12-09-2012, 04:24 PM
Harmonic Reduction In Three-Phase Parallel Connected Inverter
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Abstract
This paper presents the design and analysis of a parallel
connected inverter configuration of. The configuration consists of
parallel connected three-phase dc/ac inverter. Series resistors added
to the inverter output to maintain same current in each inverter of the
two parallel inverters, and to reduce the circulating current in the
parallel inverters to the minimum. High frequency third harmonic
injection PWM (THIPWM) employed to reduce the total harmonic
distortion and to make maximum use of the voltage source. DSP was
used to generate the THIPWM and the control algorithm for the
converter. Selected experimental results have been shown to validate
the proposed system.
INTRODUCTION
mprovements in fast switching power devices have led to an
increased interest in voltage source inverters (VSI) with
pulse width modulation control (PWM). Control methods
which generate the necessary PWM patterns could be
classified as voltage controlled and current controlled PWM.
With PWM control technologies, ac side of the three-phase
inverter has the abilities of controllable power factor,
sinusoidal output currents and bi-directional power transfer [1]
[2]. The third harmonic injection method to control the power
factor of the inverter output current used for three-phase
inverter. However, it is very difficult to generate the right third
harmonic amplitude [3] [4]. In hysteresis control the switching
frequency varies significantly according to the power level and
the dc link [5] [6].
THREE PHASE INVERTER
A standard three-phase inverter is shown in Figure 1
consisting of six controlled switches such as IGBT. In this
converter, the line currents can be shaped to be sinusoidal at a
unity power factor, as well as the output ac voltage can be
regulated at a desired value. The inverter is connected to the
load through three LC filters. THIPWM employed to make
full use of the DC bus voltage with minimum harmonic
distortion in the output voltage and current.
CONCLUSION
This paper presents a Parallel connected three-phase inverter.
The improvement of parallel connection over single inverter is
clearly shown. By comparing the THD and efficiency in single
unit and parallel connected unit the THD improve and the
efficiency as well. The THD reduced to be less than 1.5% for
the current and the voltage. The power capability of the
inverter system will be higher by connecting the inverters in
parallel. The two inverters are sharing the same current value
which reduces the circulating current to minimum.