Test Case 6

Evaluation of frequency restoration response in islanded power system

Identification

ID

6

Author

E. Rikos, L.Pellegrino, R. Lazzari

Version

1.1

Project

ERIGrid 2.0-NA4

Date

01/12/2020

Test Case Definition

Name of the Test Case

Evaluation of frequency restoration response in islanded power system

Narrative

One of the important functionalities of a microgrid is its ability to operate in islanded mode when the conditions of the system necessitate that. In such a mode the islanded microgrid should provide the functionalities to keep the frequency stable. With these functionalities the microgrid controllers (local and central) should contain frequency deviations and restore each deviation to zero from the nominal value. This test case examines the effectivity of the frequency restoration control of the microgrid under various operating conditions.

Function(s) under Investigation (FuI)
  • Secondary/tertiary frequency control
Object under Investigation (OuI)
  • Microgrid Frequency Controller (MFC)
Domain under Investigation (DuI)
  • Electrical
  • ICT (time-delays)
  • Electrochemical
  • Thermal
  • Environmental
Purpose of Investigation (PoI)
  • Validation of the controller/s for frequency stability and steady-state error elimination during restoration phase.
System under Test (SuT)

The main components and subsystems that are of interest for this TC are depicted in the above diagram and summarized below:

  • Microgrid Frequency Controller (MFC)
  • Load Controllers
  • CHP microturbines
  • Battery inverters
  • RES inverters
  • Communication channels
Functions under Test (FuT)
  • Battery Management System (BMS)
  • Maximum Power Point Tracker (MPPT)
  • Inverter control (Grid Forming, Grid Following, Grid Supporting)
  • CHP control (Heat or Power Priority)
  • Load control
  • Supervisory Control and Data Acquisition (SCADA)
  • Energy Management System (EMS)
  • Local droop control
  • Local inertia control
Test criteria (TCR)
  • Frequency response
Target Metrics (TM)
  • Frequency Restoration time
  • Steady-state frequency deviation (after restoration)
  • Frequency oscillations damping factor (trumpet curve)
  • Remaining reserves (power/energy)
  • DERs curtailment
  • Loads curtailment
Variability Attributes (VA)

Fully Controllable attributes:

  • Grid topology
  • Droop control parameters
  • Inverters control functionalities

Partly Controllable attributes:

  • Loads active/reactive power
  • Generators active/reactive power

Uncontrollable attributes:

  • Solar irradiation
  • Wind speed
  • Ambient temperature
  • ICT and control delays
Quality Attributes (QA)
  • Sampling time of signals (frequency and power flows): 100ms
  • Resolution:
    • frequency 0.05Hz,
    • power 0.01 pu
  • Points of measurement:
    • Frequency: at least 1 (at the point of common coupling)
    • Power: 1 point for each resource connected at their electrical output
  • Size of imbalance disturbance: >20%
  • Environmental conditions:
    • Enough solar irradiation and wind speed so that the combined RES portfolio produces at least 20% of its maximum power
  • State of Charge: between 35% and 90%
  • Load: at least 20%

Qualification Strategy

The selected PoI can be tackled by one Test Specification only in which only some input variables or system parameters need be changed over the test repetitions in order to achieve the desired results. In other words, aspects such as the main grid topology remain unchanged except for small reconfigurations. In our TC this topology is selected to be a LV distribution grid. Also, in order to validate the frequency response of the islanded microgrid, no specific tests are prerequisite to determine parameters and variable values necessary to conduct the main test.

Test Specification TC6.TS1

Validation of islanded microgrid ability to restore frequency deviations in a stable manner