Using the active filter in shunt applications has a lot of energy saving potential compared to using serial filters – either passive or active front end.
Here are some examples and what they mean to you as user. When seen as a system, the active filter in shunt mode offers a total system loss that is lower than that of the passive filter.
Passive Harmonic Filters
A passive filter has between 0.6-1.5% losses
Assuming a 6-pulse drive has 2% losses, 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.
NOTE! This does not include an eventual voltage drop through the passive filter and its effect on the motor’s losses.
Serial Active Filter – Front End
An active front end drive essentially has twice the loss of a standard drive as the power has 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
Unlike the serial solutions the shunt active filter only has to be sized according to the harmonic currents to be filtered out. Under normal conditions this means that in a IEEE-519 or G5/4 application the filter has to be sized 15-30% of the 6-pulse load. This means the total system loss is also much lower even though the efficiency of the Active Filter is:
Pdrive + Padf = 0.02 + 0.02* (0,15 – 0,3) = 2.3 – 2.6 % in total system losses.
Summary from a System Owner’s View
Shunt Active Harmonic filters offer between 0 and 1.17% points lower power consumption compared to Passive Harmonic Filters. This does not include 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 are a Significant Part of Your Life Cycle Cost Calculation
Minimising losses over time, especially in industrial process loads with more than 8000 hours of yearly operation, 1%-point saving in power consumption translates into significant value.
(Pdrive + Pcooling) (kW)* Yearly operation hours(h)*Net Losses(%) = Total cost saving potential
Energy Cost Estimate
Electrical power prices differ but the relation between cooling and electricity is roughly equivalent to
Pcooling = 0.3 * Pdrive
In the case of the AFE there are cases where the entire harmonic mitigation solution has been paid off in 2.5 years simply by choosing shunt Active Harmonic Filters instead of Active Front End thanks to lower power losses.
The Active Harmonic Filter is very competitive compared to both Passive filters and Active Front End. As the capital expenditure is very similar, a lower power consumption make the AHF a very good overall choice.
Furthermore the availability offered by a shunt installation where the drive can continue to operate even though the mitigation has failed offer a great upside through higher availability of the process.