Adding to what has been noted by Dr. Dreher, in case of grid connected inverter  the load of the inverter is the grid which is characterized by constant voltage and has very small  resistance and therefore it is required to control the current withdrawn from the inveverte other wise the voltage output from the inverter can not be sustained.since the the inverter side may have relatively appreciable output resistance. 

In case of stand alone the current of the load is limited as the load has specific limited power consumption. At the same time the load demand constant voltage. Therefore itis required to regulate the voltage.

So, it is the demand of the the load side which determines the suitable control parameter of the inverter.

In a grid connected inverter you have to synchronize with the grid in terms of voltage and frequency. This is what the current control scheme does.

In contrast, a standalone system does define system voltage and frequency on its own. Prior to the PV systems and until today, this is how UPS (Uninterruptible Power supply) systems work. Lacking an external voltage/frequency to synchronize on, they implement their own definition of system. In this case, the current is a function of system load. It can (has to) be limited, but cannot be controlled beyond that.

Adding to what has been noted by Dr. Dreher, in case of grid connected inverter  the load of the inverter is the grid which is characterized by constant voltage and has very small  resistance and therefore it is required to control the current withdrawn from the inveverte other wise the voltage output from the inverter can not be sustained.since the the inverter side may have relatively appreciable output resistance. 

In case of stand alone the current of the load is limited as the load has specific limited power consumption. At the same time the load demand constant voltage. Therefore itis required to regulate the voltage.

So, it is the demand of the the load side which determines the suitable control parameter of the inverter.

Thank you Mr. U. Dreher

Thank you  prof.Abdelhalim Zekry

Dear Raghavendran.

In the case of the grid-connected inverters, normally, the main objective is to inject real power to the grid. In some cases, also reactive power is added. Then, a current controller must follow a sinusoidal reference synchronized with the grid voltage with a phase lag dependent of the desired power factor. The power injected depends of the available power.  On the contrary, in the case of the stand-alone inverters, the current and power are dependent of the load. The nature of the load defines the current should be given by the inverter. Then, that current can be linear or nonlinear, the current can have an unknown amount of harmonics limiting the use of current controllers. Therefore, the control of stand-alone inverters is dedicated to ensure the quality of the voltage waveform (amplitude, RMS, low THD) and the synchronization with the main system.

In the grid connected mode the power needed to be injected into the grid. so, you need current control.once you synchronize your pv system to grid you don't have to look for voltage and frequency control you should be looking into power injection.

this is not the case in stand-alone PV system. as the inverter itself has to maintained constant voltage and frequency in order to deliver the power. so, voltage control is employed..

hope this may clarify your doubt... best of luck 

Thank you Prof. Oswaldo Lopez Santos

Thank you Pavan Kumar