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EconoMAC the first all-in-one IGBT module for matrix convertersEupec: Hr. M. Hornkamp; Hr. M. Loddenktter; Hr. M. Mnzer; Siemens A&D: Hr. O. Simon ; Hr. M. Bruckmann

Abstract: Searching for new alternatives to the state of the art technology of voltagesource inverters, research laboratories of various vendors fancy matrix converters.

Working on a concept that has been around for more than 20 years, a mayorobstacle to its success has been the lack of an efficient bi-directional low cost valve.With semiconductors getting more efficient at lower costs matrix converters are aboutto take their place in the power conversion market. After a short introduction to matrixconverters this paper discusses different concepts for the realisation of a bi-directional power switch. It shows how based on one of these concepts the completepower stage for a matrix converter with a power rating of up to 7,5 kW is realised inan EconoPack 3 sized module. In the paper an example for an application for thisnew module named EconoMAC is given. As a prove for the performance of theEconoMAC module first test results of a laboratory prototype are presented.

The concept of matrix convertersToday voltage source inverters are state ofthe art. All these inverters work in twosteps. In a first step a 3 phase line voltageis rectified to feed a capacitor bank. In asecond step this DC voltage is inverted tocreate a 3 phase output voltage. Havingtwo independent steps, it is easy to designpower stages and control strategies foreach step separately. Still the questionmust be asked, if a converter that converts

input voltage directly to output voltagewould not be of advantage. Such aconverter is the matrix converter. The ideabehind this converter is that at any timeone of the input lines has the voltage thatis required for a PWM at the output line.Therefore one only needs to connect theoutput line to the right input line at anytime. To be able to connect each inputwith each output a matrix of 9 connectionpoints is needed.

L1

L2

L3

U V W

BDS1-1

BDS2-2BDS2-1

BDS3-1 BDS3-2 BDS3-3

BDS2-3

BDS1-3BDS1-2

I

IGBT 1 IGBT 2

Figure 1: Structure of a matrix converter

In figure 1 the structure of a matrixconverter is shown. As each connecting

point needs to be able to conduct currentin both directions, a bi-directional valve isneeded. For more simplicity in figure 1

these valves are drawn as mechanicalswitches. Figure 2 shows a simulation ofthe input and output voltages and currents.

(V)

400.0

200.0

0.0

200.0

400.0

t(s)

0.0 0.002 0.004 0.006 0.008 0.01 0.012 0.014

(V)

400.0

200.0

0.0

200.0

400.0

(V)

400.0

200.0

0.0

200.0

400.0

(V)

400.0

200.0

0.0

200.0

400.0

(V) : t(s)

u_in3

(V) : t(s)

u_in2

(V) : t(s)

u_in1

(V) : t(s)

u_out1

Figure 2: Output/Input-voltage-waveforms

As can be seen it is possible to modulate

the output voltage in such a way, that itapplies only sinusoidal currents and volt-ages to the net. Therefore it creates onlylow input harmonics. Something that cannot be achieved with diode fed inverters.In contrast to diode fed inverters the matrixconverter also offers full regeneratingcapability. Another advantage of the matrixconverter is the lack of dc link capacitors,as these components are spacious andextremely heat sensitive. On top of thisthese electrolyte capacitors have to be

designed for long time reliability whichmakes them expensive. The advantage of


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having huge energy storage capacitors isthat the input rectifier can be used to step

up voltage of the dc link and that anovervoltage protection is easier toimplement. But as matrix converters donot have a dc link they can only be usedfor voltages according to the followingformula.

inoutUU

2

3

Formula 1: Ratio of sinusoidal input to output

voltage

Another drawback of the matrix converteris the fact, that it requires 9 bi-directional

switches. As this is unique no solutions tointegrate the power section have been

offered so far. All the advantages anddisadvantages are summarised in figure 3.

Dez, 2000

Mnzer/MOD-E

+ full regenerating capability

+ good rpm zero behaviour

+ sinusoidal input current

+ no dc link capacitors

+ compact drive design

+ high reliability

+ high efficiency

+ low costs

- amount of power semiconductors

- reduced output voltage

- no energy storage

- control afford

- new technology

Figure 3: Pros and cons of the matrix module

Bi-directional switchesThe central part of the power stage of amatrix converter is a bi-directional switch.Although universities already have proven,

that such a device can be implemented inone silicon die, no such device is availableup to date. Therefore a bi-directional

switch needs to be build up with devicesthat are commercially available. Based oncommon IGBTs and fast diodes there are

three different layouts, the bridge circuit,the common emitter and the commoncollector layout. The bridge circuit as it canbe seen in figure 4 has the lowest number

of switching devices. But with fivesemiconductors of which three in a roware building one conducting path the total

number of silicon dies is high. Anotherdisadvantage is that each of the 9 bi-

directional switches that are needed for amatrix converter has its own emitter

potential. Having only one switchingdevice per bi-directional switch it is not

possible to use four step commutation as itwill be described in the next paragraph.

Figure 4: Bi-directional switch as bridgecircuit

The common emitter and the commoncollector circuit are two variations of thesame principle. In both cases the circuit isbuild up with two IGBTs and two diodes.

As figure 5 shows the main difference isthat in the common emitter configurationthe emitters of the two IGBTs are tiedtogether while in the common collectorconfiguration the collectors are connected.

common emmiter circuit

common collector circuit

Figure 5: Common Emitter/Collector circuit

The advantages of both of these twocircuits are the low number of silicon diesin total and in each current path. Incontrast to the bridge configuration it is

also possible to operate the circuit in afour step commutation mode. Thedifference of the common collector and the

common emitter circuit is the possibility toconnect auxiliary emitters and collectors.In voltage source inverters the auxiliary

collectors are used to sense the voltageacross a device for overvoltage protection.

To connect the collector of a commoncollector circuit an additional connection


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point must be implemented. For a powerstage this would mean to have further nine

independent potentials on top of the sixpotentials of the three input and threeoutput lines. Having this problem in mindovervoltage protection strategies for matrixconverters which are different from thoseused for voltage source inverters havebeen developed. These protection

strategies do not need a connection tocollector potential of the common collectorcircuit. Therefore a power stage of a

matrix converter using common collectorcircuits for the bi-directional switches canbe build up with only 6 independent levels

of potential. In contrary to this a powerstage based on common emitter circuits

always needs the additional nineindependent potentials of the common

emitters. This is critical not only in terms ofisolation distance between suchindependent potentials, but also because

for the gate drive unit of IGBTs an isolatedvoltage source is needed for each emitterpotential. In case of common collector

circuits this adds up to six, a commonemitter based power stage would neednine of these. All in all the advantages ofcommon collector circuit based matrix-

converter power stages make thisconfiguration a preferable solution.

Four step commutationTo describe four step commutation for amatrix converter a circuit with two input

and one output line is drawn in figure 6.

U

IS1

S3

S2

S4

Ph R

Ph S

Figure 6: Commutation circuit

For operation of this set up two major rules

can be formulated. First it is not allowed atanytime to disconnect the output current.Secondly a short circuit between input

lines has to be avoided at any time. To

obey these rules the four switches have tobe turned on and off in an order that is

subject to direction of input voltage andoutput current as well as which bi-

directional is conducting before and afterthe commutation. For the commutationcircuit shown in figure 6 this means thatcommutation can be separated in eightdifferent cases (figure 7).

Cases C1 C2 C3 C4 C5 C6 C7 C8

U > 0 x x x x

I > 0 x x x x

Ph R to PH S x x x x

Figure 7: Cases of Commutation

In cases C1;C4;C6 and C7 the actualcommutation is driven by a turn off of a

switch. This is called forced commutation.Commutation in the other cases is due toturn on of one switch. It is called naturalcommutation. Switching sequences for alleight cases can be seen in figure 8.

Case 1 Case 2

IGBT 1 x IGBT 1 x

IGBT 2 x x x IGBT 2 x x x

IGBT 3 x IGBT 3 x


Case 4 Case 3


IGBT 2 x IGBT 2 x


IGBT 4 x IGBT 4 x

Case 6 Case 5

IGBT 1 x IGBT 1 x


IGBT 3 x IGBT 3 x


Case 7 Case 8


IGBT 2 x IGBT 2 x


IGBT 4 x IGBT 4 x

Forced Natural

Figure 8: Commutation sequences

As an example for forced commutation theswitching sequence of C1 will bedescribed now. Before commutation bothIGBTs of the bi-directional switch in phaseR are turned on. The current flows fromphase R to the output. In a first step IGBT

1 is turned off. Then IGBT4 is turned on.Due to the positive voltage across the


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input phases, the current stays in phase R.As soon as IGBT 2 is turned off, the

current is forced to commutate to phase S.In a last step IGBT 3 is turned on. Now thebi-directional switch in phase S isconducting while the bi-directional switchin phase R is turned off. As an example fornatural commutation case 2 is chosen.Starting point is the end of the

commutation case 1. Now in a first stepIGBT 3 is turned off. Then IGBT 2 isturned on and the current commutates

from phase S to phase R. As soon as thecurrent has commutated, IGBT 4 is turnedoff. The sequence is finished by turning on

IGBT1. The advantage of four stepcommutation is, that during commutation

neither high currents due to a short circuitbetween the input phases nor high voltage

overshoots due to disconnecting the loadcurrent can occur.

Implementation in a moduleTo implement a power stage of a matrixconverter in a module all 18 diodes and 18

IGBTs must be connected in such a waythat they build 9 bi-directional switches ofthe common collector type. The matrixstructure should be realised internally, so

that the 24 necessary externalconnections can be grouped into 6potentials. Further a low inductive point-

symmetric structure with equivalent inputand output behaviour would be ofadvantage. To visualise the problem

figure 9 shows an early attempt to realisea power stage of a matrix converter.

Figure 9: Power stage of a matrix converter

While emitters and gates of the input are

already sorted, emitters and gates of theoutput are still spread over the wholewidth. To get a symmetric module, the

gate and emitter connections of the output

would need to be sorted. With a bus barstructure running along the middle of the

module a symmetric module can berealised in a EconoPACK 3 sized module

for a 7,5kW matrix converter (figure 10).

Figure 10: Layout of the Matrixmodule

Using a standard package and with IGBT3

and EmCon HE the most advanced IGBT

and diode technologies EconoMACmodule as it is presented here, is a cost

effective solution with a high grade ofpower integration. Being based onEconoPACK technology all production pro-

cesses and reliability data of EconoMACcan be adapted from EconoPACK line.

Converter design based on EconoMACAs matrix converters will have to competewith converter solutions that are commonlyavailable, it is clear that they have to use

most recent production technologies.Modules being used in low and mediumpower converters usually get soldered to a

PCB and screwed on to a heat sink.EconoMAC has been designed to enablea flow through design. As can berecognised in figure 11 it is possible toentangle all connections easily on a twolayer PCB.

R S T

U V W

1

2

4

3

5

6

EW

G W1

G W2

G W3

Figure 11: PCB design

Three gates belong to each of six emitter

potentials. Every gate needs its own gateunit, but isolated power supplies are only


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needed for each emitter potential.Therefore it is reasonable to place the

three gates next to their emitter. Theemitter itself is split upon two pins. One isthe power terminal the other one is theauxiliary connection for the gate driveunits.

Test results

To verify the design of EconoMAC,Siemens A&D in co-operation with eupechas build up a laboratory prototype of a

matrix converter. This converter can beseen in figure 12.

Figure 12: Laboratory Prototype

The picture shows the power stage of a7.5kW converter. On the right side is theinput line filter. The module can be spotted

between the PCB and the heat sink on theleft side. To get a better impression of itssize a folding rule is put in front of the

matrix converter. The following test resultshave been measured with this prototype inthe laboratory of Siemens A&D in

Erlangen (figure 13). The upper graphshows the input current in blue as well asthe input voltage in red. The lower graphshows the output voltage in red and the

output current in blue. These results reflectthe same good behaviour as it could have

been expected from the simulations of amatrix converter shown in figure 2.

Figure 13: Measurement results

Conclusion

In this paper a new IGBT module formatrix converters called EconoMAC ispresented. First the matrix converter acompact efficient 4 quadrant directconverter with its long lifetime reliabilityand good zero speed behaviour isdescribed. Special focus has been put on

selection of the necessary bi-directionalswitch. For realisation a common collector

circuit is discussed in detail. Thisconfiguration with its low number ofdevices and external connections can beoperated in an four step commutation

mode. Four step commutation as it is ofadvantage is shown for common collectorcircuits. Based on common collector bi-directional switches the implementation of

a power stage for a 7,5kW matrixconverter is described. A result of theseideas is EconoMAC a module that is

designed to build up a matrix converter in

a flow through design with it. Beside thetheoretical layout of a matrix converter

based on EconoMAC a laboratoryprototype and first test results are shown.

Literature:

A Matrix converter switching controller for low losses operation without snubbersR. Cittadini, J-J- Huselstein, C. Glaize, EPE 97, pp4.199-4.203

New control strategy for matrix converter, CH2721-9/89/0000-0360 IEEE, J. Oyama,T. Higuchi, E. Yamadea, T. Koga, T. Lipo, 1989

Semi Natural two steps commutation strategy for matrix convertrs, M. Ziegler,W. Hofmann, PESC 98, pp 727-731


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A Matrix converter without Diode clamped Over-voltage Protection, J. Mahlein,

M. Braun, 3rd IPEMC; 2000; Beijing; China

A Matrix Converter with Space Vector Control Enabling Overmodulation, J. Mahlein,O. Simon, M. Braun, EPE 99; Lausanne; Switzerland; 1999

Control and Protection Strategies for Matrix Converters, O. Simon, M. Bruckmann,SPS/IPC/DRIVES; Nrnberg; Germany; 2000

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Ed Pcim01 Economac