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Simulation process: DC-grid system

System calculation is rather different whether a load profile is defined or not.

With undefined (illimited) load profile

When the load consumption (vehicle) is not defined, the delivery of the conventional power supply is irrelevant. The voltage at the output of the array is the "Main Power Supply Nominal Voltage", with a fixed value. The treatment is easy, since the array operates at this fixed voltage: current and power are directly deduced from the array I/V characteristics model. Voltage at the user's level is decreased by the "PV-system line resistance" voltage drop.

In this case the safety overvoltage regulation does not operate, since the line voltage stays at a fixed value, and the PV current production is supposed to be always absorbed.

With defined load (usually "probability" load profile)

In this case the simulation has to resolve a balance current at the user's level. User's consumption is determined by the load profile definition requirement. Available solar current is coming from the PV array, the rest being delivered by the conventional power supply.

Available solar current has to be determined from the I/V array characteristics, taking both line resistances (PV-to-user, and conventional supply-to-user) into account. Two cases can arise:

  • Either the PV production is not sufficient: in this case the line voltage at the array output will stay around the supply nominal value, only influenced by the line ohmic voltage drops.
  • Or the PV production covers the user's needs, so that the conventional supply current drops to zero. In this case the line voltage follows the PV-array I/V characteristics, and can raise up to the Voc value when the user's needs drop to zero. In this case the regulation overvoltage safety should apply if the allowable maximum voltage is reached.

Several variables are computed during and after this process.