FailureMode
Inverter-grid resonance at low short-circuit ratio
- ID
fm:inverter-grid-resonance- IRI
https://solarlattice.org/kb/fm/inverter-grid-resonance- Status
- active
- Also known as
- AC voltage resonance, low grid SCR, weak grid resonance, short-circuit ratio limit, Inverter-grid voltage resonance at low short-circuit ratio, short-circuit ratio
On a weak grid with a very low short-circuit ratio, the impedances of the inverters, the transformer and the grid can combine to cause resonance on the AC voltage waveform. If the resonance is strong enough, the inverter sees the grid voltage as too high and shuts down safely, so it looks like an overvoltage trip. The risk grows with the number of inverters connected at one point of interconnection. Check the site against the manufacturer's configuration tables, which cover SCR values from 2.0 to 6.0 and give the number of systems and the allowed range of inverters per system. Resonance is also expected when power electronics with a low switching frequency share a common 480 V AC bus with a battery system. In that case, move the equipment, add a line reactor or add an isolation transformer.
<!-- review notes
- sentence 3: support check: partial - Passages say the number of inverters per POI is limited at low SCR, implying a relation, but don't state that risk grows with count.
- sentence 5: support check: partial - Resonance is expected on a common 480 V bus with a Megapack, but only when both conditions hold (over 20% rating and under 35 kHz), and the statement omits the rating condition and says 'battery system'.
-->
Claims
caused_by
c1 drafted · lead
Low grid short-circuit ratio proposed
At very low SCR, the impedances of the inverters, transformer and grid combine to produce resonance on the AC voltage waveform.
c2 drafted · lead
Too many inverters per interconnection proposed
On a weak grid, the number of XGI 1500 inverters that can share one point of interconnection is limited. Exceeding that limit risks resonance.
review note: support check: partial - Passages say the inverter count per POI is limited at low SCR to avoid resonance, but don't explicitly say exceeding the limit causes it (implied only).
c3 drafted · lead
Power electronics on shared AC bus proposed
Tesla expects excessive resonance on a common 480 V AC bus when two conditions both hold: the other power electronics exceed 20% of the Megapack apparent power rating, and their equivalent switching frequency is below 35 kHz.
affects
c4 drafted · lead
Inverter
presents_as
c5 drafted · lead
Grid overvoltage
When the resonance is strong enough, the inverter reads the grid AC voltage as too high.
c6 drafted · lead
Inverter shutdown
The inverter shuts down safely after it detects the resonance-driven overvoltage.
mitigated_by
c7 verified · fact
Inverter count per interconnection limit proposed
Use the manufacturer's configuration tables, which cover SCR values from 2.0 to 6.0, to choose the number of systems and the inverters per system for a given plant size.
verified by: review-workflowverified on: 2026-10-24
c8 drafted · lead
Line reactor proposed
review note: support check: partial - A line reactor is listed as a mitigation for resonance on a common 480 V bus, not specifically for low-SCR grid resonance.
c9 drafted · lead
Isolation transformer proposed
review note: support check: partial - Isolation transformer is listed as a mitigation for common-bus resonance, not specifically low-SCR grid resonance.; review: partial - The passages list an isolation transformer as a mitigation for resonance between Megapack and inverters on a common 480 V AC bus, but they never mention low short-circuit ratio or grid resonance as such.
c10 drafted · lead
Equipment relocation proposed
Move the resonance-prone power electronics off the common AC bus.
review note: support check: partial - Relocating equipment is listed for common-bus resonance, not specifically low-SCR grid resonance.
Referenced by
Data