A Study on the Hybrid UPS with Electrical Energy Storage Function
A Study on the Hybrid UPS with
Electrical Energy Storage Function
Seung-Beom Lim
Department of Electrical Engineering
Graduate School, Dankook University
Advisor： Professor Soon-Chan Hong
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.
LINK
http://www.mediafire.com/view/55llpri0ilp2ock/A_Study_on_the_Hybrid_UPS_with_Electrical_Energy_Storage_Function.pdf
