1,721,254 research outputs found
Timing calculations for three level dodecagonal space vector structure from reference phase voltages
No full textA method to obtain pulse width modulation (PWM) timings for a three level dodecagonal (12-sided polygon) voltage space vector structure using only sampled reference values is proposed in this paper. Typical methods that are used to find PWM timings for dodecagonal SV structures use modulation index and the reference vector angle to get the timings by using trigonometric calculations. This method requires look-up tables, angle estimation making it difficult to implement in closed loop systems. The proposed method requires only two additions to compute these timings. For multilevel case, typical iterative methods need timing calculations (matrix multiplications) to be performed for each triangle within a sector. The proposed method does not require any iterative searching for locating the triangle in which the tip of the reference vector lies. It is also is generic and can be extended to any number of levels with symmetric structures. The algorithm outputs the triangle number and the PWM compare values - that can be used by any carrier based PWM module to obtain space vector PWM like switching sequences. Extensive simulation and experimental results for steady state and transient conditions have been presented to validate the proposed method
A Harmonic Suppression Scheme for Open-End Winding Split-Phase IM Drive Using Capacitive Filters for the Full Speed Range
No full textAbstract—Voltage source inverter (VSI)-fed six-phase induction
motor (IM) drives have high 6n ± 1, n = odd-order harmonic
currents. This is because these currents, driven by the correspond-
ing harmonic voltages in the inverter output, are limited only by
the stator leakage impedance, as these harmonics are absent in
the back electromotive force of the motor. To suppress the har-
monic currents, either bulky inductive harmonic filters or complex
pulsewidth modulation (PWM) techniques have to be used. This
paper proposes a harmonic elimination scheme using switched
capacitor filters for a VSI-fed split-phase IM drive. Two 3-phase
inverters fed from capacitors are used on the open-end side of the
motor to suppress 6n ± 1, n = odd-order harmonics. A PWM
scheme that can suppress the harmonics as well as balance the
capacitor voltage is also proposed. The capacitor fed inverters are
switched so that the fundamental voltage is not affected, and the
fundamental power is always drawn from the main inverters. The
proposed scheme is verified with a detailed experimental study.
The effectiveness of the scheme is demonstrated by comparing
the results with those obtained by disabling the capacitor fed
inverters
A 5th and 7th order harmonic suppression scheme for open-end winding asymmetrical six-phase IM drive using capacitor-fed inverter
No full textVoltage source inverter (VSI) fed six-phase induc-
tion motor drives have high
6
n
1
; n
=
odd
order harmonic
currents, due to absence of back emf for these currents. To sup-
press these harmonic currents, either bulky inductive harmonic
filters or complex pulse width modulation (PWM) techniques have
to be used. This paper proposes a simple harmonic elimination
scheme using capacitor fed inverters, for an asymmetrical six-
phase induction motor VSI fed drive. Two three phase inverters
fed from a single capacitor is used on the open-end side of
the motor, to suppress
6
n
1
; n
=
odd
order harmonics. A
PWM scheme that can suppress the harmonics, as well as
balance the capacitor voltage is also proposed. The capacitor
fed inverters are switched so that the fundamental voltage is
not affected. The proposed scheme is verified using MATLAB
Simulink simulation at different speeds. The effectiveness of the
scheme is demonstrated by comparing the results with those
obtained by disabling the capacitor fed inverters. Experimental
results are also provided to validate the functionality of the proposed controlle
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
17-level inverter with low component count for open-end induction motor drives
No full textThis study presents a 17-level inverter-based induction motor drive for high-resolution multilevel voltage space-vector (SV) generation. The proposed topology consists of a three-level inverter and a seven-level inverter connected to an open-end winding induction machine. The two inverters are powered by two unequal DC supplies, resulting in a low component count, with just 12 switches and three floating capacitors per phase. The voltage SVs applied by the two inverters are chosen to eliminate circulating power flow and prevent DC bus overcharging. In addition, the switching states of both inverters are chosen in order to keep voltages of all floating capacitors well-controlled. Since the capacitors voltages are controlled using the phase currents, additional pre-charging circuitry is not required. A modulation scheme using level-shifted carriers has also been developed, which can be used with both V/f control and d-q control. The high-voltage inverter has a low effective switching frequency and the low-voltage inverter has a high effective switching frequency, reducing the switching loss. The included results of steady-state and transient testing of an experimental prototype demonstrate that the proposed scheme is suited for industrial drives and traction applications
Fast Capacitor Balancing Scheme for Low Voltage Cascaded H-bridges in Multilevel Dodecagonal Space Vector Structure
No full textMultilevel dodecagonal space vector structure generation using switched capacitive filter with single DC link requires large filter capacitors. This paper proposes an algorithm with modified topology to reduce the large capacitance requirement. Modular units of equal low voltage cascaded H - Bridges are used to create redundancies which helps in avoiding large duration of charge or discharge of capacitor, causing voltage ripple. To utilize these created redundancies, proper selection of redundant states by considering capacitor voltage status and corresponding phase current at multiple instances within a sampling interval are made and capacitor voltages are balanced within required band with reduced value of capacitance. Results for the proposed drive scheme is included in this paper which validates the effectiveness of the algorithm
A Dense Multilevel 30-Sided Space Vector Generation Using a Single DC Link for an Induction Motor Drive
No full textModulation using a higher sided polygonal space vector structure (SVS) is an elegant method to increase the linear modulation range and to eliminate the undesired lower order harmonics from motor phase voltage. This article presents the generation of a dense 15-concentric 30-sided multilevel SVS using a single dc-link for an open end induction motor (OEIM) drive. The proposed scheme eliminates lower order harmonics till 25th order from motor phase voltage throughout the modulation range. The dv/dt stress in the phase voltage applied to the motor will also be highly reduced owing to the multilevel structure. The pulsewidth modulation scheme employed utilizes the denseness of SVS and avoids iterative searches to find the triangle, which encompasses the tip of reference voltage vector, which are typical in multilevel polygonal SVS. The topology consists of an active dc-link fed three-level primary inverter and a capacitor fed five-level secondary inverter connected to either end of an OEIM. The primary inverter acts as the active power supplier for the drive and the secondary inverter filters out the undesirable lower order harmonics from motor phase voltage. The proposed scheme is experientially validated and the results are included in this article
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