Finally, for shunt-active solutions, users may consider an active filter. It uses IGBT technology and is particularly suited to VSD harmonics. It is able to cancel out harmonic frequencies by injecting equal and opposite, phase shifted, current frequencies.
Shunt active filters provide the most efficient harmonic compensation in a compact unit which has little loss, is insensitive to grid conditions, cannot be overloaded and is easy to retrofit. Also, being parallel to the load allows redundancy to be built in. All of this comes at a slightly higher cost, which is offset by the better return on investment over the longer term. The units are sized for the actually harmonic current produced and therefor are in the order of 25-33% of the drive rating.
Effective harmonic mitigation may seem intimidating, but it doesn't have to be. Understanding the often subtle differences between various techniques can yield better cost savings, reduce complexity and prolong equipment life. So now we can feel good about embracing "good vibrations".
About the author:
John Mitchell is business development manager of CP Automation - www.cpaltd.net