ABB a leader in drives technology has released this presentation regarding the Ultra Low Harmonic Drive products. Low harmonic drives do not need any further filtering or transformers to comply with regulations such as IEEE-519.
Category Archives: Passive Harmonic Filters (PHF)
Harmonic Mitigation for Variable Speed Drives (Part 1)
Harmonic mitigation requirements for Variable Speed Drives are growing fast as standards are being enforced more diligently. Many dynamic loads on one site can cause very high levels of power quality disturbance. If the grid is weak this can have severe effects on the availability and life span of equipment as well as causing small but measureable power losses. Most of all though, power quality is a matter of availability and productivity. Power quality is a key driver for profitability in process industry.
Available Low Harmonic Drive Solutions
There are several solutions available in the market today. Here we focus on Low Harmonic Drives offering <5% THDt distortion focused on fulfilling IEEE-519 requirements. The solutions normally offered are passive multiband filters (PHF), phaseshifting 18-24 pulse drives (MPD), Serial Active Filters (AFE) and Parallel Active Harmonic Filters (AHF).
Passive Filters
Passive filters have often been used due to the low investment cost. If the cost of catastrophic risk and inability to cope with changes in load profile are included however, the passive solution can quickly become very expensive. The high risk of operation, poor performance in the field and the issue of status monitoring make these solutions less desirable.
Active solutions are slightly more expensive but improve the systems behaviour a lot. The active technologies can not be overloaded, offer monitoring and control and allow fast response in case of failure.
18-24 Pulse Systems
Phaseshifting 18-24 pulse systems are very sensitive to unbalances, which again reduce their effectiveness in the field. Foot print is also greater than that of a passive system.
Serial Active Filters (AFE)
Serial active filters or Active Front End (AFE), as they are commonly referred to, are a very common mitigation technique. The downside to these is that they are serial solutions that have to be sized at 100+% of the drive load. They are commonly comparatively inefficient, making them expensive in the long run. A serial solution also creates a far more vulnerable system a dito parallell solution.
Low Harmonic Drives and their Power Losses
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.
Low Harmonic Drives 