Practical applications of active power filters (III) [Part 5/5: Low harmonic drives (LHD) for dry lamination machines]

Low harmonic drives

Low harmonic drives (LHD for short), as a special design of shunt active power filters (APF for short), have been around since the 1990s. Description of their topology and operating principle can be found as far back as 1998. They were developed to take care economically of the power quality and energy efficiency problems created by variable speed drives (VSD for short) and electric motors that conventional passive solutions like reactors, passive harmonic filters (PHF for short), multi-pulse VSDs and slim DC link VSDs, or conventional active solutions like active front ends (AFE for short) and matrix inverter VSDs could not handle.

LHDs can be applied to small, medium or large installations in a wide range of segments. They have many low and high voltage potential applications where their use offers many benefits including any kind of machinery or system that needs constant power and/or constant or variable torque.

Functions

LHDs as a special design of shunt active power filters combine the technical advantages of AHFs with the cost-effectiveness of standard 6-pulse VSDs to form a compact economical solution with exceptionally low THD and minimal energy losses without the drawbacks of conventional passive or active solutions.

These specially designed modern LHDs, also known as AHF-based low harmonic drives (AHF-LHD for short), can take care of several power quality problems and support the development of clean energy by combining different control functions in a single device.

Connection

An AHF-based low harmonic drive is a power electronics-based device connected with the equipment generating the power quality problems or that has issues to comply with grid code and energy efficiency requirements. These LHDs can be installed together with new equipment or the VSDs of any existing equipment can be easily upgraded or retrofitted to AHF-based LHDs. They are formed by two components:

• An AHF that behaves as a controlled current source providing any kind of compensation current waveform (in terms of phase, amplitude and frequency) in real time (typical reaction time is under 50 μs and overall response time is under 100 μs).
• A standard 6-pulse VSD (or several VSDs in parallel) controlling the electric motor (or motors).

The most common operating voltage range for AHF-based LHDs is 200 V up to 690 V as the AHFs are built using low voltage IGBT switches. It is possible to connect them to higher voltages using a suitable step-up transformer for the AHF.

LHDs for dry lamination machines

Laminating is the process through which two or more flexible packaging webs are joined together using a bonding agent (adhesive). The substrates making up the webs may consist of plastic films, papers or aluminium foils. The adhesive can be solvent-based, water-based or solventless. During the laminating process an adhesive is applied to the less absorbent substrate web, after which the second web is pressed against it to produce a duplex, or two-layer, laminate. The typical combinations of web substrates include film on film, film on foil, film on paper and foil on paper.

Laminating is used to improve the appearance and barrier properties of substrates. The choice of the most suitable laminating process is mainly dictated by the end use of the product. A number of different technologies are available that cover the wide variety of applications demanded by the packaging industries.

Laminating machinery can be classified according to the type of adhesive used to produce the laminates. These types are wet lamination, dry lamination, wax lamination and solventless lamination.

Many industrial processes require extremely precise, continuously operating lamination machines. Power quality problems like high levels of harmonic distortion, voltage sags and interruptions can be devastating, leading to costly production downtime, material scrap, equipment damage, and ultimately lost profits.

Another problem that usually affects these processes is low power factor, which increases the losses of the installation and the overall energy costs.

Requirements

Background

An electrical equipment manufacturing facility designs and builds automatic high speed dry lamination machines. The machines were not able to work smoothly and efficiently. It was diagnosed that the lamination machines kept on tripping during testing due to high harmonics levels.

End users of these machines need to secure the operations at their facilities and maintain the quality and integrity of their packaging processes. The economic losses that can be caused by each trip of these machines can be quite significant.

The target of this project is to improve the operation of the dry lamination machines by reducing the harmonic distortion and at the same time getting some energy savings by improving the power factor.

System description

In the dry lamination process the adhesive dissolved into a liquid (water or a solvent) is applied to one of the webs before being evaporated in the drying oven. The adhesive coated web is laminated to the other web under strong pressure and using heated rollers, which improves the bond strength of the laminate.

Automatic high speed dry lamination machines are typically formed by:

• Unwind and rewind systems: Stations with adjustable length handling the web substrates and the end product.
• Coating system: Formed usually by a coating roller and a press rubber roller.
• Dryer: Drying oven.
• Control and protection system: Made with PLCs.

These machines use variable speed drives which are the sources of power quality and energy efficiency problems affecting the machinery and, if not taken care properly, the whole facility and process where they are installed.

Solution

Analysis

To be able to dimension a solution it was necessary to collect power quality measurement data from a lamination machine over a period of time by using a power quality analyser.

High level of harmonic distortion generated by the 6-pulse VSDs of the lamination machine was identified as the main reason of machinery tripping related issues.

The recorded power quality and energy efficiency parameters at the measurement point were:

• THDi: 39%.
• THDv: 21%.
• Power factor: 0.95 (ind.).

Proposed solution

Based on the analysis of the measurements, it is possible to dimension a solution that would comply with machine builder’s requirements of reducing the amount of harmonics to be able to comply with THDi and THDv under 5% and at the same time increasing the power factor to near unity. The solution is to upgrade these machines to low harmonic machines by using low harmonic drives. In this case, this would be done by keeping the existing 6-pulse VSDs and installing an active harmonic filter together with them.

Low harmonic drives can take care of the power quality problems related to harmonics, interharmonics, unbalances or voltage fluctuations (flicker) affecting lamination machines. In addition, they can improve the power factor and they can also improve the output voltage of motors fed from unbalanced power supplies.

Based on the values monitored, the following functions are proposed for the LHD.

Because of the nature of the application, the need for real-time harmonic filtering and power factor correction, and the space limitations of the machines, using conventional solutions like passive harmonic filters or active front ends was not an option.

The recorded power quality and energy efficiency parameters at the measurement point after the installation of the solution were:

• THDi: 4.5%.
• THDv: 3.6%.
• Power factor: 1.

Conclusions

Power quality and energy efficiency are key issues when designing and building electrical machinery. Through the implementation of power quality and energy efficiency improvement solutions it is possible to enhance the performance of machines and substantial savings can be made during their operation.

The installation of low harmonic drives in dry lamination machines reduces their harmonic distortion and increases their power factor bringing several benefits:

• Compliance with the harmonic distortion limits of local grid codes.
• Reduced energy losses.
• Machinery lifetime increased.
• Cost savings in the electricity bill.
• Economic losses related to faulty operation of lamination machines avoided.

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About the author:

Pedro Esteban is a versatile, multicultural and highly accomplished marketing, communications, sales and business development leader who holds since 2002 a broad global experience in sustainable energy transition including renewable energy, energy efficiency and energy storage. Author of over a hundred technical publications, he delivers numerous presentations each year at major international trade shows and conferences. He has been a leading expert at several management positions at General Electric, Alstom Grid and Areva T&D, and he is currently working at Merus Power Plc.