A New Perspective of Wind Power Grid Codes Under Unbalanced and Distorted Grid Conditions

Increasing penetration of wind power has led power system operators worldwide to develop new grid codes for integration of a wind power plant (WPP) onto the grid. According to the grid codes issued by Federal Energy Regulatory Commission (FERC) in the US, a WPP must have low voltage ride through (LVRT) capability, power factor design criteria, and supervisory control and data acquisition (SCADA) system to ensure power system reliability. Fast Fourier transform (FFT) is frequently used to measure root mean square (RMS) voltage, power factor, and for supervisory data acquisition in order to verify that a WPP conforms to the grid code requirements. However, FFT inherently assumes signal is periodic in nature, and it provides misleading results under unbalanced and distorted grid conditions. To overcome these issues, this work proposes a new method for wind power grid codes based on time-frequency analysis technique. Unlike FFT, it provides accurate result both in steady-state and transient conditions. The efficacy of the proposed method is verified by applying it to computer simulated and real-world cases provided by National Renewable Energy Laboratory (NREL) in the US. Time-frequency analysis is performed utilizing Time-Frequency Toolbox (TFTB) in MATLAB® developed for the analysis of non-stationary signals

Test system requirements for modelling future power systems

This paper discusses the need for new test system models to be developed and made available to researchers. A number of features of such test systems are proposed. These include sufficient size and scope to allow control interactions to be studied but not so much that phenomena associated with new technologies cannot be understood. It is recalled that the performance of new technologies and their controls should be verified on a full system model that is as faithful to the real system and its parameters as possible and that this requires access to data often owned by generating companies to which system operators have access but do not feel able to disclose. Finally, arguments are presented as to why such data should be disclosed and it is recommended that regulatory authorities take steps to achieve it

Active power control in a hybrid PV-storage power plant for frequency support

The recent increase of intermittent power generation plants connected to the electric power grids may stress the operation of power systems. So, grid codes started considering these power plants should con- tribute to the grid support functions. Recently, a power ramp rate limitation is being included in several grid codes, which is a challenge for photovoltaic installations due to the lack of inertia. This paper pre- sents a method to deal with the main grid code requirements considering a PV plant with an energy stor- age device, where a strict two-second time window ramp rate restriction is applied. A direct ramp rate control strategy is used, which includes a dynamic SOC control and battery support functionality for active power setpoint compliance. The control strategy is validated by simulations.Postprint (published version

Benefits of demand-side response in providing frequency response service in the future GB power system

The demand for ancillary service is expected to increase significantly in the future Great Britain (GB) electricity system due to high penetration of wind. In particular, the need for frequency response, required to deal with sudden frequency drops following a loss of generator, will increase because of the limited inertia capability of wind plants. This paper quantifies the requirements for primary frequency response and analyses the benefits of frequency response provision from demand-side response (DSR). The results show dramatic changes in frequency response requirements driven by high penetration of wind. Case studies carried out by using an advanced stochastic generation scheduling model suggest that the provision of frequency response from DSR could greatly reduce the system operation cost, wind curtailment, and carbon emissions in the future GB system characterized by high penetration of wind. Furthermore, the results demonstrate that the benefit of DSR shows significant diurnal and seasonal variation, whereas an even more rapid (instant) delivery of frequency response from DSR could provide significant additional value. Our studies also indicate that the competing technologies to DSR, namely battery storage, and more flexible generation could potentially reduce its value by up to 35%, still leaving significant room to deploy DSR as frequency response provider

International White Book on DER Protection : Review and Testing Procedures

This white book provides an insight into the issues surrounding the impact of increasing levels of DER on the generator and network protection and the resulting necessary improvements in protection testing practices. Particular focus is placed on ever increasing inverter-interfaced DER installations and the challenges of utility network integration. This white book should also serve as a starting point for specifying DER protection testing requirements and procedures. A comprehensive review of international DER protection practices, standards and recommendations is presented. This is accompanied by the identifi cation of the main performance challenges related to these protection schemes under varied network operational conditions and the nature of DER generator and interface technologies. Emphasis is placed on the importance of dynamic testing that can only be delivered through laboratory-based platforms such as real-time simulators, integrated substation automation infrastructure and fl exible, inverter-equipped testing microgrids. To this end, the combination of fl exible network operation and new DER technologies underlines the importance of utilising the laboratory testing facilities available within the DERlab Network of Excellence. This not only informs the shaping of new protection testing and network integration practices by end users but also enables the process of de-risking new DER protection technologies. In order to support the issues discussed in the white paper, a comparative case study between UK and German DER protection and scheme testing practices is presented. This also highlights the level of complexity associated with standardisation and approval mechanisms adopted by different countries

Impacts Power Flow And Quality Of Penetrating 50MW Wind Plant Into Stand Alone Grid

The demand for electricity is continuously growing due to the development in community's macro-economic parameters; Population and the Gross Domestic Product (GDP). Currently, electricity is mainly generated from conventional sources including fossil fuels (oil, coal, gas, etc.) and nuclear fuel. The increase in demand increases the concerns about depletion of fossil fuels, increasing of carbon dioxide (C02) and other emissions, environmental pollution, and climate changes. Global energy agencies have been urged to look for sustainable and environment friend resources. Renewable energy resources especially wind and solar resources are found ambitious sources that can be developed to share other resources in supplying sustainable environmental friend power due to their economic benefits as compared with other resources and technologies. Energy generated from wind is growing faster than other renewable resources especially at areas with proper wind speed and characteristics capable to generate high power at small land and the possibility to interconnect wind networks with distribution or transmission power networks. Predictability of wind availability and characteristics is limited; therefore, the output of wind turbines cannot be controlled to the same extent as conventional generation technologies. This study involves assessing the impact of interconnecting a 50 MW wind plant at different penetration levels into a 132-kV grid powering a region in the sultanate of Oman isolated (islanded) from the main national grid. The assessment includes mutual impacts on power quality and flow, grid voltage flickering and performance of the network and the farm under steady state and disturbance conditions. The wind plant is constructed from an 18-equal capacity DFIG wind turbines modelled using the simulation from MA TLAB/Simulink available in the college. Parameters of control and operation parameters were developed to fit the wind plant operating conditions. The penetration levels considered in the research include I, 9 & 18 wind turbines in operation respectively which represent 5.5 %, 50 % and 100 % of the maximum farm generation capacity. The research outcomes revealed that penetrating the wind plant at the levels mentioned above provide high accuracy of compliance with the national and international standards and codes and that it shall not conflict the requirements of power quality and security of supply restricted in grid code and regulations. The outcomes obtained also provide high degree of confidence for integrating the wind plant with the existing grid network at the proposed point of common connection (PCC) without any additional extra works required on the existing network rather than those required for adaptation requirements

Power Quality Improvement and Low Voltage Ride through Capability in Hybrid Wind-PV Farms Grid-Connected Using Dynamic Voltage Restorer

© 2018 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission.This paper proposes the application of a dynamic voltage restorer (DVR) to enhance the power quality and improve the low voltage ride through (LVRT) capability of a three-phase medium-voltage network connected to a hybrid distribution generation system. In this system, the photovoltaic (PV) plant and the wind turbine generator (WTG) are connected to the same point of common coupling (PCC) with a sensitive load. The WTG consists of a DFIG generator connected to the network via a step-up transformer. The PV system is connected to the PCC via a two-stage energy conversion (dc-dc converter and dc-ac inverter). This topology allows, first, the extraction of maximum power based on the incremental inductance technique. Second, it allows the connection of the PV system to the public grid through a step-up transformer. In addition, the DVR based on fuzzy logic controller is connected to the same PCC. Different fault condition scenarios are tested for improving the efficiency and the quality of the power supply and compliance with the requirements of the LVRT grid code. The results of the LVRT capability, voltage stability, active power, reactive power, injected current, and dc link voltage, speed of turbine, and power factor at the PCC are presented with and without the contribution of the DVR system.Peer reviewe

Voltage dip generator for testing wind turbines connected to electrical networks

This paper describes a new voltage dip generator that allows the shape of the time profile of the voltage generated to be configured. The use of this device as a tool to test the fault ride-through capability of wind turbines connected to the electricity grid can provide some remarkable benefits: First, this system offers the possibility of adapting the main features of the time–voltage profile generated (dip depth, dip duration, the ramp slope during the recovery process after clearing fault, etc.) to the specific requirements set forth by the grid operation codes, in accordance with different network electrical systems standards. Second, another remarkable ability of this system is to provide sinusoidal voltage and current wave forms during the overall testing process without the presence of harmonic components. This is made possible by the absence of electronic converters. Finally, the paper includes results and a discussion on the experimental data obtained with the use of a reduced size laboratory prototype that was constructed to validate the operating features of this new device

Requirements to Testing of Power System Services Provided by DER Units

The present report forms the Project Deliverable ‘D 2.2’ of the DERlab NoE project, supported by the EC under Contract No. SES6-CT-518299 NoE DERlab. The present document discuss the power system services that may be provided from DER units and the related methods to test the services actually provided, both at component level and at system level

Energy storage in the UK electrical network : estimation of the scale and review of technology options

This paper aims to clarify the difference between stores of energy in the form of non-rechargeable stores of energy such as fossil-fuels, and the storage of electricity by devices that are rechargeable. The existing scale of these two distinct types of storage is considered in the UK context, followed by a review of rechargeable technology options. The storage is found to be overwhelmingly contained within the fossil-fuel stores of conventional generators, but their scale is thought to be determined by the risks associated with long supply chains and price variability. The paper also aims to add to the debate regarding the need to have more flexible supply and demand available within the UK electrical network in order to balance the expected increase of wind derived generation. We conclude that the decarbonisation challenge facing the UK electricity sector should be seen not only as a supply and demand challenge but also as a storage challenge. (c) 2010 Elsevier Ltd. All rights reserved