Three-phase

About: Three-phase is a research topic. Over the lifetime, 16801 publications have been published within this topic receiving 159477 citations.

Two-Segment Three-Phase PMSM Drive With Carrier Phase-Shift PWM for Torque Ripple and Vibration Reduction

Abstract: This paper presents a two-segment motor system powered by two inverters with phase-shift pulsewidth modulation (PWM) to fulfill the purpose of low-torque ripple and vibration noise. Different from conventional multi-inverter structure, the inverters for this type of machine are electrically isolated between each other. First, the concept of multisegment machine is presented and the basic operation principle is analyzed with finite-element analysis (FEA) method. Then vibration caused by the switching device in machine is investigated and the control model of a two-segment motor is developed. Further, the principle of carrier phase-shift PWM is illustrated with the vibration analysis. Carrier phase shift can generate interleaved torque and force on the rotor for the two groups of windings in the machine and cancel each other for certain harmonics. Then simulation of control strategy for this type of machine has been done in MATLAB. Finally, based on the concept and principles mentioned before, a two-segment motor with its drive system is fabricated. Both the test of torque ripple and the vibration of the motor have been significantly improved. Compared with a normal three-phase motor driven by a paralleled inverter with interleaving, the proposed approach is with comparable vibration reduction but without using extra coupled inductors.

Design of phase identification system to support three-phase loading balance of distribution feeders

Abstract: In this paper, a phase identification system (PIS) is designed to incorporate a fuzzy microprocessor based controller for phase measurement of underground transformers. The proposed fuzzy calibration algorithm used in the controller aims to solve the offset and gain of frequency deviation of the real-time clock, which was generated by a voltage controlled crystal oscillator (VCXO) to maintain the timing lock with respect to the 1 Pulse per Second (1PPS) signal of the global positioning system (GPS) before phase measurement is executed. According to the field test of the PIS design, the phase deviation of the real time clock with embedded VCXO can be improved from 46.27° to 0.98° by applying the fuzzy calibration algorithm. The PIS has been applied for field measurement of underground distribution transformers to identify their phases and correct the corresponding attributes of the Automated Mapping Faulty Management (AM/FM) system in Taipower. By retrieving the information of the line segments and transformers from the AM/FM, the network modeling of distribution feeders is derived to analyze the three-phase unbalance. The rephasing strategy of laterals and distribution transformers has been derived and executed by Taipower engineers. By comparing the phase currents and neutral current of a test feeder before and after rephasing, the three-phase balance of the distribution system can be significantly enhanced with the PIS to identify the phasing of distribution transformers for deriving the rephasing strategy of the distribution feeders.

High frequency supply system for gas discharge lamps and electronic ballast therefor

Abstract: The invention is both a system for supplying high frequency alternating current to gas discharge lamps, such as fluuorescent lamps, and the like and a unit that can be placed in or adjacent to a lighting fixture to convert a direct current supply into high frequency AC and also provide the ballast needed for operation of the gas discharge lamps. This unit contains a symmetrical, class B, push-pull current-limited, tuned-collector, sinusoidal oscillator which is self starting, highly efficient and stable over a wide range of input voltage, with or without load. The number of parts is a minimum and the parts are relatively low cost, the power losses are very low and the system operates at high power factor with low acoustic and radio noise and low flicker. The system may derive the current from a commercially available source at any voltage and phase but preferably three phase primary of a building transformer can convert this into six phase at the output terminals which can be converted to DC of low ripple even without filtering. From the central building supply, it is possible to send AC at suitable voltage to subcenters in the building for rectification, inversion and use in lighting fixtures but preferably there is a single rectifier adjacent to the main transformer and the DC at proper voltage is distributed to the fixtures where the ballast unit is installed in a fixture to supply the lamps in it with the high frequency AC. However, one ballast unit can serve, in many instances, more lamps than a single fixture holds and it is necessary in such instances to supply the high frequency AC from one fixture to another and this can be done with only two wires. The invention also provides means for dimming the lights, for supplying heating current to lamp filaments at high voltage at the start and much reduced voltage after the arc has been struck in the lamps served by the ballast unit, and this reduction in filament current takes place automatically without switches, resistsors or other expensive and energy consuming means. The transformers used in the practice of the invention may also be used to supply the building with AC for customary appliances, incandescent lighting, and the like.

Single-Source Three-Phase Multilevel Inverter Assembled by Three-Phase Two-Level Inverter and Two Single-Phase Cascaded H-Bridge Inverters

Abstract: Multilevel inverters (MLIs) with reduced number of switching devices and dc sources have compact size, reduced cost, and higher efficiency. This article proposes a transformer-based single-source MLI with reduced number of components and small size transformers. The proposed topology is a hybrid three-phase MLI assembled by a conventional three-phase two-level inverter (TTI) and two single-phase cascaded H-bridge inverters (CHBIs). The proposed MLI has a low ratio of number of active switches to number of output voltage levels. In order to use only one dc source, the CHBIs are cascaded with the TTI through transformers. An individual nearest level modulation (NLM) has been developed to control voltage of this inverter. Moreover, power distribution between its modules is analyzed. The total power of the transformers is 28% of the inverter rated power. Simulation and experimental results of a 13-kVA prototype verify the efficiency of the proposed arrangement.

Leakage flux and force calculation on power transformer windings under short-circuit: 2D and 3D models based on the theory of images and the finite element method compared to measurements

Abstract: The paper compares different techniques based on the theory of images and the finite element method enabling to calculate the leakage field and the static electromagnetic forces on the windings of power transformers. The models developed have been applied to the one phase part of a three phase shell type power transformer and the results are verified experimentally. Both cases, that of approximate two dimensional analysis and the three dimensional configuration, have been studied. A particular three dimensional finite element formulation involving only a scalar potential was found to be suitable for this class of problems. >