Further on the N_NEWENSF1+2_100-INV constraint around the 14:00 dispatch interval on Wednesday 15th January 2025 … Part 8

On the day, Paul’s article About the ‘N_NEWENSF1+2_100-INV’ constraint equation that violates at 14:00 on Wednesday 15th January 2025 … Part 4 observed how the N_NEWENSF1+2_100-INV acted to restrict power energy from the two New England Solar Farms.

With the following chart we’ll attempt to understand how the units received targets of 0 MW, when the constraint appears to simply limit the inverter count to 100.

At an average size of 1.388 MW per inverter, a limit of 100 inverters means considerable capacity can still remain available.

Elements Available didn’t drop to 100 immediately

In the chart below, the top panel shows:

1. A shaded background marking the dispatch intervals when the constraint bound.
2. The number of elements (inverters) available from both NEWENSF1 and NEWENSF2, which was greater than 100 over the intervals when the constraint was binding.
3. From interval 14:40 the number of elements available at 100, persisting for 9 dispatch intervals (45 minutes), extending past the 15:00 interval.
4. The number of inverters available gradually increasing to more typical levels from the 15:30 interval.

The bottom panel shows:

1. Energy targets were 0MW during the period when the constraint was binding.
2. Targets were non-zero once the inverters available had been reduced to 100.
3. Power output (aggregate) at the sites took 4 intervals to get to 0MW, to reflect dispatch targets.

The above chart makes use of new data on intermittent generator availability information.

To unpick the N_NEWENSF1+2_100-INV constraint

If we take the Plain English Translation presented in Paul’s article;

‘Dispatch RHS =
-0.001 {Limit_zero}
+ if
(-1 x [Number of inverter available for New England Solar Farm 1]
– Number of inverter available for New England Solar Farm 2
+ 101 {Check_INV_WT}) <= 0
then
0
else
10000’

And then to simplify, omit the default term (effectively 0) and re-word it the following, we can understand where the 0 MW limit came from :

When the number of inverters available at [New England Solar Farm 1 + New England Solar Farm 2] is greater than or equal to 101:

RHS = 0 MW.

Else

Use the swamping amount. RHS = 10000 MW. 

ez2view’s Constraint Equation Dashboard shows the RHS up at the swamping level in the 14:40 interval

14:40 was the first interval when the inverters available were eventually limited to 100 in number.

Before that interval, as indicated by the red  period in the lower panel, the constraint was binding. The top panel shows the RHS was down at 0MW.

The constraint ended (ceased to be invoked) in the 15:00 interval

At 15:05 the N_NEWENSF1+2_100-INV constraint was not restricting the inverters available anymore.