Showing papers on "Variable-frequency drive published in 2006"

Variable-Frequency Drive with Regeneration Capability

Abstract: An electrical device includes a plurality of single-phase power cells electrically connected to receive power from a source and deliver power to a load. The single-phase power cells include a first rank of regenerative power cells and a second rank of non-regenerative power cells. Each non-regenerative power cell may include an inverter bridge, a capacitor set electrically connected across terminals of the inverter bridge, and a three-phase bridge rectifier electrically connected across the terminals. The non-regenerative power cells may provide reactive power when the plurality of cells are used for braking of a motor

Controlling a voltage-to-frequency ratio for a variable speed drive in refrigerant systems

Abstract: A refrigerant system is provided with at least one variable frequency drive. In the past, the variable frequency drives were operable such that the voltage-to-frequency ratio remained constant regardless of operation. The present invention realizes that variations in the voltage-to-frequency ratio may be desirable, and the refrigerant system control drives the motors associated with relevant refrigerant system components to reach an optimum voltage-to-frequency ratios in order to achieve higher efficiency, provide operational safety and prevent nuisance shutdowns.

Variable frequency drive for AC synchronous motors with application to pumps

Abstract: Two apparatuses are disclosed for controlling the speed of an AC synchronous motor-pump utilizing a series of stepped voltage pulses at the driving frequency. The first apparatus is an isolated variable frequency drive comprising step-down transformer 100 , full wave rectifier and filter 101 , micro-controller 108 , driving-voltage array generator 102 , gate driver 107 , inverter bridge 103 and step-up transformer 104 . The second apparatus is a non-isolated high voltage variable frequency drive comprising full wave rectifier and filter 201 , low voltage, dual output power supply 205 , micro-controller 208 , driving-voltage array generator 202 , gate driver 207 and inverter bridge 203 . Methods are given to determine voltage array values and pulse times to generate a stepped voltage approximation of a sine wave driving waveform.

System and method for parallel control of variable frequency drives

Abstract: A method for controlling at least two variable frequency drives connected in parallel. The method comprises, for each variable frequency drive, communicating a magnetizing current component value to a master controller, and receiving a speed demand, a flux demand, and an average magnetizing current component value from the master controller. The method also comprises determining a motor speed and a motor flux based on measurements of a stator voltage and current of a motor coupled to the variable frequency drive, determining a speed reference based on a torque current component value, and determining a flux reference based on the magnetizing current component value and the average magnetizing current component value. The method further comprises adjusting a torque current component based on the speed reference and/or adjusting a magnetizing current component based on the flux reference.

Inverter operation with over-modulation

Abstract: A variable frequency drive including a plurality of power cells that are configured as three phases of series-connected cells to deliver power to a load. The drive is operated to increase the output voltage of each power cell using overmodulation.

Drive control assembly for controlling a motor

Abstract: A drive control assembly for a motor including a variable frequency drive module for providing variable speed control for the motor, a bypass module for providing bypass control for the motor, and a switch for switching control for the motor between the variable frequency drive module and the bypass module. The bypass module can provide control for the motor even when the variable frequency drive module is removed from the drive control assembly.

Soft start system for motors utilizing variable frequency drive and autotransformer

Abstract: A soft start system for starting large motors has a power supply suitable for passing power to the motor, a variable frequency drive connected to the power supply and an autotransformer connected between the variable frequency drive and the motor for passing power of an elevated current to the motor. A switch is connected between the motor and power supply for connecting the motor to the power supply when the motor reaches a desired speed. The autotransformer includes a single core with a winding extending over the single core. The autotransformer includes a first terminal connected the variable frequency drive, a second terminal connected the motor and a grounded neutral.

Powered controlled acceleration suspension work platform hoist system

Abstract: A powered controlled acceleration suspension work platform hoist system for raising and lowering a work platform at a predetermined acceleration. The system incorporates several hoists attached to the work platform and in electrical communication with the motor control system. The motor control system is attached to the work platform and is in electrical communication with a constant frequency input power source and the hoist motors. The motor control system controls the acceleration of the work platform as it is raised and lowered by controlling the hoist motors. The controlled acceleration hoist system also includes a platform control system attached to the work platform that is in electrical communication with the motor control system and the hoist motors. Acceleration control is achieved by converting the constant frequency input power to a variable frequency power supply. This may be accomplished through the use of a variable frequency drive(s).

Cancellation of dead time effects for reducing common mode voltage in an inverter

Abstract: Methods and apparatus for canceling dead time effects in the form of common mode voltages produced by a three-phase power conversion device in a rectifier/inverter variable frequency drive (VFD) system includes limiting the voltage difference between phase voltages at certain switching transition times to an amount δ, that is a function of the dead time that is specified for the switches and delaying gating signals to the switches to remove unexpected pulses produced by common mode voltages.

A Novel Harmonic Mitigation Converter for Variable Frequency Drives

Abstract: In this paper, a novel autotransformer for 56-pulse AC-DC converter configuration is designed, modeled and simulated to feed vector controlled induction motor drive (VCIMD). The proposed autotransformer configuration consists of two paralleled 14-pulse AC-DC converters involving seven-phase shifted uncontrolled diode bridges with pulse doubling circuit. It improves power quality at AC mains and it meets IEEE-519 standard requirements at varying loads.

Dynamic reef surge generation

Abstract: Two apparatuses are disclosed for providing a dynamically varying water surge in a salt-water reef aquarium. The first apparatus is a micro-controller based variable frequency reef surge drive 100 for an AC permanent magnet synchronous motor (PMSM) submersible aquarium pump. Drive 100 comprises voltage conversion circuitry 105 , xmicro-controller 110 , reef-surge generation program 115 , variable frequency drive 118 , mode switch 130 and tidal cycle switch 135 . Three user-selectable modes of operation are provided: a random frequency mode, a fixed-program mode and a tidal mode. A second apparatus comprises a novel submersible AC PMSM pump with dual impeller assemblies and dual input and output chambers for supporting forward and reverse flow through an AC PMSM pump.

Cost-Effective Control Scheme for Reduction of Torsional Torque Oscillations in Starting Large Induction Motors

Abstract: This article presents a cost-effective variable frequency drive for starting and operating large three-phase squirrel cage induction motors. The proposed drive employs the constant V/F control scheme, which regulates the rotor frequency such that it is always kept below a predetermined value. This has the effect of drastically reducing the motor shaft torque oscillations and significantly limiting the maximum value of the motor line current. In addition to its simplicity and hence cost-effectiveness, the proposed scheme is shown to be capable of (i) reducing the shaft torque oscillations to approximately 22% of that of the direct on-line start of the large motor, and (ii) limiting the motor line current to approximately 36% of that of the direct on-line start value.

Method of operating a pumping system

Abstract: A pumping system has a motor ( 32 ) for driving a pumping mechanism ( 30 ). A variable frequency drive unit ( 36 ) has an input for receiving electrical energy of relatively high power and first, fixed frequency from a power supply, and an output coupled to an input ( 46 ) of the motor for supplying electrical energy of relatively low power and second, variable frequency to the motor. This second frequency preferably has a maximum value greater than the first frequency. A control circuit ( 50 ) is provided for selectively coupling the motor input ( 46 ) directly to the power supply for the supply of said relatively high power energy to the motor to maximise the torque that can be produced by the pumping mechanism. After a period of time the control circuit terminates the direct coupling of the motor input to the power supply for the supply of said relatively low power energy to the motor.

Variable-frequency drive with regeneration capability

Abstract: An electrical device includes a plurality of single-phase power cells electrically connected to receive power from a source and deliver power to a load. The single-phase power cells include a first rank of regenerative power cells and a second rank of non-regenerative power cells. Each non-regenerative power cell may include an inverter bridge, a capacitor set electrically connected across terminals of the inverter bridge, and a three-phase bridge rectifier electrically connected across the terminals. The non-regenerative power cells may provide reactive power when the plurality of cells are used for braking of a motor.

Common mode interference coupled via a buried armored cable

Abstract: In an industrial installation a single combination of a three-phase motor and switched mode variable frequency drive is selected. The driver and motor were connected by an 85 m long armored cable buried in wet soil. The interference generating currents produced by the drive were measured in time domain. The transmission line parameters of the cable were determined separately in the laboratory. Its transfer impedance is remarkably low in view of the open structure. The external circuit was an L.shaped aluminum proffle in the laboratory. The actual installation has many cables in parallel, which also form a part of the external circuit. Preliminary calculations show that cable common mode current can be ‘a posteriori’predicted quite well with a reasonable guess for the effective soil parameter.

Electric network related problems of the applicaton of regulated elevator drives operated with frequency conversion

Abstract: In our days application of the so-called voltage-controlled drives is driven into the background in the field of elevator controls and in some cases the variable frequency drive is unduly preferred. The latter one is significantly more sensitive to the disturbances on the mains and at the same time emits disturbances into the mains as well. For perfect operation low frequency conducted and radiated disturbances have to be decreased by filter units of optimum design and the traditional aspects of elevator drive installations and operations have to be revaluated.