Stop rules from causing power fluctuations

Scope

A power fluctuation is a value that changes at each control cycle, because one threshold starts and stops a rule. The fix is a gap between the start and stop thresholds. See Build a rule list and What a rule condition can read field definitions.

Location

• Path: the Settings dialog of the connection point, on the tab of the rule list.

Permissions

• Change a rule list: Editor, Installer or Full control.

Step 1: Fix Selection

• The Default is correct between the two thresholds: Step 2.
• The value must stay the same between the two thresholds: Step 3.
• The value must stop at a floor: Step 4.
• The reading changes quickly near the threshold: Step 5.

Step 2: Two Thresholds

1. Add a rule with the stop threshold and the usual value.
2. Add a rule with the start threshold and the exception value.
3. Drag the stop rule above the start rule.

Between the two thresholds, no rule is true, and the Default applies.

Step 3: Do Nothing Hold

1. Add the stop rule at the top, as in Step 2.
2. Add the start rule below it.
3. Add a third rule at the bottom.
4. In the third rule, set the Do Nothing switch to on.
5. Set the Expression of the third rule to Fixed Value 1 > Fixed Value 0.

Example on a grid Max Limit:

1. The state of charge falls below 10. Rule 2 wins, and the limit is 500 kW.
2. The state of charge is between 10 and 30. Rule 3 wins, and the limit stays at 500 kW.
3. The state of charge goes above 30. Rule 1 wins, and the limit is 100 kW.
4. The state of charge falls back between 30 and 10. Rule 3 keeps 100 kW.

Step 4: Floor Hold

1. Add a rule above the rule that starts a recovery charge.
2. Set its Expression to Storage % = the floor.
3. Set its Value to a small charge.

On storage Target Power, a charge is a negative number. If the hold value is 0 and the state of charge falls below the floor, the recovery rule starts again.

With one storage, Storage % is a number with no decimals. With two storages or more, it is an average, which can skip the floor. Then use a band, for example Storage % < 20 AND Storage % > 15.

Step 5: Must Hold For

1. In the rule, type the seconds in Must hold for.

The rule wins only after its condition and filters stay true for that time. A reading that stays on the threshold also starts the rule, but after that time.

Troubleshooting

• The value changes at each cycle: read the list from the top. Find the two rules that win one after the other. Give them different thresholds.
• The Do Nothing rule holds a previous value: the last value came from a rule, not from the Default. Add a rule for the value that you want.

Tips and Gotchas

• Do not add a stop-at-full rule to prevent damage to the battery. The plant control keeps charge and discharge in the BMS current limits, so the rule only adds a threshold. See Battery protection settings field definitions.
• Generator start and stop uses the same three-rule hold on the On/Off State list. See Set up generator auto start and stop.