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Small variable-frequency drive Chassis of above VFD (cover removed). A variable-frequency drive (VFD, or adjustable-frequency drive, adjustable-speed drive, variable-speed drive, AC drive, micro drive, inverter drive, variable voltage variable frequency drive, or drive) is a type of AC motor drive (system incorporating a motor) that controls speed and torque by varying the frequency of the ...
A braking chopper is an magnetical switch that limits the DC bus voltage by switching the braking energy to a resistor where the braking energy is converted to heat. Braking choppers are automatically activated when the actual DC bus voltage exceeds a specified level depending on the nominal voltage of the variable-frequency drive
Vector control, also called field-oriented control (FOC), is a variable-frequency drive (VFD) control method in which the stator currents of a three-phase AC or brushless DC electric motor are identified as two orthogonal components that can be visualized with a vector. One component defines the magnetic flux of the motor, the other the torque ...
Direct torque control (DTC) is one method used in variable-frequency drives to control the torque (and thus finally the speed) of three-phase AC electric motors.This involves calculating an estimate of the motor's magnetic flux and torque based on the measured voltage and current of the motor.
Constant voltage operation above base frequency, and therefore with reduced V/Hz ratio, provides reduced torque and constant power capability. Regenerative AC drives are a type of AC drive which have the capacity to recover the braking energy of a load moving faster than the motor speed (an overhauling load) and return it to the power system.
The braking current decays, and after a delay of about 1.5 seconds the braking relay contactor opens again. At this point the motor can be restarted. In such a unit, there are typically two potentiometers , one to vary the braking torque from the firing circuit and the other to vary the timer.
The energy draw is usually measured in kilowatts (the Nissan Leaf, for instance, uses a 160 kW motor that produces up to 340 Nm torque ). Most mass-produced electric cars feature ESCs that capture energy when the car coasts or brakes, using the motor as a generator and slowing the car down.
Prony brake dynamometers at a tractor contest in 1910 Schematic of a Prony brake Actual Prony Brake built for testing 5HP Steam Engine. The Prony brake is a simple device invented by Gaspard de Prony in 1821 to measure the torque produced by an engine. The term "brake horsepower" is one measurement of power derived from this method of measuring ...
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