|
AC/AC-Conversion
for Highly Compact Drives - What Options Do I Have? PART
I: An
Overview of AC/AC-Converter Topologies
Dr. Uwe Drofenik Gecko-Research GmbH ETH Zentrum, ETL H13 CH-8092 Zurich, Switzerland Phone +41-44-632 4267 Fax +41-44-632
1212 Email June 11,
2009 PART
I: An
Overview of AC/AC-Converter Topologies Overview – Classification of Three-Phase AC/AC
Converters For operating
a Permanent Magnet Synchronous Machine (PMSM), which allows a highly compact
design, you have to supply three-phase voltage with controllable output
frequency and controllable voltage amplitude. There are many different
alternatives for the AC/AC converter. It is very helpful to look at the
systematic classification shown in Fig. 1 which is based on a discussion in
[25]. In this report we will have a look at the converters in the green
boxes. For details of all converter systems see the references.
Fig. 1: Classification of Three-Phase AC/AC
Converters. The Classic Solution – AC/AC Conversion Employing a
DC-Link In order
to control the speed of a Permanent Magnet Synchronous Machine (PMSM) one
must be able to control voltage amplitude and frequency of the three-phase
voltage system, which connects to the PMSM. A standard
solution for AC/AC conversion with ·
Controllable output voltage
amplitude ·
Controllable output frequency ·
Approximately sinusoidal input
currents ·
Bidirectional power flow is the
coupling of two inverters via a DC-link. The topology employing a capacitor,
which gives defined voltage in the DC link, is shown in Fig. 2. The PMSM is
modelled by three inductors and three voltage sources connected to nodes A,
B, C at the output side.
Fig. 2: Topology of the three-phase AC/AC converter
with voltage DC-link. The input
side converter could be alternatively realized as simple diode bridge, but
the input current would contain significant low-frequency harmonics then. The
diode bridge could not feed back braking energy in to the mains. Therefore, a
braking resistor in the DC link would be needed. Alternatively, a thyristor
bridge at the input side could feed back braking energy, but would still
suffer from significant low-frequency input current harmonics, especially
during inverter operation.
Subscribe to the free Gecko-Research Newsletter to be informed about reports and power electronic research topics.
Unsubscribe anytime by sending an email (Subject: 'unsubscribe') to
Instead of
defining a voltage in the DC link, one could also define the current in the
DC link via DC link inductor as shown in Fig. 3. The converter system in Fig.
3 needs small capacitive filters at input- and output side for decoupling the
inductors.
Fig. 3: Topology of the three-phase AC/AC converter
with current DC-link. The big advantage
of the DC link is the decoupling (at least, to a large extent) of the control
tasks of the input-side and the output-side converter. A
disadvantage of such converter systems is the DC-link energy storage element
which shows typically a relatively large physical volume. Furthermore, in
case an electrolytic capacitor is used in the topology of Fig. 2, this bulky
passive component would reduce the system lifetime because its reliability is
relatively low in comparison with the other components in the power circuit. How the Matrix Converter Helps You to Get Rid of
Passive Components in the DC-Link Matrix
Converters achieve three-phase AC/AC conversion without any intermediate
energy storage element. This has the potential to increase power density
(output power per converter volume) significantly. Furthermore, omitting the
electrolytic capacitor in the DC-link will improve the system reliability.
Fig. 4: Topology of the Conventional Direct Matrix
Converter. The
topology of the Conventional Direct Matrix Converter is shown in Fig. 4. The
main idea is to be able to connect each input phase directly to each output
phase at any time in order to put together a three-phase output voltage
system as needed for the variable-speed drive. A disadvantage
is the complicated multi-step current commutation scheme where the current
control always has to make sure that free wheeling can occur. A large number
of states must be considered, and signs of currents and voltages have to be
taken into account when defining the switching pattern. A current control
error will result in immediate destruction of power switches. Learn more in
[26] or visit the free Java-based Matrix Commutation Animation of iPES (Interactive Power
Electronics Seminar at www.ipes.ethz.ch/).
Matrix
Converters are often seen as a future concept for variable speed drives
technology, but despite intensive research over the decades they have until
now only achieved low industrial penetration. As mentioned before, the reason
for this might be the higher complexity in modulation and analysis effort
[25]. The decision
if to select a DC-link topology or a matrix converter is dependent on the
switching frequency and on the semiconductor technology. For switching
frequencies above 30kHz matrix converters become competitive. Sparse Matrix Converter – Same Functionality But
Reduced Semiconductor Count Plus Safe Commutation The Sparse
Matrix Converter is a new kind of AC/AC converter with a reduced number of
components and a modulation scheme of low complexity and realization effort.
Sparse Matrix Converters avoid the multi-step commutation procedure of the
conventional matrix converter which could impair the system reliability for
operation in industrial environment. The
characteristics of the Sparse Matrix Converter are ·
Quasi-Direct AC-AC conversion with
no DC link energy storage elements ·
Sinusoidal input current in phase
with mains voltage ·
·
Low complexity of power circuit /
power modules available ·
Ultra-Sparse Matrix Converter,
does show very low realization effort, in case unidirectional power flow can
be accepted (admissible displacement of 30° the input current fundamental and
input voltage, as well as for the output voltage fundamental and output current),
accordingly, a possible application area would be variable speed PSM drives
of low dynamics. Sparse
Matrix Converter (SMC) The Sparse
Matrix Converter topology is characterized by 15 Transistors, 18 Diodes, and
7 Isolated Driver Potentials.
Fig. 5: Topology of the Sparse Matrix Converter. Compared
to the Direct Matrix Converter, this topology provides identical
functionality, but with a reduced number of power switches and the option of
employing an improved zero DC link current commutation scheme, which provides
lower control complexity and higher safety and reliability. Very
Sparse Matrix Converter (VSPM) Characteristics
of the Very Sparse Matrix Converter topology are 12 Transistors, 30 Diodes,
and 10 Isolated Driver Potentials. It shows identical functionality compared
to the Direct Matrix Converter and/or the Sparse Matrix Converter. Compared
to the Sparse Matrix Converter there is a smaller number of transistors, and
higher conduction losses due to the increased number of diodes in the
conduction paths.
Fig. 6: Topology of the Very Sparse Matrix
Converter. Ultra Sparse Matrix Converter
Fig. 7: Topology of the Ultra Sparse Matrix
Converter. The Ultra Sparse
Matrix Converter topology has got 9 Transistors, 18 Diodes, and 7 Isolated
Driver Potentials. As
mentioned before, the significant limitation of this converter topology as
compared to the Sparse Matrix Converter is the restriction of its maximal phase
displacement between load-side voltage and input current to ± 30°. The reason
is that the input stage of this converter is unidirectional. Possible
applications would be PMSM (small phase displacement) with no energy-feedback
into the mains. Finally a Simulation of the Sparse Matrix Converter Let’s
perform a numerical simulation of the operation of the Sparse Matrix
Converter (SMC) which is shown in Fig. 5.
Fig. 8: Java-Animation of the Sparse Matrix
Converter at www.ipes.ethz.ch. We will
employ our new simulator GeckoCIRCUITS which gives the following
benefits: ·
Easy to learn and use ·
Very fast and numerically stable ·
Multi-domain: Electric - Thermal -
EMI ·
Easy & fast calculation of
transient junction temperatures ·
Free online
version, no installation required For the
family of the Sparse Matrix Converters, we employ the Zero DC Link Current
Commutation which is described in detail in [19]. The scheme makes the
commutation safe and simple compared to the conventional multi-step
commutation scheme. One has to
define the relevant voltage sector pairs at the input and output side. There
are 12 different voltage sectors over one mains period for each side. Fig.8
shows voltage sector 2 for the input side and voltage sector 11 for the
output side as yellow shaded areas. The position of the red vertical time
slider defines the relevant pair of sectors. Dependent
on the sectors, the power switches have to be switched in certain sequences.
This is shown in Fig. 8, bottom diagram, right-hand side. The individual on-
and off-times are calculated from equations which are dependent on the
relevant sector pair. All information including the equations is given in
detail in [19] and/or [21]. All equations are fully implemented in the
Java-Applet of Fig. 8. We use the applet to debug simulation and hardware
prototypes step by step. Obviously,
there waits a lot of hard work to implement a current controller with so many
different states to be defined from measured voltages, and such a large
number of state-dependent equations and different switching sequences. That’s why
we will employ the powerful JAVA-Block of our simulator GeckoCIRCUITS. First
let’s study a simple example to understand the JAVA-Block located in
GeckoCIRCUITS’ Tab “Special”:
Fig. 9: JAVA-Block in GeckoCIRCUITS.
Fig. 10: Put the File “tools.jar” Into to Folder jre1.6/lib/ext/
of Your Actual Java Runtime Environment to make the JAVA-Block work. The
JAVA-Block allows to directly write Java-Code which is compiled before begin
of the simulation. This Java-Code is then executed within each numerical time
step, processing input variables and generating output variables. The
JAVA-Block uses the Java-compiler available in Sun’s library “tools.jar”
which you have to install in order to make the JAVA-Block work. If “tools.jar”
is not yet available on your computer and you double-click the JAVA-Block,
you will see a warning dialog which tells you where to get the file
“tools.jar” from, and into what folder you should put it. You can download
“tools.jar” for free embedded in Sun’s JDK
1.6. In case of
problems and/or difficulties please contact The
JAVA-Block allows in a very simple way the implementation of highly complex
functions, and/or creating control blocks one would need but are not included
in the control library yet. How to Use the JAVA-Block In case of
the current control of the Sparse Matrix Converter, first one has to identify
the actual voltage sectors. Straightforward, this could be implemented in
form of if-then
statements: if
((us<=0)&&(ut<=us)) seIN= 1; else if ((us>=0)&&( else if (( else if (( else if ((ut<=0)&&( else if ((ut>=0)&&(us>=ut)) seIN= 6; else if ((us>=0)&&(ut>=us)) seIN= 7; else if ((us<=0)&&( else if (( else if (( else if ((ut>=0)&&( else if ((ut<=0)&&(us<=ut)) seIN=12; seIN is the number of the input
voltage sector (e.g. seIN=2 in Fig. 8). switch (seIN) { case 1: dIN[0]= -ut/ur; break; case 2: dIN[0]= -ur/ut; break; case 3: dIN[0]= -us/ut; break; case 4: dIN[0]= -ut/us; break; case 5: dIN[0]= - case 6: dIN[0]= -us/ case
7: dIN[0]= -ut/ur; break; case 8: dIN[0]= -ur/ut; break; case 9: dIN[0]= -us/ut; break; case 10:
dIN[0]= -ut/us; break; case 11:
dIN[0]= - case 12:
dIN[0]= -us/ default:
break; } dIN[1]= 1 - dIN[0]; After
this, switching sequences have to be defined based on seIN, and with the relative
on-times exact switching sequences can be calculated (it’s a lot of code, not
shown here). For the switching pattern of the output stage similar expressions
occur. See [19] and [21] for details and algorithms. Now,
implementing if-then
and switch-statements
like above in a circuit simulator is very inconvenient. Fig. 11 shows the
control structure necessary to implement the two code blocks above in
comparison to the JAVA-Block implementation that does the same job. And that’s
just 10% of the whole code of the current controller! Download
the file of Fig. 11 (“java_block.ipes” from package ‘Example Package Matrix’,
see end of report), double-click the JAVA-Block, and have a look at the
simple code implementation.
Fig. 11: Significant Simplification of
Implementation of Control Statements by Using the JAVA-Block. We put all
current control code as described in [19] into a special control block called
“Sparse-Matrix Control” (green Tab ‘Special’) which allows to conveniently
control the Sparse Matrix Converter, the Very Sparse Matrix Converter and the
Ultra Sparse Matrix Converter. The implementation of the Sparse Matrix
Converter is shown in Fig. 12.
Fig. 12: Full Implementation of the Sparse Matrix
Converter with Zero DC-Link Current Control Scheme in GeckoCIRCUITS. Download the
file of Fig. 12 (“SparseMatrixConverter.ipes” from package ‘Example Package
Matrix’, see end of report) and run simulations. The values of uNmax (mains
voltage amplitude) and fN (mains frequency) define the input side. The values
of uLmax (load-side voltage amplitude) and fL (load-side frequency) define
the output side. The switching frequency is given by fDR which is set to
15kHz in this example. Part II will go into the details
of the Sparse Matrix Converter model of Fig. 12.
Fig. 13: Numerical Simulation of the Time Behavior
of the Sparse Matrix. Further Information Part II of this report will be
published on www.gecko-research.com The
topologies discussed here are available for free at www.gecko-research.com/applet-mode/geckocircuits_demo.html:
Sparse
Matrix Converter (Fig. 12): SparseMatrixConverter.ipes Very
Sparse Matrix Converter (Fig. 6): VerySparseMatrixConverter.ipes Ultra
Sparse Matrix Converter (Fig. 7): UltraSparseMatrixConverter.ipes Or request
a free trial version of GeckoCIRCUITS including the powerful Java-Block from
Subscribe to the free Gecko-Research Newsletter to be informed about reports and power electronic research topics.
Unsubscribe anytime by sending an email (Subject: 'unsubscribe') to
References [1] I.
Takahashi, Y. Itoh, “Electrolytic Capacitor-Less PWM Inverter“, in
Proceedings of the IPEC’90, Tokyo, Japan, , pp. 131 – 138, April 2 – 6, 1990. [2] K.
Kuusela, M. Salo, H. Tuusa, “A Current Source PWM Converter Fed Permanent
Magnet Synchronous Motor Drive with Adjustable DC-Link Current“, in
Proceedings of the NORPIE’2000, Aalborg, Denmark, pp. 54 – 58, June 15 – 16,
2000. [3] M. H.
Bierhoff, F. W. Fuchs, “Pulse Width Modulation for Current Source Converters
– A Detailed Concept,“ in Proceedings of the 32nd IEEE IECON’06, Paris,
France, Nov. 7–10, 2006. [4] R. W.
Erickson, O. A. Al-Naseem, “A New Family of Matrix Converters“, in
Proceedings of the 27th IEEE IECON’01, Denver, USA, Vol. 2, pp. 1515 – 1520,
Nov. 29 – Dec. 2, 2001. [5] C.
Klumpner, C. I. Pitic, “Hybrid Matrix Converter Topologies: An Exploration of
Benefits,“ in Proceedings of the 39th IEEE PESC’08, Rhodos, Greece, pp. 2 –
8, June 15 – 19, 2008. [6] C.
Klumpner, “Hybrid Direct Power Converters with Increased/Higher than Unity
Voltage Transfer Ratio and Improved Robustness against Voltage Supply
Disturbances“, in Proceedings of the 36th IEEE PESC’05, Recife, Brazil, pp.
2383 – 2389, June 12 – 16, 2005. [7] L.
Gyugyi, B. R. Pelly, “Static Power Frequency Changers - Theory, Performance,
& Application“, [8] W. I. Popow, “Der zwangskommutierte Direktumrichter
mit sinusförmiger Ausgangsspannung,“ Elektrie 28, No. 4, pp. 194 – 196, 1974. [9] K. K.
Mohapatra, N. Mohan, “Open-End Winding Induction Motor Driven with Matrix
Converter for Common-Mode Elimination“, in Proceedings of the PEDES’06, New
Delhi, India, Dec. 12 – 15, 2006. [10] M.
Braun, K. Hasse, “A Direct Frequency Changer with Control of Input Reactive
Power“, in Proceedings of the 3rd IFAC Symposium, Lausanne, Switzerland, pp.
187–194, 1983. [11] D. H.
Shin, G. H. Cho, S. B. Park, “Improved PWM Method of Forced Commutated
Cycloconverters“, in Proceedings of the IEE, Vol. 136, Part B, No. 3, pp. 121
– 126, 1989. [12] P. D.
Ziogas, Y. Kang, V. R. Stefanovic, “Rectifier-Inverter Frequency Changers
with Suppressed DC Link Components“, IEEE Transactions Industry Applications,
Vol. IA-22, No. 6, pp. 1027 – 1036, 1986. [13] S.
Kim, S. K. Sul, T. A. Lipo, “AC/AC Power Conversion Based on Matrix Converter
Topology with Unidirectional Switches“, IEEE Transactions Industry
Applications, Vol. 36, No. 1, pp. 139 – 145, 2000. [14] K.
Göpfrich, C. Rebbereh, L. Sack, “Fundamental Frequency Front End Converter
(F3E)“, in Proceedings of the PCIM’03, Nuremberg, Germany, pp. 59 – 64, May
20 – 22, 2003. [15] B.
Piepenbreier, L. Sack, “Regenerative Drive Converter with Line Frequency
Switched Rectifier and Without DC Link Components“, in Proceedings of the
35th IEEE PESC’04, Aachen, Germany, pp. 3917 – 3923, June 20 – 25, 2004. [16] J. Holtz,
U. Boelkens, “Direct Frequency Converter with Sinusoidal Line Currents for
Speed-Variable AC Motors“, IEEE Transactions Industry Electronics, Vol. 36,
No. 4, pp. 475–479, 1989. [17] K.
Shinohara, Y. Minari, T. Irisa, “Analysis and Fundamental Characteristics of
Induction Motor Driven by Voltage Source Inverter without DC Link Components
(in Japanese)“, IEEJ Transactions, Vol. 109-D, No. 9, pp. 637 – 644, 1989. [18] L.
Wei, T. A. Lipo, “A Novel Matrix Converter Topology with Simple Commutation“,
in Proceedings of the 36th IEEE IAS’01, Chicago, USA, vol. 3, pp. 1749 –
1754, Sept. 30 – Oct. 4, 2001. [19] J. W.
Kolar, M. Baumann, F. Stögerer, F. Schafmeister, H. Ertl, “Novel Three-Phase
AC-DC-AC Sparse Matrix Converter, Part I - Derivation, Basic Principle of
Operation, Space Vector Modulation, Dimensioning, Part II - Experimental
Analysis of the Very Sparse Matrix Converter“, in Proceedings of the 17th
IEEE APEC’02, Dallas, USA, Vol. 2, pp. 777 – 791, March 10 – 14, 2002. [20] L.
Wei, T. A. Lipo, H. Chan, “Matrix Converter Topologies with Reduced Number of
Switches“, in Proceedings of the VPEC’02, Blacksburg, USA, pp. 125 – 130,
April 14 – 18, 2002. [21] F. Schafmeister, “Sparse und Indirekte Matrix
Konverter“, PhD thesis No. 17428, ETH Zürich, Switzerland, 2007. [22] J. W.
Kolar, F. Schafmeister, S. D. Round, and H. Ertl, “Novel Three-Phase AC-AC
Sparse Matrix Converters“, Transactions Power Electronics, Vol. 22, No. 5,
pp. 1649 – 1661, 2007. [23] M. Y.
Lee, P. Wheeler, C. Klumpner, “A New Modulation Method for the
Three-Level-Output-Stage Matrix Converter“, in Proceedings of the 4th PCC’07,
Nagoya, Japan, April 2 – 5, 2007. [24] C.
Klumpner, M. Lee, P. Wheeler, “A New Three-Level Sparse Indirect Matrix
Converter“, in Proceedings of the IEEE IECON’06, pp. 1902– 1907, 2006. [25] J. W.
Kolar, T. Friedli, F. Krismer, S. D. Round, “The Essence of Three-Phase AC/AC
Converter Systems”, Proceedings of the 13th Power Electronics and Motion
Control Conference (EPE-PEMC'08), [26] P.
Wheeler, J. Rodriguez, J. Clare, L. Empringham, A. Weinstein, “Matrix
converters: A technology review”, IEEE Transactions on Industrial
Electronics, Vol. 49, No. 2, pp. 276–288, Apr. 2002. |
