You cannot modify voltage angles independently and maintain feasibility (respect the power balance constraints). In order to maintain feasibility you must modify voltage angles and generator injections together along the surface of power flow solutions.
If you modify the voltage angles along the power flow surface, that is, while maintaining feasibility, it will imply changes in generation which will result in changes in cost. Ray > On Mar 20, 2019, at 1:25 PM, Arkan Arkan <[email protected]> wrote: > > I see. Thank you for your clarification. So, is there any trick and solution > to be able to change the output cost though manipulating the voltage angles? > > Thanks. > > On Wed, Mar 20, 2019 at 7:33 PM Ray Zimmerman <[email protected] > <mailto:[email protected]>> wrote: > Ok, so you just want to evaluate the objective (or cost) function of the DC > OPF at a given solution. The issue is that the cost function depends only on > the generator injections, which are related to the voltage angles through the > constraints. So if you take a DC PF solution and make changes to the voltage > angles, without changing the generator injections, the result will be only > infeasible power balance constraints with no change in the cost function. > > Simply put, manipulating the voltage angles will affect feasibility, but not > cost. > > Ray > > >> On Mar 19, 2019, at 10:03 AM, Arkan Arkan <[email protected] >> <mailto:[email protected]>> wrote: >> >> Dear Ray, >> >> Thank you so much for your response. I very much appreciate it. What I mean >> is a little bit different. Based on my understanding, I exactly need DC for >> my work. This is my understanding. When we run "rundcopf", after some >> calculations, the phase angles are obtained and then fed into the OPF >> function which finally gives us the total cost and the whole process is done >> as a function. Now, after computing the phase angles through PF and before >> feeding into OPF function to calculate the cost, I need to somehow change >> the values of calculated phase angles a little bit so that the final cost >> will be based on the manipulated (my values) phase angles. I tried to change >> the values of phase angles in different steps of the function but wasn't >> effective and the final calculated cost is like before change. Please let me >> know your thoughts on this. >> >> Thanks. >> >> Kind regards, >> Arkan >> >> On Tue, Mar 19, 2019 at 6:21 PM Ray Zimmerman <[email protected] >> <mailto:[email protected]>> wrote: >> I’m not sure I understand what you want to do. >> >> Let’s start with the DC OPF. It sounds like you’re saying you need to run a >> DC OPF where you are directly specifying (constraining to a specific value) >> some of the voltage angles. Is that correct? The problem is that there are >> very few degrees of freedom in the voltage angles due to the power balance >> constraints. I suspect that manipulating (constraining) the voltage >> magnitudes directly will very quickly result in an infeasible OPF. >> >> But, you’re welcome to try. You can add user-defined linear constraints (A, >> l and u) to restrict the voltage angles. The first nb columns of A >> correspond to the voltage angles. See section 6.3 and Chapter 7 in the >> User’s Manual for more details. Simply use the VMIN and VMAX columns of the >> bus matrix to restrict voltage magnitudes. >> >> Ray >> >> >> >> >>> On Mar 19, 2019, at 8:26 AM, Arkan Arkan <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> Dear All, >>> >>> I hope this note finds you well. I need to run optimal power flow (both DC >>> and AC) while the input values for phase angles and voltage magnitudes are >>> manipulated. In other words, how could I run OPF with desired values of >>> phase angles and voltage magnitudes? I know that I should change the values >>> on the way and in the middle of code but I wasn't able to find the right >>> place in MATPOWER. >>> >>> I would be so grateful if you could, please, help me in this regard. >>> >>> Thank you for your time and consideration. >>> >>> Kind regards, >>> Arkan >> >
