*3.2. Active Power Reserves*

In this paper, any energy storage is used. So, to approach the active power reserves is necessary to work in deloaded operation. This operation consists that the PV generator supply a reduced output power instead of the maximum power. The reduction can be between 10 or 20% of the maximum power for each solar irradiance as it is illustrated in Figure 11. To obtain the new operation point, the dc voltage is different than the *vmpp*.

**Figure 11.** Deloading operation in PV generators.

To control the PV generator for active power reserves, it is necessary to calculate at each time step the possible maximum active power that the PV generator can supply (*Pmpp*). Then, the power reserve is given by the percentage required by the TSO of the maximum possible active power given by the expression:

$$P\_{reserve} = \Delta P\_{tso} \times P\_{mpp}(G, T). \tag{1}$$

The new reference for active power can be calculated as follows:

$$P\_{ref} = P\_{mpp} - P\_{reserv}.\tag{2}$$

With this new reference, the RPPT control explained in Section 3.1 can be applied. Then, the new P-G curve is presented according to the new performance of the PV generator in Figure 12. In this case, the RPPT can be used in region II and III of the P-G curve.

**Figure 12.** Control areas of a PV generator in a P-G curve when power reserve is considered.

In summary, the PV generator will be working with MPPT or RPPT depending on the ambient conditions and the PPC 's requirements. Then, the dc voltage (*vref*) will vary according to the control chosen until it fulfills the requirements (Figure 13).

**Figure 13.** Control scheme for control of active power in PV generators.

After the active control has been addressed, the reactive power control is explained in the following section.
