Department of Electrical Engineering
Graduate School, Chonnam National University
(Supervised by Professor Sung-Jun Park)
(Abstract)
Recently, as awareness of the finiteness of fossil energy, environmental
pollution, and the dangers of nuclear power generation has grown, the
direction of energy policy in domestic is changing to improve economic
efficiency including denuclearization and a stable supply. In accordance
with this policy direction, the operation of aging nuclear power plants is
suspended and the construction of new nuclear power plants is being
canceled. However, the power supply and demand problem due to the decrease
in nuclear power generation sources can be overcome with distributed power
using renewable energy and active idle resources. In the smart grid using
distributed power, demand management, power quality, and power reliability
improvement are important factors, and related research is ongoing. In
this paper, we proposed an uninterruptible system consisting of an
emergency generator and a short-cycle ESS, and proposed an integrated
operation algorithm that can provide stable power to the consumer and
improve power reliability
Research on uninterruptible systems using ESS has been conducted
before. However, in order to secure a long back-up time, a
large-capacity battery system is required. This greatly increases the
overall system cost, so there is no problem in the functional part, but in
the field of construction cost, the economical efficiency of the unit price
was not suitable, so the commercialization stage was not progressed.
Recently, various studies using emergency generators, which were
temporarily used for emergency power supply in case of power failure,
have been conducted. Public institutions and for-profit institutions are
also increasingly participating in DR projects for demand resources using
emergency generators. In order to use the emergency generator as a
demand resource, a power changeover switch is required, but in the
beginning, ATS (Automatic Transfer Switch) was widely used. ATS has a
disadvantage that power failure occurs within about 100[ms] when
switching over. It is participating in the DR project by replacing it with a
CTTS (Closed Transition Transfer Switch), which is a complementary
uninterruptible power changeover switch. In the case of CTTS, there is a
grid tied CTTS (G-CTTS) that directly controls the AVR and governor of
an emergency generator to operate in a grid-tied type, and by using this,
parallel operation with a power converter is possible.
The system proposed in this paper is composed of G-CTTS,
emergency generator and short-cycle ESS. The rated power capacity of
the proposed uninterruptible system is 360kW, and for each component,
the inverter is 500kW, the G-CTTS and the emergency generator are
360kW. For short-cycle ESS batteries, 500kWh of carbon batteries were
used, and a PC-based PMS operation program was used for power
management of the entire system.
This paper proposes the operation and element technology for the
uninterruptible system consisting of an emergency generator and
short-cycle ESS. The factors proposed in this paper are largely
summarized into five categories.
First, a large-capacity uninterruptible system configuration consisting
of an emergency generator and a UPS was proposed. In a system
composed of two voltage sources, power control is mainly handled by the
inverter, but in this system, power control is performed by the
emergency generator using G-CTTS. When G-CTTS performs power
control during two types of parallel operation, the required function of
the inverter is lowered, and a large-capacity uninterruptible system can
be implemented only by applying a commercial UPS.
Second, in order to improve the reliability and quick response of the
emergency generator in parallel operation, it is necessary to precisely
detect the phases of different voltage sources and control the frequency.
To this end, we propose a high-precision PLL method that synchronizes
the phase of the voltage source to be synchronized at high speed using a
virtual d-q coordinate method.
Third, high-speed response and output of the inverter are important
for non-power failure operation. In the case of the output quick response
of the inverter, the time required to the rated output increases depending
on the capacity. Therefore, it is possible to operate stably only when the
time for detecting a power failure is reduced as much as possible. In the
case of a site with a large system impedance, the voltage THD increases
when the load contains many harmonics. If the voltage condition for
power failure detection is sensitively applied, it can be recognized as a
power failure even if it is not a power failure. Therefore, we propose a
high-speed blackout detection algorithm using Perid Time Shit that can
accurately detect blackout at high speed.
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