Digital Control of Power Conversion System Used in
Battery Energy Storage System BY Wan, Kim
Department of Marine Electronic, Communication and Computer
Engineering,
Graduate School, Mokpo National Maritime University
(Supervised by Professor : Kwang-Woon, Lee)
ABSTRACT
To operate the electric power supply system more efficiently and
stably, the utilization of battery energy storage system (BESS) is
increasing. By using BESS, the residual electrical energy can be
stored at low power demand times and the stored electrical energy
can be released at high power demand times. Therefore, BESS can
counteract the frequency fluctuation of the electric power system
due to load variations. In addition, BESS can be utilized to make
stable operation of renewable energy sources such as photovoltaic
power generation and wind power generation.
An electric power conversion system is used in BESS and it
consists of bidirectional dc-to-dc converters and dc-to-ac inverters;
the role of the bidirectional dc-to-dc converters is to charge and
discharge the batteries and the dc-to-ac inverters are employed for
grid connected energy conversion. A digital control is generally used
to control the electric power conversion system of BESS and typical
digital control strategy is based on the small signal model of the
electric power conversion system. However, it is known that the
small signal model based digital control is vulnerable to the
operating point variations because the small signal model is obtained
at a specific operating point. The purpose of this paper is to
present a stable digital control strategy for the electric power
conversion system of BESS, insensitive to operating point variations.
This paper presents a design method for the power conversion
system of BESS, wherein an average model based control is
employed to solve the problem of the conventional small signal
model based control. To compare the performance of the proposed
control method with the conventional small signal model based
controller, the single input and single output (SISO) controller design
tool of MATLAB is utilized. For this purpose, the small signal model
of the bidirectional dc-to-dc converter is derived and the SISO tool
based digital controller is designed to obtain the specific bandwidth
and phase margin. The time and frequency domain responses of
the proposed average model based controller are obtained using a
PSIM software and the obtained results are compared with the
responses of the conventional small signal model based controller to
show the improved transient control performance of the proposed
method. To prove the effectiveness of the proposed method, the
proposed control method is implemented using a digital signal
processor (DSP).
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