# Synchronous Generator Power factor

1. Aug 22, 2010

### bhavi

Hello everyone,

I would like to ask a little help from you guys. I am designing a Permanent Magnet Synchronous Generator (PMSG) for a Wind turbine application which is of direct drive (DD) type. Being a DD type PMSG the frequency of the output is very low and hence I had to employ converter Inverter pair to improve the frequency. Now, how do I calculate the power factor (PF) of the PMSG? As the PMSG is not directly connected to the load, I believe that the PF does not depend on the load nature. Can someone help me by providing any equations or any research papers and any other material that can help me finding out the PF of the PMSG.

Thank you very much.

2. Aug 22, 2010

### Mike_In_Plano

Hello,

Mike here. I used to design BLDC motor drives. Generally, we'd fall with one of two windings, trapezoidal BEMF and sinusoidal BEMF. I were making a generator, I'd certainly prefer the prior, because the current can fairly be steady through each phase pair, and you'll get good conversion because the BEMF is likewise flat.

In fact, I'd simply use a high speed rectifiers in a three phase bridge directly off the motor phases and boost convert it to your link voltage using a single IGBT/FET. Easy cheesy and no complex commutation to work out. :)

- Mike

3. Aug 22, 2010

### bhavi

Thank you for the quick reply Mike. But I dont really think you got my question or may be I am unable to understand your answer. I was actually asking how to find out the Generator's power factor. Generally, the power factor of the generator is decided by the type of the load connected to it. But in my case I have a set of converter inverter connected in between the generator and the load and hence the type of the load does not affect the power factor in the generator. So I am trying to find out the way to know the power factor in the generator. Thanks once again for your time.

4. Aug 23, 2010

### Carl Pugh

For Three-Phase Bridge and resitive load
Generator RMS volts line-to-line=0.740 X Average dc voltage output
Generator RMS line current=0.816 X Average dc output current

Above from Reference Data for Radio Engineers 5th Edition
Above was for transformers, but also apply to generators

Current is distorted so power factor doesn't apply.
The KVA of the transformer/gererator is 1.05 X the KW of the load.
The preceding neglects the voltage drop of the diodes.