A Subsidiary of Regal-Beloit Corporation. AC Inverter Terminology

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3 Acceleration The rate of change in velocity as a function of time. Acceleration usually refers to increasing velocity and deceleration to decreasing velocity. Acceleration Boost During acceleration, the output voltage is increased to increase motor torque. Acceleration/Deceleration The time rate of change in velocity, acceleration refers to an increase in velocity, while deceleration refers to a decrease in velocity. Generally expressed as radians/sec/sec. Acceleration Torque Numerical difference between motor torque produced and load torque demanded at any given speed during the acceleration period. It is this net torque which is available to change the speed of the driven load. Accuracy A measure of the difference between expected position and actual position of a motor or mechanical system. Adjustable Frequency Drive Term for an AC adjustable frequency drive, inverter, or AC drive. Adjustable Speed The concept of varying the speed of applications. Adjustable Speed Drive (Electrical) The adjustable speed drive is comprised of the motor, drive controller and operator s (either manual or automatic). Base Frequency The lowest frequency at which a drive is capable of delivering maximum output power. Base Speed The motor speed while delivering rated torque. Bypass A control method whereby the drive can be isolated and the control circuit connected directly to the motor. Capacitor A device which holds electrical charge for a period of time, prevents the flow of direct current, and allows the follow of alternating current. These components serve as filters in AC drives. Carrier Frequency The base frequency (hertz) of the modulated wave. Chassis Open construction of a drive for mounting within a customer s existing enclosure. Choke A filter device consisting of an inducer and a resistor. Closed Loop A broadly applied term relating to any system in which the output is measured and compared to the input. The output is then adjusted to reach the desired condition. In motion control, the term typically describes a system utilizing a velocity and/or position transducer to generate correction signals in relation to desire parameters. Constant Horsepower Range A speed range in which the motor is capable of delivering constant horsepower above rated speed. Torque will decrease with speed, but horsepower remains constant. Constant Torque Range A speed range in which the motor is capable of delivering a constant torque, subject to cooling limitations of the motor. Constant Voltage Range The range of motor operation where the drive s output voltage is held constant as output frequency is varied. This speed range produces motor performance similar to a DC drive s constant horsepower range. Constant Volts per Hertz (V/Hz) This relationship exists in AC drives where the output voltage is varied directly proportional to frequency. This type of operation is required to allow the motor to produce constant rated torque as speed is varied. Converter The process of changing AC to DC. This is accomplished through use of a diode rectifier to thyristor rectifier circuit. The term converter may also refer to the process of changing AC to DC to AC (e.g., adjustable frequency drive). A Frequency converter, such as that found in an adjustable frequency drive, consists of a rectifier, a DC intermediate circuit, an inverter and a control unit. Current Limit An electronic method of limiting the maximum current 1

4 available to the motor. This is adjustable so that the motor s maximum current can be controlled. It can also be present as a protective device to protect both the motor and controller from extended overloads. Current Limit Acceleration A system of control in which acceleration is so governed that the motor current does not exceed an adjustable maximum value. Device Net A low cost industrial network to connect industrial devices such as motor starters and drives, and operator displays to PLCs and Pcs. The network eliminates expensive hard-wiring while providing device-level diagnostics. DIN The abbreviation for the association in West Germany that determines the standards for electrical and other equipment used in that country, Deutsche Industrie Normenausschuss. Displacement Power Factor The cosine of the phase displacement angle between the fundamental component of the voltage and current. Drive The equipment used for converting available power into mechanical power suitable for the operation of a machine. Dynamic Braking A way of quickly stopping a motor by disconnecting the power source. The rotating motor then becomes a generator. When connected to a resistor, the energy of rotation is then dissipated as heat in the resistor. Efficiency The ratio of the power delivered by the converter to the total power drawn from the plant electrical power system. Efficiency is usually expressed in percentage. Encoder An electromechanical transducer that produces a serial of parallel digital indication of mechanical angle or displacement. Essentially, an encoder provides high resolution feedback data related to shaft position and is used with other circuitry to indicate velocity and direction. The encoder produces discrete electrical pulses during each increment of shaft rotation. Feedback The element of a control system that provides an actual operation signal for comparison with the set point to establish an error signal used by the regulator circuit. Filter An electrical device used to suppress electrical noise. Flyback Diode This is a super fast recovery diode that snubs current and voltage spikes as a result of the fast transients that occur when IGBT are turned on and off quickly. Four-Quadrant Operation The four combinations of forward and reverse rotation and forward and reverse torque of which a regenerative drive is capable. The four combinations are: 1. Forward rotation/forward torque (motoring) 2. Forward rotation/reverse torque (regeneration) 3. Reverse rotation/reverse torque (motoring) 4. Reverse rotation/forward torque (regeneration) Frequency The rate at which alternating current reverses its direction of flow. Measured in hertz (Hz). Giant Transistor (GTR) GTRs are low gain devices where the control or base signal must be maintained to keep the device turned. GTO Acronym for gate turn-off or gate turn-on power semiconductor device. Harmonics Integral multiple of the fundamental frequency, often superimposed on and thus distorting the fundamental current or voltage sinusoidal wave shape. IGBT Acronym for insulated gate bipolar transistor. Instability The state or property of a system where there is an output but no corresponding input. Integrated Motor Drive 2

5 Unit where the motor and drive have been integrated into a single device. Inverter A term commonly used for an AC adjustable frequency drive. An inverter is also a term used to describe a particular section of an AC drive. This section uses the DC voltage from a previous circuit stage (intermediate DC circuit) to produce an AC current or voltage having the desired frequency. Kilowatt A unit of power equal to 1000 watts and approximately equal to 1.34 horsepower. LED An acronym for light emitting diode. Linear Acceleration/Deceleration (LAD) A circuit that controls the rate at which the motor is allowed to accelerate to a set speed or decelerate to zero speed. On most drives, this circuit is adjustable and can be set to accommodate a particular application. Metal Oxide Varistor (MOV) This device is used to suppress voltage transients that may occur on an AC line. Modbus A communication protocol widely used to establish master-slave communication between intelligent devices. A Modbus message sent from a master to a slave contains the address of the slave, the command, the data, and a check sum. Noise (EMI/RFI) Electrical disturbances that interfere with proper transmission of electrical signals. Noise can have adverse affects on the system performance. Open Collector An output signal provided by a transistor where open collector output acts like a switch closure to ground when activated. Open Loop A control system that lacks feedback. Overcurrent Relay An overcurrent relay operates when the current through the relay, during its operating period, is equal to or greater than its setting. Overload Relay An overload relay is an overcurrent relay that operates at a predetermined value of current in order to prevent overheating of the motor. Overshoot The amount that a controlled variable exceeds a desired value after a change of input. Programmable Logic Controller (PLC) A Programmable Logic Controller (PLC) uses programmed logic instructions to control banks of inputs and outputs which interface timed switch actuation to external electron mechanical devices. Position Transducer An electronic device (e.g., encoder or resolver) that measures actual position and converts this measurement into a feedback signal convenient for transmission. This signal may then be used as an input to a programmable controller that controls the parameters of the positioning system. Potentimeter (POT) A passive device (variable resistor) used to vary voltage 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 3

6 closed-loop system. Proportional This feedback loop compares error and adds an equal amount of reference beyond the original. For example: with a 20% error, the loop applies 20% more than the original reference. Integral This loop examines the average error over a number of samples and makes the correction associated with it. For example: with a 20% error reading in one window and 10% error in another, the integral loop may apply 15% error correction in the third window based on average of previous readings. Derivative This loop reads instantaneous change in error as opposed to the error itself. It analyzes how an error differs from a previous error and adjusts accordingly. PID combines all three loops resulting in an extremely accurate form of digital error correction. Each loop checks and balances the other to assure the right amount of error correction. Pulse Width Modulation (PWM) A type of AC adjustable frequency drive that accomplishes frequency and voltage control at the output section (inverter) of the drive. The drive s DC bus voltage is always a constant amplitude and by chopping (pulse width modulating), the average voltage is controlled. RS-485 An interface standard between devices that allows for multi-point communications. The RS-485 standard permits up to 32 transmitters and receivers to share a 2- wire balanced differential line. Rectifier An electronic circuit which converts alternating current into direct current. Regeneration The characteristic of a motor to act as a generator when the CEMF is larger than the drive s applied voltage (DC drives) or when the rotor s synchronous frequency is greater than the applied frequency (AC drives). Semiconductor A material, usually silicon or germanium, that permits current flow. Serial Communication Regenerative Braking The technique of slowing or stopping a drive whereby the kinetic energy of the motor and driven machinery is returned to the power supply system. Regenerative Control A regenerative drive contains the inherent capability and/or power semi-conductors to control the flow of power to the motor and from the motor back to the power supply. Regulation The ability of a control system to hold a speed once it has been set. Regulation is given in percentages of either base speed or set speed. Regulation is rated upon two separate sets of conditions: A. Speed Regulation is the percentage of speed change with a defined change in load, assuming all other parameters to be constant. B. Line Regulation is the percentage of speed change with a given line voltage change, assuming all other parameters Relay An electrically controlled device that causes electrical contacts to change status. Open contacts will close and closed contacts will open when rated voltage is applied to the coil of the relay. Repeatability The degree to which a parameter such as position or velocity can be duplicate. Resolution The smallest distinguishable increment into which a quantity can be divided (e.g., position or shaft speed). It is also the degree to which nearly equal values of a quantity can be discriminated. For encoders, it is the number of unique electrically identified positions occurring in 360 degrees of input shaft rotation. Resonance Oscillatory behavior caused by mechanical limitations. A communication scheme used between devices whereby serial data can be transmitted. Set Speed The desired operating speed. 4

7 Skip Bandwidth The ability of an AC drive to jump certain frequencies where mechanical resonance may occur. Slip Compensation Method of increasing the speed reference of the speed regulator circuit based on the value of the motor torque to maintain motor speed as the load on the motor changes. Sensorless Vector An AC drive that controls the stator and rotor flux angles to optimize motor operation. Speed Reference Follower The ability of an AC drive to follow an external signal. Speed Regulation The percentage of change in speed between full-load and no-load. Stability The ability of a drive to operate a motor at constant speed (under varying loads) without hunting (alternately speeding up and slowing down). It is related to the characteristics of the load being driven and the electrical time constants of the drive s regulator circuits. Surge Protection The process of absorbing and clipping voltage transients on an incoming AC line or control circuit. MOVs (Metal Oxide Varistors) and specially designed RC (resistorcapacitor) networks are usually used to accomplish this. Switching Frequency Switching frequency refers to the switching rate of an inverter phase pole and is synonymous with carrier frequency when a pulse width modulation (PWM) strategy is employed. Surge Suppressor These devices, like a metal oxide varistor (MOV), suppress voltage transients that can occur on the AC line. Tachometer Generator (Tach) A generator, mechanically coupled to a rotating machine whose function is to generate a voltage, the magnitude or frequency of which is used either to determine the speed of rotation of the common shaft or to supply a signal to a control circuit to provide speed regulation. Thermal Overload Relay A thermal overload relay functions (trips) by means of a thermally responsive system. Torque Control Motor torque is regulated instead of motor speed. Transducer A device that converts one energy form to another (e.g., mechanical to electrical). Also, a device that when actuated by signals from one or more systems or media, can supply related signals to one or more other systems or media. Transistor-Transistor Logic (TTL) A popular family of integrated circuit devices that operate from logic level voltages, 5 to 12 VCD. Undervoltage Protection Undervoltage or low voltage protection is the effect of a device, operative on the reduction or failure of voltage, to cause and maintain the interruption of power to the main circuit. The main objective of the device is to prevent restarting of the equipment on an undervoltage condition. Variable Frequency Drive (VFD) A VFD is composed of a frequency converter operating from a power source and a control system that directs and excites the converter. Variable Speed Where speed varies widely with load. Variable Voltage Input (VVI) The VVI design receives AC power, rectifies and controls it, and delivers variable voltage DC to the power amplifier (inverter section). The power amplifier invects the variable voltage DC to variable frequency, variable voltage AC. The output voltage from a VVI unit is commonly called a six-step waveform. Vector A quantity that has magnitude and direction. A directed line segment commonly represents this quantity whose length represents the magnitude and whose orientation in space represents the direction. Vector Drive An AC drive with enhanced processing capability that provides positioning accuracy and fast response to speed and torque changes. 5

8 Velocity The change in position as a function of time. Velocity has both a magnitude and sign. Voltage Boost Adjustment to enable an adjustable frequency drive to 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. Watt 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. 6