U.S. patent application number 13/791906 was filed with the patent office on 2014-09-11 for module and assembly with dual dc-links for three-level npc applications.
This patent application is currently assigned to IXYS Corporation. The applicant listed for this patent is Andreas Laschek-Enders. Invention is credited to Andreas Laschek-Enders.
Application Number | 20140252410 13/791906 |
Document ID | / |
Family ID | 51486755 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140252410 |
Kind Code |
A1 |
Laschek-Enders; Andreas |
September 11, 2014 |
Module and Assembly with Dual DC-Links for Three-Level NPC
Applications
Abstract
A power semiconductor module has four power terminals. An IGBT
has a collector connected to the first power terminal and an
emitter coupled to the third power terminal. An anti-parallel diode
is coupled in parallel with the IGBT. A DC-link is connected
between the second and fourth power terminals. The DC-link may
involve two diodes and two IGBTs, where the IGBTs are connected in
a common collector configuration. The first and second power
terminals are disposed in a first line along one side of the
module, and the third and fourth power terminals are disposed in a
second line along the opposite side of the module. Two identical
instances of the module can be interconnected together to form a
three-level NPC phase leg having low stray inductances, where the
phase leg has two parallel DC-links.
Inventors: |
Laschek-Enders; Andreas;
(Bensheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Laschek-Enders; Andreas |
Bensheim |
|
DE |
|
|
Assignee: |
IXYS Corporation
Milpitas
CA
|
Family ID: |
51486755 |
Appl. No.: |
13/791906 |
Filed: |
March 8, 2013 |
Current U.S.
Class: |
257/141 ;
438/127 |
Current CPC
Class: |
H01L 21/56 20130101;
H02M 7/487 20130101; H01L 27/0647 20130101; H01L 29/7393 20130101;
H01L 2924/13055 20130101; H01L 25/0652 20130101; H01L 2224/48472
20130101; H01L 2224/49111 20130101; H01L 2924/19107 20130101; H01L
25/072 20130101; H01L 2224/48472 20130101; H01L 2224/45015
20130101; H01L 2224/04042 20130101; H01L 2224/45015 20130101; H01L
2924/1305 20130101; H01L 2224/48227 20130101; H01L 2924/00
20130101; H01L 2924/2076 20130101; H01L 2924/00 20130101; H01L
2924/00 20130101; H01L 2924/00014 20130101; H01L 24/06 20130101;
H01L 2924/1305 20130101; H01L 24/45 20130101; H01L 2224/48139
20130101; H01L 2224/45124 20130101; H01L 24/49 20130101; H01L
2224/0603 20130101; H01L 2224/48227 20130101; H01L 2924/13055
20130101; H01L 24/48 20130101; H01L 2224/45124 20130101; H02M 7/003
20130101 |
Class at
Publication: |
257/141 ;
438/127 |
International
Class: |
H01L 29/739 20060101
H01L029/739; H01L 23/00 20060101 H01L023/00 |
Claims
1. An assembly comprising: (a) a first power semiconductor device
module comprising: a first housing having a first enclosure
portion; a first power terminal having a fastening hole; a second
power terminal having a fastening hole, wherein the first and
second power terminals are disposed along a first line; a third
power terminal having a fastening hole; a fourth power terminal
having a fastening hole, wherein the first and second power
terminals are disposed along a second line, wherein the second line
is parallel to the first line; a first (Insulated Gate Bipolar
Transistor) IGBT having a collector coupled to the first power
terminal and having an emitter coupled to the third power terminal;
a first recovery diode having an anode coupled to the emitter of
the first IGBT and having a cathode coupled to the collector of the
first IGBT; a second IGBT having a collector and having an emitter
coupled to the fourth power terminal; a second recovery diode
having a cathode coupled to the collector of the second IGBT and
having an anode coupled to the emitter of the second IGBT; a third
IGBT having a collector coupled to the collector of the second IGBT
and having an emitter coupled to the second power terminal; a third
recovery diode having an anode coupled to the emitter of the third
IGBT and having a cathode coupled to the collector of the third
IGBT; and a first substrate disposed in the first enclosure
portion, wherein at least one of the first, second and third IGBTs
is disposed on the first substrate, wherein the first, second and
third IGBTs are disposed in the first enclosure portion, and
wherein the first, second and third recovery diodes are disposed in
the first enclosure portion; (b) a second power semiconductor
device module comprising: a second housing having a second
enclosure portion; a fifth power terminal having a fastening hole;
a sixth power terminal having a fastening hole, wherein the fifth
and sixth power terminals are disposed along the second line; a
seventh power terminal having a fastening hole; an eighth power
terminal having a fastening hole, wherein the seventh and eighth
power terminals are disposed along the first line; a fourth IGBT
having an emitter coupled to the seventh power terminal and having
a collector coupled to the fifth power terminal; a fourth recovery
diode having an anode coupled to the emitter of the fourth IGBT and
having a cathode coupled to the collector of the fourth IGBT; a
fifth IGBT having a collector and having an emitter coupled to the
eighth power terminal; a fifth recovery diode having an anode
coupled to the emitter of the fifth IGBT and having a cathode
coupled to the collector of the fifth IGBT; a sixth IGBT having a
collector coupled to the collector of the fifth IGBT and having an
emitter coupled to the sixth power terminal; a sixth recovery diode
having an anode coupled to the emitter of the sixth IGBT and having
a cathode coupled to the collector of the sixth IGBT; and a second
substrate disposed in the second enclosure portion, wherein at
least one of the fourth, fifth and sixth IGBTs is disposed on the
second substrate, wherein the fourth, fifth, and sixth transistors
are disclosed in the second enclosure portion, and wherein the
fourth, fifth and sixth recovery diodes are disposed in the second
enclosure portion; (c) a first conductive member coupled to the
second power terminal of the first power semiconductor device
module and to the eighth power terminal of the second power
semiconductor device; and (d) a second conductive member coupled to
the third and fourth power terminals of the first power
semiconductor device module and to the fifth and sixth power
terminals of the second power semiconductor device module.
2. The assembly of claim 1, wherein the first a third power
terminals are disposed along a third line, wherein the second and
fourth power terminals are disposed along a fourth line, wherein
the third line is parallel to the fourth line, and wherein the
second line is perpendicular to the first line.
3. The assembly of claim 1, wherein the first and second power
semiconductor device modules are of substantially identical
construction.
4. The assembly of claim 1, wherein the first power semiconductor
device has no more than four power terminals that have fastening
holes, and wherein the second power semiconductor device has no
more than four power terminals that have fastening holes.
5. The assembly of claim 1, wherein a current passing from the
first power terminal to the third power terminal passes through one
and only one IGBT, and wherein a current passing from the third
power terminal to the first power terminal passes through one and
only one diode.
6. The assembly of claim 1, wherein a current passing from the
second power terminal to the fourth power terminal passes through
one and only one diode and one and only one IGBT, and wherein a
current passing from the fourth power terminal to the second power
terminal passes through one and only one diode and one and only one
IGBT.
7. The assembly of claim 1, wherein a first conductive connection
is coupled to the emitter of the first IGBT, wherein a second
conductive connection makes electrical connection to a gate of the
first IGBT, and wherein the first and second conductive connections
extends for a distance in a twisted fashion with respect to one
another.
8. The assembly of claim 7, wherein the first conductive connection
bridges over the second conductive connection.
9. A power semiconductor device module comprising: a housing having
an enclosure portion; a first power terminal having a fastening
hole; a second power terminal having a fastening hole, wherein the
first and second power terminals are disposed along a first line; a
third power terminal having a fastening hole; a fourth power
terminal having a fastening hole, wherein the third and fourth
power terminals are disposed along a second line, wherein the
second line is parallel to the first line; a first (Insulated Gate
Bipolar Transistor) IGBT having a collector coupled to the first
power terminal and having an emitter coupled to the third power
terminal; a first recovery diode having an anode coupled to the
emitter of the first IGBT and having a cathode coupled to the
collector of the first IGBT; a second IGBT having a collector and
having an emitter coupled to the fourth power terminal; a second
recovery diode having a cathode coupled to the collector of the
second IGBT and having an anode coupled to the emitter of the
second IGBT; a third IGBT having a collector coupled to the
collector of the second IGBT and having an emitter coupled to the
second power terminal; a third recovery diode having an anode
coupled to the emitter of the third IGBT and having a cathode
coupled to the collector of the third IGBT; and a substrate
disposed in the enclosure portion, wherein at least one of the
first, second and third IGBTs is disposed on the substrate, wherein
the first, second and third IGBTs are disposed in the enclosure
portion, and wherein the first, second and third recovery diodes
are disposed in the enclosure portion.
10. The power semiconductor device module of claim 9, wherein a
current passing from the first power terminal to the third power
terminal passes through at most one transistor, wherein a current
passing from the third power terminal to the first power terminal
passes through at most one diode and passes through no transistor,
wherein a current passing from the second power terminal to the
fourth power terminal passes through at most one transistor and at
most one diode, and wherein a current passing from the fourth power
terminal to the second power terminal passes through at most one
transistor and at most one diode.
11. A circuit comprising: a positive DC voltage conductor; a
negative DC voltage conductor; a zero voltage DC voltage conductor;
an output conductor; a first (Insulated Gate Bipolar Transistor)
IGBT having a collector coupled to the positive DC voltage
conductor and having an emitter coupled to the output conductor; a
first recovery diode having an anode coupled to the emitter of the
first IGBT and having a cathode coupled to the collector of the
first IGBT; a first DC-link coupled between the zero voltage DC
conductor and the output conductor, wherein the first DC-link
comprises a first pair of IGBTs coupled together in a common
collector configuration; a second DC-link coupled between the zero
voltage DC conductor and the output conductor, wherein the second
DC-link comprises a second pair of IGBTs coupled together in a
common collector configuration; a second IGBT having a collector
coupled to the output conductor and having an emitter coupled to
the negative DC voltage conductor; and a second recovery diode
having an anode coupled to the emitter of the second IGBT and
having a cathode coupled to the collector of the second IGBT.
12. The circuit of claim 11, wherein the first IGBT is coupled to
the output conductor via a first module terminal, wherein the first
DC-link is coupled to the output conductor via a second module
terminal, wherein the second DC-link is coupled to the output
conductor via a third module terminal, and wherein the second IGBT
is coupled to the output conductor via a fourth module
terminal.
13. The circuit of claim 12, wherein the output conductor is a bus
bar.
14. The circuit of claim 13, wherein the first, second, third and
fourth module terminals are disposed in a line.
15. The circuit of claim 11, wherein the circuit comprises two
substantially identical power modules, wherein the first IGBT and
the first DC-link are parts of the one of the power modules, and
wherein the second IGBT and the second DC-link are parts of the
other of the power modules.
16. A method of manufacture, comprising: coupling a collector of a
first Insulated Gate Bipolar Transistor (IGBT) to a first power
terminal; coupling an emitter of the first IGBT to a third power
terminal; coupling an anode of a first diode to the emitter of the
first IGBT; coupling a cathode of the first diode to the collector
of the first IGBT; providing a DC-link between a second power
terminal and a fourth power terminal, wherein the DC-link comprises
the first IGBT and a second IGBT coupled together in a common
collector configuration, wherein an emitter of the second IGBT is
coupled to the fourth power terminal, wherein the first and second
power terminals are disposed along a first line, wherein the first
and second power terminals are disposed along a second line,
wherein the second line is parallel to the first line; and wherein
each of the first, second, third and fourth power terminals has a
fastening hole; coupling an anode of a second diode to the emitter
of the second IGBT; coupling a cathode of the second diode to a
collector of the second IGBT; coupling a collector of a third IGBT
to the collector of the second IGBT; coupling an emitter of the
third IGBT to the second power terminal; coupling an anode of a
third diode to the emitter of the third IGBT; coupling a cathode of
the third diode to a collector of the third IGBT; mounting the
first, second and third IGBTs on a substrate; and encapsulating the
first, second and third IGBTs, the first second and third diodes,
and the DC-link in a first power semiconductor module package,
wherein the first, second, third and fourth power terminals are
terminals of the first power semiconductor module package, and
wherein the substrate is a part of the first power semiconductor
module package.
17-19. (canceled)
20. The method of claim 16, wherein the first power semiconductor
module package is substantially identical to a second power
semiconductor module package, wherein the second power
semiconductor module package has a first power terminal, a second
power terminal, a third power terminal and a fourth power terminal,
the method further comprising: coupling the third and fourth power
terminals of the first power semiconductor module package to the
first and second power terminals of the second power semiconductor
module package; and coupling the second power terminal of the first
power semiconductor module package to the fourth power terminal of
the second power semiconductor module package.
Description
TECHNICAL FIELD
[0001] The described embodiments relate to power semiconductor
modules usable in three-level NPC phase leg applications.
BACKGROUND INFORMATION
[0002] FIG. 1 (Prior Art) is a diagram of a T-type three-level
Neutral-Point-Clamped (NPC) phase leg module 1. Such a module sees
use in applications including solar inverter, motor drive and UPS
applications. The module is referred to as a "three-level" module
because the module couples an output node AC to a selected one of
three DC voltage power terminals. As compared to conventional
two-level topologies, a T-type three-level topology may provide
advantages in a given application. For example, a T-type
three-level topology may allow transistors within the module to
have lower breakdown voltages than they would otherwise be required
to have were a two-level topology used, with the added advantages
of better conduction and switching performance resulting in lower
losses. Also a T-type three-level topology may allow a motor to be
driven while emitting a reduced amount of electromagnetic energy.
When the module is performing its switching function, the amount of
emitted electromagnetic radiation generally must be below an
allowable limit. The three-level topology may reduce the cost of
filtering necessary to reduce emitted electromagnetic energy so
that it will be below the allowable limit.
[0003] The constituent transistors, diodes and other components of
a T-type three-level NPC phase leg circuit can be provided in
different types of packages. In a low power application, a T-type
three-level NPC phase leg circuit may be realized in one power
module package. In a higher power application, a T-type three-level
NPC phase leg circuit may have to be realized in multiple module
packages due to heat dissipation limitations of a single module
package and due to a lack of mounting area because of the required
die size for the high current.
[0004] FIG. 1 is a top-down diagram of a T-type three-level NPC
phase leg circuit that is realized in a single power module
package. The module 1 includes an injected molded plastic housing 2
that is formed around a metal base plate. Four power terminals 3-6
extends outward from the housing 2 as illustrated. The power
terminals are standard screw terminals for making electrical
connections of bus bars or wires. The bottom side of the module can
be attached to a heatsink or other body via screws (not shown). The
screws are made to extend through corresponding mounting holes 7-10
in mounting flaps of the housing so that the screw heads hold the
bottom side of the module (the metal base plate) down onto the
heatsink. In addition to the four power terminals, there are
smaller upwardly extending signaling/control terminals. The smaller
upwardly extending signaling/control terminals are disposed in two
rows. These upwardly extending signaling/control terminals extend
upward out of the upper surface of the plastic housing. One of
these signaling/control terminals of the upper row is identified
with reference numeral 11.
[0005] FIG. 2 (Prior Art) is a circuit diagram of the T-type
three-level NPC phase leg circuit of module 1 of FIG. 1. The
circuit includes four Insulated Gate Bipolar Transistors (IGBT)
12-15 and four fast recovery diodes 16-19. IGBTs 14, 15 and diodes
18 and 19 are sometimes referred to as the DC-link. A positive DC
voltage is generally supplied onto the P power terminal 3. A
negative DC voltage is generally supplied onto the N power terminal
4. Ground potential (zero volts) is generally supplied onto the 0
neutral power terminal 6. In operation, current can be conducted
from the P power terminal 3 to the output AC output terminal 5 by
making IGBT 12 conductive. Current can be drawn from the AC output
terminal to the N power terminal 4 by making IGBT 13 conductive.
The AC output terminal 5 can be coupled to ground potential by
making the DC-link conductive. The average current supplied out of
the module via the AC output terminal to a load, or received onto
the module via the AC output terminal from the load, is controlled
by pulse-width modulating the IGBT gate signals of the various
IGBTs of the module.
[0006] There are many considerations involved in the design of
three-level NPC phase leg circuits, including the reduction of
stray inductances. For additional background information, see, for
example: 1) A New Neutral-Point-Clamps PWM Inverter, by Akira Nabae
et al., IEEE Transactions on Industry Applications, Vol. IA-17, No.
5, pages 518-523 (1981); 2) Comparison of the Chip Area Usage of
2-Level and 3-Level Voltage Source Converter Technologies, by Mario
Schweizer et al., Proceedings of the 36.sup.th Annual IEEE
Industrial Electronics Society Conference, pages 391-396 (2010); 3)
IGBT Power Modules Utilizing New 650VV IGBT and Emitter-Controlled
Diode Chips For Three Level Converter, by Zhang Xi et al.,
Proceedings of the PCIM Europe 2009 Conference, pages 117-122
(2009); 4) Advantages of NPC Inverter Topologies With Power
Modules, by Michael Frisch et al., www.Vincotech.com, 3 pages
(2009); and 5) Power Module With Additional Low Inductive Current
Path, Michael Frisch et al., 2010 Power Electronics Europe, Issue
7, pages 22-27 (2010).
SUMMARY
[0007] A power semiconductor module has four power terminals. Each
power terminal has a fastening hole. The fastening hole may have
threads or a nut to engage the threads of a screw. An injection
molded plastic housing of the module has an enclosure portion and
it extends around a metal base plate. The metal base plate forms
the bottom surface of the enclosure. An IGBT has a collector
connected to the first power terminal and an emitter coupled to the
third power terminal. A fast recovery diode is coupled
anti-parallel with the IGBT such that the diode anode is coupled to
the emitter and the diode cathode is coupled to the collector. A
DC-link is connected between the second and fourth power terminals.
The DC-link may involve two diodes and two IGBTs, where the IGBTs
are connected in a common collector or a common emitter
configuration. Each IGBT of the DC-link has its own anti-parallel
fast recovery diode. The IGBT, the diode, and the DC-link are
disposed on a substrate such, for example, as a Direct Bonded
Copper (DBC) or Direct Bonded Aluminum (DBA) ceramic substrate. The
resulting substrate assembly is encapsulated in the enclosure
portion of the housing of the module so that the bottom surface of
the DBA substrate is in good thermal contact with the upper surface
of the metal base plate of the enclosure.
[0008] In one example, the first and second power terminals are
disposed in a first line along one side of the module. The third
and fourth power terminals are disposed in a second line along the
opposite side of the module. The first and second lines extend
parallel to one another. The first power terminal and the third
power terminal are disposed along a third line, and the third line
extends perpendicularly to the first line. Axes of the four
fastening holes of the four power terminals define a rectangle.
[0009] In one application, by turning a first such module
one-hundred eighty degrees with respect to a second identical
module, and by connecting the two modules together with metal bus
bars, two identical instances of the module are interconnected to
form a three-level NPC phase leg that exhibits low stray
inductances. The three-level NPC phase leg involves two DC-links
that are connected together in parallel. By splitting the circuitry
of a T-type three-level NPC circuit into two identical halves, each
of which includes a separate DC-link, and by providing the AC power
terminal of the DC-link (the fourth power terminal) close to the AC
power terminal of the main IGBT (the third power terminal) in each
module, the area enclosed by main conduction and commutation
current loops is reduced as compared to other multi-module
realizations of the T-type three-level NPC circuit. Due to the
smaller current loops, stray inductances are reduced as compared to
stray inductances in a multi-module realization that provides the
DC-link and the main IGBTs in different modules. The use of two
identical modules to realize the T-type three-level NPC phase leg
circuit, as compared to realizing the T-type three-level NPC phase
leg circuit using different types of modules, is advantageous in
that fewer module types may be manufactured and stocked. Higher
manufacturing quantities of one module type helps reduce module
unit manufacturing cost for overall the phase leg circuit. In
addition, the novel module may be used in power circuits other than
in a T-type three-level NPC phase leg. Due to the use of the two
parallel-connected DC-links in the three-level NPC circuit, power
dissipation of the DC-link is spread over two modules as opposed to
all be located in one module. Snubber circuits are therefore not
necessary in some applications to spread power losses, whereas if a
single DC-link were used in a standard module package then such
snubber circuits would typically be required.
[0010] Further details and embodiments and techniques are described
in the detailed description below. This summary does not purport to
define the invention. The invention is defined by the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The accompanying drawings, where like numerals indicate like
components, illustrate embodiments of the invention.
[0012] FIG. 1 (Prior Art) is a top-down diagram of a T-type NPC
power module.
[0013] FIG. 2 (Prior Art) is a circuit diagram of the circuit
within the T-type NPC power module of FIG. 1.
[0014] FIG. 3 is a top-down diagram of a power module 20 in
accordance with one novel aspect.
[0015] FIG. 4 is a circuit diagram of the circuit within the power
module 20 of FIG. 3.
[0016] FIG. 5 is a top-down diagram of the power module 20 of FIG.
3 with its cap removed, and not showing bond wires or semiconductor
topside connections
[0017] FIG. 6 is a top-down diagram of one of the two DBC substrate
(which are not identical) assemblies in the power module 20 of FIG.
3.
[0018] FIG. 7 is a circuit diagram of a three-level NPC phase leg
circuit that comprises two instances of the power module of FIG.
3.
[0019] FIG. 8 is a top-down diagram of a physical implementation of
the circuit of FIG. 7.
[0020] FIG. 9 is a circuit diagram of a system in which three
instances of the assembly of FIG. 8 are used to drive a motor.
[0021] FIG. 10 is a waveform diagram that illustrates an operation
of one of the phase legs of the system of FIG. 9.
[0022] FIG. 11 is a table that illustrates current flow and IGBT
operation in one of the phase legs of the system of FIG. 9.
[0023] FIGS. 12A-12D are diagrams that illustrate how a phase leg
of the system of FIG. 9 operates during time period T0-T1.
[0024] FIGS. 13A-13D are diagrams that illustrate how a phase leg
of the system of FIG. 9 operates during time period T1-T2.
[0025] FIGS. 14A-14D are diagrams that illustrate how a phase leg
of the system of FIG. 9 operates during time period T2-T3.
[0026] FIGS. 15A-15D are diagrams that illustrate how a phase leg
of the system of FIG. 9 operates during time period T3-T4 is
[0027] FIG. 16 is a flowchart of a method 200 in accordance with
one novel aspect.
DETAILED DESCRIPTION
[0028] Reference will now be made in detail to embodiments of the
invention, examples of which are illustrated in the accompanying
drawings.
[0029] FIG. 3 is a top-down diagram of a power semiconductor NPC
module 20. The module 20 includes an injected molded plastic
housing 21 having a central tray-shaped enclosure portion and four
laterally-extending tab-like extension portions. The plastic
housing 21 extends around a metal base plate that forms the bottom
of the central enclosure portion. A cap or lid is provided to cap
the central enclosure portion. The cap provides mechanical
strength. Four power terminals 22-25 extends outward from the
housing 21 as illustrated. The power terminals are standard screw
terminals for attachment to electrical bus bars or wires. Each
power terminal has a threaded fastening hole or a nut for engaging
the threads of a screw. The housing 21 can be attached to a
heatsink via screws (not shown) so that the metal base plate is in
good thermal contact with the heatsink. The screws are made to
extend through corresponding mounting holes 26-29 in a mounting
flap of the housing so that the screws head hold the module 20 down
onto the heatsink. In the particular embodiment illustrated, the
module has four and no more than four power terminals. In addition
to the four power terminals, there are smaller upwardly extending
signaling/control terminals disposed in two rows. These smaller
upwardly extending signaling/control terminals extend upward out of
the upper surface of the plastic housing. One of these
signaling/control terminals of the upper row is identified with
reference numeral 30.
[0030] The first P1 power terminal 22 and the second P2 power
terminal 23 are disposed along a first line 31. The third P3 power
terminal 24 and the fourth P4 power terminal P4 are disposed along
a second line 32. The first P1 power terminal 21 and the third P3
power terminal 24 are disposed along a third line 33. The second P2
power terminal 23 and the fourth P4 power terminal 25 are disposed
along a fourth line 34. Lines 31 and 32 are parallel to one another
and lines 33 and 34 are parallel to one another. Line 33 is
perpendicular to lines 31 and 32 as illustrated. The axes of the
fastening holes of the four power terminal define the corners of a
rectangle.
FIG. 4 is a circuit diagram of the circuit within module 20. The
circuit includes three IGBTs T1-T3 and three fast recovery
anti-parallel diodes D1-D3. The anode of diode D1 is connected to
the emitter of IGBT T1 and the cathode of diode D1 is connected to
the collector of IGBT T1. The collector of IGBT T1 is connected to
the P1 power terminal 22. The emitter of IGBT T1 is connected to
the P3 power terminal 24. IGBTs T2 and T3 and diodes D2 and D3 form
a DC-link. The DC-link is coupled between the P2 power terminal 23
and the P4 power terminal 25. The common collector connection of
IGBTs T2 and T3 makes it possible to attach IGBTs, via their
backside collectors, onto a single conductive pad or substrate.
Although the each of the IGBTs T1, T2 and T3 is illustrated as a
single IGBT symbol, each of the IGBTs is realized as a plurality of
parallel-connected IGBT dice. Similarly, although each of the
diodes D1, D2 and D3 is illustrated as a single diode symbol, each
of the diodes D1, D2 and D3 is realized as a plurality of
parallel-connected diode dice. The IGBT dice and the diode dice are
mounted onto one or more substrates, and the substrates are
disposed in the enclosure portion of the module so that the bottom
of the substrates are in good thermal contact with the metal base
plate of the enclosure. The substrates may, for example, be DBC
(Direct Bonded Copper) or DBA (Direct Bonded Aluminum) substrates.
There are also module constructions that do not have a metal base
plates but rather have DBC or DBA for thermal conduction out of the
package.
[0031] Any current flow between power terminals P1 and P3 is
substantially parallel to any current flow between power terminals
P2 and P3. In addition, the distance of separation 81 between power
terminals P3 and P4 and between power terminal P1 and P2 is the
smallest separation permitted between power terminals for the
design and voltage conditions of the application. There are no
other terminals between P3 and P4. There are no other terminals
between P1 and P2.
[0032] FIG. 5 is a more detailed top-down diagram of module 20 with
its enclosure cap removed so that the circuitry within the
enclosure portion can be seen shown without bond wires. Reference
numeral 82 identifies the metal base plate that forms the heat
conductive bottom of the enclosure. In the diagram, heavy loop 35
encircles the circuit components that together comprise IGBT T1 and
diode D1. IGBT T1 is realized as four parallel-connected IGBT dice.
Diode D1 is realized as four parallel-connected diode dice. Heavy
loop 36 encircles the circuit components that together comprise
IGBT T2 and diode D2. IGBT T2 is realized as four
parallel-connected IGBT dice. Diode D2 is realized as eight
parallel-connected diode dice. Heavy loop 37 encircles the circuit
components that together comprise IGBT T3 and diode D3. IGBT T3 is
realized as four parallel-connected IGBT dice. Diode D3 is realized
as eight parallel-connected diode dice. The components are mounted
(for example, by soft soldering) as illustrated on two DBC
substrates. Each of the two DBC substrates appears as a square when
viewed from the top-down perspective of FIG. 5. The two squares are
disposed side-by-side when viewed from the perspective of FIG. 5.
The two DBCs are interconnected via bond wires or equivalent
connecting techniques. Bond wires also connect the DBC assemblies
to the power terminals and to various ones of the signaling/control
terminals. The bottom surfaces of the two DBCs are in good physical
and thermal contact with the upper surface of the metal base plate
that forms the bottom of the enclosure.
[0033] FIG. 6 is a top-down diagram of the leftmost DBC assembly 38
of FIG. 5. The rightmost DBC assembly is connected in a fashion
that mirrors the connections of the leftmost DBC. FIG. 6 is
simplified, and is not an exact diagram of the DBC assembly 38, but
the drawing does illustrate the major features of interest. As
shown in FIG. 6, DBC assembly 38 includes the leftmost DBC
substrate 39, six IGBT dice 40-45, and ten diode dice 46-55.
Patterned areas 56-66 of a copper layer are disposed on the
square-shaped insulating ceramic layer 67. A first conductive
connection includes conductive area 56, wire bond 68, conductive
area 58, wire bond 69, and other parts on the rightmost DBC (not
shown). A second conductive connection includes conductive area 57,
wire bond 70, conductive area 59, wire bond 71, and other parts on
the rightmost DBC (not shown). The wire bonds are lengths of
typically 300 up to 500 .mu.m diameter aluminum wire. The first
conductive connection is coupled to the emitters of IGBT dice 40
and 41, as well as to the emitters of the IGBT dice of the
rightmost DBC (not shown) that make up main IGBT T1. The second
conductive connection is coupled to the gates of IGBT dice 40 and
41, as well as to the gates of the IGBT dice of the rightmost DBC
that make up IGBT T1. These first and second conductive connections
extend horizontally across the module in the twisted fashion
illustrated. The first conductive connection bridges over the
second conductive connection at wire bonds 68 and 69. The second
conductive connection bridges over the first conductive connection
at wire bond 70 and 71. The twisting reduces line impedance in the
first and second conductive connections and reduces induced
voltages by the magnetic field of high currents paths. In a similar
way to the way the first and second conductive connections are
twisted, the conductive connections extending to the gates and
emitters of IGBT dice 42-45 are also twisted with respect to one
another as illustrated in FIG. 6.
[0034] Rather than the gates and emitters of the IGBT dice being
directly connected to the first and second conductive connections
(the twisted conductive connections), in some embodiments each gate
and emitter is connected via a separate surface mount resistor. For
example, reference numeral 80 identifies one such resistor die. The
bottom surface of resistor die 80 is in contact with the underlying
metal of area 56, whereas the top surface of the resistor die 80
makes contact with the wire bond that extends to the emitter of
IGBT die 40. The resistor dice dampen ground loop effects and
facilitate paralleling of power dice.
[0035] FIG. 7 is a circuit diagram of a T-type three-level NPC
phase leg circuit 72 that involves module 20 as well as a second
module 73 that is of identical construction to module 20. The P3
power terminal 24 of module 20 is coupled to the P4 power terminal
25 of module 20 and to the P1 power terminal 74 of module 73 and to
the P2 power terminal 75 of module 73. This common node is the
I.sub.OUT node of the circuit. The P2 power terminal 23 of module
20 is coupled to the P4 power terminal 77 of module 73. This common
node is a "0V" node of the circuit. A DC voltage source supplies a
positive DC voltage, for example +400V, onto the P1 power terminal
22 of module 20. A DC voltage source supplies ground potential
(zero volts relative to the positive DC voltage on terminal 22)
onto the "0V" node. A DC voltage source supplies a negative DC
voltage, for example -400V, onto the P3 power terminal 76 of module
73. Connections to the signaling/control terminals of the modules
20 and 73 are not shown.
[0036] FIG. 8 is a top-down diagram that shows the modules 20 and
73 of the circuit illustrated in FIG. 7. The I.sub.OUT output node
of the circuit of FIG. 7 is provided by a first T-shaped copper bus
bar 78. First bus bar 78 has holes that align with the fastening
holes in power terminals 24 and 25 of module 20 and with the
fastening holes in power terminals 74 and 75 of module 73. The "0V"
node of the circuit of FIG. 7 is provided by a second bus bar 79.
Second bus bar 79 has holes that align with the fastening holes in
power terminal 23 of module 20 and power terminal 77 of module
73.
[0037] FIG. 9 is a circuit diagram of a system 100 involving three
three-level NPC phase legs 101-103. The three phase legs drive an
electric motor 104. Each of the three phase legs 101-103 is an
instance of the assembly of FIG. 8, and is illustrated in
simplified form as having one DC-link, even though it is understood
the this DC-link is realized as two parallel-connected DC-links.
The assembly of FIG. 8 involving modules 20 and 73 and bus bars 78
and 79 is the upper phase leg 101 in FIG. 9. Phase leg 101 is
coupled to a first winding 105 of the motor. Phase leg 102 is
coupled to a second winding 106 of the motor. Phase leg 103 is
coupled to a third winding 107 of the motor. The P power terminals
the three phase leg assemblies 101-103 are all connected together
and to a common positive DC voltage (for example, +400V). The N
power terminals of the three phase leg assemblies 101-103 are all
connected together and to a common negative DC voltage (for
example, -400V). The 0 bus bars of the three phase leg assemblies
101-103 are all connected together and to a common ground (zero
volts). Although there may be six different bus bars in some
embodiments, in other embodiments the "0V" bus bars are merged into
a single "0V" bus bar that connects to all three phase legs.
Likewise, there may be a single P bus bar that connected to the P
power terminals of all three phase legs, and there may be a single
N bus bar that connects to the N power terminals of all three phase
legs. Control and driver circuitry (not shown) for driving the
transistors of the three phase legs is known in the art and is not
described here.
[0038] Although all of one T-type three-level NPC structure could
be implemented in a single module package, in high power
applications where thermal dissipation requirements are too great
for a standard module package an undesired special non-standard
module package would be required to house all the circuitry in a
manner that could adequately dissipate heat. In one novel aspect, a
small standard four power terminal module package (such as is shown
in top-down perspective in FIG. 3) is used, and the DC-link of the
overall T-type three-level NPC structure is split into two parts
and is spread between the two small standard module packages. Each
of the two parts of the DC-link has about half the power carrying
capability as compared to a comparable design having only one
DC-link. The IGBT and diode dice of the two parallel DC-link
circuits can be made with smaller and can employ less costly power
dice. As a result of this spread out dual DC-link circuitry, the
needed thermal dissipation is achieved while at the same time use
of a single standard module package is maintained. Manufacturing
volumes of that one standard module package device are increased
because all instances of the module package needed to realize the
overall T-type three-level NPC circuit are instances of the same
module part. This may have advantages in some manufacturing
environments.
[0039] By turning module 73 of FIG. 8 one-hundred eighty degrees
with respect to module 20, and by connecting the two modules
together with bus bars 78 and 79 as illustrated in FIG. 8, two
identical instances of the same module can be interconnected to
form a T-type three-level NPC phase leg. Half of the DC-link is
disposed in module 73 and the other half of the DC-link is disposed
in module 20. By splitting the circuitry of a T-type three-level
NPC circuit into two identical halves in this way, and by providing
the AC power terminal of the DC-link half (the fourth power
terminal of module 20) close to the AC power terminal of the main
IGBT (close to the third power terminal of module 20) in each
module, the area enclosed by main current and commutation current
loops is reduced as compared to other multi-module realizations of
T-type three-level NPC circuits. Note that the distance 81 between
power terminals P3 and P4, and between power terminals P1 and P2,
in FIG. 3 is the minimum separation allowed between power terminals
for the particular design and voltage considerations. Due to the
smaller current loops, stray inductance is reduced as compared to a
multi-module realization that provides the DC-link and the main
IGBTs in different modules. The use to two identical modules to
realize the three-level NPC circuit, as compared to realizing the
three-level NPC circuit using different types of modules, is
advantageous in that fewer module types need to be manufactured and
stocked. Higher manufacturing quantities helps reduce module unit
manufacturing cost for overall the T-type NPC phase leg. In
addition, the novel module may also see use in power circuits other
than in a T-type NPC phase leg. Due to the use of the two
parallel-connected DC-links in the three-level NPC circuit, power
dissipation is spread into two modules as opposed to all power
dissipation occurring in one module. Snubber circuits are therefore
not necessary in some applications to spread power losses, whereas
if a single DC-link were used in a standard module package then
such snubber circuits would typically be required.
[0040] FIG. 10 is a waveform diagram that illustrates operation of
the system 100 of FIG. 9 in supplying a current waveform I.sub.OUT
108 out of the first phase leg circuit 101 and to the first winding
105 of the motor. I.sub.OUT waveform 108 represents the desired
mean output current as supplied to winding 105. V.sub.OUT waveform
109 represents the desired mean output voltage as supplied to
winding 105.
[0041] Between times T0 and T1, the output voltage is positive and
the output current is negative. During this time, the IGBTs of the
phase leg are controlled to cycle from the state illustrated in
FIG. 12A, to the state illustrated in FIG. 12B, to the state
illustrated in FIG. 12C, to the state illustrated in FIG. 12D, and
then back to the state illustrated in FIG. 12A. The conditions of
FIGS. 12B and 12D are maintained only for a relatively short dead
time. The dead time may, for example, be 50 ns. The duty cycle
during which current flows into the P terminal is pulse-width
modulated so that the desired I.sub.OUT current waveform is
achieved. The upper left detail of FIG. 10 shows how the duty cycle
is small during this time. The period of the pulse-width modulation
is, for example, 20 kHz. The voltage magnitude of the pulses is
positive DC voltage P.
[0042] Between times T1 and T2, the output voltage is positive and
the output current is also positive. During this time, the IGBTs of
the phase leg are controlled to cycle through the states
illustrated in FIGS. 13A, 13B, 13C and 13D. The conditions of FIGS.
13B and 13D are only maintained for the short dead time. The duty
cycle during which current flows out of the P terminal is
pulse-width modulated so that the desired IOUT current waveform is
achieved. The detail of FIG. 10 that is second from the left shows
how the duty cycle is large during this time. The voltage magnitude
of the pulses is positive DC voltage P.
[0043] Between times T2 and T3, the output voltage is negative but
the output current is positive. During this time, the IGBTs of the
phase leg are controlled to cycle through the states illustrated in
FIGS. 14A, 14B, 14C and 14D. The conditions of FIGS. 14B and 14D
are only maintained for the short dead time. The duty cycle during
which current flows out of the N terminal is pulse-width modulated
so that the desired IOUT current waveform is achieved. The detail
of FIG. 10 that is second from the right shows how the duty cycle
is small during this time. The voltage magnitude of the pulses is
negative DC voltage N.
[0044] Between times T3 and T4, the output voltage is negative and
the output current is also negative. During this time, the IGBTs of
the phase leg are controlled to cycle through the states
illustrated in FIGS. 15A, 15B, 15C and 15D. The conditions of FIGS.
15B and 15D are only maintained for the short dead time. The duty
cycle during which current flows into the N terminal is pulse-width
modulated so that the desired IOUT current waveform is achieved.
The upper right detail of FIG. 10 shows how the duty cycle is large
during this time. The voltage magnitude of the pulses is negative
DC voltage N.
[0045] FIG. 11 is a table that shows, for the condition of each of
FIGS. 12A-12D, 13A-13D, 14A-14D and 15A-15D: 1) whether each of the
IGBTs T1-T4 of phase leg 101 is on or off, 2) whether current is
flowing through each of the diodes D1-D4 of phase leg 101, and 3)
whether current is flowing through each of the IGBTs T1-T4 of phase
leg 101.
[0046] FIG. 16 is a flowchart of a method 200 in accordance with
one novel aspect. In step 201, a collector of the IGBT is coupled
to a first power terminal and an emitter of the IGBT is coupled to
a third power terminal. In step 202, an anode of a diode is coupled
to the emitter of the IGBT and a cathode of the diode is coupled to
the collector of the IGBT. In step 203, a DC-link is provided
between a second power terminal and a fourth power terminal. The
DC-link comprises a pair of diodes and a pair of IGBTs, where the
IGBTs are connected in a common collector configuration. In step
204, the IGBT, the diode, and the DC-link are encapsulated in a
power semiconductor module package. The first, second, third and
fourth power terminals are power terminals of the power
semiconductor module package. The encapsulation may involve
covering the DBC assembly in the enclosure portion of the housing
with one or more layers of an encapsulant such as silicone gel, and
then fixing the cap to the enclosure portion to close the enclosure
portion. In one example, the steps of method 200 are performed by
gluing or otherwise mounting a DBC substrate into the bottom of the
enclosure portion of a housing, mounting the IGBTs T1-T3 and the
diodes D1-D3 of the circuit of FIG. 4 onto the top of the DBC
substrate, wire bonding the components together on the DBC, wire
bonding the DBC assembly to power terminals of the module,
encapsulating the DBC assembly into the enclosure portion of the
housing, and then capping the enclosure portion to make the
finished module of FIG. 3. The steps of the flowchart of FIG. 16
therefore do not need to be done one at a time, or in any
particular sequence. In a further step, two such modules are
assembled together with bus bars to form the structure of FIG.
8.
[0047] Although certain specific embodiments are described above
for instructional purposes, the teachings of this patent document
have general applicability and are not limited to the specific
embodiments described above. Although a DC-link is described above
that involves IGBTs coupled together in a common collector
configuration, the DC-link may also be implemented using IGBTs in a
common emitter configuration, with fast recovery anti-parallel
diodes. Alternatively, a DC-link can be implemented using two
reverse blocking IGBTs coupled together in parallel. The teachings
set forth above can be applied to T-type NPC circuits that use
field effect transistors and bipolar transistors rather than IGBTs.
Accordingly, various modifications, adaptations, and combinations
of various features of the described embodiments can be practiced
without departing from the scope of the invention as set forth in
the claims.
* * * * *
References