Dear Mustafa,

The collapse of the terminal voltage on the terminals of the pv source is that a short-circuit has been occurred between these two terminals. Most probable that power transistors may be damaged due to improper sizing or false timing of control pulses. A short occurring in the pv supply is very improbable because the nature of the solar cells.

Best wishes

There are many reasons, but If you are designing the inverter you better check out the switcing states of the inverter to make sure that it doesn't have a '0' state (short circuit)

Thanks for your answers you are right of course short-circuit is one of the main causes of potential stability degradation across the PV terminals. If we put undamped input filter between the PV and the step-up converters, that is to reduced the harmonics and suppose that the inverter behaves as a constant voltage source with infinite current i.e. (infinite-bus). Is there any effect regarding the undamped input filter applied in between?

Thanks

Truly Yours

Dear Mustafa,

Filters used are composed of LC elements. They can affect DC short circuit when the capacitor is damaged and gets short. But this is very improbable and occurs when the voltage on the capacitor rises above its breakdown voltage.

I would advice you to analyse your circuit for potential shorts on the terminal of the pv generator.

If you display your circuit you can get help for this analysis.

Best wishes

What is the impedance of the grid seen from the side of PV? Assume the dc-microgrid working one grid connoted mode i.e. the DC-Bus voltage strictly controlled by DC-AC inverter.

attched is the diagram

thanks for your help

Dear Mustafa,

The impedance seen at the input of the inverter connected to the DC bus is determiner by how much power is delivered to grid from the inverter.

Assume that the power delivered to the network= Po at the voltage of the grid V, then the I = P/V , I and V are root mean squared values. The impedance Z= V/I. If there is any transformer at the output of the inverter you have to reflect the impedance at the input of the transformer using the relation:

Zi = Z/n^2 where n = Ns:Np , is the ratio of the secondary to that of the primary turns.

It is so that when you connect the inveter to the grid you have to control its power delivered to the grid by controlling its output current. This what controls the impedance of inverter.

Best wishes

Thanks for your answer Dr.Abdelhalim Zekry

In particular case I assumed the main grid share the load with PV i.e. the power delivered from main AC-grid to DC-microgrid. And the inverter behaves as voltage source, so how can I find the impedance of the grid from the side of PV.

Dear Mustafa,

Now the power flow is revered from the grid to the power system and the power electronic circuit functions as a rectifier. As you said in this case you can consider this DC source with a specific source resistance determined by the smoothing filter if present.

From the conceptual point of view sources can be constant voltage source or constant voltage source.

The load of such source according to your schematic diagram is the load connected to the dc bus LOAD. The pv generator must be made off by the diode at the output of the DC/DC converter.

Best wishes