"RC-D Fast": RC-Drives IGBT optimized for high switching frequency

RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
“RC-D Fast”: RC-Drives IGBT optimized
for high switching frequency
Application Note
Application Engineering IGBT
July 2012, Mitja Rebec
Po wer Ma nage m ent1 Dis c r etes
RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2012 Infineon Technologies AG
All Rights Reserved.
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
Table of Contents
1
INTRODUCTION AND SHORT DESCRIPTION OF THE PRODUCT FAMILY ........................................................... 4
2
STATIC AND DYNAMIC BEHAVIOR .................................................................................................................. 7
3
2.1
STATIC BEHAVIOR .............................................................................................................................................. 7
2.2
DYNAMIC BEHAVIOR .......................................................................................................................................... 8
IN-CIRCUIT APPLICATION TEST ON 200W MOTOR DRIVE BOARD ................................................................. 10
3.1
EFFICIENCY ..................................................................................................................................................... 10
3.2
THERMAL BEHAVIOR......................................................................................................................................... 11
3.3
COOLING CONSIDERATIONS................................................................................................................................ 13
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
1 Introduction and Short Description of the Product Family
The RC-Drives IGBT technology was released by Infineon at the end of 2009 as a costoptimized solution to address the price-sensitive Consumer drives market. This basic technology
provides outstanding performance in BLDC motor drives adopting block commutation–type of
modulations, were one or both IGBT in the half-bridge are left conducting for 120° of the motor
electrical angle (Dae-Woong Chung et al., IEEE TRANSACTIONS ON INDUSTRIAL
ELECTRONICS, VOL. 46, No. 3, June 1999). Thanks to the low conduction losses of both IGBT
and integrated diode the overall losses are drastically reduced. This type of control is commonly
found in Fridge compressors: by limiting the hard switching events the dV/dt and dI/dt
commutation slopes are avoided, therefore the harmonic content injected into the motor
windings (hence the EMI) is reduced. Below a typical example of this type of commutation found
on a 100W commercial fridge compressor:
Figure 1: High side and low side gate signals for 120° PWM commutation switching
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
Another application that benefits from the low on-state losses or the RC-Drives is found in
Domestic Aircon systems: the ~1.5 kW BLDC compressor is driven by IGBTs switched by full
sinusoidal PWM hard switching at moderate switching frequencies of 5 to 8 kHz. Again in this
case a device optimized for low conduction losses provides an overall loss reduction.
However the trend observed in low power drives for outdoor and indoor fan of domestic Aircon
systems as well as industrial funs and pumps up to ~200W is to increase the PWM switching
frequency. The reason is twofold: on one side the size of the output filter can be reduced by
keeping the same current ripple. On the other side in small motor drives adopting sensor-less
FOC (Field Oriented Control), were a high dynamic control (torque and speed) of the PMSM
motor is required, the higher switching frequency allows to increase the sampling rate of current
and hence the accuracy of reconstructed rotor position.
In order to meet the rising demands of the IGBTs for the low power motor drive consumer
market, a new version of the RC-Drives IGBT is developed: the IGBT and diode losses are
optimized to reduce the inverter losses at switching frequencies of 4~30kHz. The new family is
called RC-DF, and released in the current classes from 2.5A to 15A in D-PAK packages.
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
Part
number
Package
Type
Power
[W]
Switching VCE IC [A]
frequency
[V]
25°
VCEsat [V]
Ets [mJ]
tSC VF [V]
Qrr [µC]
100°C 25°C
175°C 25°C
175°C [s]
25°C 175°C 25°C 175°C
IKD03N60RF D-PAK
40..80
4..30 kHz 600 5
2.5
2.2
2.3
0.09
0.14 5
2.1
2.0
0.06
0.19
IKD04N60RF D-PAK
80..150
4..30 kHz 600 8
4
2.2
2.3
0.11
0.19 5
2.1
2.0
0.09
0.26
IKD06N60RF D-PAK
150..250 4..30 kHz 600 12
6
2.2
2.3
0.18
0.28 5
2.1
2.0
0.16
0.34
IKD10N60RF D-PAK
250-600 4..30 kHz 600 20
10
2.2
2.3
0.35
0.52 5
2.1
2.0
0.27
0.62
IKD15N60RF D-PAK
600..1000 4..30 kHz 600 30
15
2.2.
2.3
0.52
0.78 5
2.1
2.0
0.42
1.00
80..150
4
1.65
1.85
0.24
0.4
5
1.7
1.7
0.22
0.52
150-250 DC..5 kHz 600 12
6
1.65
1.85
0.33
0.56 5
1.7
1.7
0.37
0.80
250-600 DC..8kHz 600 20
10
1.65
1.85
0.59
0.93 5
1.7
1.7
0.56
1.22
600-1000 DC..8kHz 600 30
15
1.65
1.85
0.9
1.25 5
1.7
1.7
0.76
1.7
IKU04N60R I-PAK
DC..5 kHz 600 8
IKD04N60R D-PAK
IKU06N60R I-PAK
IKD06N60R D-PAK
IKU10N60R I-PAK
IKD10N60R D-PAK
IKU15N60R I-PAK
IKD15N60R D-PAK
Table 1: Product specification for RC-Drives and RC-Drives Fast
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
2 Static and Dynamic behavior
2.1
Static Behavior
Due to the optimization for fast switching, the VCEsat of the RC-DF is increased compared to the
RC-D. However for the target inverter applications in the range of ~100W the RMS currents are
usually limited below 1A and here the VCEsat increase is limited to ~ 200mV both at 25 °C and
175°C. A negative temperature coefficient of VCEsat is observed in this current range, contributing
to a reduction of conduction losses in normal operating conditions, with junction temperature Tj
typically ranging from 60 to 100°C.
Figure 2: VCEsat comparison of the RC-DF vs. the RC-D technology
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
2.2
Dynamic Behavior
The RC-DF maintains the smooth switching behavior and Rg controllability of the basic RC-D
technology, by providing drastically reduced turn-off losses of the IGBT. The internal diode is
also optimized to reduce the turn-on losses. The devices are characterized in a classical halfbridge test circuit with inductive load: the LS IGBT (DUT) is commutated over the HS diode.
Therefore the Diode switching improvement is visible in the IGBT turn-on behavior (see below).
-23%
-55%
-33%
-44%
Figure 3: Dynamic switching behavior as a function of external Rg.
The turn-on and turn-off waveforms are clearly showing significantly faster switching: both the
tail current of the IGBT, the Qrr, Irrm and trr of the integrated diode are drastically reduced.
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
RC-D
RCDF
RCRC-
D
DF
Figure 4: dynamic switching waveforms: turn-off (top) and turn-on (bottom). Note that the current
scales are different.
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
3 In-circuit Application Test on 200W Motor Drive board
3.1
Efficiency
In order to verify the improvement of the RC-DF in a real application conditions, the new devices
were tested on a demo board developed by Infineon and used as test bench to simulate a real
Air-conditioning outdoor fan. The board is designed for a 200W output and consists of an input
rectifier stage, inverter stage and output filter. The IGBTs are driven by a 600V 3-phase driver IC
from Infineon (6ED003L06-F), and the modulation pattern is provided by an 8 Bit Infineon
Microcontroller (XC-878) mounted on an external card. No heat-sink is required, just thermal
Vias through the PCB. The control method is sensor-less FOC using a single shunt-based
feedback loop. The board is driving a 200W induction motor coupled to an adjustable DC brake,
which allows controlling the output power from the inverter. The efficiency is monitored by a
Siemens Power meter and case temperature is monitored by an IR camera.
Figure 5: Test set-up for the application measurements
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
Already at switching frequency of 10 kHz a clear efficiency improvement is observed. At the
target f_sw of 18 kHz the RC-DF provides 2.8% improvement at 50W input power and 1.6% at
100W:
+2.8%
+1.6%
Figure 6: Inverter efficiency as a function of input power and switching frequency
3.2
Thermal behavior
The increased efficiency for the RC-DF translates in lower case temperature, as verified by
thermal images with Infrared camera:
-20°C
-17°C
Figure 7: Case temperature as a function of input power and switching frequency
The RC-DF shows outstanding thermal performance providing lower case temperature over the
entire frequency range: at the target switching frequency of 18 kHz, the case temperature is
lowered by 20°C.
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
The temperature distribution is quite uniform, as demonstrated by detailed analysis of the
thermal images:
Figure 8: thermal images at Pin=50W, f_sw=20 kHz
This translates in increased reliability and longer life expectancy for the device, especially in the
harsh thermal environments to be encountered in a real application. In the case of outdoor fan
for domestic split Aircon systems, for example, the board is mounted directly on the back of the
motor in a close environment without airflow. In this case high ambient temperature up to ~60°C
can be expected:
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
Figure 9: Commercial Air-conditioning split system, showing the motor drive card housed on the
back of the BLDC fan motor
3.3
Cooling considerations
When the power range of the inverter exceeds ~200W, along with careful PCB design (avoid
placing devices too close to each other or to the edge of the PCB), some type of cooling is
required for the SMD devices. In case of DPAK packages, top side cooling is not effective due to
the relatively high thickness of the mold compound on top of the chip and the poor heat
exchange. Infineon recommends cooling from the bottom of the chip by thermal vias through the
PCB. Several methods for Vias formation are adopted in the Industry:
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
Copper inlays
Production
limited
expensive concept.
and
quite
Adopted in
high efficiency converter for SMPS
applications
Copper Inlays (Ruwel GmbH)
Thermal vias
Placed around the leadframe or
partially under the drain contact.
Typical Vias diameter is 400um.
Filled with synthetic resin to avoid
solder
voids
at
RC-Drives
leadframe due to a solder reflow
through the Vias. Most common
solution in consumer drives.
Classical Thermal Vias with resin
Small drill holes
Holes diameter below 0.2 mm for
the thermal vias are filled during Cu
galvanic deposition to avoid solder
reflow. They can be placed under
the drain for the most effective heat
exchange.
Thin-Via-Concept (Small drill holes)
Figure 10: Commonly adopted Vias concepts
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
Infineon recommends, when allowed by the process capability of PCB supplier, the small drill
holes concept for optimum power dissipation. The concept was tested successfully on several
reference designs and allowed to reach up to 1.2kW Output power utilizing RC-D devices in
DPAK package.
Below an example of small drill holes vias design and related heatsink mounting with isolation
foil:
Fig 11: Example of thermal Vias and Heatsink mounting for RC-D and RC-DF test boards
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RC-Drives
Cost-Optimized IGBT for Consumer Drive Application
w w w . i n f i n e o n . c o m / r c d f
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Published by Infineon Technologies AG
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