reactive power processing

[sabu31]

Hi,

I have read that some topologies of grid connected inverters can only work for UPF, because the DC link capacitor is disconnected from grid during freewheeling period. Could some one explain or give references regarding reactive power transfer in grid connected inverter.

Thanking you.

 

[kappa_am]

you want a topology that is able to transfer reactive power?
it easy to build such inverter. consider following steps:
1-obtain grid voltage angle, using PLL
2- use obtained angle in park transform. doing so, the voltage vector will locate on d-axis.
3-now, by injecting current on d-axis you inject active power to grid, and by injecting current onq-axis you inject reactive power to grid.
you can obtain amplitude of current on d and q axis using reference active and reactive power and a controller like PI controller.

Good Luck

 

[Anna Conda]

Most grid tied inverters feed current into the mains against the mains voltage present, they do this in phase with the mains to maximise power to the mains with the least amount of reactive current - which just generates extra heat and so lowers efficiency. They essentially only operate at unity power factor, they are not designed to have leading or lagging currents (except those due to filter caps across the mains). The DC link or main bus cap is irrelevant to this.