. Therefore, high penetration of WTG will occur difficulties in power operation. The high penetration of numerous and large capacity WTG can make risk to power system adequacy, quality and stability. Therefore, the penetration of WTG is limited in the world. In recent, it is expected that BESS installed at wind farms may smooth the wind power fluctuation. This study develops a new method to assess how much is penetration of WTG able to extended when Wind Turbine Generator(WTG) is combined with Battery Energy Storage System(BESS). In this paper, the assessment equation of capacity credit of WTG combined with BESS is formulated newly. The simulation program, is called GNRL_ESS, is developed in this study. This paper demonstrates a various case studies of ELCC and capacity credit(C.C.) of power system containing WTG combined with BESS using model system as similar as Jeju island power system. The case studies demonstrate that not only reasonable BESS capacity for a WTG but also permissible penetration percent of WTG combined with BESS and reasonable WTG capacity for a BESS can be decided.

Modelling and validation of a squirrel cage induction generator wind turbine during connection to the local grid

The increasing penetration of wind turbine generators (WTGs) into power systems can affect many network operational aspects such as stability and power quality. The accurate, validated representation of these generators and their components for studying particular operational events, such as cut-in and soft-starting, short-circuit faults and generator switching, remains a challenge. Accurate simulation is particularly important for investigating stability interactions within weak grids or localised networks (e.g. micro-grids or islanded networks). One of the events producing major transient interaction between a WTG and a local grid is the grid connection itself. A simulation model of the use of a soft-starter during the grid connection of a wind turbine equipped with a squirrel cage induction generator and thyristor-based soft-start module is presented. This model has been validated using experimental measurements taken from a wind turbine generator in an operational wind farm site. The analysis focuses on verifying the transients produced during the short-time after the connection to the local grid. Existing literature presents insufficient details about this particular process as well as the practical performance of the soft-starter. It is further demonstrated that ambiguities in this subject may lead to mistaken conclusions in technical assessments carried out by wind farm operators and Distribution Network Operators (DNOs).

Penetration of Wind Turbine Generator into a 50MW Capacity Diesel Power Electric Line System.

Development of a wind turbine generator (WTG) system in Japan seems to have lagged far behind compared with that in European countries and the United States. However, NEDO (New Energy and Industrial Technology Development Organization) has recently reported that Japan is also abundant in wind energy resources, based on a several-year systematic survey conducted throughout the country and that Japan could expect to obtain electricity to meet about 10-20% of national electricity demand from wind resources alone. One of the difficulties of WTG development is the fluctuation in speed and direction of natural wind, which causes fluctuations in both voltage and frequency in the electric utility system. Therefore, the problem that needs to be solved is how far WTG capacity may penetrate into that of the conventional existing electric power systems, for instance, diesel power systems on remote islands. This paper evaluates the actual performance of two 250 kW WTG pilot plants connected to a diesel power electric line system of about 50 MW located on the Miyako islands, Okinawa, Japan. Wind energy resources and wind characteristics on the islands are reported, and the fluctuation of the WTG output and its influence on the total systems are determined and also numerically analyzed. It is confirmed that the multiple WTGs have a tendency to cancel out each other's fluctuations at a rate inversely proportional to the square root of the number. From the results of the investigation and analysis, it is estimated that on the objective island WTG capacity of as much as 10 MW may be permissible, that is, 20% of the existing diesel system only if the WTG system consists of forty 250 kW machines or a much greater number of smaller-scale wind turbine generators.