AY 2020 21 Test 4 Numerical part with solutions

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ELECTRIC CONVERSION FROM GREEN SOURCES OF ENERGY Prof. Alberto Dolara ©Prof. Alberto Dolara – All rights reserverd Numerical exercise 1 < 28 January 2022 > A power processor for photovoltaic (PV) generator is composed by the cascade connection of a DC/DC converter , a three-phase PWM inverter and a line -frequency step- up three- phase transformer. Power processor ratings are the following: ► Rated power, P 100 kW ► Rated power factor, cosϕ 1 ► Rated frequency, f 50 Hz ► Transformer rated voltage, high-voltage side, VAC,HV 15 kV (RMS, line to line) ► Transformer rated voltage, low-voltage side, VAC,LV 330 V (RMS, line to line) ► PV generator voltage range, VPV from 700 V to 1000 V ► DC/DC converter switching frequency, fs,DC/DC 8 kHz ► Inverter switching frequency, fs,inv 7.05 kHz Preliminary Definitions and Calculations 1. Calculate the DC bus voltage that allow the inverter to operate in the linear region up to a grid voltage that is 10% higher than the rated grid voltage. Assume ideal switches and neglect the voltage drop (in amplitude) across the inverter low-pass output filter. 2. Choose the type of DC/DC converter suitable for interfacing the photovoltaic generator to the inverter, and calculate the minimum and maximum value of the duty cycle. Consider the DC bus voltage previously calculated. 3. Calculate the minimum inductance that allows the DC-DC converter to operate in Continuous Conduction Mode (CCM) in the power range from 4 % to 100 % of the rated power and for any input voltages within the allowable PV generator voltage range. Consider the DC bus voltage previously calculated. The DC/DC converter switching frequency is 8 kHz. 4. Calculate the minimum DC-link capacitance that allows to keep the output voltage ripple within 3 V (peak-to- peak) for any…