Upvote 3 Downvote 0 Reply 0. Upvote 1 Downvote 0 Reply 0. Upvote 0 Downvote 0 Reply 0. Answer added by Veera Karthik Kompala 4 years ago. Answer added by Mark Sanchez, Electrical and instrumentation specialist , S-chem, saudi chevron phillips, saudi polymer company. Answer added by Robinaire Monsanto, electrical technicians , Arabian packaging 4 years ago. Using vfd ,,,process control Smooth operation.. Acceleration and deceleration control.. Allow accurate position.. This section can be unidirectional or bidirectional based on the application used like the four-quadrant operation of the motor.
A minimum of six diodes are required for the three-phase conversion, so the rectifier unit is considered as six pulse converter. DC power from the rectifier section is fed to the DC link. This section consists of capacitors and inductors to smooth against ripples and store the DC power. The main function of the DC link is to receive, store and deliver DC power. This section comprises of electronic switches like transistors, thyristors, IGBT, etc. It uses modulation techniques like pulse width modulation to vary output frequency for controlling the speed of induction motor.
It consists of a microprocessor unit and performs various functions like controlling, configuring drive settings, fault conditions, and interfacing communication protocols. It receives a feedback signal from the motor as current speed reference and accordingly regulates the ratio of voltage to frequency to control motor speed.
VFD can also be implemented by the microcontroller circuit which is given below. Similar to VFD it also consists of rectifier section, filtering, and then inverter section. Here inverter section gets the firing pulses from the programmed microcontroller to give variable voltage and frequency to the load.
The application of VFD is ac motor speed control by cyclo converters. Power from mains is fed to the rectifier circuit which converts fixed AC to fixed DC. Three leg converters consist of two diodes connected in parallel for each phase, such that one of the diodes conducts when the particular phase is comparatively more positive or negative. Pulsed DC voltage generated from the rectifier is applied to the DC link circuit.
This intermediate circuit comprises inductors and capacitors. It filters the pulsed DC by reducing ripple content and gives DC power a constant level. To provide variable voltage and variable frequency to the motor, DC power from the DC link should be converted to variable AC by inverter.
Similar to the rectifier circuit, inverter switches also belong to two groups as positive and negative. Two rectifiers are required for each phase of power. Since most large power supplies are three-phase, there will be a minimum of 6 rectifiers used. After the power flows through the rectifiers it is stored on a dc bus or dc link. The dc bus contains capacitors to accept power from the rectifier, store it, and later deliver that power through the inverter section.
The dc bus may also contain inductors, dc links, chokes, or similar items that add inductance, thereby smoothing the incoming power supply to the dc bus. The IGBT can switch on and off several thousand times per second and precisely control the power delivered to the motor. Motor speed rpm is dependent upon frequency. Varying the frequency output of the VFD controls motor speed:. Electrical savings are important but other factors should be included as part of an evaluation of the lifecycle costs of the equipment.
For example, when pumps or fans are operated at reduced speeds there are often significant maintenance savings due to reduced wear on seals, bearings, shafts, etc. Productivity increases from reduced downtimes and reduced waste from optimized process control should also be quantified for significant life cycle cost economics. The major VFD designs commonly used are:. IGBT is a very fast semiconductor switch that is actuated electronically. By applying a small positive voltage between the gate and emitter points of the IGBT, the current is allowed to flow from a collector point to an emitter point.
Therefore, without the IGBT switching the current on and off so rapidly can not be created. Based on the experience of both component manufacturers and ABB it is possible to define the average lifetime of all aging components:. Your email address will not be published.
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