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Showing papers on "Variable-frequency drive published in 1996"


Proceedings ArticleDOI
06 Oct 1996
TL;DR: Novel modifications to the PWM modulator as well as external hardware apparatus are proposed solutions to the >2 pu overvoltage problem, both are simulated and experimentally confirmed.
Abstract: This paper investigates overvoltage transients on AC induction motors when connected through a cable of arbitrary length to a variable frequency drive (VFD) consisting of a pulsewidth modulation (PWM) inverter with insulated gate bipolar transistor (IGBT) power devices. Factors contributing to a motor overvoltage transient equal to a theoretical twice DC bus voltage are first described using existing transmission line analysis. A critical cable distance I/sub c/ is defined where this 2-pu overvoltage occurs. However, literature is lacking on flow motor voltage transients >2-pu bus voltage and up to 3-4 pu are generated. This phenomenon is observed on all PWM inverters with output cable lengths greater than l/sub c/ distance. Contributing factors to the >2-pu overvoltage phenomenon are investigated by exploring the complex interaction between drive modulation techniques, carrier frequency selected, cable natural frequency of oscillation, cable high-frequency damping losses, and, to a lesser extent, inverter output rise time. Theoretical calculations of cable frequency and damping are correlated with simulation and experimental results. Novel modifications to the PWM modulator, as well as external hardware apparatus, are proposed solutions to the >2-pu overvoltage problem; both are simulated and experimentally confirmed.

278 citations


Journal ArticleDOI
TL;DR: In this paper, a variable frequency drive for electric motors has been used to adjust the pump performance to match operating conditions by reducing motor and pump RPMs, which can reasonably match the throttled conditions at a reduced horsepower demand.
Abstract: The constant revolutions per minute (RPM) of electric motors prevents adjusting the pump performance to match variable operating conditions, and thus the pump output is usually reduced or throttled with a valve in the discharge pipe. Variable frequency drives for electric motors have the potential to adjust the pump performance to match operating conditions by reducing motor and pump RPM. Field tests at five sites showed that the pump performance at the reduced RPM could reasonably match the throttled conditions at a reduced horsepower demand. However, pumping plants using a variable frequency drive should be operated at least 500–1,000 h per year to recoup costs.

26 citations


Proceedings ArticleDOI
08 Jan 1996
TL;DR: In this paper, a variable voltage variable frequency drive and a programmable controller are used to control EOT cranes using slip ring induction motors whose rotor windings are connected to a power resistance.
Abstract: Conventional AC operated electric overhead travelling (EOT) cranes uses slip ring induction motors whose rotor windings are connected to a power resistance. Speed control is performed by changing the rotor resistance in 3 to 4 steps by power contactors. Reversing is performed by changing the phase sequence of the stator supply through line contactors. Braking is achieved by a plugging operation. A crane control system has been developed using a variable voltage variable frequency drive and a programmable controller which has the advantage of continuous speed control; reversing is achieved by changing the phase sequence through an inverter. The main advantages of thi system are precise positioning, energy saving and increased motor life. This paper focuses on the application of variable voltage variable frequency induction motor drives in crane applications.

5 citations