17-04-2012, 03:08 PM
power electronics and motor drives
Power Electronics And Motor Drives.pdf (Size: 12.71 MB / Downloads: 1,590)
Power electronics deals with conversion and control of electrical power with the help
of electronic switching devices. The magnitude of power may vary widely, ranging from
a few watts to several gigawatts. Power electronics differs from signal electronics, where
the power may be from a few nanowatts to a few watts, and processing of power may be
by analog (analog electronics) or digital or switching devices (digital electronics). One
advantage of the switching mode of power conversion is its high efficiency, which can be
96% to 99%. High efficiency saves electricity. In addition, power electronic devices are
more easily cooled than analog or digital electronics devices. Power electronics is often
defined as a hybrid technology that involves the disciplines of power and electronics. The
conversion of power may include ac-to-dc, dc-to-ac, ac-to-ac at a different frequency, acto-
ac at the same frequency, and dc-to-dc (also called chopper). Often, a power electronic
system requires hybrid conversion, such as ac-to-dc-to-ac, dc-to-ac-to-dc, ac-to-ac-to-ac,
etc. Conversion and regulation of voltage, current, or power at the output go together.
GLOBAL EXPANSION OF TECHNOLOGY AND APPLICATIONS
Because power electronics equipment is based on nonlinear switching devices, it generates
undesirable harmonics in a wide frequency range that flow in the load as well as in supply
lines. A fast rate of change in voltage (dv/dt) and current (di/dt) due to switching
creates electromagnetic interference (EMI) that couples with sensitive control circuits in
its own and neighboring equipment. A switching mode converter with a discrete mode
of control constitutes a nonlinear discrete time system and adds complexity to the analysis,
mathematical modeling, computer simulation, design, and testing of the equipment. The
design and testing phases become especially difficult at high power due to harmonics and
EMI problems. In spite of this complexity, power electronics technology has been
advancing at a rapid rate during the last three decades. Dramatic cost and size reductions
and performance improvements in recent years are promoting extensive application of
power electronics in the industrial, commercial, residential, aerospace, military, utility,
and transportation environments.