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Introduction Features
Principles Classifications
Engineering Data Further Information
Explanation of Terms Troubleshooting

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Output Voltage

The voltage between the output terminals of an inverter.

Maximum Voltage

The maximum value of a voltage equivalent to the effective value that an inverter can output at the rated input voltage.

Output Current

The current that flows at the output terminals of an inverter.

Output Frequency

The voltage frequency between the output terminals of an inverter.

Braking Resistor

An external resistor that is connected to an inverter to absorb the regenerative energy generated when a load decelerates or an elevating axis descends.
This resistor prevents overvoltage trip of the inverter.

Braking Function - Glossary of Industrial Automation">Regenerative Braking Function

The Braking Function - Glossary of Industrial Automation">regenerative Braking function uses the built-in or an external regenerative Braking circuit to decrease the internal DC voltage of the inverter by converting the regenerated energy from the motor into heat via external Braking resistors.
This function is enabled only when the inverter is connected with one or more external Braking resistors/external regenerative Braking units.

Regenerative Energy

A load connected to a motor has kinetic energy while it rotates and has potential energy while it stays in a high position. The energy that returns to an inverter when a motor decelerates or a load descends.
This phenomenon is known as regeneration, and the energy is called regenerative energy.

Noise Filter

A high-frequency filter that is connected to the power supply side or load side of an inverter to absorb noise that is generated in an inverter when a power device switches.

Cooling Fan

A fan used to cool heating components, such as semiconductors, in the main circuit of an inverter.


A reactor is used to suppress harmonics generated from an inverter.
There are DC reactors and AC reactors. Both of them work to suppress rapid changes in the current.


The current distortion from the normal current sine wave generated when AC is converted to DC and then smoothed.
Inverters generate harmonics, which can affect electrical equipment and peripheral devices.


Speed Control (ASR)

A function that controls the rotation speed of a motor.
(Automatic Speed Regulator)

Control Mode

A method to control the motor speed with an inverter including V/f control, vector control, etc.

V/f Control and V/f Characteristics

A method and characteristics of controlling a motor by applying a specific current to the coil to output a specific torque.
Refer to Principles of Introduction for details.

Constant Torque Characteristics

This setting enables the output of a constant torque based on the frequency, according to the V/f characteristics that represent the proportional relationship between the output frequency and the output voltage.
However, the output voltage is proportional from 0 Hz to the base frequency, it is constant independent of the frequency, from the base frequency to the maximum frequency. This setting is suitable for cart, conveyor, overhead traveling crane, and other applications where a torque is required, independent of the motor rotation speed.

Reduced Torque Characteristics

This setting is suitable for fan, pump, and other applications that do not require large torque at low speeds.
It provides high efficiency, reduced noise, and reduced vibration, because the output voltage is reduced in the low speed range.

Special Reduced Torque Characteristics
(Squared Reduced Load Torque Characteristics)

Characteristics that are virtually constant with the square of the speed (i.e., characteristics at which the torque generation curve is a square curve) and require a large torque at low speeds.

Base Frequency

The maximum frequency at which a motor can generate the rated torque continuously. An inverter has 50 Hz or 60 Hz as its base frequency.

Vector Control

A control method that corrects the output waveform according to the voltage and current output from the inverter to an induction motor.
Refer to Principles of Introduction for details.

Sensorless Vector Control (Vector Control without PG)

Vector control with no feedback from an encoder.
Refer to Principles of Introduction for details.

Vector Control with PG

Vector control with feedback from an encoder.
Refer to Principles of Introduction for details.

Acceleration Time

The time required for the output frequency to go from 0 Hz to the maximum frequency.

Deceleration Time

The time within which an output frequency is reduced to 0 Hz from the maximum output frequency.

Starting Frequency

The frequency at which the inverter starts its output when the RUN signal turns ON.

Maximum Frequency

The maximum value of the frequency that an inverter can output.

Minimum Output Frequency

An output frequency shown when the minimum value of a frequency setting signal is input (e.g., 4 mA for 4 to 20 mA input).

Zero Speed

The condition when the frequency is lower than the minimum output frequency.

Carrier Frequency

A frequency that determines the pulse-width-modulation cycle.
Set a higher carrier frequency value to reduce the metallic noise generated by the motor.

Torque Control

A control method that enables the torque generated by a motor to be equal to a torque reference input.

Starting Torque

The torque that is output when the motor starts.
The motor will not rotate if a load larger than this torque is applied to the motor.

Torque Limit

A function that limits the output torque of a motor.

DC Braking

A function that applies a DC voltage to the induction motor for braking control (i.e., firmly stops motor rotation).
The function operates either when the motor starts or stops.

DC Braking at Startup:
DC Braking is used to stop the motor rotating by inertia without regenerative processing before starting it.

DC Braking at Stopping:
DC Braking is used if the load is large or if it will rotate by inertia and not stop with normal deceleration.


Turning OFF the power supply from the inverter to the motor by operating the protection function of the inverter against overvoltage, overcurrent, or other factors.

Fault Retry

A function that automatically restarts a tripped inverter.

Stalled Status

The status in which the rotor at the motor stator cannot follow the rotating magnetic field because the load applied to the motor is too large or the acceleration or deceleration is too rapid.
The motor loses speed or will be out of step.


The status in which a larger current than the rated output current flows in the circuit.

Overcurrent Suppression Function

function that suppresses the overcurrent caused by a steep current increase due to an impact load etc.
It causes the inverter to stop accelerating when the output current reaches a certain percentage of the rated current.


The status in which more than the rated voltage is applied to a circuit.

Overvoltage Suppression Function during Deceleration

A function that prevents overvoltage trip caused by the regenerative energy from the motor during deceleration.
Two options are available: Automatic deceleration while keeping the voltage rise at a certain level and starting acceleration when the voltage rise exceeds a certain level.


A status in which the power supply voltage is below the rated value.


A status in which the output torque is higher than the rated value.

Overtorque Detection

A function that detects that the estimated motor output torque value exceeded the set level and output the overtorque signal.

Undertorque Detection

A function that detects that the estimated motor output torque value fell below the set level and output the underorque signal.

Electronic Thermal Function

A function that prevents a motor from overloading and burning.

Motor Overload

The status in which a load that is higher than the rated torque is applied to a motor.

Inverter Overload

The status in which the inverter overload protection has been operated by an electronic thermal.

Motor Protection

A function that enables an inverter to internally have the characteristics data of the motor and to internally perform calculations during operation to protect the motor.

Input Phase Loss

A function that detects phase loss in the input power supply.
Detection is performed using the fluctuation in the main circuit's DC voltage. Detection can thus also be performed using the power supply fluctuation and unbalance or degradation in the main circuit capacitor.

Output Phase-loss Detection

A function that detects phase loss in the inverter output terminals. Detection is performed using the values of the currents flowing at the output phases.

Drive Mode

A mode in which operation commands can be received.

Digital Operator

A unit used to operate an inverter and provide display.
A digital operator can be removed from the inverter body and installed on a control panel. It can be also used for remote control.

Frequency Reference

A reference provided by the frequency of the power supply to a motor.

Analog Reference

A frequency reference of an inverter that is set with an analog signal.
Analog signal: A signal that expresses continuous quantities through the size of the signal. 0 to 5 V, 0 to 10 V, 4 to 20 mA, etc.

STOP Command

A command that stops a motor via an inverter using the digital operator or a contact input.
It enables either a free-run stop or a deceleration stop.

Deceleration Stop

A function that decelerates a motor at a certain ratio until the motor stops.

Free-run Stop

A method of shutting off the inverter output to stop the motor rotation.
Executing the free-run stop function causes the motor to fall a free-run state, in which it decelerates due to the load and friction forces exerted on the motor and/or machine and comes to a stop.

Multi-function Input

The functions, such as RUN commands and STOP commands, can be allocated to the multi-function input terminals to use them.

Multi-function Output

The functions, such as a signal during RUN, can be allocated to the multi-function output terminals to output signals.

AVR (Automatic Voltage Regulator) Function

A function that has the inverter automatically compensate for the output voltage to the motor even if the incoming voltage fluctuates.
It is useful as a preventive measure against low output torque to the motor or overexcitation.
Note, however, that the inverter cannot output voltage exceeding the incoming voltage to the inverter.

Multi-step Speed Operation

A function that sets RUN speeds using multi-step speed references and switches the set speeds via external signal input.

Jogging Operation

A function that allows you to determine and fine-tune the motor stop position.

PID Control

A control method that matches a feedback (detected) value to a set target value by combining proportional (P), integral (I), and derivative (D) operations that control the flow rate, air volume, pressure, and other processes.

Proportional (P) Operation:
In this operation, the control volume is proportional to the deviation (difference between the target value and the current value).

Integral (I) Operation:
In this operation, the control volume is proportional to the time integral value of the deviation.
The P operation is less effective as the current value approaches the target value due to smaller deviation, taking a long time to reach the target value. The I operation compensates this disadvantage.

Derivative (D) Operation:
In this operation, the control volume is proportional to the percentage of change in the deviation.
Because using only the PI operation is time-consuming, the D operation is used to effectively compensate for the disadvantage in responsiveness.


A function to automatically measure and record the circuit constants of a motor, including the constants of motor coil or amount of moment of inertia.
Auto-tuning is generally used for vector control.
There are two measuring methods: measurement using a rotating motor and using a motor that does not rotate.

Jump Frequency

A frequency that is set to maintain a stable output by not changing the output frequency to within a specified frequency zone and thus avoid a resonance frequency of a machine.

Restart During Momentary Power Interruption

A function that allows selecting tripping or retrying (i.e., restarting) when the power is momentarily interrupted or there is an undervoltage.

Torque Boost

A function that raises the output torque if it is not sufficient at low speeds.
The inverter provides two torque boost options: Manual torque boost for manual torque adjustment and torque boost - Glossary of Industrial Automation">Automatic torque boost for automatic torque adjustment.

Automatic Torque Boost

A function that automatically controls the output voltage by detecting an output current of an inverter to increase the torque when it is insufficient at low speeds.

Automatic Energy-saving Operation Function

A function that automatically adjusts the inverter output power to a minimum during constant speed operation.
This is suitable for the load of reduced torque characteristics, such as a fan and pump.

Brake Control Function

A function that allows the inverter to control the external brake (non-excitation electromagnetic brake on an induction motor) of equipment, including an elevating system.

RUN Direction Limit Selection

A function that limits the RUN direction of the motor.
(Generally, when viewed from the shaft, the forward rotation is defined as the direction in which the motor rotates counterclockwise and the reverse rotation as the direction in which the motor rotates clockwise.)

Speed Limit

Controlling the rotation speed of a motor.

Speed Deviation

The difference between the value of a set speed and the rotation speed of a motor.

Slip Compensation

A function that calculates the output torque from the output current to compensate the output frequency.

Torque Compensation

A function that increases the output torque when an increase in the motor load is detected.

Torque Compensation Limit

A limit that restricts the torque during vector control if the maximum motor torque is insufficient or to prevent outputting excessive torque.


Induction Motor

A motor that rotates a rotor by means of electromagnetic induction. An induction motor uses AC to supply current to the inner coils of the motor.

Number of Motor Poles

The number of magnetic poles in a motor.
It is equivalent to the number of magnetic poles wound on the shaft generating torque.

Motor Ratings

The limit within which a motor can be used under specified conditions. The motor ratings include the current, voltage, torque, etc.

Braking Torque

The torque that operates in the direction that prevents motor rotation.

Output Torque

The output torque of a motor. That is the moment of force generated by the rotating shaft.

Load Torque

The torque required for the motor to operate the load.
The load torque fluctuates according to the speed.

Load Ratio

The percentage of load current or load torque to the rated current or torque.

Leakage Inductance

A value that indicates the magnetic field that is leaked to the environment or given off as heat (core loss) without generating torque. It is usually given as the inductance (coil) component that generates the magnetic field.