Showing papers on "Variable-frequency drive published in 1998"

Variable frequency drive noise attenuation circuit

Abstract: A noise attenuation circuit is used in a motor drive system. The motor drive system includes a variable frequency drive having a pulse width modulated inverter converting DC power from a DC bus to three-phase power output on three-phase conductors for driving a motor. The noise attenuation circuit comprises a common-mode transformer including a common mode choke having a core, with first, second and third choke windings on the core, each connected in series with one of the three phase conductors, and a fourth winding on the core. A three-phase iron core transformer creates a neutral point representing common mode voltage. The iron core transformer has three primary windings connected in a "wye" configuration to the three phase conductors. The fourth winding has a start connected to the neutral point and an end operatively connected to the DC bus to force a current, dependent on the voltage of the neutral point relative to the DC bus, in the fourth winding of the common mode transformer in an opposite direction to cancel main common mode current.

Dimming ballast and drive method for a metal halide lamp using a frequency controlled loosely coupled transformer

Abstract: A dimmer ballast or output drive circuit and a drive method for a high intensity discharge lamp utilizes an overwound loosely coupled transformer having a turns ratio of preferably about one to one with a peaking capacitor across the secondary output terminals of the transformer and in parallel with the HID lamp arc electrodes. A control circuit provides a variable frequency drive voltage to the primary of the transformer. The frequency of the output voltage is adjustably controlled above the peak load power frequency. The load power and hence the light output of the lamp varies according to the frequency of the output voltage permitting a user to adjustably dim the high intensity discharge lamp.

Method and apparatus for handling brake failure in variable frequency drive motors

Abstract: The variable frequency drive of a motor monitors pulse generator feedback while the motor is stopped and an electromechanical brake is set When the pulse generator feedback exceeds a predetermined level indicative of brake failure, tie controller actuates the motor to operate in zero servo mode and maintain the load An alarm is also sounded, allowing an operator to safely lower the load

New approach to medium voltage variable speed drives

Abstract: This paper outlines the approach taken in the development of a new medium voltage variable frequency drive. It examines the existing medium voltage drive formats, their advantages and disadvantages. It also outlines new standards implemented overseas to limit the effect of harmonics on the electricity supply system, and how these limits impacted on the design of the new generation VSDs. It further examines the effect that advances in microprocessors and electronic power devices has had in the design of the new drive topology.

Conceptual design for sub-sea power supplies for extremely long motor lead applications

Abstract: This paper describes one concept for providing electrical power from a surface generated power source to a sub-sea, medium voltage motor(s) in water depths up to 10000 feet, and up to 10 miles away from the source. Continuous and instantaneous voltage regulation becomes an absolute necessity to maintain proper motor input voltages for these extremely long motor lead applications, due to the very large change in voltage drop between no-load and full load in the feeder cable. The heart of the design concept is a state of the art medium voltage VFD, which can handle voltages from 2.4 kV up to 7.2 kV. It also has the capability to continuously change both the frequency as well as voltage, on the output side upon command. Best of all, this unique medium voltage VFD technology eliminates most of the problems usually attributed to VFD's, such as harmonics and load sensitive power factors on the front-end, plus "ringing" problems associated with the use of fast switching IGBTs in the inverter of pulse width modulation type VFDs, so no special filtering or isolation is required on either end, no matter how long the motor lead is. This VFD technology essentially turns an AC motor into a DC motor, which allows the use of a 1 to 1 ratio of generator capacity to motor(s) capacity, which is highly desirable for single motor applications. This will really help save on weight, space and the high costs associated with any offshore platform type of application.