Efficiency Comparison of DC and AC Microgrid Ujjal Manandhar
Abhisek Ukil
Tan Keng Kiat Jonathan
School of EEE Nanyang Technological University Singapore Email:
[email protected]
School of EEE Nanyang Technological University Singapore Email:
[email protected]
School of EEE Nanyang Technological University Singapore Email:
[email protected]
Abstract— As the number of DC loads are growing in our daily uses, the low voltage DC (LVDC) distribution system is becoming important. Power supplied through the low voltage AC (LVAC) distribution system needs both the AC/DC rectifier and the DC/DC converter to supply the DC loads. In comparison, LVDC system would only need the DC/DC converter to supply the DC loads. Integration of renewable energy sources at LV level, like rooftop photovoltaic (PV), fuel cells, etc. would be relatively easier with the LVDC system than the LVAC. So, the LVDC can be the viable solution to reduce multiple conversion losses in the system. This paper presents comparison between the existing LVAC with the prospective LVDC distribution system in terms of converter conversion efficiency. Constant AC and DC loads, generally used in household applications, are simulated using PSCAD/EMTDC for both the LVAC and the LVDC distribution system. The analysis of the effectiveness of LVDC system over LVAC distribution system has been presented.
the isolation transformer and the rectifier can be eliminated. The AC loads can be operated using an inverter with the DC distribution system. The losses in the inverter are comparatively less compared to the rectifier [4]. The analysis of the LVDC, vis-à-vis the LVAC distribution system with both AC and DC loading is required to compare the feasibility of LVDC with the existing LVAC. The remainder of the paper is organized as follows. The modeling of the LVAC and LVDC distribution system and loads has been discussed in section II. Power electronics converters, its loss calculation as well as the transmission cable losses in AC and DC distribution system has been discussed in section III. The system is modeled in PSCAD and simulation results have been presented in section IV. The further improvement of the model and the system design is discussed in section V, followed by conclusion in section VI.
Keywords— converters, energy efficiency, low voltage, LVAC, LVDC, power distribution system, power loss, smart grid.
II. MODELLING COMPONENTS IN LVAC AND LVDC
I. INTRODUCTION With the increasing penetration of renewable energy sources and energy storage system, the design of electrical power system focuses on increasing utilization of the green technologies [1]. Photovoltaic system and wind turbines are two commonly known green energy technology. To integrate these renewable sources with the existing alternating current (AC) distribution grid requires number of power electronics conversion stages. This adds to the complexity, and also affects the overall efficiency of the system. The DC distribution system can achieve higher efficiency due to reduction in power conversion stages. In addition, it would be easier to integrate the renewable energy sources and storage system at low voltage (LV,
