3-phase Dynamic Voltage Restorer with Switching Cell Structured Direct AC-AC Converter Using Interphase Voltage* Hyeongmin Lee School of Electronic and Electrical Engineering Graduate School, Kyungpook National University Daegu, Korea (Supervised by Professor Heung-Geun Kim)
(Abstract)
Instantaneous voltage sag account for the largest proportion of various
grid accidents, and the economic losses resulting from them are enormous.
To solve this problem, various dynamic voltage restorer(DVR) systems are
being researched and developed. Most of these are back-to-back(BTB) types
and energy storage(ES) types. Since the BTB type uses the distribution
voltage as a voltage source, it can be compensated continuously without a
separate storage device, but energy conversion loss occurs because energy
conversion must be performed in two or more stages. Also, in order to secure
the DC-link voltage, the controller must be complicatedly configured. The
ES type utilizes an extra energy storage device and uses it as a voltage
source. This results in energy conversion in one stage, resulting in small
conversion losses. However, since the unit cost of the energy storage device
is high, there is a disadvantage that a lot of cost is incurred to construct
the system. Also, due to the capacity limitations of energy storage devices,
the compensation time is limited. If additional storage devices are
configured to extend the compensation time, the cost will be higher, and
this will determine the performance of the system.
In this paper, a DVR system consisting of a direct AC-AC converter with
a switching cell structure and using an interphase voltage source is
presented. The switching cell structure overcomes the current commutation
problem, which is a disadvantage of the conventional AC switch, and can
prevent damage to the switch due to the short circuit and open of the
conventional switch leg. In addition, it can be operated with a high
switching frequency because it can be configured as a diode with a fast
reverse recovery time instead of a body diode with poor performance. This
can reduce the volume and unit cost of passive filters, which are costly in
the system configuration. And by using the interphase voltage as a voltage
source, it overcomes the disadvantage that the compensation range of the DVR
using an ac-ac converter is limited to 50%. This can also compensate for
phase jump situations.
Compared with the BTB type, the efficiency is good due to energy conversion
in one stage, and the time to secure the DC-link voltage is not required,
so the dynamic characteristics are better. In addition, control is simple
because it is driven through DC reference. Compared with the ES type, there
is no limit to the storage device, so the compensation duration is long and
the system configuration is economical. Above all, unlike the two
conventional compensators that use a voltage source inverter(VSI), the
system reliability is excellent and there is no need to apply a bulky and
lossy filter.
Finally, to prove the feasibility of this paper, we performed a simulation
and directly configured the hardware to prove that it is compensable under
various voltage sag situations.
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