**6. Discussion**

From the controller presented in this paper and from the obtained results, some important issues are necessary to be addressed:

## *6.1. Active Power Control*

The control of active power in a suboptimal point (lower than the MPP) can be developed with a RPPT control. The PV generator can supply power according to an active power reference. The response, however, depends as well on the solar irradiance fluctuations during the day. For instance, on the second day, between 14:00 to 15:00 quick solar irradiance variations are presented and the control tries to respect the 20% of power reserve but the control does not follow this reference.

## *6.2. Reactive Power Control*

For the injection or absorption of reactive power, the response also depends on the solar irradiance when the active power generation is a priority. It can be stated that with a maximum active power, there will be a maximum reactive power that can be injected or absorbed depending on the capability curves. Because of this, if a reference of reactive power is set and at the same time the active power control is a priority, the reference will be reached only if it is lower than the maximum reactive power point possible at that instant. In the case that the reactive power is a priority and there is high solar irradiance, the reference of reactive power can be reached only if the active power point changes to other point of operation lower than the MPP.

It is important to notice that for injection of reactive power, the variation of this value does not present large fluctuation as it depends on the changes of dc voltage together with the modulation index. If the maximum modulation remains fix, then the reactive power that the PV generator can inject also remains close to a fix value. However, this value could be lower than the reference set by the control. Therefore, a change of modulation index helps to achieve the reference of reactive power asked by the PPC.

## *6.3. Compliance of Grid Codes*

Considering the response of the PV generator for the different scenarios for reactive power, it can be analised if the requirements of the grid codes can be achieved under different scenarios. Figure 30 illustrates the capability curve given by the PV generator together with the capability curve required by Puerto Rico and Germany for steady state conditions.

**Figure 30.** Capability curves comparison considering the grid codes of Puerto Rico, Germany and the capability curve extracted from the current study case.

When QPPT is utilized, the PV generator can inject or absorb reactive power according to the requirements but the active power generated could be lower than the MPP. For absorbed reactive power, if the reference is 0.623 p.u, then the new reference of active power should be 0.78 p.u. For the injection of reactive power, the modulation index has to be higher than 1 to comply this reference.

However, when the reactive power is not set as a priority then the requirements asked by the grid code of Puerto Rico cannot be accomplished for higher solar irradiance and maximum modulation index of 1. So, new equipment should be installed in order to give reactive power support as STATCOM, capacitor banks, FACTS. However, for the case of Germany, at any irradiance the PV generator can supply or inject the reference of reactive power as it is lower than 0.57 p.u without making any change on the operation of active power or the modulation index.

Additionally, it can be seen that for an active power generated lower than 0.78 p.u (corresponding to *G* = 900 W/m2), the PV generator can absorb or inject reactive power higher than the limitations imposed by the grid codes without reducing the generated active power. Thus, it is necessary that the Grid codes will consider the effect of the PV generator performance at different solar irradiance, temperature, dc voltage and modulation index in order to set higher limitations and improve the performance of the LS-PVPP.
