IEEE Power Electronics Magazine - December 2016 - 39

30
Wind Speed
(Minutes/Seconds)

20
15
10
5

8,000
8,000

6,000
6,000

7,000

5,000
5,000

7,000

4,000

3,000
3,000

4,000

2,000
2,000

0
Ambient Temp. (°C)

1,000

An Example Based on a Wind Power Inverter

15
10
5
0
-5
0

To give a review and better understanding to the introduced
approach for assessing the reliability metrics of the power
electronics converter, a simple example is demonstrated on
a wind power inverter, as detailed in [17].
A typical wind condition and wind turbine system are first
determined as a study case. As shown in Figure 19, a one-year
wind speed and ambient temperature profile is used with
3 hours averaged at an 80-m hub height, which was collected
from a wind farm located near Thyborøn, Denmark, with latitude 56.71° and longitude 8.20°. The chosen hub wind speed
belongs to the wind class IEC I with average wind speed of
8.5-10 minutes/seconds [35], [36], and a 2.0-MW wind turbine
[37] is chosen to fit the given wind condition.
With respect to the wind power converter, the most
frequently selected two-level back-to-back voltage source
converter is chosen, as shown in Figure 20. Only the gridside converter is chosen as a case study, whose parameters are designed according to Table 3, which is a stateof-the-art configuration for the two-level wind power
converter. The generator-side converter can share the
similar approach for the analysis.
In Figure 21, a simplified diagram for the analysis of
the given inverter is shown, where multidisciplinary models like the wind turbine, generator, converter, loss, and
thermal impedance of the power devices are all included
to map the reliability of the device with the mission profile of the wind turbines as well as the strength model
of component. Based on the given mission profiles and
converter designs, the thermal loading of the power semiconductor device and the rainflow counting results have
already been shown in Figures 7 and 16, respectively.
In this demonstration, the lifetime model provided by
[38] is used. The total one-year consumed B10 lifetime of the
IGBT module is shown in Figure 22, in which three failure
mechanisms like the crack of baseplate soldering (B solder,
caused by case temperature cycling), crack of chip soldering (C solder, caused by junction temperature cycling), and
bond-wire lift-off (bond wire, caused by junction temperature cycling) are illustrated. The temperature cycling on the
chip soldering (C solder) consumes more lifetime (i.e., is
quicker to failure) than the other two failure mechanisms.
It is worth mentioning that this lifetime result reflects only
those influenced by long-term thermal cycles with a period
longer than 3 hours.
The quantified reliability metrics based on the mission
profiles and converter design are very useful information,

1,000

In (7) it is assumed that the failure of an individual component will have no impacts to the loading and lifetime for
the rest of the components in the system. However, this
assumption is not always true in the power electronics
converter; in this case, a more complicated calculation for
the system reliability needs to be performed by taking into
account the cross-impact matrix results and the repairability of the system. More details can be found in [2].

Time (Hours)
FIG 19 The one-year mission profile of wind speed and ambient temperature from a wind farm (3-hour average).

1.1 kVdc
IGBT

Generator

690 Vrms
Filter

Wind
Turbine
2L
Converter

Grid

2L
Converter

FIG 20 A wind power converter for lifetime estimation.

Table 3. The parameters of the wind power
converter in Figure 20.
Rated output active power P0

2 MW

dc bus voltage Vdc

1.1 kVdc

*Rated primary side voltage Vp

690 Vrms

Rated load current

1.93 kArms

Fundamental frequency fa

50 Hz

Switching frequency./'.

1,950 Hz

Filter inductance Lf

132 μH [(0.2 p.u.)]

*Line-to-line voltage in the primary windings of a transformer.

December 2016

z IEEE PowEr ElEctronIcs MagazInE

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