Showing papers on "Variable-frequency drive published in 2000"

Apparatus for cooling the power electronis of a refrigeration compressor drive

Abstract: Apparatus for cooling the power electronics components (27) of a variable frequency drive for the motor of a refrigerant system compressor. The components are mounted upon a heat sink (30) and refrigerant from the system condenser (13) is passed through the heat sink (30) by means of a flow line (32) and returned to the low pressure side of the system. A control valve (40) is mounted in the flow line (32) which throttles refrigerant passing through the line to produce cooling of the heat sink (30) to maintain the temperature of the components within a desired range.

Gas turbine system and method

Abstract: A gas booster system in which a variable frequency drive is used to control, by means of a variable speed motor, the compression rate of a pump in a gas turbine combustion engine. The rate of the variable speed motor, and thus the rate of compression, is controlled by monitoring turbine temperature. The gas turbine system responds to the turbine temperature to regulate the rate of compression of the fuel.

Control algorithm for brushless DC motor/blower system

Abstract: An apparatus and method for controlling a brushless direct current motor having a pulse width modulated variable frequency drive in a blower system so that the blower system provides a specific fluid flow. A start-up program causes the motor to ramp up to approximately a predetermined steady state speed. A required blower torque is calculated by operating on a table of blower constants, a selected flow rate and a motor speed which is read from a commutation Hall sensor in the motor. A developed motor torque is calculated by operating on a table of motor specific constants, a modulation index and the motor speed taken from the commutation Hall sensor. The calculated required blower torque is repeatedly compared with the calculated developed motor torque. The modulation index to the pulse width modulated variable frequency drive is modified to force the developed motor torque to converge with the required blower torque in a steady state.

Control algorithm for induction motor/blower system

Abstract: An apparatus and method for controlling an induction motor having a variable frequency drive in a blower system so that the blower system provides a specific fluid flow. A start-up program causes the motor to ramp up to approximately a predetermined steady state speed. A required blower torque is calculated by operating on a table of blower constants, a selected flow rate and a motor speed which is read from a speed sensor in the motor/blower system. A developed motor torque is calculated by operating on a table of motor specific constants, a voltage-frequency index and the motor speed taken from the speed sensor. The calculated required blower torque is repeatedly compared with the calculated developed motor torque. The voltage-frequency index to the variable frequency drive is modified to force the developed motor torque to converge with the required blower torque in a steady state.

Synchronous generator having auxiliary power windings and variable frequency power source

Abstract: A synchronous generator is disclosed having main power windings and auxiliary power windings, where the auxiliary power winding is coupled to a variable frequency drive system. The variable frequency drive causes the generator to function as a motor and turn a drive shaft to start a gas turbine. Switching circuits are used to connect and disconnect the auxiliary windings of the generator with the variable frequency power supply.

Fuzzy efficient-optimization controller for induction motor drives

Abstract: Induction motors have good efficiencies when operating at full load. At lower than rated loads, however, efficiency is greatly re - duced. This letter describes using fuzzy logic to optimize the efficiency of an induction motor drive while keeping good dynamic response. The proposed fuzzy controller adjusts the magnetizing current component with respect to the torque current component to give the minimum total copper and iron losses. Nomenclature: VV sr () : stator (rotor) voltage II sr () : stator (rotor) current ϕ: stator current and voltage phase delay angle ω s : stator frequency ω : mechanical frequency µ: magnetization subscript o: nominal value subscript Introduction: Electrical machines normally operate at rated flux in a variable frequency drive to get the best transient response. Most of the

The use of variable frequency drives as a final control element in the petroleum industry

Abstract: The concept of using a variable frequency drive to control electric driven centrifugal pumps has been well known for some time, but seldom used in the petroleum industry. The reasons given for this range from: misinformed economic data, unease of using unfamiliar electrical technology, to an ignorance of how these devices react as a control device. One still sees the majority of flow, pressure and temperature control being performed by using constant speed centrifugal machines being throttled by a control valve to provide the desired control of fluids. This paper sets out to provide application guidelines on the correct selection of a variable frequency drive for use with a centrifugal pump, to provide flow, pressure or temperature control. The topics covered include the effect on the pump-system curve when using a variable frequency drive, the economic considerations of a variable frequency drive vs. a control valve, the correct selection of a drive for a given pump and fluid characteristics, the correct planning and installation considerations for VF drives, tuning a control loop when a VF drive is used as the final control element. Also discussed are the additional benefits which a VF drive can bring including reduced fugitive emissions, the enhanced diagnostic information about the running motor which can be brought into the control system, and the reduced wear on bearings and seals in a pump by using a VF drive. The paper concludes by giving some application examples of where VF drives have been used in both the upstream and down stream sectors of the petroleum industry, as a final control element.

9500 HP high speed motor driven compressor

Abstract: The paper discusses a motor driven compressor used to compress and inject natural gas as a part of the Greater Point McIntyre Oil Field-Enhanced Oil Recovery Program on the North Slope of Alaska. The motor and compressor are direct coupled (there is no gearbox), have magnetic bearings, and the compressor has dry gas seals. The induction motor is controlled by a medium voltage, liquid cooled, variable frequency drive (VFD) that generates frequencies up to 246 Hertz and runs the 2-pole motor up to 14700 RPM. The project was required to be inspected and approved by a Nationally Recognized Testing Laboratory (NRTL), and there were challenges to get the European manufactured systems built to US Standards.

Speed computation function for induction motor/blower systems control algorithm

Abstract: An apparatus and method for controlling an induction motor having a variable frequency drive in a blower system so that the blower system provides a specific fluid flow. A start-up program causes the motor to ramp up to approximately a predetermined steady state speed. A required blower torque is calculated by operating on a table of blower constants, a selected flow rate and a motor speed. The motor speed is calculated by operating on a table of motor specific constants, a voltage-frequency index and a measured direct current bus current. A developed motor torque is calculated by operating on a table of motor specific constants, a voltage-frequency index and the calculated motor speed. The calculated required blower torque is repeatedly compared with the calculated developed motor torque. The voltage-frequency index to the variable frequency drive is modified to force the developed motor torque to converge with the required blower torque in a steady state.

Quick accelerating device and backup device of variable frequency drive motor

Abstract: PROBLEM TO BE SOLVED: To shorten the time required for restarting by detecting a residual voltage when a motor is in the free-running condition, obtaining a corrected number of rotation instructing value by obtaining the frequency and phase from such residual voltage, and then forming a gate signal. SOLUTION: A residual voltage when a motor 11 is in the free-running condition is detected with a transformer 13 for a gage and a velocity setting device 17 obtains the corrected number of rotations command value obtaining frequency and phase from such residual voltage. A gate signal generator 18 generates a gate signal based on a timing matching signal for matching the corrected number of rotation instruction and the phase, and then outputs this gate signal to a VVVF device 12, and the ignition timing of the switching element can be changed. Accordingly, an AC power synchronized with the residual voltage during the free-running may be supplied from the VVVF device 12, and the number of rotation instruction value comes near to the actual number of rotations of the motor 11. The time required to restart the motor 11 can be shortened with improvement in the tracking ability to velocity.

Improved variable frequency drive reflected wave suppressors

Abstract: The invention provides a circuit to protect an AC motor powered by a Variable Frequency Drive (VFD) from overvoltages caused by reflected waves. A full wave bridge rectifier circuit across the lines of the motor to be protected provides rectified voltage output to a capacitor, across which a low resistance discharge resistor in series with one or more zener diodes is attached. When an overvoltage above the clamping voltage of the zener diode(s) occurs across the protected lines, the zener diode(s) will conduct, causing the excess charge acro ss the capacitor to discharge through the resistor until the voltage drops below th e clamping voltage of the diode(s).

The application of a medium voltage (4160 VAC) variable frequency drive on an underground mine belt conveyor system

Abstract: High performance underground mine conveyor belts require special starting and operating characteristics. This paper is a summary of how a medium voltage (4160 VAC) variable frequency drive (VFD) was used to meet these requirements. The belt drive system consists of a mandated primary switch gear, drive rated transformer with controlled inductance, variable frequency drive, output switchgear and operational requirements. Items addressed are as follows: repackaging and reconfiguring of a commercial drive for an underground mine environment; harmonic cancellation in feeder circuits; basic control concepts; and special electrical safety requirements such as high resistance neutral grounding with sensitive ground fault tripping, belt slip, belt sequence, belt take-up requirements, etc. At the time of the writing of this paper the belt drive system has completed one year of successful and reliable operation.

Inverter applied to reconstruct of elevator

Abstract: Vector-controlled variable frequency drive and PLC are used to reconstruct the electric control system of demoded elevator. Improved reliability and comfort are achieved. It could contribute to save energy and deduce wastage and has a realism significance and popularize value. This paper discusses the design of the system tructure, the selections of inverter capacity and braking resistor and the controlling graph for speed.