The IT servers for a medium-sized company need to be protected from grid failures (e.g. blackout) and thus is powered through an uninterruptable power supply (UPS) unit. The UPS consists of a 3- phase diode rectifier powering the dc bus, which then splits between a 3-phase inverter unit and a battery energy storage system (BESS). UPS parameters are given in Table B2 and a general schematic is shown in Figure B2. Assuming that the inverter and BESS pull a combined constant current, IDC, from the dc bus, draw the approximate waveforms over one full ac cycle for: (i) the three ac line voltages, (ii) the three ac currents, and (iii) the total dc bus voltage. Explain how the single-phase inverter operates and draw an approximate waveform of the load-side ac voltage. Comment on the chosen switching frequency for the inverter. Choose a dc/dc converter topology for the BESS. Draw the converter diagram for your chosen topology and justify each of your design choices. Estimate the battery capacity (in kWh) needed to sustain grid failure for 48 hours under full load. Comment on your answer. Main input voltage Rated total power Inverter switching frequency Output voltage Power efficiency BESS voltage 400 V, 3-phase 8 kW 10 kHz 230 V, single phase 93.3% (full load) 800 V