AN2357 Freescale Semiconductor / Motorola, AN2357 Datasheet - Page 4

• Manufacturer Part Number: AN2357
• Description: Sine Voltage Powered 3-Phase Permanent Magnet Motor with Hall Sensor
• Manufacturer: Freescale Semiconductor / Motorola

AN2357/D
Vector of Stator
Voltage is Placed 90°
Relative to the
Vector of Rotor
Permanent Magnet
Flux
4
Sine Voltage Powered 3-Phase Permanent Magnet Motor with Hall Sensor
Motor speed can be controlled by the amplitude of the voltage vector, while the
direction of the voltage vector depends on the rotor position. Several methods
can be used to control the voltage vector direction. The three basic method are:
The most important criterion is to run the motor with maximum efficiency. In this
case, the angle of current will be higher than 90° relative to the rotor permanent
magnet flux, but lower than shown in method 3 above where the current has
the same direction as the voltage. The motor parameters have to be known or
some experimental control strategy has to be used to achieve this criterion.
The control strategy keeps the vector of stator voltage at 90° relative to the
vector of rotor permanent magnet flux. This control strategy is shown in
Figure
of the rotor position is required.
Where three Hall sensors are used to get the rotor position, we obtain six
positions per electrical revolution. To each rotor position, a vector position of
stator voltage is assigned. The motor is commutated each 60°, so that the
phase voltage is rectangular. This algorithm is mostly used for the control of
BLDC (brushless dc) motors. Twelve commutations instead of six can be used
to decrease the acoustic noise. For a more detailed description refer to
References
1. Vector of stator voltage is placed 90° relative to the vector of rotor
2. Vector of stator current is kept 90° relative to the vector of rotor
3. Voltage vector is kept in the direction of the current vector
Freescale Semiconductor, Inc.
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permanent magnet flux
permanent magnet flux
2. The advantage of this strategy is control simplicity. Only knowledge
[1].
Go to: www.freescale.com
Figure 2. Voltage is 90° Relative to Rotor Flux
U
s
E
j
ω
I
R
s
.L
s
s
I
s
.I
90°
s
Ψ
s
Ψ
r
Ψ
MOTOROLA