Showing papers on "Variable-frequency drive published in 2004"

Variable speed pumping: A guide to successful applications

Abstract: Author(s): Tutterow, Vestal; McKane, Aimee T. | Abstract: Pumping systems account for nearly 20% of the world's energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities. Significant opportunities exist to reduce pumping system energy consumption through smart design, retrofitting, and operating practices. In particular, the many pumping applications with variable-duty requirements offer great potential for savings. The savings often go well beyond energy, and may include improved performance, improved reliability, and reduced life cycle costs.Most existing systems requiring flow control make use of bypass lines, throttling valves, or pump speed adjustments. The most efficient of these is pump speed control.When a pump's speed is reduced, less energy is imparted to the fluid and less energy needs to be throttled or bypassed. Speed can be controlled in a number of ways, with the most popular type of variable speed drive (VSD) being the variable frequency drive (VFD). Pump speed adjustment is not appropriate for all pumping systems, however. This overview provides highlights from Variable Speed Pumping A Guide To Successful Applications, which has been developed by Europump and the Hydraulic Institute as a primer and tool to assist plant owners and designers as well as pump, motor,and drive manufacturers and distributors. When the requirements of a pump and system are understood, the user can consult this guide to help determine whether variable speed pumping is the correct choice. The guide is applicable for both new and retrofit installations and contains flowcharts to assist in the selection process.

Method for efficient nonsynchronous lng production

Abstract: A drive system for a refrigeration compressor such as is used in a natural gas liquefaction plant, allowing the desired compressor speed and maximum turbine efficiency to be maintained throughout varying ambient temperature conditions A gas turbine is used with an electric starter motor with drive-through capability located on a common drive shaft between the turbine and the compressor A variable frequency drive (VFD) is connected between the electrical power grid and the electric motor for smooth startups, but also to allow excess turbine mechanical power to be converted to electrical power by the motor operating as a generator, and delivered to the grid at the grid frequency Pulse width modulation technology may be used to reduce harmonic distortion in the VFD's output The starter motor also functions as a helper motor when the turbine output is insufficient to drive the compressor at the rotational speed needed to meet throughput requirements

Method and apparatus for determining and handling brake failures in open loop variable frequency drive motors

Abstract: A controller for a variable frequency drive monitors electrical power from a variable frequency drive motor while a brake is maintaining a load driven or moved by the motor without requiring additional feedback components of a closed loop configuration. If excess electrical power is being generated by the motor, an undesirable condition in the brake is indicated. Support or maintenance of the load is assumed by the motor in that event. Appropriate alarms or indicators are also activated.

Novel electric drive with power-regenerating capability: modeling and simulation

Abstract: This paper provides a detailed modeling of the variable voltage variable frequency drive system (VVVF) proposed by previous research. The AC/DC converter performance at low speed is tested and propulsion drive startup has been evaluated. The ability of the drive to provide power regeneration has been investigated, and the simulations suggest that the VVVF drive would have the ability to support substantial levels of pulse loads.

Variable frequency drive pwm control strategy for hybrid 7-level inverter

Abstract: This paper proposes a multilevel direct PWM control strategy based on reference voltage decomposition, analyzes and gives the application of the proposed strategy in hybrid 7-level VSI. Relationship between switching frequency of individual switching component and the control frequency is given. Possible DC voltage unbalance is studied through PSCAD simulation and the appropriate modulation mode is obtained. The dead time effect of hybrid 7-level inverter is analyzed and a modified compensation method is proposed. An experimental drive system based on hybrid 7-level inverter is developed. Various experimental results demonstrate the validity of the proposed PWM control strategy and the modified dead time compensation method.

Variable speed control stall detection and response system

Abstract: A variable frequency drive for an AC induction motor includes a stall sensing system coupled with a voltage frequency response system. Upon sensing a rise in the current which suggests a stall, and before triggering a motor shutdown, the VFD is caused to increase the V/f ratio to the motor and thereby induce a high-torque shaking response and seek to overcome any mechanically induced stall. The motor can be cycled between a first V/f ratio and a second V/f ratio in several attempts to release the stall.

A New Medium Voltage Speed-Variable Drive for Fans and Pumps—Rotor-side Variable Frequency Drive

Abstract: This paper introduces a novel VVVF method, i.e. rotor side frequency-variable drive, which can be used to regulate the rotating velocity of high power fan and medium-voltage motor for pumpe by using a medium power low voltage IGBT inverter. In the new method, the stator winding is directly connected to 6 kV or 10 kV network and the inverter is removed from stator side to rotor side. The new method is featured by simple main circuit, reactance-less, high power factor and low harmonics, easy to start and by-pass operation.

Energy optimization in rapid flow variation systems

Abstract: The paper tries to analyse the technical feasibility of optimizing the excess energy consumption in a quench blower using a variable frequency drive. Major application engineering considerations, like the cycle time of the blower and the mechanical stresses generated in the mechanical system of the blower, are analysed using computer simulation taking a specific case from a glass processing facility. One of the major findings of the simulation is that the acceleration and deceleration times of the blower are well within the limits set out by the process. The peak mechanical stresses generated in the system, namely the shaft, impeller and bearing, of the blower are also within permissible design limits. However, mechanical components, like impeller and shaft, could be susceptible to fatigue failure in the long run. As far as the drive is concerned, the regenerative energy during deceleration of the blower should be handled either by external equipment or by selecting an appropriate drive with regenerative capability.

Use a less power low voltage IGBT converter to adjust speed of a full power medium voltage induction motor of fan or pump

Abstract: To solve the difficulty of medium voltage variable frequency drive of fan or pump, a technique, rotor-side variable frequency drive (RVFD), is introduced that a less power (0.2-0.3P/sub N/) low voltage (<400 V) IGBT converter is used to adjust speed of a full power medium voltage (6-10 kV) motor. The features of the technique are: simple circuit, less large devices, better power factor and smaller harmonics. An improved RVFD based on PFC technique is proposed, it can remove the influence caused by diode rectifier.

Device for automatic control of vacuum system suction pressures using variable frequency drive motors

Abstract: A valve regulator is connected to the vacuum system(b) through a duct(2). The vacuum in the regulator acts on a spring biased(12) diaphragm(8) to move an arm(13,14) linked to a potentiometer(d). The potentiometer is wired to a frequency converter(e) that supplies the drive motor(f) rotating the system vacuum pump.