AN1915D Freescale Semiconductor / Motorola, AN1915D Datasheet - Page 5

• Manufacturer Part Number: AN1915D
• Description: 3-Phase BLDC Motor Control with Quadrature Encoder using DSP56F80x
• Manufacturer: Freescale Semiconductor / Motorola

MOTOROLA
3.1.1 Independent Switching of Power Transistors
For the common 3-phase BLDC motor a standard 3-phase power stage is used. Such a power stage for
3-phase BLDC motors is illustrated in
independent switching. The power transistors may be switched to independent or complementary mode.
In both modes the 3-phase power stage supplies two motor phases concurrently. The third phase is not
powered (see
motor.
to the DC Bus Voltage. The lower voltage is generated using a PWM technique (see
Figure
complementary switching.
With independent switching, only two transistors are switched on when the current is conducted from
the power supply to the phase of the BLDC motor. In one phase, the top transistor is switched on, in
the second phase the bottom transistor is switched on and the third phase is not powered. During
freewheeling, all transistors are switched off (see
Figure 3-2
3-5). There are two basic types of power transistor switching: independent switching and
U
DCB
Figure 3-2. Voltage Strokes Applied onto the 3-ph BLDC Motor
GND
Phase A
Phase B
Phase C
Figure
Voltage
+U
+U
+U
-U
-U
-U
shows the maximum voltage amplitude applied to the BLDC motor, which is equal
DCB
DCB
DCB
DCB
DCB
DCB
C1
PWM_Q1
PWM_Q2
3-Phase BLDC Motor Control with Quadrature Encoder
3-2). Thus, we get six possible voltage vectors that are applied to the BLDC
Freescale Semiconductor, Inc.
30º
Figure 3-3. 3-phase BLDC Power Stage
For More Information On This Product,
60º
90º
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Q1
Q2
120º
Figure
Phase_A
150º
PWM_Q3
PWM_Q4
3-3. The power stage utilizes six power transistors with
180º
Figure
210º
3-4).
240º
Q3
Q4
Phase_B
270º
PWM_Q5
PWM_Q6
300º
330º Electrical
angle
Q5
Q6
Phase_C
Target Motor Theory
Figure 3-4
and
5