A lot of electrical energy can be saved using active filter in shunt in comparison to using either serial filters or passive or active front end.

I have compiled a few examples and what they mean to the user. When looking at the active filter in shunt mode as a system, it offers a considerably lower total system loss than the passive filter.

Passive Harmonic Filters

The losses of a passive filter are between 0.6-1.5%.

Assuming a 2% loss on a 6-pulse drive, the total system loss is the sum of the losses.

Pdrive*PFilter = 2% + (1.5 <-> 0.6)%  =>  3.5% to 2.6% total system loss.

Please NOTE! This calculation does not include an eventual voltage drop through the passive filter and its effect on the motor’s losses.

Front End – Serial Active Filter

The losses of an Active Front End drive are essentially twice those of a standard drive, due to the power having to pass through two IGBTs.

Pafe = 2% + 2% + 1% for the LCL-filter = 5% losses. Total system losses observed in documentation are 4.7-5%.

Shunt Active Filter

The shunt Active Filter, unlike the serial solutions, only has to be sized in accordance with the harmonic currents to be filtered. Under normal conditions, this means that in a IEEE-519 or G5/4 application, a filter sized to 15-30% of the 6 pulse load is sufficient. This also gives a much lower total system loss, despite the efficiency of he Active Filter being:

Pdrive + Padf = 0.02 + 0.02* (0,15 – 0,3) = 2.3 – 2.6 % in total system losses.

From a System Owner’s View – a Summary

Shunt Active Harmonic filters offer between 0 and 1.17%-points lower power consumption compared to Passive Harmonic Filters.  This is not including any effect from voltage drop through the serial passive filter.

Shunt Active Harmonic Filters offer between 2.7 – 2.4 % lower power consumption compared to Active Front End drives.

Power Losses – Significant in Life Cycle Cost Calculations

Over time, minimising losses in industrial process loads with over 8000 hours of annual operation, one percentage point saving on power concumption translates to a significant financial value.
(Pdrive + Pcooling) (kW)* Yearly operation hours(h)*Net Losses(%) = Total cost saving potential

Estimating the Cost of Energy

Energy cost estimates and prices of electrical power differ but the relation between cooling and electricity is roughly equivalent to:

Pcooling = 0.3 * Pdrive

When discussing payback and AFE, there are cases where the entire harmonic mitigation solution has been paid off in 2,5 years. This by using shunt Active Harmonic Filters instead of Active Front End – all thanks to lower power losses.

The Active Harmonic Filter is very competitive compared to both Passive filters and Active Front End. The necessary capital expenditure is very similar, which means that a lower power consumption makes the Active Harmonic Filter a very good overall choice.

A further benefit offered by the shunt installation is the increased availability of the process. Due to the non serial connection of the Active Harmonic Filter, the drive can continue to operate even though the mitigation has failed.