**2. Power Variabilities of a PV Generator**

#### *2.1. Abrupt Disturbances in PV Generation*

Cloud movements cause abrupt changes in solar irradiation, Figure 1. To study the impact of these abrupt power changes, a hybrid dc/ac system is considered in this paper as shown in Figure 2. The parameters of the dc microgrid and the ac system are shown in Tables 1 and 2, respectively. The details of the PV control used in this study are given in Section 4.1.1.

The PV generator of Figure 2 is controlled using a maximum power point tracking (MPPT) algorithm. The control structure and the parameters are shown in Section 4. Figure 3 shows the voltage and frequency fluctuations, at the point of coupling between dc and ac systems, to abrupt PV disturbances. The solar intensity falls from 1000 W/m<sup>2</sup> to 250 W/m2 at *t* = 5.0 s, and it rises back to 1000 W/m<sup>2</sup> at *t* = 50.0 s. The dc voltage has a peak of 10% that oscillates over a second, and the ac voltage (rms) has a peak close to 5%. The frequency oscillates with a peak of 0.23 Hz, and it takes several seconds to settle.

**Figure 1.** Solar intensity measured at Lowry Range Solar Station on 18 March 2013 [31].

**Figure 2.** A hybrid dc/ac system to study the abrupt power disturbances of the photovoltaic (PV) generator.



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**Table 2.** Parameters of ac system.

**Figure 3.** Voltage and frequency fluctuations at point of common coupling (PCC) of the study system due to the abrupt PV disturbances.
