3 phase AC DC converter with high power factor

3 phase AC DC converter with high power factor -...

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Three-phase AC/DC converter with high power factor B.-R. Lin and T.-Y. Yang Abstract: The paper presents a three-phase AC/DC converter to achieve power-factor correction, harmonics elimination, DC-bus-voltage regulation and neutral-point-voltage compensation. The proposed converter can achieve bidirectional power-flow capability. Therefore the converter can be applied for active power-Flter operation. Two legs are adopted in the proposed converter to achieve three-level pulse-width modulation (PWM) and control the line currents to be sinusoidal waves in phase with supply voltages. Three control loops, DC-link-voltage control, neutral-point-voltage compensation and line current control, were used in the control scheme to achieve DC-bus-voltage regulation, to balance neutral-point voltage and to draw the sinusoidal line currents. The mathematical model of the converter was derived and the control scheme is provided. The effectiveness of the proposed control scheme is veriFed through computer simulation and experiments. 1 Introduction Power pollution owing to the use of power converters results in serious power-quality problems in distribution and transmission systems. Thus, international standards such as IEC 1000-3-2 [1] are deFned to restrict the harmonic contents on the AC-source current. Passive power Flters were widely used to reduce harmonic currents. However, the main drawbacks of passive Flters are Fxed compensa- tion characteristics, bulk and heavy weight, and series and parallel resonances with the system impedance. Active- wave-shaping techniques based on pulse-width-modulated (PWM) schemes have been proposed in [2–6] to eliminate harmonics and compensate reactive power so that a sinusoidal line current with nearly unity power factor is drawn from the supply voltage. The conventional three- phase bidirectional converter is shown in ±ig. 1 a .S ixact ive switches were used in the converter to achieve power-factor correction, draw sinusoidal line currents from the AC source and obtain a constant DC-link voltage on the DC side. Bipolar PWM voltage waveforms are generated on the AC terminal voltages. However, the series connection of active switches should be adopted in the conventional three- phase two-level AC/DC converter for medium- or high- voltage applications. Multilevel converters [7, 8] and inverters [9–12] adopted series connection of power semiconductors with the low-voltage stress to achieve the medium-voltage applications. Normally, there are some clamped devices in the circuit to generate a multilevel voltage waveform on the AC terminal. These clamped devices can be active switches [8] shownin± ig .1 b ,c lamped diodes [7, 9] i g c and flying capacitors [9] d . Sixteen active switches, two capacitors and three boost inductors are used in the switch-clamped converter shown ±ig. 1 b . Three boost inverters, 16 active switches, six clamped diodes and two capacitors are adopted in the diode-clamped converter shown in ±ig. 1 c .
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This note was uploaded on 03/31/2012 for the course CHEMICAL 111 taught by Professor Ammar during the Spring '12 term at NED Univ. of Engineering & Tech..

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3 phase AC DC converter with high power factor -...

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