Nilesh Modi

Presentations:

Power system operation with a high share of inverter-based resources

Traditionally, power system operation has been dominated by a large share from synchronous generators to meet the demand. They have provided a number of inherent system security needs such as system strength, inertia, voltage and frequency control when dispatched to meet the demand. With increase uptake of transmission and distribution connected inverter-based resources (IBR) such as wind farms, solar farms, batteries and rooftop photovoltaic puts downward pressure on traditional synchronous generator dispatch. The marginal cost of generation from wind farms, solar farms and batteries are much cheaper than traditional fossil fuel generation. Also, increased generation from rooftop photovoltaic reduces the operational demand to be supplied from the grid-connected generators.

The displacement of synchronous generators from the grid also reduces some of the inherently provided system security services such as fault current and inertia. System strength is important for the normal power system operation, for the power systems dynamic response during a disturbance, as well as for returning the power system to stable operating conditions. System inertia is a key quantity for power system operation which helps to reduce the rate of change of frequency following a disturbance. Power system operation with a high share of IBR requires the development of unique solutions to some power system challenges such as system strength and inertia. Accurate assessment of system strength requires fit for purpose models. As power system transition towards a large share of IBR power system security assessment using traditional root-mean-square (RMS) models would not fully capture model dynamics associated with IBR Electromagnetic transient (EMT) models, which are used by original equipment manufacturers (OEMs) for designing their equipment, captures these fast-changing dynamics which are particularly important for low system strength conditions. Batteries that can provide fast frequency response could help to stabilize power system frequency in a low inertia grid and can substitute power system inertia.

This lecture will highlight system security challenges associated with operating a grid with high transmission and distributed connected IBR, discuss key aspects of system strength, inertia and fit for purpose modelling tools. The Australian power system will be used as a case study and share the operational experience of operating a grid with a high share of inverter-based resources.

Emerging bulk power system security challenges

The increasing penetration of renewable generation to decarbonize power grids around the world has given rise to widespread impacts on the power system operation and planning. As a result, the generation mix in many power systems worldwide is changing rapidly over the last few years. This increases the complexities of power system operation and present unprecedented operational challenges due to increased penetration of inverter-based resources (IBR). Large update in transmission and distribution connected IBR often results into early retirement or mothballing of traditional synchronous generators which provide some of the system security services such as inertia, contribution to system strength, voltage and frequency control. With a change in the generation mix, these services are required to be sourced from new technologies such as IBR. Often, IBR are located in the remote areas of the grid, typically far from load centers and conventional synchronous generators. Being in the remote and weak part of the network a small reduction in system strength either during a planned or forced outage of a network element could manifest into system security issues such as undesired interaction between IBR. With the displacement of the synchronous generators, the system inertia reduces which could result in frequency control challenges. The use of fast frequency response from IBR can help to substitute some inertia and can support the power system operation of low inertia grids. The accurate assessment of emerging system security challenges require fit for purpose tool, particularly for a grid with a high share of IBR. Validated power system models play a key role in assessing and addressing these challenges.

This lecture will discuss emerging bulk power system security challenges such as system strength, inertia, need for fit for purpose power system tools. The presentation will show real-life example of emerging bulk power system security challenges and some of the solutions to address them.

Large-scale Electromagnetic Transient modeling for assessing impacts of high penetration of inverter-based resources on power system security

The increase in transmission- and distribution-connected inverter-based resources (IBR) increases the complexities of power system operation, particularly when they are connected to the remote part of the network and in the close proximity to each other. Compared to Root-mean-square (RMS) simulation tools, Electromagnetic Transient (EMT) simulation tools are increasingly used to assess power system performance and develop secure operating envelope specifically for a grid with high penetration of inverter-based resources. This is largely because of the ability of EMT simulation tools to capture complex phenomenon associated with inverter-based resources which are often cannot be captured through RMS simulation tools. Although, EMT simulations tools provide opportunity to assess complex phenomenon associated with IBR, often they are difficult to integrate in large power system and the development of large-scale power system with number of EMT models is a complex task. The provision of site-specific EMT model provides necessary information to accurately capture power system dynamics however, they often require small simulation time-steps which lead to slower simulation speed when number of site-specific EMT models are integrated to develop large-scale power system model. There are number of ways such as splitting the large network into smaller projects, use of separate projects for IBRs and interfacing them through network interface etc can help efficient development of large-scale EMT models.

This lecture will discuss need for EMT models, provide a comparison between EMT and RMS models, and comprehensively discuss how large-scale EMT models can be developed and used for power system security assessment for a grid with high penetration of inverter-based resources.