IEEE Power Electronics Magazine Compendium - March 2018 - 102

Fault Detection and condition
Monitoring

emitter turn-off thyristor, improving
the speed and dynamic performance of
Issues such as cost,
the device [42]. In [43], a full bridge
Under severe operating conditions,
space, weight, and
converter was realized using SiC
there should be accurate techniques
metal-oxide-semiconductor fieldfor fault diagnosis and condition monplatform balance can
effect transistors. In semiconductor
itoring of MV drives to avoid financial
be improved
research, SiC power switches promise
losses due to unscheduled and forced
to increase efficiency by 10% due to
shutdown. Therefore, condition monisignificantly with
reduced switching losses. However, up
toring and fault diagnosis of electrical
fewer transformers
to now no MV drive manufacturer has
motors is another important challenge
declared adoption of SiC devices. This
to be met for MV drive systems. In
for an offshore
may be due to the high cost of the
this area, a significant amount of
platform.
devices and anticipation of the highwork has been done in recent years,
current switching devices yet to come
and a comprehensive review is preon the market.
sented in [38]. The interesting possiAn Intelligent Power Module has been developed to
bility of sensorless fault detection involves using observerprotect IGBTs from short circuit and to provide a negative
based diagnostic methods for mechanical fault detection
voltage to avoid false switching signals, which reduces
[39]. More advanced solutions are also possible to detect
switching losses [44]. Furthermore, to obtain closed-loop
failures when LC inverter output filters are installed on the
gate control, a new technique has been proposed in [45].
drive [40]. Any partial discharge in the stator of high-voltThe voltage across parasitic inductance of IGBTs is moniage rating machines can be monitored by using high-fretored to measure switching speed and di/dt, so that the gate
quency current transformer sensors located at hazardous
drive voltages are adjusted to control the switching speed,
locations such as oil and gas facilities [41].
allowing the full capability of power devices to be utilized.

research and Industrial trends
Topologies
Components
The present research and industrial trends in the area of MV
drives are multidimensional, encompassing the front-end
converter, inverters, motor, and control. A new trend is using
advanced materials for power semiconductor switches, such
as silicon carbide (SiC)-based switches. Simulation of SiC
thyristors has given excellent conduction and switching performance. So SiC thyristors hold promise as devices for highpower applications. They have the drawback that they need
a di/dt snubber and also a dv/dt snubber for turn-off. This
drawback has been overcome by development of the SiC

FIT

5.0

× 104

4.5
4.0
3.5
3.0
2.5

System with
Transformer

2.0
1.5
1.0
0.5
0.0

2-Level

6.5-kV IGBT

3-Level
NPC

3-Level
FC

4.5-kV IGBT

4-Level
FC
3.5-kV IGBT

FIG 11 A comparison of the reliability of converters.

102

IEEE PowEr ElEctronIcs MagazInE

z June 2016

For more than 6 kV, the modular multilevel converter is the
best solution to dispense with transformers and isolated
power sources. But they have the problem of voltage fluctuation and voltage balance of capacitors. The research trends
in modular multilevel cascaded inverters have been discussed in [46], which proposes methods to mitigate the fluctuation in ac voltage to stabilize operation at low speed and
low frequency, and those methods are compared with two
other methods.

Control and Modulation Techniques
To control MIs at low switching frequency, the synchronous
optimal PWM technique was proposed in [47]. This modulation technique provides considerable benefits. For
example, the THD level of the machine current doesn't
affect low switching frequency. The technique also maintains an optimal CM voltage and neutral point potential
balance. To improve the dynamics of the control system,
the hybrid direct torque control was proposed in [48]. In
this control system, the torque is shown to be proportional
to the quadrature axis component of the current. This can
improve the calculations of error (between quadrature reference current and actual quadrature current). Initially
selected harmonic elimination was proposed in [49] and
then in [50]. After that, new techniques to eliminate the
selective harmonic elimination PWM schemes were suggested, such as Programmed PWM [51], and Multilevel SHEPWM for series-connected inverters [52], [53]. The major
challenge with SHE is solving online the algebraic equations
obtained for specific harmonic cancellation [54].

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine Compendium - March 2018