# dq0 transformation

Discussion in 'General Electronics Chat' started by bonanza, Sep 11, 2012.

1. ### bonanza Thread Starter New Member

Sep 11, 2012
1
0
Hey,

i've got some question regarding the dq0 and the alpha-beta-zero transformation. In the case I have a 3 phase system, why do i sometimes still use the alpha-beta-zero-transformation, if its in genereal easier to deal with DC values delivered by the dq0 tranformation ? Is there any disadvantage of using dq0 transformation? what is the physical meaning of the power definintions in dq0 domain?

many thanks for your help in advance!

2. ### steveb Senior Member

Jul 3, 2008
2,433
469
As far as power, the physical meaning of power is the same but you need to be careful to evaluate power correctly based on the particular form of the transform used. Some transforms produce voltages and current amplitudes in rms and some based on peak values. Also, the scaling of the zero axis can be different. There is the power invariant scaling and the average value scaling. Hence you should be very careful to use the correct power formula for your particular transform.

As far as why alpha/ beta versus dq frame, it all depends on what you are doing as to which is easier or more direct. The alpha/ beta is a stationary frame two orthoganal axis equivalent of the three axis abc frame. The frequencies are correctly retained in this frame, which is sometimes useful. You will have two sine waves typically 90 degrees apart rather that three 120 degrees apart.

Basically, it is just a reference frame choice: stationary versus moving. In physics, you might solve a simple mechanics problem and you may decide that a train problem is better solved in the reference frame that moves with the train, or you might prefer a frame that is fixed to the earth. Or, you might solve a merrygoround problem and might chose a frame that rotates with the wheel or you might choose a non rotating frame.