Test Specification 18.02

Test Rationale

This test investigates aggregator services that are involved in regulating the grid properties towards desired values in case of emerging deviations:

• Coordinated voltage control
• Fast frequency response
• Virtual inertia provision

In the process, the individual activation patterns of the services undergo assessment. Simulation software provides the various auxiliary services required for their functionality:

• Collection of updated capabilities from DERs
• Evaluation of automatic restoration reserve provision by DERs, storage units and controllable loads
• Computation of optimal and feasible P/Q set-point
• Verification of actual P/Q produced and possible recalculation

ICT-related effects are abstracted as activation delays, making this an “idealized” case.

Specific Test System

This Test Specification requires a simulator of a grid (MV/LV distribution network or single LV distribution feeder) with several connected DERs / storage units.

Target measures

• Safe and robust voltage for all nodes: Direct voltage operating regions not violated
• Frequency restoration time: <120sec
• Steady-state deviation: <0.1Hz
• Reserves availability (power/energy): >20%
• DERs curtailment: <30%
• Loads curtailment: <5%

Input and output parameters

Uncontrollable input parameters:

• Grid topology
• Generation and load profiles
• DER controllers parameters
• Tie-line exchange specifications

Controllable input parameters:

• Voltage set-point
• Frequency set-point
• Load value

Output parameters:

• Node voltages
• Power losses

Test Design

The test considers several consecutive imbalances and voltage/frequency deviations in order to sufficiently evaluate the capability of the voltage/frequency control system to cope with such incidents. The following border cases are defined:

• Maximally decrease input voltage/frequency, use constant voltage/frequency set-point
• Maximally increase input voltage/frequency, use constant voltage/frequency set-point
• Decrease voltage/frequency set-point from maximal to minimal value, do not artificially vary input voltage/frequency
• Increase voltage/frequency set-point from minimal to maximal value, do not artificially vary input voltage/frequency

1. The operating set-points are determined.
2. The output stabilizes.
3. The input voltage/frequency and/or the set-points are varied according to the current border case.
4. The test criteria are assessed.
5. Steps 2-4 are repeated until the testing of each predefined border case was concluded.

Initial system state

Initial power flow conditions:

• The voltage/frequency value (output) matches the voltage/frequency set-point.
• The combination of the RES units should provide at least 20% of their nominal power.
• The consumption of the loads should be at least 20% of the maximum consumption.
• The imbalance should be under 5%.

Evolution of system state and test signals

• At first, the system is sufficiently balanced with only a small amount of reserves (ideally zero) implemented and the voltage/frequency nominal.
• An imbalance emerges which leads to a significant voltage/frequency deviation and the consequent activation of a large part of reserves after a simulated communication delay.
• Consumption or production changes in order to reduce the variation.
• Subsequent disturbances emerge either before or after the restoration of voltage/frequency to its nominal value.
• Having started at Inp0, the voltage/frequency changes up to Val1, then down to Val2 etc. with varying step sizes (St1, St2, …). For example, changes to the frequency could occur with a fixed ramp rate and amplitude.
• The test is successful if load voltage/frequency is always regulated within its operating interval [TOL-, TOL+].

Other parameters

N/A

Temporal resolution

The simulation is continuous, with time step sizes depending on the software experiment:

• Time constants inside SuT in-between 50 μs and 5 s
• Monitoring quantities with a maximum sampling time of 0.1 sec.
• Internal time resolution of communication simulation

Source of uncertainty

• Grid parameters variability (i.e. resistance/inductance ratio)
• Timing deviations, communication delays
• Consumers’ demand
• Environmental conditions

Suspension criteria / Stopping criteria

• Restoration and stabilization of regular network behavior and properties (according to power quality standard EN50160)
• Passage of predetermined critical amount of time
• Violation of quality attributes
• Deviation from initial conditions during start

Mapping to Research Infrastructure