In this context of changing and challenging market requirements, Gas Insulated Substation GIS has found a broad range of applications in power systems for more than two decades because of its high reliability, easy maintenance and small ground space requirement etc.
This thesis discusses the advantages and drawbacks of three different PWM techniques: These three methods are compared by discussing their ease of implementation and by analyzing the output harmonic spectra of various output voltages poles voltages, line-to-neutral voltages, and line-to-line voltages and their total harmonic distortion THD.
Three-Phase Sinusoidal PWM Inverter A six-step inverter is composed of six switches S1 through S6 with each phase output connected to the middle of each inverter leg as shown in Figure 2. The output of the comparators in Figure 2.
Two switches in each phase make up one leg and open and close in a complementary fashion.
That is, when one switch is open, the other is closed and vice-versa. As mentioned above, this is approximately Consequently, it provides a better utilization of the DC supply voltage. Under-modulation and Over-modulation Regions in Space Vector Representation SVPWM is accomplished by rotating a reference vector around the state diagram, which is composed of six basic non-zero vectors forming a hexagon.
A circle can be inscribed inside the state map and corresponds to sinusoidal operation.
The area inside the inscribed circle is called the linear modulation region or under-modulation region. As seen in Figure 3. The switch combinations can be represented as binary codes that correspond to the top switches S1, S3, and S5 of the inverter as shown in Figure 3.
These voltages are also called pole voltages. Switching Sequence of all Six Sectors The switching pulse patterns of six different sectors in Figure 3. It is obvious that in the odd sector the active state sequence is in ascending-descending order; whereas, it is in a descending- ascending order in an even sector.
The over-modulation range can be considered as one region or it can be divided into two regions see Figure 4. In this thesis, the over-modulation region is considered as two regions with two modes of operation depending on the modulation index values. Modulation Index in Mode 2 At the end of mode 1, the component of the reference voltage changes to a piecewise linear waveform.
When the modulation index is higher than 0. Both the reference magnitude and the phase angle have to be changed compared to the linear region. The modified reference vector is held at a vertex of the hexagon in every sector for the rest of the switching period.Power amplifier classes are, in electronics, letter symbols applied to different power amplifier types.
The class gives a broad indication of an amplifer's characteristics and performance. The classes are related to the time period that the active amplifier device is passing current, expressed as a fraction of the period of a signal waveform applied to the input.
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Journal of Low Power Electronics and Applications (ISSN ) is an international, interdisciplinary, peer-reviewed, open access journal on low power electronics and is published quarterly online by MDPI..
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