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controller [12], dynamic voltage restorer [13] and so on. Paper [14] presented
a new modulation scheme for three-level MC. Paper [15] presented the exper-
imental evaluation of three-level MC. From the researches above, three-level
and multi-level MCs produce less harmonic component and the output voltage
waveform is much closer to standard sinusoidal wave. BLDCM is also called
Trapezoidal Permanent Magnet Synchronous Motor, which has the advantages
of simple structure, convenient operation, high power density and high eciency.
It is widely used in AC drive area. In this paper, a BLDCM drive system fed
by IMC is proposed. The IMC is a superior AC-AC converter while BLDCM
is a commonly used motor. By combination of the two, we could overlap the
advantages of them.
2IMC-FEDBLDCMDRIVE
2.1 BLDCM Drive
The BLDCM is a kind of permanent magnet synchronous motor. Because of
its simple structure, good performance and high reliability, BLDCM is widely
used in servo system. Different from sinusoidal permanent magnet synchronous
motor, the air-gap magnetic field of BLDCM is square-wave. The back EMFs of
BLDCM are trapezoid-wave and the phase current is square-wave.
The mathematical equations of BLDCM are
V
a,b,c
=
Ri
a,b,c
+(
L−M
)
d
i
a,b,c
/
d
t
+
E
a,b,c
.
(1)
The mechanical equations of BLDCM are
E
a
i
a
+
E
b
i
b
+
E
c
i
c
J
d
ω
d
t
=
T
e
−
Bω
−
T
L
dθ
r
/dt
=
Pω/
2
.
(2)
In this paper, 120 electrical degrees control method is proper for BLDCM drive.
The IMC's output DC voltage applies a voltage during 120 electrical degrees
to the motor inductances. This is similar to conventional converter-fed BLDCM
drive system. The desired stator current is shown in Figure 1.
We know that the electromagnetic torque of BLDCM is caused by the in-
teraction between stator winding current and rotor magnetic field [16]. Electro-
magnetic torque is proportional to the amplitude of stator currents. In order to
produce constant electromagnetic torque, square-waves for stator currents and
trapezoid-waves for back EMFs are required. Just like Figrue 1, in each half cy-
cle, square-wave stator currents last for 120 electrical degrees and the flat top of
the trapezoid-wave back EMFs are all 120 electrical degrees as well. The square-
wave stator currents and the trapezoid-wave back EMFs must be synchronous.
At any time, only two phases are conducted.
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