A-5 Overview of Inverter Selection
Motor Capacity Selection
Before selecting an inverter, first the motor should be chosen. In
selecting the motor, calculate the load inertia appropriate to the
• Example in conveyor application
application, and then calculate the required capacity and torque.
This method of calculation helps you select a motor by
calculating the output (kW) required by the motor to maintain
its steady rotations. To use this method for motor selection,
make allowance for the calculated result because it does not
include acceleration/deceleration and other transient state
calculations. The simplified selection method is suitable for
fan, conveyor, mixer, and other applications where a constant
state continues for a while.
* The simplified selection method cannot be used for the
following applications. For these applications, use the detailed
selection method.
•
Those requiring rapid startup (acceleration).
•
Those that frequently repeat run and stop.
•
Those that have a large inertia at the power transfer part.
•
Those that have an inefficient power transfer part.
J
W
: Shaft conversion inertia (Cylinder-1-shaft conversion) [kg·m
2
]
J1 : Inertia of cylinder 1 (Cylinder-1-shaft conversion) [kg·m
2
]
J2 : Inertia of cylinder 2 (Cylinder-1-shaft conversion) [kg·m
2
]
J
3
: Inertia of workpiece (Cylinder-1-shaft conversion) [kg·m
2
]
J4 : Inertia of belt (Cylinder-1-shaft conversion) [kg·m
2
]
M1 : Mass of cylinder 1 [kg]
M2 : Mass of cylinder 2 [kg]
M3 : Mass of workpiece [kg]
M4 : Mass of belt [kg]
D1 : Diameter of cylinder 1 [mm]
D2 : Diameter of cylinder 2 [mm]
ï‚—
For linear motion: Steady power P0 [kW]
• Example in roller application
* The same calculating formula is applicable to belt conveyors.
ï‚—
For rotation motion: Steady power P0 [kW]
J
W
: Shaft conversion inertia (Roller-1-shaft conversion) [kg·m
2
]
J1 : Inertia of roller 1 (Roller-1-shaft conversion) [kg·m
2
]
J2 : Inertia of roller 2 (Roller-2-shaft conversion) [kg·m
2
]
M : Mass of workpiece [kg]
D1 : Diameter of roller 1 [mm]
D2 : Diameter of roller 2 [mm]
• Example of conversion into motor-shaft inertia
This method helps you select a motor by calculating the effective torque and maximum
torque values required to achieve a certain pattern of operation for the application. It
selects a motor that is optimal for a particular operation pattern.
ï‚—
Calculation of load inertia and motor-shaft conversion inertia Depending on the type of
the motor transfer system, calculate the inertia for all parts and convert it into
the motor-shaft inertia.
• Example in hoist application
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