Permanent Magnet Motor (Pm Motor); Brushless Dc Motor (Bldc Motor) - Eaton PowerXL DB1 Installation Manual

2.8.3 Permanent magnet motor (PM motor)

2.8.4 Brushless DC motor (BLDC motor)

PM motors are three-phase motors that are excited by permanent magnets
and have a speed that is directly proportional to the supply frequency.
Together with a high-pole-count, three-phase stator winding, the permanent
magnets on the rotor make it possible to produce large torques at low
speeds, which in turn makes it possible to forgo the use of a gearbox in
many applications.
By combining high efficiency and good power factor characteristics with a
lightweight and compact construction, PM motors make for a compelling
choice when compared to asynchronous motors. Accordingly, these high-
efficiency motors are primarily found in roller and press drives, agitator and
mill drives, drives for extruder screws, and drives used by the crane industry
for a variety of applications.
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In order to use vector control with permanent magnet motors,
the values for parameters P-60, P-61, and P-62 on DB1 variable
frequency drives need to be adjusted:
• Set the value for P-60 to 2 ("PM motor speed control").
• Set P-61 to 1 ("Motor Identification").
Automatic auto-tuning to determine the motor parameter
during downtime.
• P-62 ("MSC gain"). Adjust the gain factor for the speed
controller.
Contrary to what their name might seem to imply, brushless DC motors
(BLDC, also referred to as "EC motors") do not have the same configuration
as a DC motor, but are instead put together in the same way as three-phase
synchronous motors. The three-phase AC current winding generates a rotat-
ing magnetic field, which carries the permanently energized rotor with it.
The rotor position is determined during sensorless vector control by way of
the counter-voltage (counter electromotive force) generated in the stator
coils. This means that the variable frequency drive's output voltage must
always be live in all three phases (block voltage control), even when the sys-
tem is stationary. If this condition is met, short current pulses will be gener-
ated when the system is stationary – these pulses will not move the motor,
but they will have an effect on the rotor's magnetic field.
The control response for BLDC motors is to a large extent the same as that
for a shunt DC motor. BLDC motors are primarily used in drive systems for
machine tools, servo drives in conveyor systems, and compressors and
metering pumps.
DB1 Variable Frequency Drives 09/17 MN040031EN www.eaton.com
2 Engineering
2.8 Three-phase motors
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