Motor Capacity Selection
Before selecting an inverter, first the motor should be chosen. In
selecting the motor, first calculate the load inertia for the
applications, and then calculate the required capacity and torque.
¦ Make a simple selection (use Formulas for the
required output power)
This method of calculation helps select a motor by calculating the output
(W) required by the motor to maintain its regular rotations. It does not
include calculation of the effect of acceleration//deceleration.
Therefore, make allowance for the calculated value to select a motor. This
calculation method can be applied to applications that operate constantly
such as fans, conveyors, agitators etc.
This calculation method must not be applied to the following applications:

Those requiring instant startup.

Those that frequently repeat operation and stop.

Those that have a large inertia at the power transfer part.

Those that have an inefficient power transfer part.
For StraightLine Operation: Normal Power Po [kW]
For Rotating Operation: Normal Power Po [kW]
¦ Detailed Selection Method (R.M.S Algorithm)
This method helps to select a motor by calculating the effective torque
and maximum torque required to achieve a certain pattern of operation for
the application. It selects a motor that is optimal for a particular
operation pattern.
Calculate the inertia with a Motor Shaft Conversion
Value
Calculate inertias of all the components with the formula for inertia
calculation shown below to convert them to a motor conversion value.
Calculate Motor Shaft Conversion Torque and
Effective Torque
Calculate the acceleration torque from the load torque calculated from
both the motor shaft conversion value and the motor rotor inertia. Then
Combine this acceleration torque and the load torque calculated from the
friction force and the external force that are applied to the load. Now
you get the required torque to operate a motor.
Acceleration Torque
Motor Shaft Conversion Load Torque (External Force/Friction)
Calculation of Total Torque and Effective Torque
Maximum Torque: T_{MAX} = T_{1} = T_{A} + T_{L}
* Please make use of the Servo Motor selection software, which can
calculate the motor shaft conversion inertia and effective/maximum torque,
as above.
Motor Selection
Use the formula below to calculate the motor capacity from the effective
torque and the maximum torque that were obtained above.
Select the larger of the two generated values as the motor capacity.
Select a motor the capacity of which is larger than the calculated value
and makes allowance for an error.

Motor Capacity corresponding to Effective Torque
Motor Capacity [kW] = 1.048·N·T_{RMS}·10^{4}
N: Maximum Rotations (r/min)

Motor Capacity capable of Providing Maximum Torque
Motor Capacity [kW] = 1.048·N·T_{MAX}·10^{4}/1.5
N: Maximum Rotations (r/min)
Inverter Capacity Selection
Select an inverter that can be used for the selected motor in the process
of "Motor Selection".
Generally, select an inverter which fits the maximum applicable motor
capacity of the selected motor.
After selecting an inverter, check if it meets with all of the following
conditions. If it does not, select an inverter that has a one class larger
capacity and check the feasibility again.
Motor Rated Current = Inverter Rated Output
Current Maximum Time of Continuous Torque Output Time in an Application =
1 minute
* Where the inverter overload capacity is "120% of Rated Output Current
for 1 minute", check it for 0.8 minute.
* Where a 0 Hz sensorless vector control is being used, or where torque
must be maintained for 0 (r/min) rotation speed and where 150% of the
rated torque is frequently required, use an inverter which is one rank
larger than the one selected by the above method.
Outline of Braking Resistor Selection
¦ Importance of Braking Resistor
If the regenerative energy generated in deceleration or descent in an
application is too great, the main circuit of an inverter may have an
increased voltage and it may be damaged.
Because the inverter usually contains the overvoltage LAD stop function,
it is not actually damaged. However, the motor stops detecting an error,
making a stable and continuous operation disabled. Therefore, you must
discharge the regenerative energy outside of the inverter.
What is Regenerative Energy?
A load connected to a motor has kinetic energy when rotating, and
potential energy when it is located in a high position. When the motor
decelerates, or when the load descends, the energy is returned to an
inverter. It is known as regeneration, and the energy generated by the
phenomenon is known as regenerative energy.
Preventing Breaking Resistance
The following are methods to prevent the connection of braking resistance.
These methods will make the deceleration time increase, so check if it
will not cause problems.

Enable the deceleration stall prevention (enabled in factory settings) (It
will automatically increase deceleration time not to cause an overvoltage
to stop the motor).

Set a longer deceleration time. (Cause the regenerative energy to decrease
per unit of time.)

Disable FreeRun. (Prevent the regenerative energy from returning to an
inverter.)
¦ Make a Simple Selection for Braking Resistors
It can be a simple selecting method by using the ratio of time in which
regenerative energy is produced in a normal operating pattern.
Calculate the usage ratio from the following operating pattern.
Usage Rate = t/T × 100 (% ED)
t: Deceleration Time (Regenerative Time)
T: Single Cycle Operation Time
¦ Make a Simple Selection of Braking Resistor
When the usage ratio for the braking resistor selected on the previous
page exceeds 10% ED, or when an extremely large braking torque is
required, use the method below to calculate a regenerative energy and make
your selection.
Calculation of Required Braking Resistor
V: 200V class inverter 385 [V]
400V class inverter 760 [V]
T: Maximum Braking Torque [N·m]
Tm: Motor Rated Torque [N·m]
N: Maximum Rotation Speed [r/min]
* Calculate a braking torque using the above "Motor Capacity Selection".
Calculation of Average Regenerative Energy
Regenerative Energy is produced when the motor rotation direction and the
torque direction are opposite.
Use the following formula to calculate a Regenerative Energy per cycle
interval.
* Forward rotation direction is Forward for the speed, and the torque in
the Forward rotation direction is Forward for the torque.
* Calculate a braking torque using the above "Motor Capacity Selection".
Motor Selection
Select a Braking Resistor from the required braking resistance and average
regenerative energy on the left.

Required Braking Resistance = Resistance of Braking Resistor = Minimum
Connection Resistance of Inverter or Regenerative Braking Unit

Average Regenerative Energy = Permissible Power for Braking Resistor
* If a resistance that has a less then the minimum connectable value is
connected on an inverter or regenerative braking resistor unit, the
internal breaking transistor can be damaged. When the required braking
resistance is less than the minimum connectable resistance, change the
inverter or regenerative energy braking to the one having a larger
capacity and a minimum connection resistance less than the required
braking resistance.
* Two or more regenerative braking units can be operated in parallel.
Refer to the following formula to know the braking resistance value in
such a case.
braking Resistance (O) = (Required braking Resistance as calculated above)
× (No. of Units in use)
* Do not use the above formula to select a generative braking resistance
value. 150W does not reflect a permissible power capacity, but the maximum
rated power per unit of resistance. The actual permissible power varies
according to a resistance.
