A grid-connected PV system consists of a PV array, a maximum power point trackin

Question

A grid-connected PV system consists of a PV array, a maximum power point tracking (MPPT) boost DC-DC converter and a single-phase DC-AC inverter as shown in Fig. 1. The PV array consists of 3 parallel strings, each string consisting of 19 series-connected Shell PowerMax Ultra SQ85-P modules. The boost converter DC output voltage is V_DC = 450 V, and the AC grid line voltage is V_RMS = 240 V, with the line frequency of 60 Hz. The Boost DC-DC converter and the DC-AC inverter losses can be neglected. Assume full-sun insolation (1.000 W/m^2) for all modules. You can also assume the MPP tracking algorithm works perfectly. The energy-storage capacitance C is selected so that Delta V_DC (the voltage ripple at twice the line frequency) is 30 V. Find: The PV voltage V_PV The PV current I_PV The Boost converter duty-cycle D_boost Output AC current RMS value, I_RMS Average output power P_ac

Explanation / Answer

From the data sheet the important parameter values of given module are

Pr = 85 W

Voc = 22.2 V

Isc = 5.45 A

Vmpp  = 17.2 V

Impp = 4.95 A

Toatal system DC rating is P = 5 kW

Three strings of 19 panels in each string

a) PV Voltage Vpv = 19*Vmpp = 19*17.2 = 326.8 V under STC and MPP.

b) PV current Ipv = 3 * Impp = 3*4.95 = 14.85 A

Given boost converter output is VDC = 450 V

c) Input to boost coverter is Vpv = 326.8 V and Output from boost converter is VDC = 450 V

Duty - Cycle of boost converter is Dboost = 1 - ( Vpv / VDC ) = 1 - (326.8/450) = 0.273

d) Under ideal conditions power converted from sunlight to electricity 100% then average ac output is P = 240*I = VDC *Idc = Vpv * Ipv

Idc = (326.8*14.85) / 450 = 10.7844 A

I = (326.8*14.85) / 240 = 20.22 A rms value of output current.

e )

Average output power

Pac = 240 * 20.22 = 4852.98 W

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