Basic VFD Parameters and What They Mean

A prior warning

Each manufacturer names and numbers parameters in its own way, and often organizes them in a quick start menu and an advanced one. This guide describes the common functions, so you know what you are deciding, and gives no values or menu paths. The settings of a real installation are defined with the equipment manual, the motor data and the needs of the process.

Group 1: motor data

This is the first and most important group, because the rest of the behavior is calculated from it.

An error in these data carries through everything. A motor connected in delta or wye changes the nameplate voltage and current: use the data for the actual connection.

Many drives offer an autotune or motor identification, which measures resistance and inductances, needed for vector control. What is measured and how it runs is defined by each drive; see V/f, vector and DTC control. The drive stages and PWM modulation are explained in how a variable frequency drive works.

Group 2: control mode

It defines the algorithm with which the drive governs the motor: scalar V/f, sensorless vector, encoder vector or others. It determines which additional parameters appear, such as the low-frequency voltage boost (V/f) or the speed loop gains (vector).

Group 3: command and reference source

These are two different decisions:

• Command source: who gives the run and stop command. It can be the drive keypad, the digital inputs on the control terminal, or a communication bus.
• Speed reference source: who says how fast. A potentiometer, a 0-10 V or 4-20 mA analog input, fixed speeds through digital inputs, the output of an internal PID loop or a value over fieldbus.

A frequent field error is that the command arrives from one source and the reference from another, or that the drive was left in local keypad mode and the PLC cannot control it. The local/remote switchover must be planned in the design.

Analog inputs need the signal type (voltage or current) to match the physical hardware selector, and the ends of the scale to correspond to the minimum and maximum frequencies.

Group 4: ramps

The acceleration ramp is the time the drive takes to bring speed from zero to maximum frequency (or to the reference the manufacturer defines). The deceleration ramp is the time to come down. Some brands allow S-curve ramps to soften the ends of the motion.

• Acceleration ramp too short: the drive reaches the current limit or trips on overcurrent, because the motor must overcome the load inertia.
• Deceleration ramp too short: regenerated energy raises the bus voltage and the drive trips on overvoltage, unless there is a braking resistor or a regenerative unit, as explained in the guide on drive braking.

Group 5: limits

• Minimum and maximum frequency. They bound the speed range. The minimum protects motor cooling and the lubrication of equipment such as pumps; the maximum, the mechanics.
• Current limit. Prevents the current from exceeding a value and, if needed, reduces frequency while accelerating or under overload.
• Torque limit. In vector modes, caps the torque demanded from the motor.
• Switching frequency. A trade-off between noise and losses, with the effect on drive capacity described in sizing and derating.
• Skip frequencies. Avoid speeds that excite mechanical resonances.

Group 6: protections

Most drives include:

• Electronic motor thermal protection, based on a model of current and speed, or on an input for a PTC probe or thermistor. Setting it requires the nameplate current; it does not replace the motor protection relay in applications that demand one (see motor protection relay).
• Protection against overcurrent, overvoltage and bus undervoltage.
• Ground fault at the output.
• Phase loss at input and output.
• Overtemperature of the drive.
• Loss of the analog reference, which defines what the unit does if the cable is cut.

The behavior on each fault (trip, warning, continue at a fixed speed) is parameterized and must match what the process tolerates.

Group 7: inputs and outputs

Digital inputs receive commands (run, stop, direction, speed selection, fault reset, safe stop). Relay or transistor outputs report status (running, fault, speed reached). Analog ones carry the reference or process feedback, and an analog output can deliver speed or current to a PLC. The logic (NO/NC, sink/source) must match that of the PLC or the pushbutton station, and the emergency stop does not depend on a digital input alone: see STO and SS1.

Illustrative example

Illustrative data, not from a real plant. A pump starts fine from the keypad, but does not respond to PLC commands.

1. Check the command source: it was on keypad; change it to terminals or fieldbus per the design.
2. Check the reference source: it was still on the keypad potentiometer.
3. Check the digital input logic against the PLC outputs.
4. Check the analog input scale with a known signal value.

None of these steps changes hardware: they are parameters for the origin of the command.

Parameter management

Parameters are part of the project documentation, like the drawings. Some practices that save time over the life of the equipment:

• Record the final list of parameters changed from factory defaults, with date, firmware version and the person who made the change. Many drives let you export it with their commissioning software or from the panel.
• Keep a copy outside the unit. If the drive fails, the copy lets you configure the replacement without rebuilding the settings blindly.
• Control changes. An emergency adjustment at two in the morning must be logged and reviewed afterward. Otherwise, months later nobody knows why the unit behaves differently.
• Protect the parameters with a password or lock, especially safety parameters and those that affect motor protection.
• Coordinate with the PLC. Parameters the PLC writes over fieldbus should not also be changed from the keypad; define who owns each parameter.
• Check on replacement. A replacement drive, even with the same model number, may carry other firmware. Review differences in functions and scales before loading the copy.
• Validate with a functional test. After loading or changing the parameters, test run, stop, directions, limits, a simulated fault and loss of reference.

Orderly parameterization also eases diagnosis: most drive fault logs are interpreted with the current and ramp values at that moment.

Common mistakes

• Nameplate data copied from another motor.
• Leaving factory values for ramps and limits unreviewed.
• Analog input hardware selector on voltage and signal on current.
• Leaving the unit in local mode at handover.
• Parameters never backed up: without a backup, replacing the drive is a long job.
• Changing parameters live without logging the change.
• Raising the thermal protection setting to avoid trips, hiding the cause.

Checklist

• Motor nameplate data entered and verified against the actual connection.
• Control mode and autotune done and recorded.
• Command and reference sources defined, with local/remote switchover.
• Analog input scales consistent with the hardware.
• Ramps, frequency and current limits suited to the load.
• Protections enabled and their fault action defined.
• Inputs and outputs tested against the PLC or pushbutton station.
• Parameter backup with date and version.

How we help

The parameterization of each drive depends on the motor, the load and the control system. In Engineering design and studies we define the control scheme and the signals, and during commissioning, in Colombia or elsewhere on request, we verify that the unit responds to the process as designed. Write to us through the contact page.

Related guides

• Siemens SINAMICS drives
• Schneider Altivar drives
• Allen-Bradley PowerFlex drives
• WEG CFW drives
• Induction motor and its protections
• Drive tripping: causes in the power system
• Drive sizing and derating
• Drive communication: Modbus, PROFINET and EtherNet/IP

References

• Parameter and startup manuals from the drive manufacturers cited in the equipment guides.
• IEC 61800, adjustable speed electrical power drive systems.

Frequently asked questions