*2.2. Solar Photovoltaic System*

The solar photovoltaic (PV) plant consists of components such as solar PV plates, boost converter, maximum power point tracking (MPPT) system, inverter, transformer, grid coupling inductor and capacitor. The solar panel where actual power is generated (solar to electrical energy transformation) comprises of series and parallel combinations of solar cells. Solar cell is fabricated in a thin layer of

semiconductor in the form of p-n junction (p-n diode), which has the same operational characteristics as the p-n junction diode. Characteristics are dependent on the quantity of solar radiations and temperature of PV plates. A single diode equivalent model of solar PV cell with parallel and series resistances is used in this study and illustrated in Figure 2. This is simple in nature and has sufficient accuracy [23]. This solar PV system is interfaced to the test system to design a hybrid grid.

**Figure 2.** Solar cell modelled using single diode equivalent.

The solar PV plant of capacity 1 MW is formed using the ten units (each with capacity 100 kW) and integrated in parallel. The output voltage (V) of a solar cell (single-diode equivalent circuit) is related to the output current (I) as per following relation [24].

$$I = I\_{ph} - I\_0 \left\{ \exp\left[\frac{q(V + IR\_s)}{AkT}\right] - 1 \right\} - \left(\frac{V + IR\_s}{R\_{sh}}\right) \tag{3}$$

where *Iph*: photo-current of solar PV cell, *I*0: saturation current of PV cell, A: curve fitting factor of PV cell, *Rsh*: shunt resistance of PV cell, *Rs*: series resistance of PV cell, q: electronic charge, and k: Boltzmann constant.

Magnitude of *Rsh* is infinite at short circuit conditions. At this condition slope of I-V characteristics tends to zero [24]. Hence, *Iph* is equal to short circuit current (*Isc*) [23]. For a PV array organized in *Np* parallel and *Ns* series connected solar cells, the current is expressed as below.

$$I = N\_p I\_{\rm sc} - N\_p I\_0 \left\{ \exp \left[ \frac{q \left( V + I (N\_s / N\_p) R\_s \right)}{N\_s A kT} \right] - 1 \right\} \tag{4}$$

Parameters simulated in this study for each module (at standard test condition) are as *Voc* = 64.2*V*, *Isc* = 5.96*A*, *Vmp* = 54.7*V*, *Imp* = 5.58*A*, *Rs* = 0.037998Ω, *Rsh* = 993.51Ω, *I*<sup>0</sup> = 1.1753*e*−8*A*, diode quality factor *Qd* = 1.3, and *Iph* = 5.9602*A* [25]. The *Vmp* and *Imp* are respectively the voltage and current at point of maximum power tracking.
