08-05-2012, 03:01 PM
MODELING OF MULTI-PULSE TRANSFORMER RECTIFIER UNITS IN POWER DISTRIBUTION SYSTEMS
[attachment=21567]
INTRODUCTION
Motivation
This work was motivated by the need to simulate large power distribution systems
and to study interactions between the individual subsystems. Aircraft power system is
one of the applications in which these large scale power distribution simulation models
prove useful [1]. As the move towards the More Electric Aircraft (MEA) continues, there
is a desire to e ectively model these systems in both the time domain and the frequency
domain [1], [2], [3]. A simpli ed aircraft power distribution system is presented in Figure
1.1 [2]. This system di ers from the traditional aircraft power system in that the aircraft
starter/generator supplies a variable frequency. One of the main components of this
system is the AC/DC converter that provides the 270 V dc bus voltage. It has been
shown in literature that one possible solution is the 18-pulse autotransformer recti er
unit (ATRU) [4]. This ATRU topology has the advantages of reduced kVA ratings and
improved line current harmonics [4].
Multi-pulse transformer/recti er overview
This section will provide an overview of multi-pulse transformer/recti er systems.
The operation of the 12-pulse transformer recti er will be reviewed, and some applications
of these circuits will be provided.
Applications
The multi-pulse transformer topology generally acts as an interface between the power
electronics load and the utility supply. Some of the most common applications for multipulse
transformer/recti er systems include motor drives, interruptible power supplies
(UPS) systems, aircraft variable speed constant frequency (VSCF) systems, and frequency
changer systems [10], [12]. In other work [13], the author develops an 18-pulse
autotransformer recti er system that does not require the use of interphase transformers.
He instead takes advantage of the unequal current sharing in the three bridges. He
is able to reduce the system size by eliminating the interphase transformers, and also
achieves a harmonic current that is reduced as compared with that of a 12-pulse system.
Some other applications of multi-pulse transformer topologies involve adding switching
circuitry to the interphase transformers to improve the pulse number of the line current
Di erent types of models
This section will provide some background information on the di erent types of models
available for analyses. For this work, the focus will be directed toward switching models
and average models.
Switching models
Simulation models that account for the turning on and o of semiconductor switches
are commonly referred to as switching models. These detailed computer simulation models
are used to observe the operation of the converter during steady-state and transient
operation.
Operation
Literature on multi-pulse transformer/recti er topology has existed for several years
[9]. The term multi-pulse is de ned as any number of n 6-pulse bridge recti ers connected
in series or parallel, where n is greater than 1. The two main advantages to
using multi-pulse transformer/recti er topologies are a reduction in the ac input line
current harmonics and a reduction in the dc output voltage ripple [6]. The input current
harmonics are reduced through the use of phase-shifting transformers.
[attachment=21567]
INTRODUCTION
Motivation
This work was motivated by the need to simulate large power distribution systems
and to study interactions between the individual subsystems. Aircraft power system is
one of the applications in which these large scale power distribution simulation models
prove useful [1]. As the move towards the More Electric Aircraft (MEA) continues, there
is a desire to e ectively model these systems in both the time domain and the frequency
domain [1], [2], [3]. A simpli ed aircraft power distribution system is presented in Figure
1.1 [2]. This system di ers from the traditional aircraft power system in that the aircraft
starter/generator supplies a variable frequency. One of the main components of this
system is the AC/DC converter that provides the 270 V dc bus voltage. It has been
shown in literature that one possible solution is the 18-pulse autotransformer recti er
unit (ATRU) [4]. This ATRU topology has the advantages of reduced kVA ratings and
improved line current harmonics [4].
Multi-pulse transformer/recti er overview
This section will provide an overview of multi-pulse transformer/recti er systems.
The operation of the 12-pulse transformer recti er will be reviewed, and some applications
of these circuits will be provided.
Applications
The multi-pulse transformer topology generally acts as an interface between the power
electronics load and the utility supply. Some of the most common applications for multipulse
transformer/recti er systems include motor drives, interruptible power supplies
(UPS) systems, aircraft variable speed constant frequency (VSCF) systems, and frequency
changer systems [10], [12]. In other work [13], the author develops an 18-pulse
autotransformer recti er system that does not require the use of interphase transformers.
He instead takes advantage of the unequal current sharing in the three bridges. He
is able to reduce the system size by eliminating the interphase transformers, and also
achieves a harmonic current that is reduced as compared with that of a 12-pulse system.
Some other applications of multi-pulse transformer topologies involve adding switching
circuitry to the interphase transformers to improve the pulse number of the line current
Di erent types of models
This section will provide some background information on the di erent types of models
available for analyses. For this work, the focus will be directed toward switching models
and average models.
Switching models
Simulation models that account for the turning on and o of semiconductor switches
are commonly referred to as switching models. These detailed computer simulation models
are used to observe the operation of the converter during steady-state and transient
operation.
Operation
Literature on multi-pulse transformer/recti er topology has existed for several years
[9]. The term multi-pulse is de ned as any number of n 6-pulse bridge recti ers connected
in series or parallel, where n is greater than 1. The two main advantages to
using multi-pulse transformer/recti er topologies are a reduction in the ac input line
current harmonics and a reduction in the dc output voltage ripple [6]. The input current
harmonics are reduced through the use of phase-shifting transformers.