Design and Implementation of a Series Voltage Sag

lzmyl

Abstract—Voltage sags have become one of the most important
power quality concerns in recent years. According to survey re-
sults across the U.S., voltage sags and short-duration power out-
ages account for 92% of power quality problems encountered by
industrial customers. Voltage sags often cause undervoltage faults
invarioussensitiveloadsandsubsequentlyinterruptthemanufac-
turing processes. Such interruptions often inflict severe losses for
industries. In Taiwan, R.O.C., most high-tech manufacturers use
uninterruptiblepowersuppliestoavoidinterruptions,butthecost
effectiveness of such an approach remains unclear.
Astheutilitygridcontinuestoimprovethereliabilityofelectric
power, the inverter-based voltage sag compensator has become a
viable solution to preventproduction interruptionsresulting from
voltage sags. The existing sag compensation systems accomplish
a fast response within a small fraction of a fundamental cycle
by tracking the line voltages closely, and switch on the compen-
sator whenever the voltage waveforms deviate from the normal
values. However, the utility voltages often contain transient
spikes with amplitudes up to 200% resulting from switching of
power-factor-correction capacitors, circuit breakers switchings,
lightning strikes, and so on. Such transient disturbances may
trigger the sag compensator into operation if its controller is very
sensitive.Theswitchingfrequencyofthesagcompensatorinverter
is inadequate to compensate the narrow pulses of voltage spikes.
Furthermore, the power semiconductor devices (like insulated
gate bipolar transistors)of the inverter may also be damaged due
to overvoltage by the surges.
In this paper, a brief overview of power quality issues of a
high-tech industry park in Taiwan will be provided to validate
the need for ride-through technologies. A synchronous-refer-
ence-frame-based controller for the inverter-based voltage sag
compensator is also presented. A sag detection mechanism is
included in the controller for correct and prompt identification
of voltage sags. Disturbances like voltage spikes are attenuated
to avoid any false triggering of the compensator. The overall
system responds to voltage sags and restores the voltage back to
balanced 1.0 pu for critical loads within one-eighth to one-fourth
of a cycle, which meet the requirement of industry standards like
the SEMI-F47 standard. Simulation and laboratory test results
are presented to verify the functionalityof the proposed system.

hypo_qu

多谢楼主的无私奉献！