Test Case TC14

Version management

Author

Version

Project

ERIGrid2.0

Date

12/04/2021

Narrative

The increasing penetration of DERs is reducing the inertia of existing power systems. However, power converters can provide services such as FFR and SI, in order to limit the frequency deviations. An assessment of the frequency dynamics requires multiple experiments to take into account the interaction between the traditional components and the converters as well as the specifications provided by different TSOs.

Function(s) under Investigation (FuI)

The FuIs are implemented in each converter controller.

In this TC, several FuIs are investigated: Fast frequency response and Synthetic Inertia provided by converters, considering the specification of different countries.

Fast Frequency Response

ENTSO-E specification: Main requirements: Activation threshold frequency and maximum full activation time (3 configurable values):

• 49.7 Hz, 1.3 s
• 49.6 Hz, 1 s
• 49.5 Hz, 0.7 s Minimum support duration = 5 s Maximum power overshoot = 0.35Ppre (being Ppre the prequalified FFR capacity) Deactivation rate = 0.2Ppre/s (measured as the average rate over an integration window of one second) and with no power step higher than 0.2Ppre Buffer + recovery time = 900 s Recovery maximum power = 0.25 Ppre Dead-band = +/-50 mHz

Italian specification: Activation instant <= 300 ms Activation time <= 1 s Support duration = 30 s Deactivation time = 300 s Buffer time + Recovery time = 200 s FFR Maximum Power = 5 ÷ 25 MW Recovery Maximum Power = 2 MW (or more if the frequency is within the dead-band) Dead-band = +/- 50 mHz ΔP/Δf = tbd

UK specification: Dead-band: +/- 15 mHz Small linear delivery: between 15 mHz and 200 mHz (maximum of 5% at 200 mHz) Knee point activation: +/- 200 mHz Full delivery: +/- 500 mHz is 100% Linear delivery knee point: 200 mHz Activation time <=1s (but no faster than 0.5 s)

Synthetic inertia Hydro-Québec Transmission system: Inertial response requirements:

• Activated at a given frequency threshold (frequency deviation)
• An adjustable dead band from -0.1 Hz to -1.0 Hz (with respect to nominal frequency)
• Rise time (1-2): ≤ 1.5 s
• Maximum power overproduction (2-3): at least 6% of rated power
• Max. overproduction duration (1-4): at least 9s
• Transition time (3-5): ≥ 3.5 s
• Max. power decrease during recovery (5-6): 20% of rated power
• Be able to operate repeatedly with a 2 min delay after the end of the recovery period following the previous operation
• Recovery time: not defined yet

Nationalgrid-UK (proposal):

• Activated scheme: ROCOF (df/dt)
• Max. power overproduction: 5.4% of rated power for a ROCOF ≥ 0.325 Hz/s.
• Rise time: 200 ms
• Max. power decrease during recovery: 5% of rated power
• Max. overproduction duration: not defined yet
• Recovery time: not defined yet
• Transition time: not defined yet

Object under Investigation (OuI)

Domain under Investigation (DuI)

Electrical domain. ICT domain (in case of remote control by system operator for changing function parameters).

Purpose of Investigation (PoI)

PoI 1: Verification of the behavior of providing FFR and SI for different devices (PV, Wind, ESS, etc).

PoI 2: Validate that FFR and SI limit the Rate Of Change Of Frequency (ROCOF) and the frequency deviations considering different specification and also the interaction among power converters and synchronous machine.

System under Test (SuT)

For PoI 1: Grid simulator which sets the frequency connected to a power converter with the OuI.

For PoI 1, PoI 2: In order to get insights from the test results, a simple benchmark is selected. The SuT (see figure below) is composed of:

• 3 synchronous generators that will be increasingly replaced by power converters.
• 3 loads (considering asynchronous machines, constant power loads, constant impedance loads, etc.).

Functions under Test (FuT)

Other frequency control such as Frequency Containment Reserve (FCR). Other high-level controllers (i.e., active and reactive power control).

Test criteria (TCR)

For PoI 1: Comparison between the FFR and SI specification requirements (listed in Function(s) under Investigation field) and the experiment results. The test answers to the following question: Is the power converter compliant with the FFR specification? Is the power converter compliant with the SI specification?

For PoI 2: Evaluation of the ROCOF and the frequency deviation considering different system configuration in terms of DERs penetration. The test answers to the following questions: Is the system stable under the different configurations? Is the frequency and ROCOF maintained within the limits? Is there any interaction between the devices providing grid services?

Target Metrics (TM)

For PoI 1: see Function(s) under Investigation field.

For PoI 2: At power system level: Frequency variation (ROCOF, Frequency nadir, Steady State frequency, time recovery).
At component level: Speed of response, Settling time, Power Overshoot, support duration, max power undershoot during recovery

Variability Attributes (VA)

For PoI 1: Frequency variation, power set-point, voltage and current harmonics, measures accuracy.

For PoI 2: Mechanical Inertia, Non-controllable DER production and load consumption, grid parameters, communication and controller delay, interaction between each power converter providing FFR and SI and other components.

Quality Attributes (QA)

For PoI 1: Pass/fail criteria:

• All the specification listed in the FuI field.
• System fail (one or more components disconnected) Quality attributes:
• Sampling time: 100 µs
• Resolution: frequency 0.01 Hz, voltage 0.001 pu and current 0.01 pu
• Measurement point: one for each resource

For PoI 2: Pass/fail criteria:

• Frequency nadir: 48 Hz
• System fail (one or more components disconnected) Quality attributes:
• Sampling time: 100 µs
• Resolution: frequency 0.01 Hz, voltage 0.001 pu and current 0.01 pu
• Measurement point: one for each resource

Qualification Strategy

Two test specifications will be implemented: one for verifying the FFR and SI control in case of the power converter is independent from other components and one for the verification of the OuI in case of interaction with other grid components and validation of the power system stability.