AY 2020 21 Test 2 Numerical part with solutions

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ELECTRIC CONVERSION FROM GREEN SOURCES OF ENERGY Prof. Alberto Dolara Numerical exercise 1 < 20 July 2021 > The numerical data of this problem depend on your ID number, as follows: Example: ID number = 10123456 → U = 1, V = 2; W = 3; X = 4; Y = 5; Z = 6. Numerical data that depend on your ID number are highlighted by the symbol “←” along the text. A DC/AC three phase full bridge inverter interfaces a PV generator with the AC distribution grid. The PV generator is directly connected to the DC bus. The converter ratings, as well as the IGBT module ratings, are reported in the following. ► Rated input voltage, Vin,n from 700 to 900 VDC ► Rated output voltage, Vout,n 400 VRMS ► Rated output frequency, fn 50 Hz ► Rated output power, Pout,n 30 kW ► Rated power factor, cosϕ 1 ► Switching frequency, fsw 12.45 kHz ► Gate signal range, VGE 0 – 15 V. Each IGBT module integrates one inverter leg, i.e. two IGBTs and two antiparallel diodes connected as in the figure. Each IGBT module is cooled by its own heat sink, whose thermal resistance, Rth,hs, is 0.15 K/W. The PV generator is composed by 4 strings, which in turn are composed by 24 PV modules whose ratings are reported below: ► Maximum power (in STC), PMPP 295 W ► Voltage at maximum power, VMPP 31.4 V ► Current at maximum power, IMPP 9.39 A The DC/AC converter operates the PV generator at its Maximum Power Point (MPP) as long as the junction temperature of power semiconductor devices is below 125°C; for higher junction temperatures the input power is automatically reduced. Assume the following operating conditions: ► Output voltage, VAC (384 + 4 ∙ X) V (RMS, line to line) ← Calculate: 1. The frequency modulation ratio. 2. The amplitude modulation ratio. 3. The maximum ambient temperature that allows the DC/DC converter to…