Active Front End (AFE) variable frequency drive has some harmonic filtering at the input to the VFD that is "programmable" on the fly. Basically, a microprocessor "brain" in the VFD monitors the harmonics being generated by the power electronics and "actively" supplies a waveform through the filters to dampen the upstream harmonic content. This is important, because not all equipment is capable of handling the amplitudes of voltage and/or current harmonics produced by modern, large-scale power inverters and converters (VFDs).
VFD manufacturers have responded to this demand by manufacturing a variety of VFDs. The combination of the many types of VFDs available and the abundance of applications has made the selection of the optimum VFD for a given application a challenge.
The best way to mitigate power harmonics is with an active filter solution. No matter how low or high the load (VFD) runs at an active mitigation solution is best. There are many non-active solutions on the market but they all fall flat under varying load conditions most are based on LC filters and need the C component switched out at low load conditions. Power factor is a vital consideration when looking at any harmonic mitigation.
Analog control signal 4ma to 20ma is usually preferred over 0V to 10V due to its characteristics of fending off interference and knowing when there are faults in a control system, for example, a broken wire. Typically what I have seen is that nearly all field instrumentation is 4-20mA. The only time we come across 0-10V signals really is interfacing to drive systems, older VFDs or specialist sensors. Newer VFDs mostly now have a 4-20mA option or we interface with comms.
All variable frequency drives, who is in market definitely working with pump application. Normally in pump application didn't have any rocket science. Almost all VFDs can do quadratic V/f curve which fits perfectly a centrifugal pump torque-speed characteristic. Apart from that, there are already many explanations about multi-pump staging heretofore mentioned.
Some VFD Manufacturers have a function called "Motor Pre-heat function" that can be enabled via a couple of parameters. This function produces a low level DC Current (actually AC at 0 Hz) that heats up the motor windings to prevent condensation, while motor is de-energized/at rest, which is the same function of motor space heaters.
This helps to protect the front end of a VFD (Variable Frequency Drive) from typically unintended input transient damage from any number of sources to include unintended grounding, Capacitor bank switching, storms, unstable loading and unstable power supplies.
A Run permissive in Bypass (or just for a VFD) is typically a Normally open contact that requires a certain condition to be true in order to close and Permit the Bypass Motor Starter (or VFD) to close (Be placed in a Run condition) and cause the motor to Run
It is the load that you have to be concerned about in the first instance. Is the load variable torque such as a centrifugal fan or pump or is a constant torque load such as a conveyor. If a variable torque load what is the power at the maximum speed you require. If a constant torque load what torque do you require and what turn down ratio are you looking for? When you know these things the selection of the motor and variable frequency drive is a very simple process.
It is essential in today's market for the VFD to be capable of communicating (if possible even at the same time) using different communication protocols over different port types. That being said, while it is "easy" to bypass this need by adding a protocol converter or a serial/ethernet converter (for those units that only come with serial ports), it is still an added point of failure in the integrated system.
Cloud Based Management is a great Idea ... long on promise, yet shorter on delivery because/as it requires much investigation and critical design decision making. Just remember Remote Control requires much oversight because typical control has feet on the ground, close to the system being given control commands, especially for VFD Drives or other devices that cause motion.
Today's Variable Frequency Drives (VFDs) utilizing IGBT technology generates high frequency ground currents (HFGC). HFES is used with switching power supply / VFD applications, where damaging VFD generated HFGC are present. Damaging VFD generated currents cannot be eliminated although, they can be contained controlled and / or redirected, which is exactly what the HFES System Solution does. HFES is tested, proven and now patented.
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