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In the thesis, a single-phase three-wire transformerless,
small battery energy storage system (BESS) is designed
and implemented. The power circuit of the proposed BESS is
simple, since it consists of only one converter. It has
three legs to provide single-phase three-wire 220/110V
output without using transformer. For switching control, the
BESS is decoupled into differential mode and common mode
subsystems. Every subsystem has its own inner-loop current-
forced switching control mechanism and outer-loop controller
for producing current commands of various operating modes.
The controllers of the differential mode are mainly designed
to control the magnitude and waveform of main voltage (220V)
source and to achieve the functions of BESS. As to the common
mode subsystem, its controllers are used to maintain the
balance between two subcircuits (110V circuits). In addition,
the common mode controllers can also keep the current in
neutral line of utility grid be zero. The operation
principle of the proposed BESS and the design of controllers
in various operating modes are described in detail.
Feasibility of the proposed BESS is first confirmed by some
EMTP simulation results. Then the implementation of a 2KVA
BESS is made. The performance of the proposed BESS is further
demonstrated by some experimental results.
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