A Study on the Hybrid UPS with Electrical Energy Storage Function EES 기능을 갖는 하이브리드 UPS에 관한 연구 -2014 Seung-Beom Lim Department of Electrical Engineering Graduate School, Dankook University
ABSTRACT
EES(Electrical Energy Storage) is the system which stores the remaining energy during the time of light load or night time with the cheap electricity price, and then discharges the stored energy during the time of peak load or electric power shortage. This system improves usage efficiency and stabilizes the power supply system. UPS(Uninterruptible Power Supply) can be divided into three parts according to dependency between input and output voltage : Passive-Standby, Line-Interactive, and Double-Conversion. Double- Conversion type UPSs are used to supply the stable power to industrial high-tech/medical equipments and finance/data centers, where loads are sensitive to the blackout and voltage fluctuation.
In this paper, it is proposed a double-conversion hybrid UPS with EES function. The proposed hybrid UPS is operating in four states, which are normal state, battery state, bypass state, and EES state.
When the AC input source is normal, the system operates in normal state which supplies the stable power to the load through the PFC and inverter, and charges batteries simultaneously. In case of black out or unstable input, the system operates in battery state which supplies the energy from the batteries to the load. In bypass state in case of overload or failure of the inverter, the system supply the input power to the load directly. When the system is needed to operate in EES state, AC input is cut off by the user command and the energy stored in the batteries is supplied to the load. Thereby the system can manage the power efficiently and make the power system more stable. The proposed system is composed of a rectifier, an inverter, a battery charger, and batteries. The rectifier operates as the PFC in normal state and as the battery discharger in battery state and EES state. In the proposed system, there is no battery discharger which is essential in the conventional system. As a natural consequence, the size and weight of the system are reduced. In addition, by designing the inverter as 3-level TNPC(T-type Neutral Point Clamp) inverter, efficiency is improved compared to the conventional 2-level type.
To verify the proposed system, it is simulated through the C-block of PSIM. Also, the proposed system with the output rating of 2,700 Watts is constructed and experimented. As a result, it was verified that the proposed system has excellent performances in the viewpoints of efficiency, input power factor, and THDs in input current and output voltage.
LINK FULL PAPER ORIGINAL WEB
http://society.kisti.re.kr/sv/SV_svpsbs03VR.do?method=detail&menuid=1&subid=11&cn2=JRJJC3_2014_v19n3_266
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