Real-time power on the inverter

Based on real-time measurement of the grid impedance, the unintended reactive power is estimated and autonomously compensated in the inverter. The method removes the fluctuating reactive power component, while still permitting unrestricted manual control of the reactive power.

Power generation flowing through the transmission line causes unintended flow of reactive power to the grid side, as the transmission reactance consumes reactive power. Thus, the grid-side reactive power becomes coupled with the active power production of the photovoltaic inverter, which fluctuates along with irradiance conditions.

The present work proposes a method for real-time compensation of the unintended reactive power, which decouples the reactive power from the active power of a photovoltaic inverter. Based on real-time measurement of the grid impedance, the unintended reactive power is estimated and autonomously compensated in the inverter.

The flow of reactive power in the transmission line increases the total current and Joule losses in the line. In addition, a large proportion of unintended reactive power may destabilize the inverter in very weak grids. Consequently, the unintended reactive power imposes limitations to maximum active power feed from the PV inverter.

The inverter for renewable production is synchronized to a local point of connection (PoC), where the measurements are taken for control feedback. The current fed to the PoC causes an unintended flow of reactive power when flowing through the reactive grid impedance of the transmission line.

Thus, in a weak grid the active power of a PV inverter becomes coupled with reactive power seen by the grid. Unintended reactive power increases transmission losses, reduces the maximum transmission capacity, compromises system stability, and strains the grid with excessive reactive power requirements, , , , .