AN1931D Freescale Semiconductor / Motorola, AN1931D Datasheet - Page 10

• Manufacturer Part Number: AN1931D
• Description: 3-Phase PM Synchronous Motor Vector Control
• Manufacturer: Freescale Semiconductor / Motorola

Target Motor Theory
3.3.1 Vector Control of PM Synchronous Motor
10
The inverter consists of three half-bridge units where the upper and lower switches are controlled
complementarily, meaning when the upper one is turned on, the lower one must be turned off, and vice
versa. Because the power device’s turn off time is longer than its turn on time, some deadtime must be
inserted between the turn off of one transistor of the half-bridge, and the turn on of its complementary
device. The output voltage is mostly created by a pulse width modulation (PWM) technique, where an
isosceles triangle carrier wave is compared with a fundamental-frequency sine modulating wave, and
the natural points of intersection determine the switching points of the power devices of a half bridge
inverter. This technique is shown in
other and, thus, a 3-phase motor can be supplied.
The most popular power devices for motor control applications are Power MOSFETs and IGBTs.
A Power MOSFET is a voltage-controlled transistor. It is designed for high-frequency operation and
has a low voltage drop; thus, it has low power losses. However, the saturation temperature sensitivity
limits the MOSFET application in high-power applications.
An insulated-gate bipolar transistor (IGBT) is a bipolar transistor controlled by a MOSFET on its base.
The IGBT requires low drive current, has fast switching time, and is suitable for high switching
frequencies. The disadvantage is the higher voltage drop of a bipolar transistor, causing higher
conduction losses.
Vector Control is an elegant control method of a PM synchronous motor, where field-oriented theory
is used to control space vectors of magnetic flux, current, and voltage. It is possible to set up the
coordinate system to decompose the vectors into a magnetic field-generating part and a
torque-generating part. The structure of the motor controller (Vector Control controller) is then almost
the same as for a separately-excited DC motor, which simplifies the control of PM synchronous motor.
This Vector Control technique was developed specifically to achieve a similarly dynamic performance
in PM synchronous motors.
As explained in
where the rotor flux is controlled by a field-weakening controller.
Section
P WM Output T
P WM Output T
(L ower S witch)
(U pper S witch)
Freescale Semiconductor, Inc.
3-Phase PM Synchronous Motor Vector Control
4.2, we chose a widely used speed control with inner current closed-loop,
-1
For More Information On This Product,
1
0
2
1
Figure 3-5. Pulse Width Modulation
0
1
0
1
Go to: www.freescale.com
Figure
3-5. The 3-phase voltage waves are shifted 120
S ine Wave
Generated
P WM Carrier
Wave
t
t
t
MOTOROLA
o
to each