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Improving end-to-end system efficiency with variable speed drives and magnet-assisted synchronous reluctance motor technology (Part 2)

Reaching IE5 efficiency with magnet-assisted synchronous reluctance motors

Currently, magnet-assisted synchronous reluctance motors offer the most efficient performance available. This type of motor will reliably deliver IE5 performance when it is paired with a variable speed drive (VSD). Together, magnet-assisted synchronous reluctance motors with VSDs enable significant efficiency gains over induction motors across a wide speed range, and they offer benefits when operated with partial loads. Integrated motor drive packages are available in standard sizes meaning that they can be used as drop-in replacements for other NEMA motors. Note that synchronous reluctance motors require VSDs to enable precise control of the motor speed and torque and ensure that they operate with the optimal efficiency. It’s also worth noting that the IE5 class applies to the motor but not the drive: the VSD enables the motor to run with IE5 efficiency.

How magnet-assisted synchronous reluctance motors work 

A synchronous reluctance motor has two main components: the stator and the rotor. The stator is similar to that of an induction motor, with coils of wire that produce a rotating magnetic field. However, the rotor design is quite different from a traditional induction motor, and it works on a different principle – no current is induced in the rotor. The rotor is made from multiple laminated iron layers and its shape is precisely designed to guide magnetic reluctance. Permanent magnets are also incorporated into the rotor to add torque generation and field strength. 

Because the rotor guides magnetic reluctance throughout its structure, when the stator applies a rotating magnetic field, the rotor aligns itself with the magnetic field and “locks” into position. This enables it to rotate at the same speed as the magnetic field. In other words, the rotor moves synchronously with the magnetic field, which is why this type of motor is called a synchronous reluctance motor.

Benefits of magnet-assisted synchronous reluctance technology 

Magnet-assisted synchronous reluctance motors have several benefits over induction motors. First, they are more efficient since there are no losses in the rotor because no current is induced. The higher field strength provided by the magnets further improves overall efficiency.

Second, magnet-assisted synchronous reluctance motors are well suited to continuous or variable-torque applications, and they maintain their efficiency over a wide torque, speed and load range. This makes them particularly efficient in applications that require lower speeds and load points, and they have excellent partial load performance. 

Magnet-assisted synchronous reluctance motors have a lower operating temperature than induction motors since no current is induced in the rotor and because they have a higher power density. This type of motor has a power factor of 0.92 to 0.98, meaning that they deliver more horsepower per amp than an equivalent induction motor. The result is that they can be operated with smaller power converters, and the motors can run as much as 20 percent cooler than an equivalent induction motor.

Because they have a higher power density and lower current draw, magnet-assisted synchronous reluctance motor and VSD packages can be much more compact than equivalent induction motor installations. For example, with ABB’s EC Titanium technology, the drive is small enough to be integrated into the motor for quick and convenient plug-and-play installation.

Integrated motor drive technology enables IE5 efficiency over a broad operating range 

Many industrial systems operate at partial load, and most older motors suffer from a noticeable drop in efficiency when operated outside their peak operating range. In contrast, magnet-assisted synchronous reluctance motors offer a broad peak operating range, which enables them to run with IE5 efficiency at any speed and at partial load. This means that motor-drive packages like EC Titanium can be configured to the optimum settings for each individual application and deliver improved overall system performance and efficiency. And, because they are available in standard NEMA sizes, integrated motor drive packages can be retro¬fitted to improve the efficiency of existing equipment, without further modification.

It’s worth noting that IE5 motor-drive packages offer the greatest benefits over older motor systems at partial load. At full load, the incremental energy savings are around 4 percent, while at partial load the savings are much greater, at around 12.5 percent. Since systems like HVAC operate at 80 percent load or less most of the time, updating them to IE5 efficiency is clearly worthwhile.

Better lifetime efficiency for the entire system 

IE5 magnet-assisted synchronous reluctance motors with drives enable better overall system efficiency. With pumps and fans, which are usually run at partial load, this translates to better wire-to-water and wire-to-air efficiency. Although replacing older motor systems with more efficient ones does carry an initial financial cost, the long-term savings over the lifetime of the application far outweigh the cost of purchase. In fact, the initial investment can often be paid back in one to three years.

It’s important to realize that these energy and cost savings apply to the entire system and not just to the motor-drive package. For example, improving the efficiency of motor systems in an HVAC installation improves the efficiency of the whole HVAC installation. Since HVAC systems account for about 50 percent of energy consumed by an average commercial building, improving the efficiency of HVAC systems can translate to significant savings over the building’s lifetime.

In addition, magnet-assisted synchronous reluctance motors operate at lower temperatures than induction motors. This improves their reliability and extends their operational life, which therefore lowers maintenance requirements and costs throughout the lifetime of the application, as well. 

In the bigger picture, when companies improve their energy efficiency and use less electricity, they lower demand on the grid, freeing up capacity at utilities, meaning that fewer utilities need to be built to support the grid and emissions are reduced.

Compared to traditional induction motors, which deliver peak performance and efficiency at fixed operating points, magnet-assisted synchronous reluctance motors offer more flexibility. Because they can deliver optimum efficiency at a wide range or speeds and torques, they can be sized and configured to match the needs of the system, making it easier for designers to optimize the performance of their designs and the system overall. In addition, motors are usually built into systems, like fan assemblies. With older motors, the efficiency of the assembly is fixed, and changing operating speeds while maintaining the same level of efficiency usually means changing the motor. However, with VSD control and a magnet-assisted synchronous reluctance motor, the only things that needs to be changed are the settings.

Although motors and drives are just components in the overall system, modernizing these components can still pay off. For older installations that lack a VSD, a convenient option is to replace the motor with an integrated motor-drive package. They are small enough to fit into the space vacated by the existing motor, and they provide the benefits of magnet-assisted synchronous reluctance motors and VSD control. By doing this, designers can keep their preferred fan or pump design in operation, while also improving its overall efficiency and flexibility.

As stated, there are several proven ways to improve the energy efficiency and reduce operating costs of industrial processes that currently rely on older motors. Adding variable speed drives to directly regulate motor speed, eliminate mechanical speed and flow control is one method. Updating motors to newer, IE5 designs like magnet-assisted synchronous reluctance motors is another. When a VSD is combined with an IE5 magnet-assisted synchronous reluctance motor in a single package, like ABB’s EC Titanium integrated motor drive, upgrading is quick, easy and convenient. Moreover, IE5 VSD-motor packages give users the flexibility to select the best components for their needs and configure the entire system for the optimum performance and efficiency at a range of different speeds and torques. 

Overall, using VSDs and upgrading to IE5 motors can significantly reduce overall energy use. Better still, the initial investment is likely to pay back within a few years, while the energy and cost savings will last for the entire lifetime of the installation, which can be 20 years or more.


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