voltage-reactive power mode, Q(U), Q(V), volt-var control, DVVR
Category
Grid support
Function kind
grid-support
Volt-VAr changes the reactive power output in response to grid voltage, following a programmable curve. It injects reactive power when voltage is below nominal and absorbs it when voltage is above nominal. IEEE 1547-2018 calls this the voltage-reactive power mode. One set of default settings requirements for that standard lists the function as OFF by default. The curve is set with four voltage points (V1 to V4), a reactive power value at each point (Q1 to Q4), and a response time constant for reaching 95% of the requested reactive power. In the Tesla commercial controls manuals, Volt-VAr is an open-loop response to voltage measured at the point of interconnection meter. Its output is added to any direct reactive power command, and the curve can be written over Modbus or DNP3. On Solis inverters using the EN50549 grid standard, you turn Q(U) on from the inverter screen under Working Mode, Mode 2. It can deliver up to 60% reactive power, and P lock-in and lock-out levels switch the mode on and off. With the SMA Data Manager M, Q(U) needs exactly one meter at the point of interconnection, and that meter must measure both voltage and current. Splitting the voltage and current measurements across two meters produces faulty power values.
<!-- review notes
sentence 6: support check: partial - Passages say only one measuring device is supported at the POI, it must measure both voltage and current, and splitting gives mismatched values; but they don't name Data Manager M's 'exactly one' meter requirement beyond 'Data Manager' and say 'faulty measurements' rather than specifically power values (they do say active/reactive power values), so minor detail on product variant.
-->
review note: support check: partial - Passages show voltage-reactive power (volt-var) mode in Table 6 for Category A and B DER, but the table's contents aren't shown; the 'one of the functions' framing is only implied.
review note: possible conflict with c4 (same source; check the conditions); possible conflict with c6 (same source; check the conditions); possible conflict with c8 (same source; check the conditions)
review note: possible conflict with c2 (same source; check the conditions); possible conflict with c6 (same source; check the conditions); possible conflict with c8 (same source; check the conditions)
review note: possible conflict with c2 (same source; check the conditions); possible conflict with c4 (same source; check the conditions); possible conflict with c8 (same source; check the conditions)
review note: possible conflict with c2 (same source; check the conditions); possible conflict with c4 (same source; check the conditions); possible conflict with c6 (same source; check the conditions)
review note: possible conflict with c12 (same source; check the conditions); possible conflict with c14 (same source; check the conditions); possible conflict with c15 (same source; check the conditions)
review note: possible conflict with c10 (same source; check the conditions); possible conflict with c14 (same source; check the conditions); possible conflict with c15 (same source; check the conditions)
review note: possible conflict with c10 (same source; check the conditions); possible conflict with c12 (same source; check the conditions); possible conflict with c15 (same source; check the conditions)
verified by: review-workflowverified on: 2026-10-24review note: possible conflict with c10 (same source; check the conditions); possible conflict with c12 (same source; check the conditions); possible conflict with c14 (same source; check the conditions)