Optional Regenerative Or Braking Parts - Savch SDA2 Series User Manual

9.3 Optional Regenerative Or Braking Parts

How magnitude is the resistor applied depends on the load torque inertia, rotating speed before braking, the
time within which the braking can be finished, and maximal withstand current for brake circuit. To facilitate the
analysis, the braking process can be divided into two phases. We will take a SDA2-2T2.0G as the example to
make a introduction, with the normal bus voltage of 310V。
· Phase 1:
Firstly we consider the situation that, under the condition of non-friction resistance torque and non
regenerative resistor, the dynamic energy of the rotor will all charge into a capacitor. Then, the voltage applied on
the capacitor can be calculated in following formula。
J:The sum of all inertias of the rotors connected on same shaft, unit: kg· m
n:The rotating speed of the rotor before braking, unit: radian/s;
V:Under non-friction resistance torque and non- regenerative resistor condition, the voltage that has been
charged into the capacitor;
C:Capacitance inside servo motor drive;
· Phase 2:
The electric energy that has been charged into is turning into thermal energy. The voltage threshold value to
activate the brake of servo motor drive is 370V, the voltage threshold value to inactivate the brake is 360V, so the
voltage value for whole braking process is the average value of these two, which is 365V.
R: Resistance value of regenerative resistor；
t:Braking time；
When the value of the regenerative resistor is confirmed, you shall confirm its power now. P=370*370/R.
Since the braking status won't last in a long term, the actual power can just take a value a little smaller than P in
accordance with the braking duty ratio. For example, if the braking duty ratio is 20%, the resistor power could be
0.2P. Feed more vacancy, take 0.2×P×150%=0.3P.
In order to simplifying the treatment, in above analysis, it's believed that the dynamic energy of the rotor is
finally transferred into the thermal energy consumed by the resistor and the electric energy left in the capacitor,
and assumed that the braking operation is completed During once process. Actually certain part of the energy of
the rotor will be consumed for other reasons, such as load friction resistance force and driving damping. Besides,
after turning on the brake, the voltage may be within 360~370V. If the voltage drops to be lower than 360V, the
brake will be shut down. So it may take several times to start the brake, and the braking process may not be
accomplished for just once try. Customers can make some adjustments based on actual situations.
●
The resistance value of regenerative resistor shall attain the requirement to maximal current limit. After
parallel connection, the current=bus voltage during braking/R, so the value must be guaranteed not to be
exceed the maximal brake current limit.
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CAUTION
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