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
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.
Using Low Harmonic Drives to save money
Low harmonic drives have a greater worth than simply fulfilling regulations such as IEEE-519 and G5/4. Low harmonic drives have clear effects on delivering both power savings and productivity increases. The following presentation by ABB exemplifies some of their early case studies where active harmonic filters are used to create a low harmonic drive solution indicating savings of up to 10%. Note that these savings are compared to having no harmonic mitigation in place.
The cases illustrated by ABB, clearly demonstrate the great business value of implementing a high power quality standard for your installation and especially specifying low harmonic drives solutions for processes where many operational hours are involved. Complying with IEEE 519 or similar standards further enables the local grid to be dimensioned for less reactive power and harmonic current, leading to further monetary savings through thinner cabling, smaller transformers etc. Low harmonic drives are far more than a cost in the general investment calculation but should be considered as a tool to create direct financial savings.
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.
Optimizing Your Low Harmonic Drive
In previous articles we have defined the Active Harmonic Filter (AHF) as the best low harmonic choice for variable speed drives. There are often questions whether the drive has to be fitted with a line filter as well.
In theory a well designed Active Filter can compensate a drive without a choke but this may not be the best solution. The Active Filter would then need to be bigger and the drives rectifier would be stressed by the compensation power from the filter, reducing the drives life span.
A very common solution is to install a 2% or 5% choke on the drive. Many high quality drives are fitted with such chokes as standard. The choke reduce the harmonics from 85-100% to about 35-40% which therefore is a very cost effective solution. The remaining THD is significantly lower meaning the size of the final and more expensive filtering is much smaller.
The choke will also dampen the compensation power affecting the drive. Without the choke the drives rectifier will degrade over time.
So the answer is yes, a Low Harmonic Drive system using Active Harmonic Filters will benefit from using a choke as well. The overall system will have lower cost and higher availability.
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.
Active Harmonic Filters – More Powerful than You Know
Harmonics are a problem for a wide number of business sectors. The costs are high and rising as the number of disturbances are increasing and modern production equipment becomes more sensitive to these disturbances. The use of active harmonic filters is one way to deal with these problems.
Active Harmonic Filters have been available on the market for many years but have often been given a back seat to the more common mitigation technique of Active Front End or AFE. Unlike the AFE technology, an Active Harmonic Filter is connected parallel to the load, which means that should something happen to the filter, production can continue without disturbance. Further flexibility offered by AHF in combination with variable speed drives is that they offer a wide range of harmonic cancellation, with the possibility of adding further units should the harmonic profile change in the future.
Active Harmonic Filter – A Versatile Solution
Active Harmonic Filters are also far more versatile than many of their competitors. A modern AHF does not just eliminate harmonics, but deals with other power quality problems such as:
- flicker
- voltage variations
- resonances
- reactive energy
This is achieved by using a highly dynamic, stepless digitally controlled compensation and filtering approach. By continuously monitoring the network and injecting just the right amount of compensation current – at exactly the right time – a highly efficient and accurate solution to any power quality problem can be achieved.
This approach enables the current waveform to be restored instantaneously, the current consumption to be lowered and changes in load or installation conditions to be fully compensated at all times.
For modern facilities, where load and network change constantly, the active harmonic filter may be the only adequate solution.
Common Misconceptions on AHF
A common misconception regarding Active Harmonic Filters is that they are only effective in reducing harmonic oscillations up to 2 kHz or within a specific frequency span. This however applies to just about all mitigation techniques. Active harmonic filters exist for different power levels and are adapted to fit the particular needs of the installation. Modern AHF products can operate in the range 7kHz and even some up to 17kHz. This means that it can compensate even up to the 100th harmonic.
Active Harmonic Filters are also commonly accused of causing high losses. However, as with most technology, AHF have come a long way and today exhibit very low losses. Low losses mean improved reliability and longer component life, as well a larger energy savings for the compensated load or process. Further, cooling requirements are reduced, which reduces the size and weight of the unit, positively affecting the total cost of ownership.
Many Active Harmonic Filters today are delivered with built-in automatic overload protection and extensive software controlled monitoring functions, which guarantees system safety and reliability under all operating conditions.
Harmonics
Harmonics are disturbances to the sinusoidal voltage waveform. They are multiples of the supply frequency, i.e. the fifth harmonic would be 250 Hz if the supply frequency is 50 Hz. These deviations from the pure sine function are caused by non-linear loads from electrical machinery and appliances ranging from flourescent lighting and battery chargers to pumps and variable speed drives. High levels of harmonics can create voltage distortions and power quality problems.
Simply put: Harmonics are unwanted frequency components and unbalance in terms of uneven power distribution between the phases in the electrical network.
Power quality problems caused by harmonics can have detrimental and often expensive effects on machinery and appliances. Electric motors can become overheated with a higher frequency of break downs and a shortened life span. Some common direct impacts of poor power quality in the shape of harmonics are:
- Reduced production speed
- Increased energy consumption
- Charges for reactive power consumption
- Equipment damage
- Premature equipment aging
- Data loss
Harmonic Distortion Standards
Harmonics caused by large machine parks can also effect the grid, which is the reason for an increase in regulations and standards required by municipals. Some examples are IEEE 519, G5/4, EN 61000, EN 50160, D-A-CH-CZ, among others. There are also standards specific to certain applications, such as DNV or ABS for offshore applications. Most often the standards require voltage harmonic distortion to be below 5-8%.
Low Harmonic Drives 