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Converting mains to 300Hz in order to reduce size of PFC equipment?


Suppose I have a 10kW installation. It has a three phase supply. It comprises a 3-ph mains transformer which transforms down to 40VAC….this is then rectified by loads of paralleled 6 pulse,3phase rectifiers. Lots of 40W loads feed off this.

The power factor is obviously not going to be unity. However, is there some way of adding extra equipment which can make the power factor unity?........ie some way that involves converting the incoming mains to 300Hz (or whatever) and then that being easy to correct the power factor for?


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You'll never get unity power factor, although you may get very close.

I don't think that lots of phases help. Anything that simply rectifies to smoothed DC will end up taking a most of its power when the voltage is highest, which leads to a very poor power factor.

Some big power supplies have a boost converter before the smoothing capacitors so that when the mains voltage is at a low part of the cycle, current is still taken from the supply. The manufacturers even say how they do it:- https://www.meanwelldirect.co.uk/glossary/what-is-power-factor-correction/

Some LED lights have power factor correction that turns on separate groups of lights depending on the instantaneous voltage. The current that those systems take is stepped, but much nearer a sinewave than a simple rectifier. Of course, that depends on being able to use the lower voltages. It can also result in flicker.

I suppose that a rotary converter would work, but it would be big, heavy, noisy and expensive. It might be inefficient and high maintenance as well.


Well-Known Member
Most Helpful Member
The first part of an electronic frequency converter (an inverter or VFD etc.) is a rectifier, probably with PFC on any sizable system.

You cannot convert frequency electronically without causing more cost and complexity.

You would likely be better off with a number of smaller switched mode supplies that each include PFC and avoid the low frequency transformer completely.

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