Test Case TC10

Version management

Author

E. Rikos

Version

1.1

Project

ERIGrid 2.0

Date

04/02/2021

Narrative

One of the functionalities that a microgrid should accommodate is its ability to automatically switch from grid-connected to islanded mode. The scope of this functionality is to isolate the microgrid’s customers from the local distribution grid when in the latter some disturbances appear. The transition from grid-connected to islanded mode should be made in a seamless way in order to eliminate loss of power supply on the microgrid consumer’s side (Uninterruptible Power Supply) and it is based on an automatic switch that disconnects the microgrid at the point of common coupling (PCC) as well as on at least one DER unit that has the ability to form the grid voltage once connection to the upstream grid is lost.

Function(s) under Investigation (FuI)

• Over/under voltage detection
• Over/under frequency detection
• ROCOF detection
• Primary voltage control
• Primary frequency control

Object under Investigation (OuI)

• Protection relay
• Static Switch
• DER inverters

Domain under Investigation (DuI)

• Electrical
• ICT (time-delays)
• Electrochemical
• Thermal
• Environmental

Purpose of Investigation (PoI)

• Validation of Uninterruptible Power Supply capability

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:

• Protection Relay
• Static Switch
• CHP microturbines
• Battery inverters
• Communication channels

Functions under Test (FuT)

• Microgrid Frequency Controller (MFC)
• Battery Management System
• MPPT
• Load control
• SCADA
• Energy Management System

Test criteria (TCR)

• Frequency response
• Voltage response

Target Metrics (TM)

• Maximum Voltage deviations
• Maximum frequency deviations
• Maximum ROCOF
• Response/stabilization time

Variability Attributes (VA)

Fully Controllable attributes:

• Protection relay parameters
• Droop control parameters
• Inverter control functionalities

Partly Controllable attributes:

• Load active/reactive power
• Generator active/reactive power

Uncontrollable attributes:

• Solar irradiation
• Wind speed
• Ambient temperature
• ICT and control delays

Quality Attributes (QA)

• Sampling time of signals (frequency, voltages): <1ms
• Resolution:
  • frequency 0.05Hz,
  • voltage 0.005 pu
• Points of measurement:
  • Frequency: at least 1 (at the point of common coupling)
  • Voltage: 1 point for each resource connected at their electrical output

Qualification Strategy

In order to meet the specific PoI, which is the evaluation of the microgrid’s capability of UPS, three test specifications are required: -One test is related to the protection equipment and its effective detection of disturbances in the upstream distribution grid. This test ensures that the combination of the protection relay and the static switch can adequately disconnect the microgrid when frequency disturbances appear. This test examines the response of the protection subsystem for various kinds of disturbances including over/underfrequency and increased ROCOF. -The second test is related to the protection subsystem and its ability to detect voltage disturbances. The reason why this functionality is addressed separately than the frequency test is the different requirements in the test system topology. In the voltage test, specifically, the detailed microgrid topology is considered since it can affect the voltage level at the Point of Common Coupling. -The third test is related to the response of the grid-supporting voltage source inverters of the microgrid after the disconnection. In principle, the test aims to assess the capability of these resources to maintain a voltage/frequency deviation within specific limits thanks to the primary control. The test is conducted under different initial conditions depending on the event that activates the protection equipment (for example, over/underfrequency).