3544 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 59, NO. 9, SEPTEMBER 2012
Fig. 3. Twelve regions of three-phase voltage supply.
TAB LE I
S
EVEN-LEVEL VOLTAGES.(V +++)MOST POSITIVE VOLTAGE.
(V −−−)M
OST NEGATIVE VOLTAGE
B. DB Hysteresis Control
Double-band (DB) control is more complicated and intelli-
gent, although it is based on the same principle as SB control. It
uses both inner and outer hysteresis bands to control the output
current. The supply voltages can be divided into 12 regions
(1–12) based on the points at which the phase voltages cross
each other and cross zero, as shown in Fig. 3.
In each region, the supply voltage needs to be identified as
seven levels depending on their relative magnitudes, as listed
in Table I, in order to control its current. These are defined as
V +++, V ++, V +,0,V −, V −−, and V −−− which
represent the most positive to the most negative voltages.
When the current is below the lower outer band, the V +++
voltage is applied (area a), as shown in Fig. 4. The current
begins to increase. When the current reaches the upper inner
band, the applied voltage level begins stepping down until a
change in direction of current is observed. If the current rises
above the upper outer band before the current begins to reduce
Fig. 4. DB control.
(area c), the V −−− voltage is automatically applied and
would be held constant until the current drops below the lower
inner band. If the current rises above the upper inner band but
below the upper outer band when the current begins to reduce,
at this point, the applied voltage level is held constant until the
current drops below the lower inner band (area g). Then, the
voltage level applied is stepped up until the direction of change
of current becomes positive (areas d and h). The voltage applied
when the current begins to increase will be held until the current
reaches the upper inner band (areas e and i) which is back to the
previous state at the beginning of the paragraph.
IV. M
ULTIPHASE DESIGN
A three-phase drive, the most common topology for indus-
trial drives, cannot achieve the aerospace requirements in terms
of safety and reliability for this application which instead can be
fulfilled by a multiphase motor-drive design [18]–[20]. There
are many possible configurations for the power converter and
the number of motor phases. The three-, four-, five- and six-
phase BLDC motor drives fed by an SSMC will be compared
in this paper.
A basic unit of the SSMC is shown in Fig. 2. It can be seen
that only unidirectional load current is possible. Each phase
winding will be connected to one unit of the SSMC. A total
of three units is required for a three-phase drive.
When an even number of phases is used, an alternative to
the individually driven motor phase method is available for
the SSMC drive. By connecting the motor phases to create a
neutral point, two phases can be connected to one SSMC unit,
and therefore, only half of the power devices are required but
with reduced fault tolerance. For odd number of phases, the
neutral point can only be connected when bidirectional current
is available; therefore, it cannot be applied with SSMC.
The performance of the multiphase drives is investigated.
Simulations were carried out using Matlab and finite-element
method software. The average torque and the torque ripple for
the phase numbers considered are shown in Table II.