Scenario 3 – DR resources and RLXD variable on AS dispatch

These two conditions combined give rise to the need for dispatching external suppliers and, expensive generators with some freedom of production to meet the service requirements for each region.

Figure 4.25 – Non-spinning reserve dispatch by each region.

In Annex C, Figure C.12 illustrates the global dispatch of the service considering the types of resources surrounding the dispatch of the referred service.

4.6.2.3. Scenario 3 – DR resources and RLXD variable on AS dispatch

In this scenario the results for the introduction of the types of DR and relaxation variables of the problem for the ancillary services are presented. From the point of view of energy service, this scenario does not involve significant changes in the energy dispatch, this occurs due to the maximum limits of resources for the energy service that has not changed. In this way, the results and conclusions of this scenario focus on the AS dispatches.

The Regulation Down dispatch does not consider the use of types of DR established in the model. The types of DR consider only the load reduction, which is infeasible for the

RD service. This service hires resources to reduce generation or increase the consumption in the network. Thus, the proposed types of DR are not suitable for this service.

In this context, Figure C.13 and Figure C.14 in Annex C provide the dispatch and their percentage of contribution of each resource to the RD service.

With regards to the Regulation Up service, the contribution of Demand Response is quite considerable. In Figure 4.26 it is possible to see a large participation of DR in regional dispatch of RU. In this way, the types of DR are fairly useful for the RU dispatch, thereby reducing the operation cost compared to the service requirement, if provided only by DG technologies and external suppliers. In Annex C one can find the global dispatch of the RU reserve in Figure C.15.

Figure 4.26 – Regulation up dispatch considering DR resources.

In the context of the widespread use of DR for RU service and for each region of the network, Figure 4.27 presents the contribution of each Type of DR in each region for this service.

Depending on the region, the contribution of each Type of DR may vary considerably. For example in Regions 1, 2 and 3 there is a greater participation of DR Reduce type, while in Region 4, the DR Cut is clearly superior to the DR Reduce. Briefly, the Demand Response Cut type to the loads of Region 4 is less expensive, and has, therefore, a greater contribution in the regulation up dispatch.

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Figure 4.27 – Types of DR dispatch in each region for RU service.

With regards to the Spinning Reserve dispatch, Figure C.16 of Annex C illustrates the global dispatch of SP service, in which can be seen the impact that the DG, DR and external suppliers has in the dispatch. Following this perspective, the contribution of each type of resource by network region is shown in Figure C.17 of Annex C.

The maximum capacity of each DR resource in this service is equivalent to 10% of the maximum capacity for the same resource for the Regulation Up service. In this way, for the SP service the DR was fully used, implying that to satisfy the regional requirement it is required more power of the DG and external suppliers, as compared to the RU service.

Thus, based on Figure C.16, it is concluded that the DR and external suppliers are a crucial part of the SP dispatch, since the maximum capacity generation of DG resources in both services (RU and SP) is similar.

Figure 4.28 – Types of DR dispatch in each region for SP service.

Figure 4.28 illustrates the DR dispatch by network regions for the SP service.

Comparing Figure 4.28 with Figure 4.27 (concerning the RU dispatch) one can see an increased contribution of the DR Cut type in regions 2 and 3.

In this context, the use of almost the total generation capacity of DG and DR resources leads to the availability of using relaxation variables when resources fail to generate enough energy to supply the load.

The use of relaxation variables are typically used in two different ways. Firstly, the relaxation variables can only be used in the optimization process as a means for the VPP to identify the situation in which the dispatch is infeasible, creating a problem to VPP towards solving the problem of infeasible solution.

Secondly, the VPP knows through the relaxation variables what are the problems of the dispatch, and through bilateral contracts with generation units it ensures the feasibility of the dispatch. This is the way normally used by the ISO or VPP to solve the problem of the infeasible dispatch.

The model developed presents a third way of looking at the problem, which consists in the procurement of resources in the market optimization that could contribute to the feasibility of the dispatch regarding all regions. However, from the beginning one does not know in which regions of the network these situations can happen. In this way, it is possible to implement a constraint on the model which uses the resources of other regions of the network to meet the requirement of a particular region.

In this context, Figure 4.29 shows the Spinning Reserve dispatch of region 2 in which is evident the use of the relaxation variable RLXD.

Figure 4.29 – SP dispatch in region 2, by each resource.

In this case, the relaxation variable will be entirely provided by the external supplier, because the DG and DR were completely used in all regions of the network. All internal

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resources of region 2 have insufficient capacity to provide at least 50% of the Spinning requirement of its region. In this way, the generation provided by the external supplier for the variable is remunerated at a high price, in which the relaxation variable is only used to achieve the 50% of the regional AS requirement, since it is mandatory to offset at least 50% of requirement be provided by the internal resources of the region. It can be concluded that the relaxation variable complements the needs of generation in case of internal resources of the region being insufficient to provide partial or full regional AS requirement.

The respective regional dispatch to the remaining network regions can be found in Annex C, Figure C.18, Figure C.19 and Figure C.20.

Regarding to the Non-Spinning reserve dispatch, one can verify that the DG and DR generation are practically sufficient to meet the load in all time periods except for the period corresponding to hour 3.

In this way, the regional NS service dispatch is illustrated in Figure 4.30 (the global dispatch of the service by all kind of resources is shown in Figure C.21 and presented in Annex C).

Figure 4.30 – NS dispatch by network regions, considering DR resources.

Regarding the contribution of DR in this service dispatch (Figure 4.31), it seems that regions 3 and 4 cover a greater sharing of types of DR while regions 1 and 2 contemplates greater involvement of DG in these regions dispatch. This is mainly due to the price and generation capacities provided by DR resources in certain regions of the network.

The types of DR can be very useful in the stability of power systems. Through the scenario presented is clear the need to consider these resources in the complex managing of ancillary services.

Figure 4.31 – Types of DR dispatch in each region for NS service.

These resources may reach a more economical management of the energy and AS joint market. However, it is important to note that the excessive use of a particular resource type is not good for the stability and management of all kind of resources in the power systems. Briefly, this scenario shows the potentiality of DR in a efficient ancillary services dispatch, as well as the use of generators in special cases, such as situations in which the internal energy generation in a region is not enough to satisfy the AS requirements imposed by the VPP. In these cases, the implemented relaxation variables are a way to ensure the feasible dispatch of ancillary services.