Abstract
This work describes a novel method in improving the
input current total harmonic distortion (THD) as well as the power
factor of a three-phase suppressed-link rectifier-inverter circuit.
This proposed method makes use of only three bi-directional low
power static switches with a relatively simple gating circuit. This
paper illustrates how the proposed method is superior in reducing
the input current THD of a rectifier-inverter set to about 5%,
which is in line with the requirements of IEEE standard 519–1992.
This is accomplished without the use of any filter or complex
wave shaping techniques. A delta-modulated (DM) voltage source
inverter (VSI) with proportional integrator forms the output
stage of the converter. It helps to provide constant volts per hertz
operation without the need for additional feedback circuitry
and complexity. Moreover, this novel DM technique also helps
to provide a smooth transition from the pulse width modulation
(PWM) to square wave, hence allowing full utilization of the dc
bus voltage.
Index Terms—Delta modulation, three-phase rectifier, total harmonic
distortion (THD), voltage source inverter (VSI).
I. INTRODUCTION
IN this work, the method of improving the input current total
harmonic distortion (THD) and power factor of the front-end
rectifier relies on only three bi-directional static switches as
shown in Fig. 1. These switches are gated on during a given overlapping
duration of the input line voltages. This method includes
features like low cost, small size, high-efficiency, and simplicity
[1]. The delta modulation (DM) technique with proportional
integrator is used for the control of the output stage of the
voltage source inverter (VSI) to provide constant volts per hertz
operation for ac motor drives without feedback complexity.
The novelty of this proposed work is the incorporation of a
simple power factor (PF) correction circuit into a complex rectifier
inverter structure. It also aims to explore the effect of inverter
generated frequency harmonics on the PF corrector, and inverter
output voltage boosting capability over a wide power range.
II. FRONT-END RECTIFIER ANALYSIS AND PRINCIPLE OF OPERATION
With reference to Fig. 1, , and represents the voltage
sources of the three-phase ac system. and are input
inductors (additional to source inductances), as load, and
Manuscript received April 13, 2000; revised May 5, 2002. Recommended by
Associate Editor L. Xu.
A. I. Maswood and A. K. Yusop are with the Power Electronics and Drives
Laboratory, School of Electrical and Electronic Engineering, Nanyang Technological
University, Singapore 639798 (e-mail: eamaswood[at]ntu.edu.sg).
M. A. Rahman is with the Memorial University of Newfoundland, St. Johns,
NF, Canada.
Publisher Item Identifier 10.1109/TPEL.2002.802172.
Fig. 1. Proposed improved high-power-factor three-phase front-end rectifier.
Fig. 2. Implementation of bi-directional switch (D+: active during positive
input voltage, D