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Summary

Array-Level AC Losses account for power dissipation between the inverter output and the AC collection system output, calculated independently for each array. The loss chain proceeds in sequence: auxiliary load deductions, MV transformer losses, and AC collection system losses. Array outputs are then aggregated to the block level using repeater counts.

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Inputs

NameSymbolUnitsDescription
Degraded AC PowerPAC,degP_{AC,deg}WAC power after degradation (from AC degradation)
DAS LoadLDASL_{DAS}WData acquisition system power consumption
Cooling LoadLcoolL_{cool}WInverter/equipment cooling power consumption
Tracker Motor LoadLtrackL_{track}WTracker motor power consumption
MV Transformer RatingSMVS_{MV}kVAArray-level transformer nameplate capacity
MV No-Load LossLNLL_{NL}—MV transformer no-load loss fraction
MV Full-Load LossLFLL_{FL}—MV transformer full-load loss fraction
AC Collection Lossfcollf_{coll}—AC collection system loss fraction

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Outputs

NameSymbolUnitsDescription
Block PowerPblockP_{block}WAggregated AC power at block level, after all array-level losses

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Detailed Description

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Auxiliary Loads

Auxiliary loads are constant power deductions subtracted from the degraded AC power before transformer losses: Paux=PAC,deg−LDAS−Lcool−LtrackP_{aux} = P_{AC,deg} - L_{DAS} - L_{cool} - L_{track} The DAS load is applied whenever the system is energized. Cooling and tracker motor loads are applied only when inverter power output is positive. When nighttime disconnect is triggered (all inverters in the array are in shutdown or low-power regions), all auxiliary loads are set to zero.

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MV Transformer

The MV transformer applies the shared Transformer Loss Model to PauxP_{aux}: PMV=Paux−LMV,transP_{MV} = P_{aux} - L_{MV,trans} where LMV,transL_{MV,trans} is computed from the quadratic loss equation using SMVS_{MV}, LNLL_{NL}, and LFLL_{FL}. If the transformer is disabled for the array, LMV,trans=0L_{MV,trans} = 0 and PMV=PauxP_{MV} = P_{aux}. During nighttime disconnect, the transformer no-load loss is set to zero, eliminating standby core losses.

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AC Collection System

AC collection losses represent resistive (I²R) losses in the medium-voltage cabling between the MV transformer and the plant-level collection point. Version 12+ (Quadratic Model): Loss scales quadratically with power flow, reflecting the I²R characteristic of conductor losses: Lcoll=∣PMV2PAC,rated×fcoll∣L_{coll} = \left| \frac{P_{MV}^2}{P_{AC,rated}} \times f_{coll} \right| where PAC,ratedP_{AC,rated} is the total inverter rated capacity for the array: PAC,rated=∑inverterskVArated×Nrep×1000P_{AC,rated} = \sum_{inverters} kVA_{rated} \times N_{rep} \times 1000 Versions 3–11 (Flat Percentage Model): During daytime operation (PMV>0P_{MV} > 0): Lcoll=PMV×fcollL_{coll} = P_{MV} \times f_{coll} During nighttime operation (PMV≤0P_{MV} \leq 0), the system draws power from the grid to keep transformers energized. Losses are applied to both the consumed power and the additional grid draw: Lcoll=∣PMV×fcoll∣L_{coll} = |P_{MV} \times f_{coll}| Pcoll=(PMV−Lcoll)×(1+fcoll)P_{coll} = (P_{MV} - L_{coll}) \times (1 + f_{coll}) In both versions, the AC collection output is: Pcoll=PMV−LcollP_{coll} = P_{MV} - L_{coll}

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Block Aggregation

Array outputs are aggregated to the block level using repeater counts: Pblock=∑arraysPcoll×NrepP_{block} = \sum_{arrays} P_{coll} \times N_{rep}

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References

  • IEEE Std C57.12.00. IEEE Standard for General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers.