Dear Ranvir Kaur,

Generally, the application like AC drives rated in kW or MW power level. For higher power ratings the available AC is converted into DC by using rectifier system with added power quality improvement. Since the power rating is high and hence it can be derived from the available AC mains. For low power applications, a direct constant source might be a possible choice. Moreover, the quality of AC mains is in control as well as controlling the drive system is easy while the drive system is fed from the front-end rectifier.

Thank you. 

Thanks sir

Dear Ranvir,

It is not necessary to use a rectifier to supply an inverter. What you need is a dc source at the input of the inverter.

Now the question is how to realize a dc source which is advantageous with respect to performance, lifetime and affordability. Now, the options are to use rectifier, battery, PV source, Fuel cell etc. to use as dc sources. Now if you consider the option of the rectifier which converts ac to dc can be the most advantageous one depending upon the application. 

The reason behind this is ac is abundantly available and most popular form of power in the current day. On the other hand, PV is costly and gives fluctuating power, a battery is costly and has a low lifetime. This makes ac-dc conversion via rectifier is the obvious choice for most of the application.

Although where grid is not available you may have to switch to other kinds of dc sources

Hope this answers your query.

Thanks a lot.That means i can go for Direct inverter in simulation but at later stage in practical need rectifier part also.

AS every body above mentioned, by using rectifier as a DC link, you can also have controlled DC i.e. variable DC voltage DC output, which is easy way to ultimately control the AC output.