Analysis on AC-DC Hybrid Power Supply System: A Case Study for a Hospital Building in Kathmandu, Nepal

Abstract

Because of some limitations found to use either completely Direct Current (DC) supply system or completely Alternating Current (AC) supply system, hybrid AC-DC supply system become prone topic of the discussion for effective power supply solution as it helps to reduces multiple conversion losses that may occur from generation to end use point. Implementation of hybrid supply system within the hospital building can save the energy as maximum numbers of DC loads like Light Emitting Diode (LED) lights, fan and computer charging system are operated for maximum number of hours in comparison with other buildings. This research includes the development of hybrid supply system for a hospital building in which all lighting devices, fan and computer charging system were supplied from DC side and remaining loads being supplied from existing AC line. 48 volt DC line has been developed by converting existing AC supply. Required AC-DC and DC-DC converter with regulator is designed and simulated in PLECS (Piecewise Linear Electrical Circuit Simulation) software. Wire sizes required to develop DC wiring model is selected by maintaining 4 percent voltage drop limit from DC source point (AC to DC conversion point). Based on the simulation results losses in developed model is calculated and energy saving opportunity on implementing this model is evaluated and found 18.6 kWh of energy saving opportunity while supplying 18.853kW of DC load and 10kVA uninterruptible power supply ( eliminating need of rectification and invert process) from DC line of hybrid power supply structure. Certainty and sensitivity on energy saving with assumption in possible variation in factors like hour of operation per day and percentage of load supplied at a time is analyzed using crystal ball simulation and found a certainty of 31.5% that the energy saving being more than 18kWh.