Brushless Motor Circuit
Electric Drive Design
Brushless Motor
Drives & Control June 2003 A. Jansen 3
BLDC with Hall Sensors -- Topology
Typical Circuit Block Diagram
Hall Sensors detect the position
Over current protection and control via ADC
Wiring
Structure and windings arrangement of the 5-phase PM BLDC motor.
f.e.m. inducida por fase
Corrientes en los devanados de un motor BLDC
BLDC motor outside rotor
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Switching Table for 120o Hall Spacing
Clockwise Motion Counter-clockwise Motion
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a
c
b
ia
b
c
a ib ic
Step 1
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a
-c g
a
c
b
Step 2
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a
c
b
b -c
g
Step 3
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a
c
b
-a
b
g
Step 1: With Rotor Magnet
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a
-c g
m
Force
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g
b -c
m
Force
Step 2: With Rotor Magnet
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-a
b
g
m
Force
Step 3: With Rotor Magnet
Power Circuit
Step 1: Activated Transistors
Step 2: Activated Transistors
Step 6: Activated Transistors
Switching Signals
Voltage Regulation - Fixed Width Modulation
W ithout modullation ,the voltage during�����is� ��
With Modulation ,� ���=� �� �
�=∑ ���
�����
Voltage Regulation - Fixed Width Modulation
W ithout modullation ,the voltage during�����is� ��
With Modulation , phase voltage ����=√2�
3 ���
�=∑���
�����
Problem
Facts:
• Transistors do not
immediately commutate (open)
• Transistors do not immediately close Problem:
• There could be periods where high transient current exist.
Solution
• Make before break
BLDC in Theory – Back Electro Magnetic Force• Theory
• UP = (R x i) + (L x di/dt) + eP
• where
"UP" stands for phase voltage
"R" stands for winding resistance
"i" stands for actual phase current
"L" stands for phase inductance
"di/dt" stands for changment of phase current over time
"eP" stands for electromagnetic voltage caused by magnet
• while
i = 0 and di/dt = 0:
UP = eP
• by measuring UP
a position detection is possible
Dynamic Braking
Method 1:
Open all top transistors
Close and regulate all lower transistors
Dynamic Braking
Method 2:
Open all transistors
Close and regulate the triacs
