Active Filtering just got simpler with Sensorless Control
Comsys has released a new solution for controlling the Active Harmonic
Filter. The sensorless active filter control reduces the cost and
complexity of the system as it does not require any current transformer
In this case study they describe the retrofit on a small diesel
electric powered oil tanker, Fox Luna. The sensorless active filtering
approach is well equipped for protecting sensitive loads from dirty grids.
Vacon joins Danfoss as the second tier 1 drives manufacturer to integrate an active harmonic filter with a drive to lower harmonics. Vacons stand-alone NXC range previously offered 12 pulse as well as active front end drive solutions.
The Low Harmonic NXC was recently shown at a large exhibition in Sweden and is reportedly offered on a project by project basis but will become a standard offering in the near future. The system shown, verifies the smaller foot print and weight of the Active Filter drive system compared to the more common Active Front End drives. The active filter NXC also has a lower power loss, which is becoming more important as the EN 50598-2 standard is introduced.
Power quality mitigation products are not only used to fulfil regulations such as IEEE-519 and G5/4. They have actual effects saving both power and increasing productivity. This presentation by ABB exemplifies some of their early case studies indicating savings of up to 10%. Note that these savings compare to having no harmonic mitigation.
The cases below clearly show the great business value of implementing a high power quality standard within your facility. The secondary effects of complying with IEEE 519 or similar standards enables the local grid to be dimensioned for less reactive power and harmonic current thus saving money through thinner cabling, smaller transformers etc. Power quality mitigation is not only a cost in the general investment calculation but a tool to save money.
Standards governing distiortion 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%. These are all recommended, not obligatory practices.
Although adherence to standards such as IEEE 519 is not obligatory, more and more utilities and other parties of interest are using these standards as a benchmark to place demands on their customers. This is a way for them to be able to guarantee disturbance free delivery on their end. It is also used as a part of an active environmental agenda to show a decreased energy usage and reduced energy costs for many energy intensive processes.
One way to meet the new requirements is to simply reduce the harmonics to an acceptable level. Many modern active harmonic filters can pinpoint the harmonic orders that are contributing, and the compensation power can be optimized to meet the requirements in the most cost efficient way.
The modern Active Harmonic Filter is one of the most efficient harmonic solutions 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. This is all in keeping with the spirit of standards such as the IEEE 519 toward a sustainable energy future.
Earlier on the blog, we have defined the Active Harmonic Filter (AHF) as the best low harmonic choice for variable speed drives. A common question often put is 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 optimal solution. This would create the need for a bigger Active Filter, and the drives rectifier would be stressed by the compensation power from the filter. This in turn would reduce the drive’s life span.
A very common solution is to install a 2% or 5% choke on the drive. Many high quality drives have such chokes fitted as standard. Fitting a choke reduces the harmonics from 85-100% to about 35-40% which is a very cost effective solution. The remaining, and significantly lower THD, means the size of the final and more expensive filtering is much smaller.
The choke will also dampen the compensation power affecting the drive. Leaving out the choke, the drive’s 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 to complement. It gives the overall system a lower cost and higher availability.
Active Harmonic Filters are growing in popularity as a method to mitigate power quality issues. There are several factors to consider when specifying an active harmonic filter. Typical applications for active filters are compensation of variable frequency drives and data-centers to reduce the load on UPS systems or compensating the effects of renewable energy sources on the grid.
What is an Active Harmonic Filter and what is its Application.
The general definition to describe this application is an analog or digital device that measures the power quality on the grid side. It then injects current to compensate any unwanted deviations from the standard 50 or 60 Hz supply. Deviations can be mitigated in full or partially.
What Factors to Consider when Specifying an Active Harmonic Filter
Sensor or sensorless control
There are suppliers that provide sensorless control eliminating the need for current transformers. This solution reduce the installation cost. Sensorless is not used in all applications so make sure to check the application with the supplier. Sensorless control or voltage control as it is sometimes defined compensates the total THD. It is not possible to select a single source such as a single VFD. On the plus-side it is possible to protect a sensitive subgrid from a noisy primary grid.
Depending on design, the filter has higher or lower losses. Check the losses as this will reduce the Life Cycle Cost on your investment. Some active filters have up to 1%-point lower losses, which depending on your user profile, means a potential for considerable financial savings if calculated LCC over 5 years.
Harmonic Compensation Capacity
Harmonics are normally seen in the odd. Common capacity for active filters is 25th or 50th harmonic. Sometimes there is a claim of being able to mitigate the 51st harmonic, which has little value as harmonic order of 51 and above are normally not important.
Harmonics above the 50th are more difficult to measure as there are few PQ-meters that can handle such orders. There are however quite common sources such as Active Front End Drives that cause switching ripple above 3kHz, above the 60th harmonic (or above the 50th in 60 Hz systems).
There are a few Active Harmonic Filters capable of compensating such frequencies. Choose a filter according to the needs specified by your measurements.
A filter’s capacity to compensate a certain harmonic order is only part of the story. Another important factor is de-rating, discussed below.
Some power quality phenomena occur extremely fast requiring the mitigation to be even faster. If your process is affected by fast flicker or transients, take special care to evaluate the response capacity of the filter. Flicker is a specific phenomena that normally requires special software to compensate flicker in a controlled environment.
Interharmonics is commonly caused by syncronisation issues. If your installation includes such interharmonic sources, the type of active filter changes and the vendor has to be consulted. This is a common issue on some types of older wind turbines.
In Europe there are strict guidelines regarding EMC. If you want to be sure that the active filter does not interfere, the filter must be fitted with a properly tuned EMC-filter.
An Active Harmonic Filter’s rating is normally defined at nominal load, meaning at 50/60Hz. As the filter works further up the harmonics its capacity compared to nominal starts to de-rate. The de-rating curve is documented by all serious suppliers and should be available if you ask them.
A de-rating of 50%, at say the 13th harmonic, means that a 100A filter only has the capacity to compensate 50A at the 13th. Naturally if you have harmonics of higher order it becomes more important to check the de-rating.
De-rating is a matter of how robustly the filter is designed. Some suppliers offer zero de-rating up to the 7th before capacity starts to fall.
Physical Footprint – How Much Cabinet Space is Required?
Most active filter suppliers offer several alternatives regarding installation. Wall mount, Cabinet and IP00 modules to install in cabinets. Efficient use of cabinet space translates to lower system cost. Some filters have a modular design and can be enhanced with further capacity without adding to the footprint.
As mentioned, a modular design of your Active Harmonic Filter enables you to adapt the filter to potential changes in your future power compensation needs. The modular design means that you can easily add to the filter’s capacity within the existing cabinet, saving both cost and space.
Does the filter have built in commissioning software? Commissioning and service of Active Filters can be quite time consuming. Ask for a review of the support software included in the machine. Some suppliers have an extra charge for the necessary software. Minimum required functionality should be that the system performs a self-check of Voltage and CT phase order, CT polarity check, self-diagnosis, and self-calibration. Such features will quickly find installation errors before they can cause problems and will also shorten the needed commissioning time.
If the filter does not have this type of support software the commissioning becomes much more complex and might even require external support adding to the system cost.
There are different HMI setups. Some have a very simple front HMI while others include graphs showing the current and voltage waveforms and many further functions. A great added value is to have at least a web-based interface allowing in-depth monitoring and control functionality. Then no extra PQ-meter is necessary.
Smart Grid Functionality
Active filters have a built in rudimentary power and power quality meter to calculate the required compensation. Some filter manufacturers make use of this fact and enable the user to connect all filters on site and company wide through a web based architecture. An operator can then have an overview of the status of all connected cabinets and log them. This enables the possibility to log events that could or should have caused production disturbances, status monitoring of individual filters as well as remote control capability. Email and text alerts to dedicated service personnel from the filter reduce response time dramatically.
IP/NEMA Class and Water Cooling
Water-cooled Active Filters enable very good cooling of the IGBTs, the most critical component in the Active Filter. Water-cooling reduces overheating immensely, which increases availability in the same way as for Variable Frequency Drives. The power density of the installation is also improved.
Active Harmonic Filters are offered in a range of voltages. Most common ranges are 380–415V, up to 480 V. Higher voltages up to 600 and 690V are also available without step-up transformer, reducing foot print. Some suppliers have the capacity to supply MV ratings as well, normally using a step-up transformer. The active filter can then act as STATCOM.
In recent years several suppliers are offering battery connectivity to create a battery energy storage system for FCR and peak shaving. The active filters on-load capabilities are perfect for grid connectivity applications.
Sensorless Voltage Control
Recently a new type of sensorless solution make it much easier to install as no CTs are required which is standard for active harmonic filters. This method can not control specific frequencies but can be used to even mitigate noise from the grid.
Some filters offer resonance damping making them ideal in highly complex situations.
Active Harmonic Filter Technology have many potential applications where its use can offer plenty of benefits. Active Filters have been proven to provide lowered disturbances, lower carbon dioxide emissions through improved energy efficiency, lower current consumption and increased production stability to name a few. Just as other technology has evolved, so have various production technologies. Today’s semiconductor loads require far more sophisticated solutions than was necessary in the past – a need met by modern Active Filtering technology.
Some of the most common applications for Active Harmonic Filters are:
Variable Speed Drives
The most common application for Active Filters is the compensation of harmonics generated by variable speed drives, often referred to as VFDs or Frequency Converters. Drive systems have the benefits of lower losses and increased production flexibility at the cost of higher harmonics emissions. Harmonics emissions make passive compensation unsuitable. Active harmonic filtering, especially with a modular approach, allows successive installation and mitigation of selected harmonics.
Electrical welding systems place uneven demands with extremely high peaks in current demand during short periods. The resulting highly fluctuating voltage levels cause flicker. Flicker emissions can cause disturbances with other electrical consumers such as neighboring industries or residential areas and can cause reliability issues with nearby equipment. Active Filters can mitigate Flicker.
Furnaces and casting processes are known to give rise to both flicker and harmonics. This is largely due to being some of the most energy intensive production processes today. Active Filtering technology is ideal to combat both of these issues to increase production stability and reduce effects on the grid.
Wind and Solar Power Systems
A major problem inherent in many renewable energy sources today is the inconstant load delivered to the grid. Both wind and solar energy is delivered as wind and sun is available, causing surges of energy that the existing grid is usually not built for. The remote location of these energy plants also means that grid connections are suboptimal.
Wind power systems cause flicker, harmonics or interharmonics as well as other problems. Solar power plants cause harmonics and interharmonics. In some cases, especially in weaker networks, resonances may be excited by the harmonic output of the solar inverters. Modern Active Filtering technology is very effective in combatting these problems; reducing the stress placed on the grid and making these renewable energy sources more effective and widely viable.
Light systems can cause harmonics that heat neutral conductors and disturb nearby equipment. This can mean production disturbances and unnecessary maintenance costs. Modern energy saving lamps may be more likely to cause disturbances depending on type. Active Filters are well suited to combat these problems.
UPS or Uniterruptible Power Suplies can save lives as well as data and financial loss. A UPS system connected to a network polluted with harmonics can malfunction and has a shortened life span. Connecting an Active Filter to secure uninterrupted power supply will ensure production uptime.
What is Harmonics
Simply put: Harmonics are unwanted frequency components and unbalance in terms of uneven power distribution between the phases in the electrical network.
More exactly: Harmonics are disturbances to the sinusoidal voltage waveform. They are multiples of the supply frequency, in other words if the supply frequency is 50 Hz the fifth harmonic would be 250 Hz. These variations from the pure sine form are caused by non-linear loads from electrical machinery and appliances. These non-linear loads can be caused by anything from battery chargers to variable speed drives or flourescent lighting. High levels of harmonics can cause power quality problems and voltage distortions.
Harmonics and the power quality problems they cause can have expensive and often detrimental effects on machinery and appliances. Flourescent lighting may need to be changed continuously, electric motors may have 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:
- Lower production speed
- Increased energy consumption
- Charges for reactive power consumption
- Damaged equipment
- Premature equipment aging
- Data loss
The fact is that harmonics have become a problem for many business sectors and the costs are consistently rising. The number of disturbances are increasing and modern production equipment is becoming more sensitive to these disturbances.
Harmonic Distortion Standards
Harmonics caused by large machine parks can also have an effect the grid. This is why there has been an increase in regulations and standards required by municipals. Some examples of standards governing harmonics emissions are IEEE 519, G5/4, EN 61000, EN 50160, D-A-CH-CZ, among others. Some standards are also specific to certain applications, such as DNV or ABS for offshore applications. The standards most commonly require a voltage harmonic distortion below 5-8%.
Harmonic Filter Restores Power Quality and Reduces Downtime Caused by Harmonics
Problems with power quality often become apparent through problems in production and surrounding equipment such as lighting.
This is what happened at one of the largest printers in Holland.
The printing company consists of two printing plants located in Amsterdam. The plant employs 170 people, producing six daily newspapers and several other free local papers and magazines. The plant prints up to 1 million papers every day with printing presses running almost nonstop.
Poor Power Quality – the Challenge
The printers had been struggling with power quality problems for many years. Flourescent lighting had to be changed continuously as the tubes kept failing. The electrical ballast had to be changed every six months instead of every 5 years. This kept one employee busy 2-3 days a week. In 2011 just the lighting problems and other broken components cost the printers about
300 000 €. In addition to these losses, the plant had power quality related problems during startup of the presses, which resulted in additional losses through production downtime.
Active Harmonic Filters – the Solution
The printing group decided on an investment in power quality and quite literally, a brighter future. Six harmonic filters with a total compensation current of 1800 A were installed to optimize the power grid and reduce harmonics.
Harmonic Filtering Gave Quick Results
Following installation and commisioning of the active harmonic filters all previous problems disappeared. The printing plant can nowuse their printing presses without disturbances from poor power quality. Due to the continuous stops in production and equipment failure, which had been a daily occurrance, the return on investment for the harmonic filtering system was very short.
Active Harmonic Filters Improve Dynamic Test-Bed
A major pioneer in the manufacturing industry caused problems on the power supply network with their dynamic test bed. Here, an installation of the right combination of active harmonic filters now compensates harmonics up to the 100th order with great results. Both harmonics and voltage notches are reduced to enable top performance of the equipment.
The test benches, owned by the development department of a major European production plant, are used to test components in the development phase. Varying test conditions can be programmed, which gives the test bench very dynamic properties.
Harmonics Compensation Challenge
The same transformer is connected to two parts of the test bench. With a very dynamic load whose load current amplitude can change from zero to maximum in approximately 100 ms, it was impossible to run both parts of the test bench simultaneously. The voltage notches of up to 25% in combination with very high harmonic disturbances prevented this. This caused serious delay in the testing facility as well as exceeding the limits in EN61000-2-4.
Active Harmonic Filters – the Solution
To solve the power quality issues, several active harmonic filters were installed to compensate the disturbances. Two 200/480V filters were installed together with one 100/480V filter that in combination compensate all frequencies up to the 100th harmonic order. The first two filters can be used to compensate lower harmonics while the third compensates for higher order harmonics and interharmonics. The three units were configured to share the
load with the 100/480V filter working on higher orders only. This resulted in extremely short response times and considerably lowered load disturbances.
Harmonics Compensation – the Result
Thanks to the active harmonic filter installation, voltage notches could be reduced to 10%. In addition, harmonics were lowered to the required level stipulated in EN61000-2-4. Now, both test benches can be run simultaneously without any of the problems caused by poor power quality.