Rockwell has developed an Active Front End drive solution for their low harmonic offering. The Allen Bradley 755TL is offered up to 690 V.
Source: Rockwell Automation
Category Archives: Active Front End (AFE)
ABB presentation about ULHD
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.
Harmonic Mitigation for Variable Speed Drives (Part 2)
Active Harmonic Filters Offer the Best Properties for a Low Harmonic Drive
Active Harmonic Filters are installed in parallel with a standard 6-pulse drive fitted with a small filter. This allows the drive to operate even if the filter is not in operation.
Serial vs Parallell installation
Using a parallel filter solution offers many advantages relating to sizing, foot print, system losses and availability. A parallel filter only needs to be sized to the mitigation load, generally 15-30% of the drive load unlike the serial solutions that have to be sized at 100+% of the drive load. As the shunt filter is smaller relatively to the drive the total system loss is smaller.
Lower system losses means less need for cooling and dramatically improve the Life Cycle Cost for the end user.
Availability
The cost of a component failure/standstill must be included in any production process related investment calculation. The cost of lost production income that can not be sold and potentially discarded is many times much more valuable than the capital cost of the equipment itself. Hence the availability of the drive function is one of the most important aspects when designing a drive system.
Serial installation means additive Mean Time Between Failures(MTBF). This means a serial filter will have 50% lower MTBF compared to a shunt filter.
Other more practical issues such as sourcing 6-pulse drives is also much easier compared to sourcing special AFE drives or 18-24 pulse units in case the drive itself needs to be changed.
Foot print and weight
Availability of drive function is the primary factor in keeping the production running.
Foot print lowers the system installation cost by reducing cost of cabinet and floor space. In retrofit projects as well as space constrained segments such as marine and offshore foot print and weight management is often crucial.
Installation
The design of many Active Harmonic Filters allow very compact installations where the cabinet is utilised at a maximum. The AHF’s power density is among the highest in the world among active filters. The filter design enables easy and economical use of cabinet footprint. Integrating the filter with single and multiple drives is simple and the filter normally does not need on site commissioning by external service engineers.
Future proof and flexible design options
It is good to ensure that the installed load can grow and change over time. Some AHF adapt to the load and more AHF capacity is easy to add by separate modules. The solution is flexible and can be installed centrally compensating many drives.
Commissioning
An easy to use web interface and commissioning software should guide the user through the process and allows for customer specific parameters settings. The filter is simple to configure to automatically focus on harmonics and use extra capacity for power factor correction. Integration through Modbus and Ethernet is standard.
Guarantee risk
By using a shunt installation the guarantee risk is reduced. The availability of the fundamental drive function is very important to the end customer. The AHF in shunt does not risk the drive function because even if the AHF fails the parallel installation allow the drive to operate.
In larger installations with multiple AHFs in parallel the filter function availability is vastly improved as the compensation is only partly reduced if one out of several filters fail.
Modern running master functionality allow a group of AHFs to automatically reconfigure themselves with a new master-slave relationship even if the original master-filter would stop. Automatic alarm functions to the responsible technician allow early and prompt response.
Finally, the drive + AHF system does not have issues with high frequency switching ripple that can cause EMC issues in larger AFE installations.
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.
IEEE 519 and Low Harmonic Drives
Standards governing distortion parameters in the electric grid such as IEEE 519, G5/4, EN 61000, EN 50160 and D-A-CH-CZ among others most often require voltage harmonic distortion to be below 5-8%. As yet, these standards are all recommended practices, used on a voluntary basis.
Although adherence to standards such as IEEE 519 is not obligatory, utilities and other parties of interest are using these standards to a growing extent as a benchmark to place demands on their customers. This is a way for them to be able to guarantee delivery on their end. Distortion standards are also used as a way to communicate and deliver an active environmental agenda with decreased energy usage and reduced energy costs for many energy intensive processes.
Low Harmonic Solutions to Meeting IEEE Standards
Reducing harmonics to an acceptable level is one way to meet the new requirements. Many modern active harmonic filters can pinpoint the contributing harmonic orders to optimize the compensation power and meet the requirements in the most cost efficient way.
Another popular, and potentially more common solution available, is the Active-Front-End (AFE). This was developed with the main target to feed back energy to the grid when breaking a motor or process. AFE can also be used to reduce harmonic loads, but in a very inefficient way, and in most cases an expensive way.
The modern Active Harmonic Filter is one of the most efficient Low Harmonic Drives in the market today. Filters are commonly available in a 208 – 480V version and a 480 – 690V. The Active Harmonic Filter can be combined with 6 pulse drives and will be placed in parallel with the load, minimizing the need of compensation power to 20 – 30 % of the load. The parallel placement will also ensure the redundancy in the design, which is a major advantage in a critical applications. Modular solutions, which are now more commonly available gives a dynamic and agile solution to work for future improvements to existing machinery.
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 