Share

JWG C2/C4.41 Impact of high penetration of inverter-based generation on system inertia of networks

Background:

The worldwide drive to reduce carbon emissions in the environment has led to the global community looking for alternative sources of energy that are less polluting and cheaper to harness than traditional primary energy sources that are currently widely used such as fossil fuel sources. This has led to the widespread introduction of renewable energy sources (RES) as alternative energy sources for the future. While the introduction of RES generation onto the electrical grid brings with it some major benefits, it is certainly not without challenges. 

Not all RES are non-synchronous but a majority of them are and this is expected to have a significant impact on the way the power system is operated. One major challenge with the introduction of non-synchronous generation on the grid is the reduction of natural inertia that is provided by conventional synchronous machines on the grid. This natural inertial response from synchronous generating sources helps in damping frequency excursions during system disturbances such as generator trips or sudden loss of a large load. With depleting inertial energy, the rate of change of frequency (RoCoF) increases substantially, leading to a lower nadir, such that Primary Frequency Response (PFR) systems and even defence schemes such as Under Frequency Load Shedding Schemes (UFLS) may fail to protect the system during major frequency excursions. This has become a big challenge for system operators across the globe as penetration of inverter-based renewable sources is increasing tremendously and RES are seen as an imminent replacement of conventional generating sources. System operators have to be prepared for a more dynamic system, not only operating the system within tight security constraints, but also performing congestion management and facilitating a competitive electricity market. 

Scope:

The objective of this WG is to advise and formulate philosophies for system operations in order to prepare the on-going energy transition. Primary Frequency Response studies will be carried out (or existing studies will be reviewed) in order to analyse and mitigate against the impact of the reduction of synchronous inertial energy on the power system as a result of integration of non-synchronous renewable generation using various networks around the globe as case studies. The integration of the existing knowledge between system operation and system performance, as well as the interaction with system planning, is crucial to achieve the proposed goals.   

The JWG will address amongst others the following issues: 

a) Review of previous (CIGRE) work relating to the current topic (e.g. TB 527 and TB 666) and the connection with on-going work (e.g. JWG C2/B4.38 and JWG C4/C6.35).

b) Survey existing practises used to determine primary frequency response requirements. 

c) Define operational measures to manage the dispatch of inertia and reduce the risk when operating with low inertia on the system. 

d) Quantify Primary Frequency Requirements (PFR) with increasing RES penetration

  1. Demand Response (DR) requirements
  2. Primary Reserves requirements
  3. Fast Frequency Response (FFR) techniques and requirements
  4. Trade-offs between inertia and FFR /DR techniques (checking if FFR can be a substitute for inertial response) 

e) Methodology to establish rate of change of frequency (RoCoF) limits with increasing non-synchronous RES penetration levels, and the integration of the methodology into the operational environment. 

f) Review existing Grid Code policy around PFR requirements in light of higher penetration levels of RES. 

g) Investigate possible control strategies for inverter-based generation in order to provide wider future designs possibilities of inverters/converters and to achieve the most efficient way to use the technology. Also to work in connection with JWG C2/B4.38. 

h) Survey possible/ existing mitigation techniques and increased system controllability

  1. Synthetic inertia (including technologies based on voltage source converters)
  2. Flywheels etc.
  3. FFR
  4. DR etc.
Deliverables:

Technical Brochure and Executive summary in Electra

Electra report

Tutorial

Time Schedule:

Start: July 2018      Final Report: Dec 2020

Convener: Mpeli Rampokanyo (South Africa)