Development of Boundary Conditions to Select Suitable AC and DC Wiring Topology for Future Residential Houses

Qureshi, Junaid Ahmed
Lie, Tek Tjing
Gunawardane, Kosala
Kularatna, Nihal
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Doctor of Philosophy
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Auckland University of Technology

Photovoltaic (PV) panels are installed on present-day residential houses which generate Direct Current (DC) power, and the energy is then stored in Battery Energy Storage Systems (BESS). DC power from the PV panels is usually converted into Alternating Current (AC) as the existing electrical power distribution is AC. Then the AC power is converted back into DC to energise the DC-based appliances. DC-based appliances such as laptops, mobile phones, Tablets, Light Emitting Diode (LED) lamps, etc usage is exponentially increasing in the present market. This scenario opens the opportunity to directly utilise the DC electricity produced by PV panels without going through the conversion stages. Therefore, using DC wiring based residential houses, electrical energy losses will be reduced substantially by avoiding the conversion from DC power to AC and back to DC. The low voltage DC concept is not new, but significant progress could not be achieved due to lack of tools and standards for DC power distribution. Some research has been reported in the literature to experimentally test and compare AC and DC wiring options. However, extensive accurate and precise experimental measurements are vital for establishing a sound theoretical basis, and this is difficult due to cost and time constraints. House wiring simulation models were developed using standard cable impedance without consideration of ambient temperature, proximity and skin effect. Similarly, simplified converter circuits with oversized components were considered which is not practical. Moreover, there is no validated simulated model or tool reported in the literature to verify the simulation model results of AC and DC homes.
As reported in the literature, power losses in AC and DC cables have been compared using mathematical models. It is a significant contribution; however environmental and installation considerations were not considered to compare power losses. Furthermore, the mathematical comparison doesn’t include the converter modelling to compare complete AC and DC wiring options. Power loss equations for different types of converters use different approaches, however, there is no validated mathematical model which has used a similar approach to estimate the losses of all types of converters along with the power losses in cables. Moreover, the cost factor is not covered in previous research work which does not include the installation cost along with the running cost of energy losses. Based on the previous research work, it is difficult for residential consumers to select the most efficient and cost-effective wiring topology from 230V AC, 12V DC, 24V DC and 48V DC. Addressing the gaps in the literature, this PhD research developed a mathematical model for AC and DC wiring systems which includes the total power losses in cables and converters. This research is further supported by the validation of these models through experiments and simulations studies.
Finally, the boundary conditions are developed to select an efficient wiring topology among AC and DC systems for a house based on the operating conditions such as power rating of load, size and length of conductors. Using the developed boundary conditions, all residential houses with DC-based sources will have three wiring topology options AC, DC or mix. The mathematical modelling is limited to the technical aspects therefore, three-bedroom and single bedroom house scenarios have been investigated from the cost-benefit perspective. The results show that the 48V DC or the hybrid wiring options would be the most suitable going forward based on this research. Since the most efficient and cost-effective wiring option depends on the number of factors including the house design, living standard, these results would continue to evolve with the continuous changes in the technology of DC sources, DC loads and converters.

AC System , DC System , Mathematical Modelling , Efficient DC loads , Energy Efficiency , House Wiring , Wiring Topologies , Climate Change
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