IEEE Power Electronics Magazine - December 2016 - 33

Q*
Vdc*
Control

Tambient

Iin
Duty
Ratio

Converter

Electric
Parameter

p Loss

Loss

∆T

Thermal
Impedance

Feedback

+
+

Device
Temp.

Feedback

Control and Electrical Models

Loss and Thermal Models

FIG 5 The typical signal flows and model block diagram to assess the thermal stress of power electronics components in a grid-tied
inverter [16].Vdc*: dc link voltage control reference; Q*: reactive power reference; Iin: input current on the dc link; PLoss: power loss
on the device; DT : temperature variation of the device; Tambient: ambient temperature.

Microseconds

Milliseconds

Seconds

Minutes

Hours

Days

Temp./Wind

Wind

Environment

Turbine

Mechanical

Generator

Control

Electrical

Grid Switching

Main Disturber
Ambient
Temperature,
Wind Speed
Variation

Wind Control, Device
Variation, Grid Switching
MPPT

FIG 6 The multitime scale disturbances for the thermal behaviors in the wind power converter [17]. MPPT: maximum power
point tracking.

7,000

6,000

5,000

4,000

3,000

2,000

Tj

Tc
8,000

120
110
100
90
80
70
60
50
40
30
20
10
0
1,000

The existing methods/tools for the power electronics are
not sufficient to model the complete stress behaviors in the
power device driven by the mission profiles. Either very
detailed and refined models/methods (such as finite element
methods or PSpice circuit models) are used but restrained
to a very limited time span and small time steps, or only
steady-state conditions are focused on with compromised
accuracy of certain important thermal dynamics.

Time Scale

0

Multitime scale Modeling approaches

To establish a more complete thermal behavior of
the power devices according to the mission profile of the
converter, newer approaches have to be used. A potential
method is demonstrated in Figure 9 [17]. As lenses with
different focus lengths are used in the photography, the

Temperature (°C)

and tools, and finding out the correct connection or interaction among the results from different physical domains is of
great importance.
The major disturbances and dominant time constants of the factors in a wind power generation system-a typical application of power electronics-that
have influence on the loading of power semiconductor
devices are illustrated in Figure 6 [17]. These factors
have very different time constants, ranging from microseconds (power semiconductor device switching) to
years (ambient temperature changes).
Examples of different time scales of thermal loading on the chips inside the power semiconductor device
are shown in Figures 7 and 8. In Figure 7, the simulation
results of a 2-MW full-scale wind power converter with a
1,100-V dc input, 690-V root mean square (rms) output dc/
ac three-phase two-level topology is provided. In Figure 8,
the experimental results of a 10-kW power converter with
a 600-V dc input, 380-V rms output dc/ac three-phase threelevel topology is shown by using an infrared camera [17].
The loading conditions are illustrated under different
time scales: first, at a one-year span with a 3-hour sampling time and, then, at a 0.2-second span with a 350-Hz
sampling rate. It can be clearly seen that the behavior of
the thermal cycling under different time scales is quite different. The longer-term thermal cycling in Figure 7 is quite
unregulated and mainly caused by the variations of converting power, depending on the wind speeds and turbine/
generator operating conditions, while the short-term thermal cycling in Figure 8 is more stable and mainly disturbed
by the alternating of load current at the grid line frequency.

Time (Hours)
FIG 7 The simulation results of long-term thermal behaviors within
one year with the temperature sampling rate at 3 hours (junction
temperature Tj and case temperature Tc of the IGBT) [16].

December 2016

z	IEEE PowEr ElEctronIcs MagazInE

33



Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - December 2016

IEEE Power Electronics Magazine - December 2016 - Cover1
IEEE Power Electronics Magazine - December 2016 - Cover2
IEEE Power Electronics Magazine - December 2016 - 1
IEEE Power Electronics Magazine - December 2016 - 2
IEEE Power Electronics Magazine - December 2016 - 3
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