Showing papers on "Variable-frequency drive published in 1999"

Gearless motorized conveyor roller

Abstract: The drive roller of this invention utilizes a brushless D.C. motor which has a stator or armature mounted on a fixed shaft which directly drives a permanent magnet rotor mounted inside a roller tube. A variable frequency drive supplies three-phase power to a Y-connected three phase winding which is composed of three groups of two coils. Thus twelve electromagnets are formed which drive the permanent magnet rotor which has sixteen poles. The brushless D.C. motor is of a modular design and can be easily built in one inch length increments to supply one lb-in of torque for each one-inch increment. The variable frequency controller operates at a relatively low frequency of 15-75 Hz. Hall effect sensors are used to provide feedback on motor speed and position. The armature laminations making up the brushless D.C. motor core are also relatively thick because of the relatively low power necessary to drive the motor and the resultant relatively low eddy currents present in the motor core. For a motor with a 4.0 lb-in design torque and a rotor and stator length of four inches, the current draw will be approximately 0.8 amps consuming about 15 Watts of power.

Variable frequency drive principles and practices (above NEMA) AC motors for variable frequency application

Abstract: Since AC motors are increasingly used in applications traditionally served by DC motors, a comparison of some characteristics of AC and DC motors seems appropriate. Aspects of motor design and application is reviewed, including typical construction, torque production, equivalent circuits, power and torque density ratings, speed and load ranges. Understanding the effects of variable frequency on the motor's characteristics helps in the selection process of a motor and control unit matched to the application. Depending on the type of inverter, the input voltage and current waveform supplied to the motor will cause some degree of distortion from a pure sine wave. This distortion can be mathematically expressed in terms of harmonics. Harmonic currents create no useful torque at the motor shaft, just additional heating in the motor. The motor application must also be considered. Different load types have different effects on the motor. Constant torque, variable torque, and constant horsepower are the three different load requirements typically considered, and affect motor heating in different ways. While all three are discussed, the primary focus of this paper is on the "constant torque" applications with PWM inverters, as applied to process machines such as paper machines and winders.

Use of variable frequency drives for extruder application

Abstract: This paper describes a case study of replacing an eddy current clutch (ECC) with a modern medium voltage variable frequency drive (VFD) for 2250 HP extruder application. It covers key issues, justification, factory and field measurements of torque-speed profile through 0.5-60 Hz as well as power quality analysis. The paper reviews manufacturers' capability to build medium voltage VFDs that produce very high and stable torque at very low speed.

***WITHDRAWN PATENT AS PER THE LATEST USPTO WITHDRAWN LIST***Vacuum level control system using variable frequency drive

Abstract: A vacuum control for milking systems includes a vacuum pump driven by an electric motor which is activated by a variable frequency drive (VFD). The VFD is controlled during a milking phase by plc programmable controller and a proportional/integral (PI) controller which respond to a vacuum feedback sensor connected to the milking system. The plc controller differentiates between milk and wash phases and also provides a fixed preset speed control for a washing phase for the milking system. The integrator interfaces between a milk/wash controller and the plc.

A three-phase TMS320C30 DSP based resonant-commutated converter

Abstract: A three-phase variable frequency converter that accomplishes resonant commutation in its operation to minimize switching losses is presented. Switching strategies for the converter are detailed and the TMS320C30 DSP based realization of the controller is discussed. Pspice simulation of the converter and its results are presented. Experimental work on a laboratory prototype is described. Results from the tests and simulation are compared and observations summarized. Scope of future work is highlighted and the performance parameters of the converter as a potential variable frequency drive in electric/hybrid vehicle applications are identified.