12.09.2019
12
QUICK START GUIDE :
brake
unit extern
High brake voltage could ensure that the brake unit would not misact but too high voltage will do
damage to the long running equipments, especially to the inverter with spares of low voltage. At the
same time, high voltage will also make the motor voltage saturated, motor waste and decline control
precision.
7.2.
PB60 brake unit characteristic :
•
Special circuit design for any resistor in the market, no need for senseless resistor.
•
When abnormal working, no damage to the inverter. P-N will not be short circuited if the cable
connection is good.
•
Suitable for domestic electric net, normal running in 300V to 460V.
•
Profession manufacture, keeps improving.
7.3.
Brake unit function :
In the system of frequency conversion, motor decelerates and stops by reducing the frequency. At the
moment
of frequency reduction, motor’s synchronization rotate speed declines, and because o
f
machinery inertia, motor rotor rotate speed remains. When synchronization rotate speed is smaller
than rotor rotate speed, the phase of rotor current almost becomes 180
,
motor turns from
electromotion to electricity generation. Meanwhile torque of motor axis changes to brake torque and
decelerate the motor speed quickly, motor is during regeneration brake, motor regeneration energy
feedback to DC bus via fly-wheel diode. Because the energy in the DC circuit could not feedback to
electric net by diode bridge but only absorbed by inverter, although other section could waste some
energy but capacitor could
accumulate electric charge for a short time and forms “ pumps raise
voltage” to enlarge the DC bus voltage.
Too high DC voltage will damage the spares. So to manage such
regeneration energy, brake unit (resistor) should be used to waste them, otherwise the inverter will be
OU or faulted.
7.4.
Brake current calculation :
Brake current is the DC current in the brake unit and brake resistor.
380V Standard AC motor
：
P Motor power
。
K---------- Conversion efficiency of the machine energy when feedback comes. Usually 0.7 (applicable
for most occasion)
V
DC working voltage. 670V
I
Brake current.
Calculation norm
：
Motor electricity regeneration should be absorbed completely by resistor.
Motor electricity regeneration=1000*P*K=Resistor absorbing power.
