What are all these numbers (6, 12, 18, 24) about in drives?
Issues of power quality are mainly concerned with the deviation of the current or voltage from its ideal waveform. The major cause of this deviation is because of the harmonics introduced by the switching of solid state devices. Such devices are of vital importance in the multiple pulse power electronic converter devices. All the switches used for power conversion will inject harmonics and all together leads to a power quality issue or event accordingly. Power quality of such converters are improved by increasing the number pulses required for their operation.
In variable speed drive (VSD) systems, both AC and DC, the first stage of power conversion is from AC to DC. In a DC drive, it’s the only stage – from fixed AC to variable DC. In an AC drive there are two additional stages: filtration and inversion back to AC.
The simplest converter is a full-wave diode bridge, which converts the incoming AC to a fixed DC voltage. This isn’t useful in a DC drive, but works fine for AC variable frequency drive (VFD). Standard industrial drives – both AC and DC – use six rectifier devices to form a three-phase full-wave bridge. This type of converter is called a “six-pulse” design, because it draws current in six distinct pulses from the AC line.
In general, a 12-pulse drive system is better than a 6-pulse drive system, but unless your distribution system has a large proportion of non-linear loads on it, harmonic content is (generally) not particularly concerning. This requires an 18-pulse bridge (and correspondingly expensive input transformer) at a minimum, and generally 24-pulse or higher for large drive systems. As an alternate, “active” front ends consisting of what is for all intents and purposes a transistor based inverter section can also be used. Multi-pulse and active front-ends add significantly to the initial cost of the drive equipment over a simple six-diode full-wave bridge.
Fortunately Triol Corporation has successfully solved this issue!
Let me represent Triol AK06! Triol AK06 VSD is a machine that is used to regulate the speed and rotational force of an AC induction motor (with constant speed). Motors, regulated by means of a valve or a vane as well as two-speed motors or their control by switching on or off, are inefficient tools from an energy aspect. The usage of energy in many motor applications can be reduced when the speed of the motor varies in response to the changed process conditions. Variable Speed Drives make this possible. In pumps, fans and compressors’ motor applications, the mechanical power needed is proportional to the fluid flow in the cube. Therefore, if we reduce the flow from 100% to 80% of the nominal value it would halve the required mechanical power. Also a lot of energy is lost in motors regulated by dampers or valves. The application of VSD, on the contrary, lets the motor to respond to the changed requirement of the flow, and therefore directly transforms this potential into electricity savings.
In addition to cost, consider many other factors when selecting a VSD. The carrier frequency is critical to reduce impact on the motor bearings and motor life. Install the output and input inductors to reduce harmonic distortion at the motor for most applications. To minimize resonance of higher order harmonics, an 18-pulse VSD is mostly required.
Whether you need a brief consultation or the most comprehensive solution, our experts are available anywhere and anytime. Our service team provide innovative and advanced solutions for the control, automation, remote monitoring. These experts help ensure the efficient and economical use of power by analyzing power system components including VSDs, and by delivering customized solutions.
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