Supercapacitor-assisted refrigerator for DC powered households

Energy efficiency is a prime concern in power generation as well as in usage. Product developers and end users are encouraged to reduce their carbon footprint for help in the fight against climate change. In this effect designing power electronic systems with high end to end efficiency is paramount. Direct DC application with tactical circuit topologies show promising results for improved efficiency gains resulting in increased attention for the DC microgrid concept. DC powered households are developed, where solar photovoltaics on rooftops generate purely DC electricity to power the immediate community. Recent developments have made solar generation quite economical for this to be realized. Unfortunately, solar power is not consistent due to environmental factors, thus needing an alternate DC source or energy storage for uninterrupted supply of power. To meet this demand research into energy storage has ramped up. As a result, supercapacitor technology has advanced considerably with superior characteristics compared to rechargeable batteries. Almost all modern white goods run on DC internally. The inverter-based refrigerator operates using a variable frequency inverter for efficient and smooth operation. The refrigerator has shown to function efficiently within a range around the nominal operating voltage. This has allowed the application of the well matured supercapacitor assisted loss management (SCALoM) technique to develop a power converter to operate the refrigerator with the characteristic DC power supply of a solar photovoltaic (PV) array. The system benefits from the replacement of the battery and Maximum Power Point Tracking (MPPT) Charge controller with supercapacitors for a solar power system with long operation time in between of service intervals. While MPPT charge controller is based on a high frequency switch mode DC-DC converter, the proposed power converter allows for switching frequencies in the mHz region, allowing lower switching losses and reduction in potential electromagnetic interference and radio frequency interference. The concept was proven by using a 24V DC camping fridge and obtaining an efficiency of up to 94%. This work will lead to the development of the converter for a consumer grade 240Vac inverter driven refrigerator where the AC-DC converter is bypassed to achieve improved efficiency. This thesis covers the broader design and technical aspects of the power converter.
Type of thesis
The University of Waikato
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