Abstract
With the increasing proportion of inverter-connected power resources (ICPR), commonly known as variable renewable energy (VRE), has posed excessive challenge to maintain the frequency of dynamic stability on the electrical power grid, in addition to causing the displacement of traditional synchronous generators, which has resulted in a lower inertial response and a lower frequency response capacity. Non-synchronous generating units, wind turbines and photovoltaic units are fundamentally different technologies: rotating turbines and static solar panels, which can also augment frequency degradation during an under frequency transient.The work presents a technique for assessing the available inertia level in the network based on the measured frequency in three mapped local zones. Analysis is performed on how inertia is affected in different specific local zones of the power system while a loss of large generation units occurred.
In this study, stationary grid storage systems are investigated as a means of supporting system inertia and providing fast compensation to stabilise the frequency with an acceptable range, thus preventing the degradation of inertial response and the severity of ROCOF. These grid energy storage systems (GESS) are also being studied to show how their frequency response on an electrical power grid can allow the required level of frequency regulation to be provided to reduce excursions and minimise the initial rate of change of frequency. The impact of fast triggered response via its droop response on frequency deviation and nadir is demonstrated in terms of additional power response from stationary GESS deployed into the systems. Stationary GESS can be connected at the network level to coordinate the provision of fast triggered response to help maintain the frequency stability during grid under frequency transients.
This thesis introduces new concepts that can help to change the existing operational policies to ensure safe and reliable network services and develop a range of frequency services based on the grid battery energy storage. There is a need for services that can increase system resiliency based on a fast-triggered response using a droop mechanism with a deadband around the acceptable frequency range to preserve system stability with limited synchronising torque and governor response. The modification of ROCOF and new operational strategies are also Abstract iii proposed in this study to address the problems of low inertia systems due to the increasing share of non-synchronous generating units.
Model simulations include sources of thermal and wind generation units (22% to 60% wind penetration) to investigate the various and adverse impacts of realistic changes to power system frequency. This work has analysed and adopted vanadium redox battery (VRB) units to deliver grid-level storage. VRBs offer highly appropriate resources for grid-level applications including: 1) deep (80%) depth of discharge (DoD) for repetitive and recurrent events; 2) long (>20 years) operating lifetime (MTBF); 3) low terminal voltages; and 4) low battery operating. A storage model has been developed (using MATLAB/Simulink software) to validate the use of VRBs in transient event applications. This flow battery energy storage can serve to solve the challenge of frequency control on the transmission grid and solve problems with the distribution network because the transmission grid has different problems compared to the distribution systems. A VRB model is proposed and a hybrid centralised VRB unit has been developed to provide fast response for large-scale grid applications.
A simulation model of the eastern Danish transmission system with a large wind farm (60% penetration) has been developed in DIgSILENT Power-Factory to analyse system stability following generation loss. The hybrid battery-supercapacitor unit exhibits important dynamic responses, which restrict frequency nadir and support responses, principally under the most demanding conditions when the integration level of inverter-connected wind generation is >50%. The study includes discussion of transitional issues affecting grid code revision and evolution.
| Date of Award | Dec 2022 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | D John Morrow (Supervisor) & Timothy Littler (Supervisor) |