IEEE Power Electronics Magazine Compendium - March 2018 - 112

Temperature (°C)

41
Tj
40
39
38
Tc
37
36
35
34
33
32
0.00
0.04

0.08
0.12
Time (Seconds)

0.16

0.20

FIG 8 The experimental results of short-term thermal behaviors
within 0.2 seconds with temperature sampling rate at 350 Hz
(junction temperature Tj and case temperature Tc of the IGBT) [16].

loading analysis and modeling of the converter are separated under several time constants with different focuses
and details of the systems. As an example, for the wind
turbine application, three different modeling levels can be
defined with different modeling techniques/tools [17]. Each
of the modeling levels covers different aspects of the power
converter from the component level to environmental level
and thereby can correctly reflect different causes of thermal dynamics. More details of this multitime scale thermal
modeling approach can be found in [18], and the interaction
between different levels of modeling techniques was demonstrated in [19].

Another approach to handle the widespread time scales
in the stress analysis of power electronics components is
to establish frequency-domain models, which can transfer the various disturbances in the mission profiles to the
dynamics stresses in the components regardless of the time
scale. A frequency domain thermal impedance model for a
power semiconductor device is thereby proposed for this
purpose [20], as illustrated in Figure 10, in which a low-pass
filter (LPF) is added to the thermal path. The new thermal
impedance model can achieve more accurate modeling of
the thermal dynamics of the power semiconductors at different locations from chips to the case and heat sink, which
have quite different thermal dynamics and are difficult to
be covered by the conventional modeling techniques.

Strength Testing and Modeling of Components
The target of this group of analyses is to test and model the
reliability/lifetime of power electronics components under
different stress levels, which is also referred as reliability/
lifetime models of components. By knowing this critical
information, the previously acquired component stress
translated from the mission profiles can be mapped into the
reliability of components under given mission profiles.
Accelerated testing is an important way to obtain component models of degradation, lifetime, and reliability or
weak design points. Among various testing concepts, accelerated lifetime testing (ALT) [21], calibrated ALT (CALT)
[22], multiple environment overstress tests (MEOST) [23],
and highly accelerated limit testing (HALT) [24] have been

Environment Level (Day/Year)
Converter
System

* Environmental Variance
* Steady State
* Analytical Model
* No Thermal Dynamics

*
*
*
*

Mechanical Variance
Control Dynamics
Ts Averaged Model
Slow Thermal Dynamics

MPPT
Control

Wind
Mechanics

System Level (Second/Hour)

Converter Environment
Inverter
Control

dinverter

+
-

LCL Filter
Grid

+
-

Zg

Control and Mechanics
1.1 kVdc

* Electrical Variance
* Switching Dynamics
* Detail Circuit Model
* Fast Thermal Dynamics

Generator

690 Vrms

GBT

Circuit Level (Millisecond/Second)

Filter

Wind Turbine
2L
Converter

2L
Converter

Circuit and Control
FIG 9 The multitime scale stress modeling approach of the power electronics converter in wind turbine generation.

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