Power factor correction or regulation (whatever that means) of single phase systems is not a big enough problem to be worth spending a lot of time on in most areas of the world. Poor power factor is a result of unloaded motors (primarily) and in single phase installations, those are usually household appliances. First off, most 1 phase motors have capacitors built-in to start with because of needing them for starting. Secondly, most household appliances are not run continuously in an unloaded state to where correction would make much of a difference, and lastly, most power utilities do not assess penalties for poor power factor on single phase installations.
So again, Why?
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