Inverters are typically rated in units of kVA at a nominal ambient temperature (typically 50 °C) and at sea level. Maximum inverter kVA capacity can vary with ambient temperature and elevation. It increases at lower temperatures and elevations, and decreas at higher temperatures and elevations. This algorithm calculates the actual maximum AC operating kVA given the ambient temperature, and elevation. An example of the elevation and temperature derate curves is shown in Figure 40.

Figure 40. Example Inverter Derate at Different Elevations and Temperatures.

 

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Algorithm

1.) Find the inverter apparent power, for the given ambient temperature T_a and site elevation h, by linearly interpolating the tabular inverter derate breakpoints along the ambient temperature. There is only interpolation along the ambient temperature axis, not along the elevation.

For Example:

2.) Determine if the set point or calculated apparent power governs maximum real power in the inverter operation. This is the lesser of the desired setpoint P_set or the maximum available temperature adjusted apparent power the inverter can produce.

Switch on Inverter Model selection

Case: Temperature Derate

Case: None

Find the inverter clipping limit: