Chapter 2 Product Information
-21-
capacity as specified in the instruction manual.
Due attention shall be paid to the comparison
between the rated currents of motor and
inverter. The overload capacity of the
inverter only affects the startup and brake
process. In case short-time overload occurs
during the running process, variation of load
speed may arise. If the requirement for the
speed precision is relatively high, it can
consider increasing the level.
Fan and pump type: Their requirements
for the overload capacity are relatively low.
Since the load torque is proportional to the
square of the velocity, the load is relatively
light (except Roots fan) when running at low
velocity. In addition, this type of load has no
special requirements for the rotation precision.
Thus, square torque V/F is selected.
Constant torque load: Most of loads have
constant toque characteristics, but the
requirements for rotation velocity and dynamic
performance are low. Extruding machine,
agitator, belt conveyer, transporting trolley in
the factory, and translational unit of crane are
the examples. It can select MS V/F running
mode when performing prototyping test.
There are certain static and dynamic
index requirements for controlled object:
Generally, such load requires strong
mechanical characteristics at the low speed
so as to meet the dynamic and static index
requirements of the control system by
manufacturing process.The open-loop vector
control mode can be selected.
2.10 Guide to Prototyping of
Brake Components
Table 2-5 MD300 Inverter Bake
Components Prototyping Table,The data can
be used as guidance. The user can select
different resistances and powers in
accordance with the actual situation (However,
the resistance must be larger than the
recommended value in the table and the
power can be very big.). The selection of
braking resistor shall be determined according
to the power of the motor in the actual
application system, which is also influenced
by system inertia, deceleration time, potential
energy of load. The larger the system inertia is,
the shorter the deceleration time will be and
the braking will be more frequent. Therefore, it
is required to select the braking resistor with
larger power and smaller resistance.
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