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Summary

The maximum AC power PAC,deratedP_{AC,derated} sets the upper bound for the operating region logic, determining the threshold. The AC power setpoint PAC,setP_{AC,set} is defined in the inverter configuration from the nameplate rating and the design derate factor. Alternatively, the setpoint or the derate factor can be set per timestep using a user-uploaded time series. When manufacturer derate curves are provided, the setpoint may be further reduced depending on ambient temperature and site elevation.

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Inputs

NameSymbolUnitsDescription
Rated AC PowerPAC,ratedP_{AC,rated}kVAInverter nameplate AC power rating
Design Deratedd—Fractional multiplier on rated power (0 to 1)
AC Power SetpointPAC,setP_{AC,set}kVAEffective AC power limit
AltitudehhmElevation above sea level
Ambient Air TemperatureTaT_a°CAmbient air temperature
Inverter Derate CurvesPAC,derate,hk(Tj)P_{AC,derate,h_k}(T_j)°C, kVATemperature-power data points at rated elevations hkh_k

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Outputs

NameSymbolUnitsDescription
Temperature-Corrected Max PowerPAC,deratedP_{AC,derated}WDerated AC power capacity

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Detailed Description

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Setpoint Determination

The AC power setpoint is the baseline upper bound on inverter output. It is derived from the inverter nameplate rating and the user-configured design derate: PAC,set=d×PAC,ratedP_{AC,set} = d \times P_{AC,rated} A design derate of d=1.0d = 1.0 uses the full nameplate; lower values curtail the inverter (e.g., d=0.95d = 0.95 limits output to 95% of rated capacity). The user can set either the design derate dd or the absolute setpoint PAC,setP_{AC,set}; the other value is adjusted automatically to satisfy the equation above. Both values can also be overridden on a per-timestep basis by uploading a time series. A setpoint time series provides PAC,setP_{AC,set} directly in kVA, while a derate time series provides dd as a ratio (0 to 1). If both are configured, the setpoint time series takes priority.

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Curve Selection by Elevation

Example Inverter Temperature / Elevation Derate Curve
Inverter manufacturers may provide multiple derate curves at different elevation ratings h1<h2<⋯<hKh_1 < h_2 < \cdots < h_K. If these curves are available, PlantPredict selects the curve whose elevation is the smallest value still strictly above the site altitude: h∗=min⁡{hk:hk>h}h^* = \min \{ h_k : h_k > h \} If the site altitude exceeds all available curve elevations (h>hKh > h_K), the highest curve is used: h∗=hKh^* = h_K

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Temperature Interpolation

Once the curve PAC,derate,h∗P_{AC,derate,h^*} is selected, the ambient temperature TaT_a is linearly interpolated against its data points to obtain PAC,derate,h∗(Ta)P_{AC,derate,h^*}(T_a). If TaT_a falls outside the curve’s temperature range, the inverter is derated to zero (PAC,derated=0P_{AC,derated} = 0).

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Final Output

The final AC power limit is the lesser of the setpoint and the temperature-derated capacity: PAC,derated=min⁡(PAC,set, PAC,derate,h∗(Ta))P_{AC,derated} = \min\bigl(P_{AC,set},\, P_{AC,derate,h^*}(T_a)\bigr) The prediction engine converts PAC,deratedP_{AC,derated} from kVA to W (× 1000\times\,1000) before passing it to the inverter operating region logic. When derate curves are not enabled, the temperature derating step is skipped and PAC,derated=PAC,setP_{AC,derated} = P_{AC,set}.