Dynamic Frequency Response (DFR)

The dynamic frequency regulation (DFR) application was designed to provide frequency support to the grid in case of frequency variation. The BESS operates according to measured grid frequency instantaneously based on frequency triggers and corresponding droop setting. Droop, frequency deadband, and frequency triggers are computed

dynamically using the new control logics and past 7 days frequency data for the respective time slot. The BESS response also takes into account the current BESS state of charge.

The application functions based upon the criteria below:

If f>f_limh,P_{BESS_OUT}=-P_{BESS_max} If f<f_liml,P_{BESS_OUT} =P_{BESS_max}

If f_liml<f<f_dbl,P_{BESS_OUT}=P_{BESS_max}+ f- f_liml × P_{BESS_max}-P_{BESS_limh} / f_liml - f_dbl If f_dbh≤f ≤ f_limh,P_{BESS_OUT}= f-f_limh×P_{BESS_max}+P V_{BESS_liml} / f_dbh-f_limh -P_{BESS_max}

The BESS response considers the batteries’ current state of charge (SOC). Even if the instantaneous frequency measured at the PCC falls within the frequency deadband limit, the BESS charges if its SOC level is below the lower limit of the optimal SOC zone (SOC_{low_pa}) and discharges if the SOC level is beyond the upper limit of the optimal SOC zone (SOC_{High _pa}).

The BESS remains idle if the measured frequency lies between the lower limit of the deadzone of frequency (f_dbl) and the upper limit of the deadzone of frequency (f_dbh,), and the SOC level lies between the lower limit of the optimal SOC zone (SOC_{low_pa}) and the upper limit of the optimal SOC zone (SOC_{High _pa}).

If f_dbl≤f≤f_dbh ,& SOC_ave> SOC_{high_pa} ,P_{BESS_OUT}=P_{BESS_limh} If f_dbl≤f≤f_dbh ,& SOC_{low_pa}≤SOC_ave≤ SOC_{high_pa} ,P_{BESS_OUT}= 0 If f_dbl ≤f≤ f_dbh ,& SOC_ave< ,SOC_{low_pa} ,P_{BESS_OUT}=P_{BESS_liml} Where:

P_{BESS_OUT}: Active power Value of BESS

P_{BESS_limh}: Upper Limit of the deadzone of the power of BESS P_{BESS_liml}: Lower Limit of the deadzone of the power of BESS f_dbh: Upper Limit of the deadzone of frequency

f_dbl: Lower Limit of the deadzone of frequency

f_limh: Upper Limit of the adjustment range of frequency f_liml: Lower Limit of the adjustment range of frequency SOC_ave: Average SOC of the Batteries

SOC_{low_pa}: Lower Limit of the optimal SOC zone SOC_{High _pa}: Upper Limit of the optimal SOC zone Figure 25: Dynamic Frequency Response - Illustration

1 Data Analysis

Historical data from the SCADA system was extracted and analysed to understand the variation in system parameters, including the upper limit of the deadzone of frequency (fdbh) , the lower limit of the deadzone of frequency (fdbl), the upper limit of the adjustment range of frequency (flimh), and the lower limit of the adjustment range of frequency (fliml), The average SOC of the batteries (SOCave), along with BESS parameters such as the upper limit of the optimal SOC zone (SOCHigh_pa), and the lower limit of the optimal SOC zone (SOClow_pa) were recorded while running the application.

The bandlimit for Dynamic Frequency Response application Upper Limit of the deadzone of frequency (fdbh) , Lower Limit of the deadzone of frequency (fdbl), Upper Limit of the adjustment range of frequency (flimh), Lower Limit of the adjustment range of frequency (fliml) were estimated based on upon the trend analysis of frequency observed in real time at the PCC.

2 BESS Operation and Response During Dynamic Frequency Response

The dynamic frequency response application was run continuously for a sustained period of time within reasonable parameter ranges. Oarameters such as the, Upper Limit of the deadzone of frequency (fdbh), Lower Limit of the deadzone of frequency (fdbl), Upper Limit of the adjustment range of frequency (flimh), Lower Limit of the adjustment range of frequency (fliml) and the BESS SOC level were recorded while running the application.

During the trial run, predefined voltage bandlimits such as the Upper Limit of the deadzone of frequency (fdbh), the Lower Limit of the deadzone of frequency (fdbl), the Upper Limit of the adjustment range of frequency (flimh), and the Lower Limit of the adjustment range of frequency (fliml) were configured into the application SCADA settings.

Table 15: Frequency Limits for Dynamic Frequency Application Time Lower Limit of

adjustment range of frequency (f_liml)

B Lower Limit of dead zone of frequency (_fdbl)

Upper Limit of dead zone of

frequency (f_dbh) E Upper Limit of adjustment range of frequency (f_limh)

10:00:00-14:00:00 49.5 49.75 49.95 50.05 50.25 50.5

After the test was completed, data was extracted, and the BESS response analysed. The actual BESS response was in line with the expected BESS output based upon the application logics.

Figure 26: BESS in Dynamic Frequency Response – Real time

Figure 26 above shows how the BESS response varies in accordance with changes in the instantaneous measured system voltage or in accordance with the system SOC requirement. The graph shows that BESS discharges during the initial period to maintain an optimum SOC level, even though the instantaneous frequency measured is within the frequency deadband.

The BESS starts discharging whenever frequency measured at the PCC is below the lower limit of the deadzone of frequency (f_dbl) and starts charging whenever the measured frequency exceeds the upper limit of the deadzone of frequency (f_dbh).

3 Sample Case A: BESS response During Dynamic Frequency Response (Idle to Discharging) The real time data set provides an example of BESS response to the dynamic frequency regulation application.

For Discharging Mode:

If f_liml<f<f_dbl ,P_{BESS_OUT}=P_{BESS_max}+ f- f_liml × P_{BESS_max}-P_{BESS_limh}/f_liml - f_dbl For Idle Mode:

If f_dbl≤f≤f_dbh,& SOC_{low_pa}≤SOC_ave≤SOC_{high_pa},P_{BESS_OUT} = 0

Table 16: BESS Response Mode in Real Time During Dynamic Frequency Response (Idle-Discharging) Time Frequency (Hz) PBESS (kW) BESS Response Mode Remark

12:16:20 49.99 0 Idle The measured frequency is between

frequency deadband ( f_dbh ≤ f ≤ f_dbl) and SOC is within optimal SOC zone SO_{Clow_pa} < SOC_ave < SOC_{High_pa}, therefore BESS response is 0 kW.

12:24:30 49.93 97 Discharging The measured frequency is between the

lower limit of the adjustment range of frequency (f_liml) and the lower limit of the deadzone of frequency (f_dbl), therefore BESS response is 97 kW.

The figure below shows BESS response during the transition from idle to discharging mode with a change in the instantaneous measured frequency at the PCC.

Figure 28: Dynamic Frequency Response – Transition (Idle to discharging)

4 Sample Case B: BESS Response During Dynamic Frequency Response (Charging to Idle) The real time data set provides an example of BESS response to the dynamic frequency regulation application.

For Idle Mode:

If f_dbl≤f≤f_dbh ,& SOC_{low_pa}≤ SOC_ave≤ SOC_{high_pa} ,P_{BESS_OUT} = 0 For Charging Mode:

If f_dbh≤f ≤ f_limh ,P_{BESS_OUT} = f-f_limh× P_{BESS_max}+P_{BESS_liml} / f_dbh-f_limh-P_{BESS_max}

Table 17: BESS Response Mode in Real Time During Dynamic Frequency Response (Charging-Idle) Time f (Hz) PBESS (kW) BESS Response Mode Remark

13:08:10 50.08 -103 Charging The measured frequency is between the upper limit of the deadzone of frequency (f_dbh) and the upper limit of the adjustment range of frequency (f_limh), so the BESS response is -103 kW.

13:16:30 49.96 0 Idle The measured frequency is between the frequency

deadband ( f_dbh ≤ f ≤ f_dbl) and the SOC is within the optimal SOC zone SOC_{low_pa} < SOC_ave < SOC_{High_pa}, so the BESS response is 0 kW.

Figure 29 below shows BESS response during the transition from charging to idle mode with a change in the instantaneous measured frequency at the PCC.

Figure 29: Dynamic Frequency Response – Transition (Charging to Idle)

5 Sample Case C: Dynamic Frequency Response (SOC management) The BESS response during SOC management follows pre-set frequency band limits.

For SOC Management Mode:

If f_dbl≤f≤f_dbh ,& SOC_ave> SOC_{high_pa} ,P_{BESS_OUT}=P_{BESS_limh} and

If f_dbl≤f≤f_dbh,& SOC_{low_pa}≤SOC_ave≤SOC_{high_pa} ,P_{BESS_OUT} = 0 and

If f_dbl ≤f≤ f_dbh ,& SOC_ave< ,SOC_{low_pa} ,P_{BESS_OUT}=P_{BESS_liml}

Table 18: BESS Response Mode in Real Time During Dynamic Frequency Response (SoC Management) Time f (Hz) PBESS (kW) SOC (%) BESS Response Mode Remark

11:51:50 50.02 88 71 Discharging The measured frequency is between

frequency deadband ( f_dbh ≤ f ≤ f_dbl) but SOC_ave>SOC_{High_pa} so the BESS is discharging and its response is 88 kW.

11:56:50 50.02 0 70 Idle The measured frequency is between

frequency deadband ( f_dbh ≤ f ≤ f_dbl) and SOC is within optimal SOC zone SOC_{low_pa} < SOC_ave < SOC_{High_pa} so the BESS response is 0 kW.

Figure 30 shows BESS response during the transition from discharging to idle mode to maintain its SOC level within the optimal SOC zone, with the instantaneous measured frequency the PCC between the lower limit of the deadzone of frequency (fdbl) and the upper limit of the deadzone of frequency (fdbh).

Figure 30: Dynamic Frequency Response – Transition (SOC Management)