LGWR is switching frequently in every 3,4,7 minutes. what should i do
The output size of archivelogs are maximum 90mb to 100mb.


Its not necessary to have archived log file should be same. 


  during night session logs get filled upto 180mb out of 200mb. but during morning session logs get maximum to 90mb to 100mb


Its not necessary to have log switch occur when online redo log file is 100% full. There is also an algorithm inside Oracle which determines the timing for the log switch.
After the log switch, the archiver process will copy only the actual information from the
redo log files. Since the redo logs are not 100% full after the log switch this results in uneven, smaller files than the original redo log files.

Some of the factors which may enforce frequent log switch are listed below:
Online redo log file size
LOG_BUFFER_SIZE parameter.
Current load of the database
 Logfile space reservation algorithm

Details are given in an Oracle knowledge based document.(MOS account required)
Archived redolog is (significant) smaller than the redologfile. (Doc ID 1356604.1)