Introduction to Variable Frequency Drives 325

AC

Alternating current. Electricity that regularly reverses the direction of flow. AC switches direction 120 times per second, or at a frequency of 60 hertz, in the U.S.

AC motor

A type of electric motor that runs on alternating current (AC). AC motors are the most common type of industrial motor.

Across-the-line starters

A motor starter that connects the motor directly to the power circuit on startup. Across-the-line starters are easier to set up than VFDs but offer less control functionality.

Alternating current

AC. Electricity that regularly reverses the direction of flow. Alternating current switches direction 120 times per second, or at a frequency of 60 hertz, in the U.S.

amperage

The strength of an electrical current. Amperage is measured in amperes (A).

Amplitude

The maximum strength or height of an AC waveform. Amplitude can describe the maximum current in amperes (A) or the maximum voltage in volts (V).

Anti-parallel diodes

A diode configuration that provides a safe path for excess current from voltage spikes when power is shut off. Anti-parallel diodes, or freewheeling diodes, are typically found in the inverter section of a VFD alongside power output switches.

Artificial intelligence

AI. A computer program with algorithms that function as behavioral rules, allowing a machine or computer to imitate intelligent human behavior. Artificial intelligence allows machines to perform a process with autonomy.

Autonomous

Self-governing. Autonomous systems can be programmed to make decisions without human interaction.

Bearings

A friction-reducing device that allows machine parts to move together without excess wear or friction. Bearings can be damaged by excess vibration during processes like motor startup.

Bleed resistors

A type of resistor used in combination with capacitors to safely drain stored energy. Bleed resistors in a VFD help prevent electric shock when the VFD is not in operation.

Bushings

A hardened metal tube, either fixed or removable, that is used to constrain or guide tools or to reduce friction. Bushings can be damaged by excess vibration during processes like motor startup.

Capacitors

A device consisting of one or more pairs of conductors separated by an insulator that resists a change in voltage, preventing surges or spikes. Capacitors release stored electricity when it is needed.

Compressors

A component that pressurizes ambient air and directs it into a pneumatic system. Compressors squeeze the air and move it under pressure.

Control circuit

The part of a motor circuit that determines when and how a motor is energized or de-energized. Control circuits consist of control devices and usually carry lower voltages than power circuits.

control mode

A setting on a VFD that determines how it will calculate speed adjustments. Control modes on VFDs typically include volts per hertz (V/f), vector control, and direct torque control (DTC).

Converter

An electrical control device used to change electrical power from one form to another. Converters include rectifiers, which change AC into DC.

Conveyor systems

A mechanical system consisting of a flexible belt and at least two fixed pulleys that is used to transmit motion. Conveyor systems should have their belts removed prior to maintenance work.

Current

The flow of electricity. Current strength is called amperage and is measured in amperes (A), also called amps.

DC

Direct current. Electricity that flows in one direction. DC does not reverse the direction of flow.

DC bus

The part of a variable frequency drive that filters electricity flowing from the rectifier to the inverter. The DC bus uses capacitors to smooth out ripple and electrical noise.

DC Fast Charging

A method of charging electric vehicles that converts large amounts of AC from the electric grid to DC within the external charging components, then transfers it directly to the battery engine. DC Fast Charging, which is sometimes called Level 3 Charging, provides much faster charging speeds since it converts much higher AC voltages.

DC filtering

The process of removing unwanted noise, or interference, from a direct current. DC filtering reduces ripple in DC energy to output a smoother, more stable current.

Diode bridge

A circuit consisting of four or more diodes that is used to control the direction of alternating current (AC) by converting it to direct current (DC). Diode bridges in three-phase power applications like variable frequency drives (VFDs) typically consist of six diodes.

Diodes

A semiconductor device with two terminals that allows electric current to flow in only one direction. Diodes are used by variable frequency drive (VFD) rectifiers to convert alternating current (AC) power to direct current (DC) power.

Direct current

DC. Electricity that flows in one direction. Direct current does not reverse the direction of flow.

Direct torque control

DTC. A control mode on a VFD that calculates torque using a feedback device to adjust motor speeds. Direct torque control is the most complex control mode to set up but provides the fastest response times.

Electric vehicles

EVs. A vehicle that is fully or partially propelled by an electric motor that draws its power from a battery. Electric vehicles, including hybrid electric vehicles, require high-energy, lightweight, rechargeable batteries.

electrical noise

Fluctuation of voltage that results from the AC supplied to a variable frequency drive. Electrical noise, or ripple, must be eliminated by the DC bus before the voltage reaches the inverter.

Emissions

Any chemical released into the air during the use or production of a substance. Emissions can be reduced when using VFDs because they greatly reduce unneeded energy usage.

Error codes

An alphanumeric message that references a specific cause of malfunctioning. Error codes on a VFD can indicate a number of issues, including wiring faults and communication issues.

forward-bias

A condition in which a diode allows current to flow from the anode to the cathode when represented as conventional current. Forward-bias diodes have a positive anode and a negative cathode.

freewheeling diodes

A diode configuration that provides a safe path for excess current from voltage spikes when power is shut off. Freewheeling diodes, or anti-parallel diodes, are typically found in the inverter section of a VFD alongside power output switches.

Frequency

The number of complete AC cycles that occur in one second. Frequency is measured in hertz (Hz).

Gate turn-off

GTO. An advanced type of thyristor used to switch DC power on and off at high voltage. Gate turn-off thyristors are typically are slower than IGBTs and MOSFETs but can be used in applications with extremely high voltage.

Heat sinks

A device that cools an electrical system by dissipating heat. Heat sinks are commonly used to cool components in rectifiers and other electronic devices.

Hertz

Hz. A unit of frequency equal to one cycle per second. The hertz unit is used to measure the oscillation of electric current and other waveform occurrences.

Horsepower

hp. A unit used to measure power in large electrical devices, such as motors. One horsepower equals 33,000 foot-pounds of work per minute, or 746 watts.

Hz

Hertz. A unit of frequency equal to one cycle per second. The Hz unit is used to measure the oscillation of electric current and other waveform occurrences.

Induction motors

An AC motor in which the stator generates a magnetic field that energizes the rotor. Induction motors must be VFD-rated in order to be used safely with VFDs.

Inductor

A device that resists a change in amperage, preventing surges or spikes. Inductors consist of a coil of conducting wire that creates a magnetic field when current passes through it.

Industrial Internet of Things

IIoT. A network of physical devices used in manufacturing that contain computing systems. The Industrial Internet of Things allows devices to exchange data and automate processes with limited human intervention.

Insulated Gate Bipolar Transistors

IGBTs. A semiconductor device used to rapidly switch DC power on and off, typically at medium to high voltages. Insulated gate bipolar transistors are used for pulse width modulation in VFD inverters, typically in mid-frequency, high-amplitude applications.

Inverter

A device that converts DC power into a signal that resembles AC power. Inverters in VFDs use pulse width modulation to output pulsed DC that a motor interprets as AC.

Kilowatt

kW. A unit used to measure electrical power that is equal to one ampere multiplied by 1,000 volts. A kilowatt is equal to 1,000 watts.

Metal-oxide-semiconductor field-effect transistors

MOSFETs. A semiconductor device used to rapidly switch DC power on and off or change its amplitude, typically at lower voltages. Metal-oxide-semiconductor field-effect transistors are typically used for high-frequency, lower-amplitude applications and are faster than IGBTs.

Nameplate

A label attached to a device, such as a motor, that displays manufacturer-provided ratings and information. Nameplates include information such as voltage and current ratings.

Oscillation

Back and forth directional changes of alternating current. Oscillation speed is the number of times current moves back and forth, or oscillates, within a specific time.

Parameters

A set of measurable factors or characteristics that define the scope of an operation. Parameters must always match job requirements.

Phase

A measurement of the number of voltages in one alternating current (AC) cycle. Alternating current is either single-phase or three-phase.

Photovoltaic cells

A device that converts light energy into electrical energy. Photovoltaic cells, or solar cells, are used with photodiodes in solar panels.

Pneumatic

A form of fluid dynamics that uses the motion and pressure of gas, usually compressed air, to create power. Pneumatic power converts the potential energy of pressurized gas into mechanical energy.

Pole pieces

A metallic object used to create a magnetic field inside a motor. Pole pieces are used with windings to form electromagnets in a motor.

Pre-charge circuit

An electrical circuit in a VFD that uses resistors to reduce high voltage spikes. The pre-charge circuit allows capacitors in a DC bus to charge at a slower, controlled rate.

Process control

A method of checking product performance and batch consistency by regularly measuring and regulating processes that yield a product. Process control involves collecting and analyzing data to help reduce error.

Process optimization

The practice of constantly measuring the effectiveness of processes and striving to meet more difficult objectives to satisfy customers. Process optimization is driven by the collection and analysis of data.

Product lifecycle

The series of stages a product goes through during use until it is replaced or fails. The product lifecycle of motor components can be improved by using VFDs.

Pulse width

The distance from the start of a single pulse wave to the end of the wave. Pulse width, along with frequency, determines the rotational speed of the motor.

Pulse width modulation

PWM. A method of converting a DC energy source into an artificial AC waveform by rapidly switching the power output on and off. Pulse width modulation produces the output signal that a variable frequency drive sends to a motor.

Pumps

A mechanical device used to move liquids in a hydraulic system. Pumps use suction or pressure in order to operate.

PWM

Pulse width modulation. A method of converting a DC energy source into an artificial AC waveform by rapidly switching the power output on and off. PWM produces the output signal that a variable frequency drive sends to a motor.

Rectifier

A device used in an electrical circuit to convert AC to DC. Rectifiers use diodes, thyristors, or a combination of both to prevent current form flowing in more than one direction.

Resistance

The opposition to current flow. Resistance is measured in ohms (Ω).

Resistors

A device that opposes and restricts current flow. Resistors convert current into work, such as heat or light.

Reverse voltage

A voltage that is applied from the anode to the cathode of a forward-bias diode. Reverse voltage will destroy most forward-bias devices.

reverse-bias

A condition in which a diode prevents the flow of significant current between its anode and cathode in a diode. Reverse-bias prevents current from flowing back toward the AC power source in a VFD.

ripple

Fluctuation of voltage that results from the AC supplied to a variable frequency drive. Ripple, or electrical noise, must be eliminated by the DC bus before the voltage reaches the inverter.

Rotary screw compressors

A pneumatic compressor that derives its pressurizing ability from two interlocking threaded cylinders. The rotary screw compressor has screws that trap and compress air.

Semiconductor

A material that restricts electrons but still allows them to flow. Semiconductors, such as silicon, have more electrical conductivity than insulators but less than conductors.

Sensors

A device that detects the presence or absence of an object, or certain properties of that object, and provides feedback. Sensors send feedback in the form of signals, which can be measured and recorded.

Sine wave filter

An electronic device that levels out the frequency of direct current, turning square waves into sine waves. Sine wave filters reduce noise in an electronic signal to further improve control precision.

Sine waves

An AC waveform with a curved shape that resembles a sideways letter “S.” Sine waves, also known as sinusoidal waves, are the most common AC waveforms and are produced by alternators and generators.

Sinusoidal waves

An AC waveform with a curved shape that resembles a sideways letter “S.” Sinusoidal waves, also known as sine waves, are the most common AC waveforms and are produced by alternators and generators.

Solar panels

A circuit of linked photovoltaic cells. Solar panels are used to provide large amounts of solar power.

speed

The rate at which an object travels in a given period of time. In motors, speed reflects rotational movement and is measured in revolutions per minute (rpm).

Square waves

A waveform created by using pulse width modulation to convert DC to artificial AC. Square waves produced by PWM form a pattern of high and low voltage levels that closely mimic or approximate sine waves.

Squirrel cage motor

An AC induction motor with a rotor that consists of metal bars connected at either end. The squirrel cage motor is the most common AC motor.

Three-phase

Alternating current power that consists of three overlapping waves. Three-phase power is used for all large AC motors and is the standard power supply for factories and industrial buildings.

Thyristors

A complex semiconductor switch that has a four-layer sandwich and four terminals called the gate, base, anode, and cathode. Thyristors are primarily used for high-power and high-voltage motor applications.

torque

A force that causes rotation. Torque determines how much work a motor or generator can accomplish.

Troubleshooting

The systematic elimination of the various components of a system, circuit, or process to locate a malfunctioning part. Troubleshooting a motor circuit often involves using electrical diagrams as a guide to find the problem area.

Ultrasonic sensors

A type of non-contact sensor that emits and analyzes high-frequency sound waves. Ultrasonic sensors are extremely precise and can be used with almost any type of material.

variable frequency drives

VFDs. A device that converts incoming AC power into other desired frequencies to allow for AC motor speed control. A variable frequency drive adjusts the speed of a motor to match a required load by adjusting the frequency and voltage of electrical power.

Vector control

A control mode on a VFD that uses sensors and external components to adjust motor speeds. Vector control is more complex to set up than volts per hertz but provides more precise control.

VFD

Variable frequency drive. A device that converts incoming alternating current (AC) power into other desired frequencies to allow for AC motor speed control. A VFD adjusts the speed of a motor to match a required load by adjusting the frequency and voltage of electrical power.

volt

V. A unit of measurement that indicates the amount of electrical force or pressure in a circuit. The volts unit measures voltage, which is also known as electromotive force.

Voltage

The electrical pressure or potential that forces current to flow through a circuit. Voltage is measured in volts (V) and is also called electromotive force.

Voltage spikes

A sharp, sudden increase in voltage in a circuit that can damage equipment. Voltage spikes are caused by malfunctions or changing load conditions.

Volts per hertz

V/f. A control mode on a VFD that adjusts motor speeds based on a ratio of voltage to frequency. Volts per hertz is the most common control mode used with VFDs.

Wireless networks

A network that uses radio waves instead of copper or fiber optic cable. In wireless networks, devices transmit a radio signal through an antenna.