Frequency control modes (with Hybrid EMS)

About frequency dependent control

All countries have a standard grid frequency, e.g. 50 Hz in Europe, and it is essential to maintain the frequency to prevent blackouts and damage. The grid code of each country requires energy-producing systems to apply frequency dependent control, which adjusts the system frequency during inadmissible changes. Depending on the requirements, this can be carried out by the inverters or a plant controller such as the blue’Log.

The blue’Log interface allows you to regulate the active power output in three different modes:

• Limited frequency sensitive mode - underfrequency (LFSM-U)

• Limited frequency sensitive mode - overfrequency (LFSM-O)

• Frequency sensitive mode (FSM)

Limited frequency sensitive mode - underfrequency (LFSM-U)

Underfrequency occurs when the frequency of the electrical grid falls below the nominal operating frequency. To correct this, the active power output of the system is increased according to a characteristic curve P (f) until the grid frequency returns to the permissible range. 

When setting LFSM-U on the blue’Log, consider the following:

• Each parameter is described in the info buttons next to each parameter

• Refer to your local grid operator requirements when setting the parameters

• You can configure additional frequency bands/slopes if necessary

• You can prioritize the grid operator setpoint via the Prioritising grid operator setpoint toggle. See Prioritization between different control modes (with Hybrid EMS)

Limited frequency sensitive mode - overfrequency (LFSM-O)

Overfrequency occurs when the frequency of the electrical grid exceeds the nominal operating frequency. To correct this, the active power output of the system is limited according to a characteristic curve P (f) until the system frequency returns to the permissible range.

When setting LFSM-O on the blue’Log, consider the following:

• Each parameter is described in the info buttons next to each parameter

• Refer to your local grid operator requirements when setting the parameters

• You can configure additional frequency bands/slopes if necessary

• You can prioritize the grid operator setpoint via the Prioritising grid operator setpoint toggle. See Prioritization between different control modes (under Further power control topics, Hybrid EMS and without Hybrid EMS )

Frequency sensitive mode (FSM)

In this mode, the active power is also adjusted according to a defined P(f) curve to provide the ancillary service frequency containment reserves (FCR, also known as primary control reserves). Thus, FSM is only relevant if your system participates in the electricity balancing market. Compared to the LFSM-O and LFSM-U modes, FSM mode is usually active during smaller frequency deviations. In case of overlap LFSM-O and LFSM-U have priority over FSM.

When setting FSM on the blue’Log, consider the following:

• Each parameter is described in the info buttons next to each parameter

• Refer to your local grid operator requirements when setting the parameters

• Some parameters can be configured via Modbus. The Modbus Power Control license is required for this. Refer to the data sheet for the relevant addresses.

  • Activate FSM via an external signal via the Activate FSM via Modbus toggle.

  • Set the active power range via the Set active power range via Modbus toggle.

FSM working principle and example

The example below illustrates how the FSM mode is working. The following settings are used:

• Active power range |ΔP₁|/P_max= 6%

• Frequency droop s_f = 5%

• Deadband Δf_DB = 50 mHz

• Reference active power P_ref = Momentary active power P_mom

• Nominal system frequency f_n = 50 Hz

• Base value = Momentary active power P_mom (Note: the option to choose the base value is only available if the RPC license is installed)

These settings result in the following P(f) characteristic curve:

In FSM mode, the frequency is continuously measured and the active power is adjusted according to the defined P(f) characteristic curve

• Frequency within deadband Δf_DB (f > 49.95 and f < 50.05 Hz): no active power adjustment

• Frequency outside deadband Δf_DB (f < 49,95 or f > 50,05 Hz): active power adjustment according to the following formula:

• With a measured frequency f_measured = 50,2 Hz and the above settings, the resulting relative active power change ΔP/P_ref equals -6%.

• The absolute active power change ΔP depends on the set reference active power P_ref.

• In the example here, P_ref equals P_mom (e.g. 3,5 MW). Thus, the absolute active power change ΔP equals -210 kW.

• The absolute active power change ΔP is added to the base value P_base to obtain the final setpoint of this mode.

• The base value P_base can only be selected if the RPC license is installed.

• If the RPC license is not installed, the base value P_base always corresponds to P_mom.

• Setting the base value to P_RPC also enables energy traders to adjust the active power output during FSM events.

Activate frequency-dependent control

Prerequisites

• Only the user group Service can make changes. See Users

• Your meter/power analyzer is compatible with blue'Log. See Compatability check

• Your meter/power analyzer fulfills the measurement requirements for frequency dependent control
  Example: Your grid code requires the frequency to be measured with a certain accuracy

• Frequency-dependent control is only available for the operation mode Setpoint command. See Active power (with Hybrid EMS )

• For configuration assistance, we recommend our project-specific controller tuning services.

Steps

1. Go to Power control > Active power > Active power management > Select Setpoint command.

2. Go to Options and activate the Frequency dependent control toggle.

3. Activate the toggle for the desired control mode and select the Gear icon to configure the parameters.

Set a simulated test frequency via Modbus Power Control

Many markets require verification of the settings, for example during the commissioning process.

To test your frequency dependent control settings, activate the Set a simulated test frequency via Modbus Power Control toggle. The Modbus Power Control license is required for this.

For more on verification and compliance, see Grid code compliance engineering services.

Set a ramp rate limiter (after frequency restoration)

If the frequency event ends and the frequency is restored, a ramp rate limiter can be applied to the transition to normal operation.

Example: power was reduced to 500 kW during the frequency event, but the plant can deliver 800 kW after the frequency event ends, and no power limitations are present. In this scenario, if the ramp rate limiter is activated after frequency restoration, the power does not immediately return to maximum power (800 kW) but has a configurable rate of change.

This function applies only after LFSM-U and LFSM-O events and cannot be set if FSM is activated.