Test Case 02

Complying with the fault-ride-through (FRT) requirements in inverter-based droop-controlled microgrids

Identification

ID	02
Author	Alexandros G.Paspatis, Alkistis Kontou
Version	2
Project	ERIGRID 2.0
Date	13/04/2020

Test Case Definition


Name of the Test Case		Complying with the fault-ride-through (FRT) requirements in inverter-based droop-controlled microgrids
Narrative		An inverter-based microgrid is considered, with inverter-interfaced distributed energy resources (DERs) operating in parallel to feed the microgrid load. At some point, a network fault occurs, either inside the microgrid (when considering an islanded microgrid) or at the main grid (when considering a grid-connected microgrid). Through the control design of the inverter-interfaced distributed energy resources, power sharing is achieved between the multiple inverters during normal grid conditions. In this way, all inverters are equally stressed while the voltage and frequency of the microgrid are regulated close to their nominal values (droop control operation). Furthermore, when the network fault occurs, the inverters inject power according to the international standards to provide grid voltage support.
Function(s) under Investigation (FuI)		Power sharing in inverter-based microgrids and grid voltage support from inverters, during grid faults
Object under Investigation (OuI)		Inverter-interfaced distributed energy resources controllers
Domain under Investigation (DuI)		Electrical Power
Purpose of Investigation (PoI)		Transition to future smart-grids, where inverter-interfaced DERs provide multiple ancillary services Characterization and validation of the SuT Verification and validation of the OuI Verification and validation of the FuT
System under Test (SuT)		An inverter-based microgrid consisting of multiple inverter-interfaced distributed energy resources (DERs), lines, loads, etc.
Functions under Test (FuT)		A unified inverter controller that incorporates droop control and fault-ride-through techniques.

Test criteria (TCR)		Microgrid operation according to the designed control algorithm
	Target Metrics (TM)	Is power sharing achieved according to the droop control technique? Is voltage support provided to the grid when grid faults occur according to the international standards?
	Variability Attributes (VA)	Different microgrid loading Different grid faults
	Quality Attributes (QA)	During the normal operation, the acceptable load voltages values should be inside the ±5% of the nominal voltage and the acceptable frequency values should be inside ±1% of the nominal frequency Reactive power injection during grid faults, as a percentage of Smax Inverter currents below their maximum threshold Imax

Qualification Strategy

The major ancillary services required from inverter-interfaced DERs during i) normal operation (droop control) and ii) during grid faulty operation (fault-ride-through) will be investigated through a single test where the inverters are equipped with the appropriate smart control algorithms.

Test Specification 02.01

Complying with the fault-ride-through (FRT) requirements while maintaining power sharing