You are correct. Typical simple power flow models assume a constant power (independent of voltage) for loads and generators. Some software models load using a “ZIP” model, that is, a combination of constant impedance, constant current and constant power elements. This gives the flexibility to more accurately reflect a load’s actual relationship between voltage and power. Currently MATPOWER does not include a ZIP load model, though the constant impedance portions could be placed in the GS and BS columns of the bus matrix, though they would not be reported as part of the load.
Ray On Mar 11, 2014, at 5:53 AM, mateusz wanka <[email protected]> wrote: > Dear all, > > I'm starting to model and analyse power systems and I've decided to use > Matpower. I have a question regarding creating admittance matrix which is > needed to performe a load flow. Text books say that diagonal elements of this > matrix is a sum of admittances all branches connected to a particular node > and 'include also the admittance to ground of line charging susceptance and > any other fixed admittance to ground' (from 'Power System Analysis' by > H.Saadat). There is also presented a way how to convert impedance diagram of > a system into the admittance diagram and the admittance matrix of such a > systm is calculated. The diagonal elements include also admittance of the > current sources. (chapter 6 of the book) > > My question is: why in Matpower (but also in examples of power flow > calculations from above book) we don't consider admittance of sources/loads? > Is this because we assume that there are 'ideal power sources/consumers' with > constant power and if we considered internal admittances, their power would > be variable and depending on the system load and therefore couldn't be > PQ-nodes anymore? Similarly for PV- and slack node? > If not, what is a reason for that? I cannot find any explicit explanation in > the literature. > > Thank you in advance and best regards, > Mateusz Wanka
