See responses below ... Ray
> On May 22, 2018, at 11:58 AM, Shady Mamdouh > <[email protected]> wrote: > > Thanks for your appreciated answers but I'm still little confused about these > points: > > 1- The contract value "Pc": I understood that it is obtained in the 1st > stage optimization solution and the deviations from it "P+" & "P-" are > obtained at the 2nd stage. Am I right? MOST does not define two stages. But if you use it to solve two stages, e.g. a day-ahead unit commitment problem, followed by a real-time re-dispatch, then the day-ahead problem could include both a reference dispatch Pc that you could use to define some day-ahead contract, and the “what-if” incremental and decremental dispatches (P+ and P-) that would be required as deviations from that reference point if particular scenarios are realized. > 2- Each run of MOST give optimization solution for only one stage, so we > got solutions of stage1 (in one run) and use the values of stage 1 to run > MOST again for stage2 solution. Am I right here? This is a very reasonable way to use MOST. However, given that a second stage (e.g. real-time re-dispatch) will hopefully have more up-to-date information available as inputs, the dispatches coming out of this problem need not match the dispatches of any of the probabilistic states considered in the day-ahead problem. > 3- Definition of "zones" in zonal reserve and how to specify them. A zone is simply a subset of generators, defined by the mpc.reserves.zones matrix as described in Section 7.5.1 of the MATPOWER User’s Manual <http://www.pserc.cornell.edu/matpower/docs/MATPOWER-manual-6.0.pdf>, especially see Table 7-4. See also the description in Section 7.2 on page 66. > 4- Meaning of ramping costs (wear and tear). These are intended to model real physical costs incurred due to ramping from one period to the next, modeled as C_∂ * (P_t - P_t+1)^2. > Thanks in advance > > > من: Ray Zimmerman <[email protected]> > إلى: MATPOWER discussion forum <[email protected]> > تاريخ الإرسال: الإثنين 21 مايو، 2018 3:49 م > الموضوع: Re: Issues about Problem Formulation in MOST > > The main thing I would recommend is to study the mathematical formulation in > Chapter 4 of the MOST User’s Manual > <http://www.pserc.cornell.edu/matpower/docs/MOST-manual-1.0.pdf>. See my > responses below for more comments ... > >> On May 20, 2018, at 5:43 PM, Shady Mamdouh >> <[email protected] <mailto:[email protected]>> wrote: >> >> Hello Dear, >> Regarding the problem formulation in MOST program, I have these questions >> that I am confused about. >> >> 1- Difference between zonal reserve and contingency reserve : I understand >> that zonal reserve are some constant amount of reserve specified before the >> solution, but what is the definition of "zone" and how can I specify zones? >> and what is the difference between zone and area in bus data? And what is >> the difference between zonal reserve and contingency reserve? > > See section 3.2 of the MOST User’s Manual > <http://www.pserc.cornell.edu/matpower/docs/MOST-manual-1.0.pdf>, along with > section 7.5.1 in the MATPOWER User’s Manual > <http://www.pserc.cornell.edu/matpower/docs/MATPOWER-manual-6.0.pdf>. The > BUS_AREA column of the bus matrix is used for area summaries in the pretty > printed output of MATPOWER and also can be used by a few other functions such > as scale_load() and apply_changes() to make area-wide modifications to a > case. The ZONE column is a loss zone identifier originally from IEEE and/or > PSS/E formats, but is not currently used at all by MATPOWER or MOST. > >> 2- Contingency reserves: what is meant by it? and how can this reserve >> amount be determined or calculated? is its value determined after MOST >> solution or pre-specified? > > See section 3.2 of the MOST User’s Manual > <http://www.pserc.cornell.edu/matpower/docs/MOST-manual-1.0.pdf>. It is > determined by the MOST solution and is defined as the maximum upward and > downward deviations across all base and contingency dispatches from the > reference dispatch. > >> 3-Difference between contingency reserve limits and physical ramping limits? > > Physical ramping limits are used to constrain all base dispatches in one > period with respect to all base dispatches in adjacent periods. Contingency > reserves are limited by both physical capabilities and offered reserve > capacity and are determined by the optimization (and thus also depend on the > cost) and they apply only within a given period to the deviations across base > and contingency cases from the reference dispatch for that period. See also > Figure 3-3. > >> 4- Difference between load following ramping (wear & tear) and load >> following ramp reserves? > > See section 3.5 and Figure 3-6. Load following ramp is used to impose a > probability-weighted quadratic cost on all base-case transitions. > Load-following ramp reserve quantities are (like contingency reserves) > outputs of the optimization determined by the cost of the maximum ramps from > a base state in one period to a base state in the next and the quantity can > be restricted by physical ramp limits as well as an offered ramping capacity. > >> 5-Active contract value "Pc": what does it mean? (Is this a contract >> between consumers and utility or what?) >> and how its value be determined? (After MOST solution or the user specifies >> its value?) and what about the deviations from it ? >> From my reading on the manual and the papers "Secure Planning and Operations >> of Systems with Stochastic Sources, Energy Storage, and Active Demand" & >> "Stochastically Optimized, Carbon-Reducing Dispatch of Storage, Generation, >> and Loads", I understand that we have 2 stages, stage 1 determines the >> contract value and stage 2 determines the deviations from this value as a >> recourse action. > > MOST solves the problem with the formulation given in Chapter 4 of the > manual. This can be used to implement a two stage market (e.g. day-ahead that > determines the contract value and real-time that determines recourse > deviations from the contract) by using it to solve separate problems for each > stage, but any given run of MOST is simply solving a problem which is > (potentially a subset) of the form given in Chapter 4. In this formulation, > Pc only has meaning for stochastic problems where you have multiple base > cases and/or contingencies. Pc is an optimization variable which is simply > the reference dispatch from which upward and downward deviations are defined > for inc/dec costs and contingency reserves. In a day ahead problem, for > example, it could be used as the day-ahead contract quantity between the ISO > and the generators, but this is a matter of market design. It’s value need > not be used at all. The full range from Pc – downward contingency reserves to > Pc + upward contingency reserves is required to be able to meet the > contingencies. The value of Pc simply determines how much of the reserves are > “upward” and how much are “downward” and, depending on the problem, may not > even be well-defined. > >> 6- Details about the cost functions Cp(P), CR(r), Cδ(δ)….. : the form of >> the equations ,is it a quadratic or what type? And the coefficient needed to >> specify them? > > These are specified in the xGenData as described in Table 5-1. C_P() and > C_R() are linear and C_∂() is quadratic. > >> 7-Confusion about the usage of probabilities in the objective functions: >> ψα: probability of contingency used in cost of dispatch and redispatch >> function f(p,p+,p-).(why it used in this cost function only?) > > Because the summations in this term are over all individual states, each of > which has it’s own probability of occurring. Dispatch and deviation variables > are per state. > >> ϒ: probability of making it to period 't' (what does "it" refer to here?) >> and why this probability used in all objective functions except the cost of >> dispatch & redispatch f(p,p+,p-)? > > Other cost terms are summed over period only, so the probability is of > “making it to period t” or to put it another way “the probability of avoiding > all contingencies before arriving at period t”. For example, reserve > variables are per-period, not per-state, so there is no summation over the > states in period t for reserve costs. The summations are only over period. > >> 8-When using the DC network model instead of nonlinear network network the >> problem is converted from MINLP to MIQP, How does this happen? (Why not >> converted to MILP problem?) > > MOST does not implement the AC network model case, so the choice is between a > DC network or no network. With a DC network there are two cost terms that can > be quadratic, one is the generator costs themselves and the other is the > ramping wear-and-tear costs. This makes it a MIQP problem. If you don’t want > to do unit commitment it turns into a QP. If you have linear generator costs > and no ramping wear-and-tear costs it is an MILP. And with no UC, linear gen > costs and no ramping wear-and-tear costs, it becomes a simple LP. > >> 9- What does "Nodal energy prices" mean? and what is the difference between >> it and "shadow prices" and "marginal prices”? > > Shadow price is a general term referring to the Kuhn-Tucker/Lagrange > multiplier on any given constraint. Nodal energy prices refers to the > expected marginal prices of energy at a node and is the sum of the shadow > prices on the power balance constraints for that node across the states in > that period (adjusted by the probability of making it to that period). > >> 10- I understand that MOST is used to model transmission systems and one can >> add wind and storage sources, but if I want to model a Microgrid, how can I >> use MOST to model it? And what about adding PV generation? > > If a DC model is appropriate, there should be no difference. You could model > PV as an uncertain source of generation, just like wind. > >> 11- What meant by transmission congestion and its effect on nodal energy >> prices, storage, and min up&down times? > > Transmission congestion simply refers to binding branch flow constraints. The > presence or absence of binding transmission flow limits can affect the entire > solution, including all prices, dispatches and commitments. > > Hope this helps, > > Ray > > > > > > <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> > Virus-free. www.avg.com > <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> > <x-msg://129/#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
