AC Inverter Terminology

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					A Subsidiary of Regal-Beloit Corporation

                    AC Inverter Terminology
AP200 - 9/01
                                                                        AC Inverter Terminology
A Subsidiary of Regal-Beloit Corporation

The rate of change in velocity as a function of time.            Carrier Frequency
Acceleration usually refers to increasing velocity and           The base frequency (hertz) of the modulated wave.
deceleration to decreasing velocity.
Acceleration Boost                                               Open construction of a drive for mounting within a
During acceleration, the output voltage is increased to          customer’s existing enclosure.
increase motor torque.
Acceleration/Deceleration                                        A filter device consisting of an inducer and a resistor.
The time rate of change in velocity, acceleration refers
to an increase in velocity, while deceleration refers to a       Closed Loop
decrease in velocity.        Generally expressed as              A broadly applied term relating to any system in which
radians/sec/sec.                                                 the output is measured and compared to the input. The
                                                                 output is then adjusted to reach the desired condition.
Acceleration Torque                                               In motion control, the term typically describes a system
Numerical difference between motor torque produced               utilizing a velocity and/or position transducer to generate
and load torque demanded at any given speed during               correction signals in relation to desire parameters.
the acceleration period. It is this net torque which is
available to change the speed of the driven load.                Constant Horsepower Range
                                                                 A speed range in which the motor is capable of delivering
Accuracy                                                         constant horsepower above rated speed. Torque will
A measure of the difference between expected position            decrease with speed, but horsepower remains constant.
and actual position of a motor or mechanical system.
                                                                 Constant Torque Range
Adjustable Frequency Drive                                       A speed range in which the motor is capable of delivering
Term for an AC adjustable frequency drive, inverter, or          a constant torque, subject to cooling limitations of the
AC drive.                                                        motor.

Adjustable Speed                                                 Constant Voltage Range
The concept of varying the speed of applications.                The range of motor operation where the drive’s output
                                                                 voltage is held constant as output frequency is varied.
Adjustable Speed Drive (Electrical)                               This speed range produces motor performance similar
The adjustable speed drive is comprised of the motor,            to a DC drive’s constant horsepower range.
drive controller and operator’s (either manual or
automatic).                                                      Constant Volts per Hertz (V/Hz)
                                                                 This relationship exists in AC drives where the output
Base Frequency                                                   voltage is varied directly proportional to frequency. This
The lowest frequency at which a drive is capable of              type of operation is required to allow the motor to
delivering maximum output power.                                 produce constant rated torque as speed is varied.

Base Speed                                                       Converter
The motor speed while delivering rated torque.                   The process of changing AC to DC.                This is
                                                                 accomplished through use of a diode rectifier to thyristor
Bypass                                                           rectifier circuit. The term “converter” may also refer to
A control method whereby the drive can be isolated and           the process of changing AC to DC to AC (e.g., adjustable
the control circuit connected directly to the motor.             frequency drive). A “Frequency converter”, such as that
                                                                 found in an adjustable frequency drive, consists of a
Capacitor                                                        rectifier, a DC intermediate circuit, an inverter and a
A device which holds electrical charge for a period of           control unit.
time, prevents the flow of direct current, and allows the
follow of alternating current. These components serve            Current Limit
as filters in AC drives.                                         An electronic method of limiting the maximum current

                                                                          AC Inverter Terminology
A Subsidiary of Regal-Beloit Corporation

available to the motor. This is adjustable so that the            resolution feedback data related to shaft position and is
motor’s maximum current can be controlled. It can also            used with other circuitry to indicate velocity and direction.
be present as a protective device to protect both the              The encoder produces discrete electrical pulses during
motor and controller from extended overloads.                     each increment of shaft rotation.

Current Limit Acceleration                                        Feedback
A system of control in which acceleration is so governed          The element of a control system that provides an actual
that the motor current does not exceed an adjustable              operation signal for comparison with the set point to
maximum value.                                                    establish an error signal used by the regulator circuit.

Device Net                                                        Filter
A low cost industrial network to connect industrial devices       An electrical device used to suppress electrical noise.
such as motor starters and drives, and operator displays
to PLCs and Pcs. The network eliminates expensive                 Flyback Diode
hard-wiring while providing device-level diagnostics.             This is a super fast recovery diode that snubs current
                                                                  and voltage spikes as a result of the fast transients that
DIN                                                               occur when IGBT are turned on and off quickly.
The abbreviation for the association in West Germany
that determines the standards for electrical and other            Four-Quadrant Operation
equipment used in that country, Deutsche Industrie                The four combinations of forward and reverse rotation
Normenausschuss.                                                  and forward and reverse torque of which a regenerative
                                                                  drive is capable. The four combinations are:
Displacement Power Factor
The cosine of the phase displacement angle between the            1.   Forward rotation/forward torque (motoring)
fundamental component of the voltage and current.                 2.   Forward rotation/reverse torque (regeneration)
                                                                  3.   Reverse rotation/reverse torque (motoring)
Drive                                                             4.   Reverse rotation/forward torque (regeneration)
The equipment used for converting available power into
mechanical power suitable for the operation of a                  Frequency
machine.                                                          The rate at which alternating current reverses its
                                                                  direction of flow. Measured in hertz (Hz).
Dynamic Braking
A way of quickly stopping a motor by disconnecting the            Giant Transistor (GTR)
power source. The rotating motor then becomes a                   GTRs are low gain devices where the control or base
generator. When connected to a resistor, the energy of            signal must be maintained to keep the device turned.
rotation is then dissipated as heat in the resistor.
Efficiency                                                        Acronym for gate turn-off or gate turn-on power
The ratio of the power delivered by the converter to the          semiconductor device.
total power drawn from the plant electrical power system.
 Efficiency is usually expressed in percentage.                   Harmonics
Encoder                                                           Integral multiple of the fundamental frequency, often
An electromechanical transducer that produces a serial            superimposed on and thus distorting the fundamental
of parallel digital indication of mechanical angle or             current or voltage sinusoidal wave shape.
displacement. Essentially, an encoder provides high
                                                                  Acronym for insulated gate bipolar transistor.

                                                                  The state or property of a system where there is an
                                                                  output but no corresponding input.

                                                                  Integrated Motor Drive

                                                                        AC Inverter Terminology
A Subsidiary of Regal-Beloit Corporation

Unit where the motor and drive have been integrated into         Open Collector
a single device.                                                 An output signal provided by a transistor where “open
                                                                 collector output” acts like a switch closure to ground
Inverter                                                         when activated.
A term commonly used for an AC adjustable frequency
drive. An inverter is also a term used to describe a             Open Loop
particular section of an AC drive. This section uses the         A control system that lacks feedback.
DC voltage from a previous circuit stage (intermediate
DC circuit) to produce an AC current or voltage having           Overcurrent Relay
the desired frequency.                                           An overcurrent relay operates when the current through
                                                                 the relay, during its operating period, is equal to or
Kilowatt                                                         greater than its setting.
A unit of power equal to 1000 watts and approximately
equal to 1.34 horsepower.                                        Overload Relay
                                                                 An overload relay is an overcurrent relay that operates
LED                                                              at a predetermined value of current in order to prevent
An acronym for light emitting diode.                             overheating of the motor.

Linear Acceleration/Deceleration (LAD)                           Overshoot
A circuit that controls the rate at which the motor is           The amount that a controlled variable exceeds a desired
allowed to accelerate to a set speed or decelerate to            value after a change of input.
zero speed. On most drives, this circuit is adjustable and
can be set to accommodate a particular application.              Programmable Logic Controller (PLC)
                                                                 A Programmable Logic Controller (PLC) uses
Metal Oxide Varistor (MOV)                                       programmed logic instructions to control banks of inputs
This device is used to suppress voltage transients that          and outputs which interface timed switch actuation to
may occur on an AC line.                                         external electron mechanical devices.

Modbus ®                                                         Position Transducer
A communication protocol widely used to establish                An electronic device (e.g., encoder or resolver) that
master-slave communication between intelligent devices.          measures actual position and converts this measurement
 A Modbus® message sent from a master to a slave                 into a feedback signal convenient for transmission. This
contains the address of the slave, the “command”, the            signal may then be used as an input to a programmable
data, and a check sum.                                           controller that controls the parameters of the positioning
Noise (EMI/RFI)
Electrical disturbances that interfere with proper               Potentimeter (POT)
transmission of electrical signals. Noise can have               A passive device (variable resistor) used to vary voltage
adverse affects on the system performance.                       between a minimum and maximum level. The standard
                                                                 speed POT is a 300° or single-turn. Operators control
                                                                 the speed of a motor from the potentiometer connected
                                                                 to a drive.

                                                                 Preset Speed
                                                                 Preset speed refers to one or more fixed speeds at which
                                                                 the drive will operate.

                                                                 Proportional-Integrated-Derivative (PID)
                                                                 The act of recognizing a velocity or position error in a
                                                                 system and applying correction (or voltage change) to
                                                                 the system amplifier, thereby changing the motor’s speed
                                                                 or altering position. PID refers to a group of gain
                                                                 parameters that tune or optimize the response of a

                                                                        AC Inverter Terminology
A Subsidiary of Regal-Beloit Corporation

closed-loop system.
                                                                 Regenerative Braking
• Proportional                                                   The technique of slowing or stopping a drive whereby the
  This feedback loop compares error and adds an equal            kinetic energy of the motor and driven machinery is
  amount of reference beyond the original. For                   returned to the power supply system.
  example: with a 20% error, the loop applies 20% more
  than the original reference.                                   Regenerative Control
                                                                 A regenerative drive contains the inherent capability
• Integral                                                       and/or power semi-conductors to control the flow of
  This loop examines the average error over a number             power to the motor and from the motor back to the power
  of samples and makes the correction associated with            supply.
  it. For example: with a 20% error reading in one
  window and 10% error in another, the integral loop             Regulation
  may apply 15% error correction in the third window             The ability of a control system to hold a speed once it
  based on average of previous readings.                         has been set. Regulation is given in percentages of
                                                                 either base speed or set speed. Regulation is rated
• Derivative                                                     upon two separate sets of conditions:
  This loop reads instantaneous change in error as
  opposed to the error itself. It analyzes how an error          A. Speed Regulation is the percentage of speed
  differs from a previous error and adjusts accordingly.            change with a defined change in load, assuming all
   PID combines all three loops resulting in an extremely           other parameters to be constant.
  accurate form of digital error correction. Each loop
  checks and balances the other to assure the right              B. Line Regulation is the percentage of speed change
  amount of error correction.                                       with a given line voltage change, assuming all other
Pulse Width Modulation (PWM)
A type of AC adjustable frequency drive that                     Relay
accomplishes frequency and voltage control at the                An electrically controlled device that causes electrical
output section (inverter) of the drive. The drive’s DC bus       contacts to change status. Open contacts will close and
voltage is always a constant amplitude and by “chopping”         closed contacts will open when rated voltage is applied
(pulse width modulating), the average voltage is                 to the coil of the relay.
RS-485                                                           The degree to which a parameter such as position or
An interface standard between devices that allows for            velocity can be duplicate.
multi-point communications. The RS-485 standard
permits up to 32 transmitters and receivers to share a 2-        Resolution
wire balanced differential line.                                 The smallest distinguishable increment into which a
                                                                 quantity can be divided (e.g., position or shaft speed).
Rectifier                                                         It is also the degree to which nearly equal values of a
An electronic circuit which converts alternating current         quantity can be discriminated. For encoders, it is the
into direct current.                                             number of unique electrically identified positions
                                                                 occurring in 360 degrees of input shaft rotation.
The characteristic of a motor to act as a generator when         Resonance
the CEMF is larger than the drive’s applied voltage (DC          Oscillatory behavior caused by mechanical limitations.
drives) or when the rotor’s synchronous frequency is
greater than the applied frequency (AC drives).
Semiconductor                                                    A communication scheme used between devices
A material, usually silicon or germanium, that permits           whereby serial data can be transmitted.
current flow.
                                                                 Set Speed
Serial Communication                                             The desired operating speed.

                                                                          AC Inverter Terminology
A Subsidiary of Regal-Beloit Corporation

                                                                   Thermal Overload Relay
Skip Bandwidth                                                     A thermal overload relay functions (trips) by means of a
The ability of an AC drive to jump certain frequencies             thermally responsive system.
where mechanical resonance may occur.
                                                                   Torque Control
Slip Compensation                                                  Motor torque is regulated instead of motor speed.
Method of increasing the speed reference of the speed
regulator circuit based on the value of the motor torque           Transducer
to maintain motor speed as the load on the motor                   A device that converts one energy form to another (e.g.,
changes.                                                           mechanical to electrical). Also, a device that when
                                                                   actuated by signals from one or more systems or media,
Sensorless Vector                                                  can supply related signals to one or more other systems
An AC drive that controls the stator and rotor flux angles         or media.
to optimize motor operation.
                                                                   Transistor-Transistor Logic (TTL)
Speed Reference Follower                                           A popular family of integrated circuit devices that operate
The ability of an AC drive to follow an external signal.           from logic level voltages, 5 to 12 VCD.

Speed Regulation                                                   Undervoltage Protection
The percentage of change in speed between full-load                Undervoltage or low voltage protection is the effect of a
and no-load.                                                       device, operative on the reduction or failure of voltage,
                                                                   to cause and maintain the interruption of power to the
Stability                                                          main circuit. The main objective of the device is to
The ability of a drive to operate a motor at constant              prevent restarting of the equipment on an undervoltage
speed (under varying loads) without “hunting”                      condition.
(alternately speeding up and slowing down). It is related
to the characteristics of the load being driven and the            Variable Frequency Drive (VFD)
electrical time constants of the drive’s regulator circuits.       A VFD is composed of a frequency converter operating
                                                                   from a power source and a control system that directs
Surge Protection                                                   and excites the converter.
The process of absorbing and clipping voltage transients
on an incoming AC line or control circuit. MOVs (Metal             Variable Speed
Oxide Varistors) and specially designed RC (resistor-              Where speed varies widely with load.
capacitor) networks are usually used to accomplish this.
                                                                   Variable Voltage Input (VVI)
Switching Frequency                                                The VVI design receives AC power, rectifies and controls
Switching frequency refers to the switching rate of an             it, and delivers variable voltage DC to the power amplifier
inverter phase pole and is synonymous with carrier                 (inverter section). The power amplifier invects the
frequency when a pulse width modulation (PWM)                      variable voltage DC to variable frequency, variable
strategy is employed.                                              voltage AC. The output voltage from a VVI unit is
                                                                   commonly called a six-step waveform.
Surge Suppressor
These devices, like a metal oxide varistor (MOV),                  Vector
suppress voltage transients that can occur on the AC               A quantity that has magnitude and direction. A directed
line.                                                              line segment commonly represents this quantity whose
                                                                   length represents the magnitude and whose orientation
Tachometer Generator (Tach)                                        in space represents the direction.
A generator, mechanically coupled to a rotating machine
whose function is to generate a voltage, the magnitude             Vector Drive
or frequency of which is used either to determine the              An AC drive with enhanced processing capability that
speed of rotation of the common shaft or to supply a               provides positioning accuracy and fast response to
signal to a control circuit to provide speed regulation.           speed and torque changes.

                                                                    AC Inverter Terminology
A Subsidiary of Regal-Beloit Corporation

Velocity                                                     Voltage Boost
The change in position as a function of time. Velocity       Adjustment to enable an adjustable frequency drive to
has both a magnitude and sign.                               give a larger than normal voltage at low frequencies so
                                                             the motor can start with extra short-term torque for
                                                             breakaway and initial acceleration.

                                                             Volts per Hertz (V/Hz)
                                                             The basic measurement of proper AC motor excitation
                                                             level for adjustable frequency AC drive operation.

                                                             Voltage Source Inverter
                                                             An inverter produces variable frequency AC from a
                                                             constant voltage DC bus.

                                                             The amount of power required to maintain a current of 1
                                                             ampere at a pressure of 1 volt. One horsepower is equal
                                                             to 746 watts. The symbol for watt is “W”.