IEEE Power Electronics Magazine Compendium - March 2018 - 95

va
vb
vc

Line Filter

Transformer

Rectifier

∼

dc Filter

Inverter
∼
∼

Motor Filter

Motor

∼
∼
∼

∼
Grid Side

Motor Side

FIG 3 A typical MV ASD.

range of 1-4 MW, with voltage ratings of 3.3-6.6 kV [6]. A typiChallenges and Requirements of MV Drives
cal block diagram of a MV drive is shown in Figure 3. Small
size, lower cost, high efficiency and reliability, fault protecPower Quality and LC resonance suppression
tion, ease of installation and maintenance, high dynamic perHarmonics in the voltage and current waveforms of the utilformance, and regenerative capability in some applications
ity grid is a crucial problem that needs to be effectively
are the essential requirements for MV
resolved. Diode-based rectifiers draw
drives. A list of some of the industrial
distorted current from the grid and
drives is presented in Table 2. This
cause notches in the voltage waveSmall size, lower cost,
table presents the power rating,
forms. This results in numerous probhigh efficiency and
devices and topology used, and control
lems in the power grid, such as equipmethods. Furthermore, the popular
ment failure, computer data loss, and
reliability, fault
converter topologies in MV drives are
malfunction of communications equipprotection, ease of
summarized in Figure 4 [7], [8].
ment. Various standards such as IEEE
The main disadvantage of multi519-1999, IEC 1000-3-2, and IEC 61000installation and
level inverters (MIs) is the complex3-2 define the limit of harmonics
maintenance, high
ity of the power circuit and controls.
injected into the power grid [6]-[8]. To
dynamic performance,
However, the use of MIs in MV drives
reduce current harmonics or to comoffers improved power quality, lower
pensate for the input power factor, an
and regenerative
switching losses, high voltage capaLC line-side filter is a common solucapability in some
bility, and lower dv/dt [9]. There are
tion. However, the low damping LC
different types of power switches
resonances may cause undesired
applications are the
that could be adopted for MV
oscillations or overvoltages in the grid
essential requirements
drives. These include the injection
side because of the low impedance of
enhanced gate transistor (IEGT), the
the MV grid. This may destroy the
for MV drives.
integrated gate-commutated thyrisswitching devices or other compotor (IGCT), and the insulated-gate
nents of the rectifier circuits. Solubipolar transistor (IGBT). The gate
tions to this problem should assure
drive circuits of IEGTs are more reliable than IGCT drive
low harmonics and low dv/dt using just a reactor instead of
circuits. The failures in time (FIT) ratio of IEGTs versus
an LC filter, or using a small filter.
IGCTs is four to one. Furthermore, the IGBT gate drive
circuit is simpler and has fewer components than IEGT
Inverter switching Frequency
gate drive circuits. Hence, IGBT gate drive circuits are
High dv/dt is generated with the use of high-switchingmore reliable than IEGTs [10].
frequency semiconductor devices in power electronic
Modern power semiconductor switches have a peak voltconverters, which can produce CM voltage and currents,
age blocking capability of nearly 6.5 kV, which restricts the
electromagnetic interference (EMI), shaft voltages, bearmaximum voltage ratings of the inverter and the motor in MV
ing currents, and high voltage stress that negatively
high-power drives. The apparent power that can be obtained
affect the insulation life of motors and transformers [12].
is limited by the available MV IGBT switches, which have a
The harmonic distortion of the output waveforms
peak current conducting capability of 750 A. Series or paralincreases with the decrease of inverter switching frelel combinations of semiconductor switches are used to overquency. MIs provide voltage/current waveforms with
come the limits of switch ratings, but with these arrangeimproved harmonic spectrum and lower dv/dt, which limments, a balance of the current and voltage between devices
its the insulation stress on the motor windings. However,
is achieved using extra measurements [11].
the higher number of switching devices in MIs tends to

June 2016

z IEEE PowEr ElEctronIcs MagazInE

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