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Variable-frequency drives and harmonics
Published in Raymond F. Gardner, Introduction to Plant Automation and Controls, 2020
Multi-pulse transformers are installed in the VFD front end and are designed to increase the number of pulses produced by the rectifier section. The additional pulses increase the number of humps, which reduces the magnitude of the humps and greatly smoothing the dc-link current ripple before any filtering is applied as shown in Figure 6.25. The additional pulses result in more of the ac source sine wave being used, as opposed to just six sharp spikes of current coinciding with each three-phase sinusoidal peak, as would be the case in a conventional three-phase, six-pulse arrangement. As more of the ac-input sinusoidal current is used, the associated voltage distortion it causes in the electrical distribution system is reduced. Multi-pulse multi-phase transformers have been designed to produce 12, 18, 24, and 36 pulses. A three-phase, 18-pulse transformer is shown in Figure 6.26 (left) and another transformer having an integral ac line reactor is shown on the right. Multi-pulse transformers can be constructed using delta-delta-wye transformers, or multi-tap three-phase transformers.
Sound reinforcement and public address
Published in John Borwick, Loudspeaker and Headphone Handbook, 2012
The second two channels (reverberation and warmth) are provided through the use of a custom, multi-tap, digital-reverberation device and distributed 200 mm coaxial and 300 mm loudspeakers. The custom reverberator provides a diffuse package of late-arriving reflections, gradually decaying but pseudo-randomly varying in amplitude and time spacing, which combines with the natural reverberation decay of the room. The reverberation time or the level of the reverberant field, or both, may be increased. Each transducer requires 20-50 W of amplifier power. Such systems are now enabling the architect to design the shape and size of hall needed to fulfil seating and economic requirements, while the acoustics can be tailored to create a totally different environment to suit the particular presentation required.
Generation and Photonic Processing of Radio Waves, Tera-Waves and Multi-Carrier Lightwaves
Published in Le Nguyen Binh, Photonic Signal Processing, 2019
The key component for the multi-tap filter is the multi-wavelength power equalized laser. It can be a Raman fiber laser, semiconductor optical amplifier (SOA)-based laser, or an EDF laser. As experienced, it is quite difficult to achieve stable room temperature operation of an EDF laser. We propose to solve this problem by using FWM in a high nonlinearity dispersion-shifted fiber (NLDSF) and, thus, avoiding the mode competition of the EDF. Figure 9.16a and b shows the EDF laser using a ring cavity and a linear cavity, respectively. The lasing wavelengths can also be controlled by the polarization controller. The number of channels and wavelength spacing can be controlled flexibly by a Sampled Chirped Fiber Bragg grating (SCFBG).
Cascaded H-bridge multilevel inverters with discrete variation of DC sources
Published in International Journal of Electronics, 2019
Ahmad Behzadi Nezhad, Alireza Namadmalan, Ali Rahdarian
The proposed discrete variation of DC sources can be utilised for all kind of CHBs to reduce the number of required converters. However, for simplicity and popularity, asymmetric nine-level CHB is considered in this paper. Figure 2 shows schematic of the proposed structure, which is implemented based on an asymmetric nine-level CHBs. Cell 2 has the highest voltage connected to a regulated DC source which can be supplied by a three-phase transformer and a controlled rectifier. Cell 1 which is the lowest voltage cell, is fed by a discrete variable DC source. Cell 1 is supplied by AC grid by connecting a three-phase multi-tap transformer and an uncontrolled rectifier.
Minimization of Harmonics in BLDC Motor Drive Using Fuzzy Logic Based Variable Inductor Filter Drive
Published in Australian Journal of Electrical and Electronics Engineering, 2020
Parag S. Chaudhari, Sanjaykumar L. Patil
Servo controlled variable inductor whose value varies according to the supply frequency (rotor speed). Filter elements shall be selected very thoroughly. For variation of inductance there are two choices, either to use multi-tap inductor or use variable inductor. Major factors like line voltage, back emf, line current and supply frequency range, should be considered while its design. Selection of inductor is done first. For designing variable inductor approaches like using multi-tap inductor or using continuously varying inductor are widely used in practice (Kim and Sul 2011), (A. Houari, H. Renaudineau, J. P. Martin, S. Pierfederici, and F. Meibody-Tabar).
Distributed polar-coded OFDM based on Plotkin’s construction for half duplex wireless communication
Published in International Journal of Electronics, 2018
Rahim Umar, Fengfan Yang, Shoaib Mughal, HongJun Xu
where is the frequency response of multi-tap frequency selective Rayleigh fading channel defined in Equation (8), for .