*4.2. Scenarios*

In order to examine the impact of the DRA on the operation of the active distribution system, seven simulation scenarios were proposed (Table 3). Each scenario presents different services provided by the maximum utilization of the resources coordinated by the DRA depending on various assumptions.


**Table 3.** Description of the simulation scenarios.

#### **5. Results and Discussion**

The reference scenario assumes a lack of influence of the DRA on the operation of subordinate resources such as RESs, DERs, ESs and ALs. All the resources aim for maximum profit without performing any ASs. The simulation output describes power flow at the PCC formed by all entities located inside the distribution network and is presented as *PCC\_%\_ref* in Figure 9. The results of this scenario form a basis for comparisons with further scenarios.

**Figure 9.** Results of the reference scenario—power flow at the point of common coupling (PCC).

The obtained value resulting from the objective function in the reference scenario is denoted as 100% for the purpose of future comparisons. The maximum percentage change in the power flow at the PCC between two adjacent hours is 19%/h when the demand change (Equation (14)) stands at 46.7%. The shape of the profile results from the assumptions presented earlier in Tables 1 and 2 and from the uncontrolled operation of distributed resources.

The shapes of the load profiles at the PCC for Scenarios 1–6 compared with reference simulation are presented in Figure 10.

The presented results are characterized by the di fferent impact on the shape of the load profile at the PCC. The first column of Figure 10 (Scenarios 1, 3 and 5) corresponds to services provided without renewable curtailment, while in the second column (Scenarios 2, 4 and 6), curtailment is allowed. *PCC\_%\_ref* denotes reference load profile, while *PCC\_%\_S1-6* correspond to modified profiles according to the simulation scenarios.

In Scenarios 1, 3 and 5, ASs are provided mainly through ESs, ALs and non-renewable DERs; hence, the modifications of the load profile are visibly lower than in Scenarios 2, 4 and 6 where the services are provided also by wind and solar renewables. The analyzed di fferences are related also to the assumed share of di fferent resources presented previously in Tables 1 and 2. Following the

assumptions, the share of generating units to be curtailed (wind and solar) corresponds to 25% of the peak demand.

**Figure 10.** Results of Scenarios 1–6—power flow at the PCC.

From the scenarios assuming a lack of renewable curtailment, the best results are visible in Scenario 5. The load profile is significantly smoother, resulting in milder up and down ramps. Nevertheless, the impact of the RES curtailment and the combination of both services (smoothing of the load profile and load levelling) gives the best results: the profile is smooth, peak demand is slightly reduced and night valleys of the demand are visibly filled (Scenario 6). The slight reduction of the peak demand in all scenarios is associated with a relatively low share of entities that are able to shift the demand from night valleys to the peaks: ESSs and ALs.

Table 4 presents a summary of the obtained results, where:


• Demand change denotes the percentage ratio of the difference between the maximum and the minimum demand regarding the maximum demand during the simulations' time horizon (Equation (14)).



The provision of the ASs caused deviation from the reference operation points of aggregated resources, hence, the values of the objective function for all scenarios were lower compared to the reference case. The difference between the obtained value of the objective function (for Scenarios 1–6) and reference value should be treated as the minimum price of the offer for AS provision (Figure 11). The lowest profits were obtained in Scenarios 2, 4 and 6 in which RES curtailment was allowed, and a significant decrease in incomes due to lost generation occurred. For this reason, the AS provision has to be properly valued in order to ensure the desired income for DRAs and therefore encourage them to participate in different markets.

**Figure 11.** Minimum required revenues from the ancillary service (AS) provision for each scenario.

In summary, Scenarios 2, 4 and 6 were characterized by the best technical performance. RES curtailment caused significant smoothing of the load profile at the PCC and visibly reduced the difference between the maximum and the minimum demand. Such actions can have a positive impact on the operation of the whole power system, as load levelling and smoothing of the demand profile facilitate the real-time balancing of the load and generation due to the reduction of the profile's variability, and they may allow further RES development.

In Scenarios 1, 3 and 5 where RES curtailment was not allowed, ASs were provided mainly by active resources like ESs and ALs. The assumed share of such entities (Tables 1 and 2) was lower than the share of RESs; therefore, the quality of the services' provision was strongly dependent on the contribution of different distributed resources inside the aggregator's structure.
