Power Quality Improvement in DC Drives Using Matlab/Simulink
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Abstract
Power Quality (PQ) has become an important
topic of discussion and research, especially in a deregulated
environment. As per IEEE 519 std. these parameters of
power quality measurement, are four in number, of which
Total Harmonic Distortion is most widely used.
Semiconductor switching devices which are generally used
in converter circuits produce significant harmonic voltages
as they chop voltage waveforms during the transition
between the conducting and cutoff stages. The diode bridge
rectifiers/converters are considered as a major contributor
to the power system harmonics and the consequences are
varying from components overheating to communication
interference. Our work links the field of electrical power
conversion and electrical drives (DC), where these power
converters find applications.
HARMONIC ANALSYSIS
For the purposes of harmonic analysis, the dc drive
loads can be represented as sources of harmonic currents.
The system looks stiff to these loads and the current
waveform is relatively independent of the voltage
distortion at the drive location. This assumption of a
harmonic current source permits the system response
characteristics to be evaluated separately from the dc
drive characteristics. The representation of the drives as
harmonic current sources is shown.
COMPLETE SOLUTION
The problem of eliminating harmonics in switching
converters has been the focus of research for many years.
The Selective harmonic elimination (SHE) PWM based
methods can theoretically provide the highest quality
output among all the PWM methods. SHE offers several
advantages compared to traditional modulation methods
including acceptable performance with low switching
frequency to fundamental frequency ratios, direct control
over output waveform harmonics, and the ability to leave
triplen harmonics uncontrolled to take advantage of
circuit topology in three phase systems. These key
advantages make SHE a viable alternative to other
methods of modulation in applications such as variable
speed drives, or dual frequency induction heating. This
method is sometimes called a programmed PWM
technique. However, the drawback of these methods is a
heavy computational burden and a complicated hardware.
The main challenge of solving the associated nonlinear
equations, which are transcendental in nature and
therefore have multiple solutions, is the convergence. It is
generally accepted that the performance of an inverter,
with any switching strategy, can be related to the
harmonic contents of its output voltage. Power electronics
researchers have always studied many novel control
techniques to reduce harmonics in such waveforms.
CONCLUSION
Power Quality related issues, standards concerned
with power quality are discussed in detail and various
suppression techniques are thus simulated. All the
reduction techniques do have its own area of application.
Owing to IEEE 519 Std, suitable technique can be
adopted. Passive Filters are cheaper and Shunt Active
Filters are found to be advantageous than other reduction
techniques. Selective Harmonic Elimination Technique
can be used to suppress dominant harmonics and thus
lower the THD of entire system.