How to calculate magnetic losses in electric motors

February 27, 2023

Reza Zeinali defended his PhD thesis at the department of Electrical Engineering on February 24th.

Source: iStockPhoto.

Electric motors are the driving force behind the modern world, powering an array of everyday appliances, such as refrigerators and automatic car windows, and technologies used in industrial processes. Fundamentally, electric motors convert electrical energy into mechanical energy, but this conversion process is not 100% efficient. Invariably, energy is lost due to mechanical loss, resistive loss, and magnetic losses. For his PhD researcher, Reza Zeinali, has developed accurate modeling frameworks for calculating magnetic losses in high-speed electric motors.

In electric motors, the process of converting electricity into mechanical energy is always accompanied by energy dissipation, where part of the input electric energy is transformed into heat. Mechanical loss, resistive loss, and magnetic losses are the three main loss mechanisms in electric motors.

Around 40% of the globally produced electric energy is consumed by electric motors. This means that even a few percent improvements in the efficiency of electric motors can lead to a significant reduction in worldwide electric energy production. Therefore, high-efficiency electric motors are a crucial step toward a sustainable future, as governments are regulating energy efficiency standards to encourage electric motor manufacturers to improve the efficiency of their products.

Reza Zeinali.

Demand for High Power Density electric motors

Besides the efficiency improvement requirements, there is an ever-increasing demand for High Power Density (HPD) electric motors in different industries. HPD motors operate at high rotational speed and reduce the material consumption, cost of the final product, and subsequently the cost of the system in which they are used.

Furthermore, HPD motors are more compact and lighter, which is a crucial feature in most industrial applications such as aviation and transportation. Additionally, they offer a good compromise between efficiency and power density. Despite all of these appealing features, design and manufacturing challenges, such as high magnetic losses, are one of the main obstacles against the widespread use of these machines.

Design challenges

The term magnetic losses refer to the energy dissipated in the iron core of electric motors made of electrical steel sheets. These losses are composed of two main components; namely hysteresis and eddy currents.

To design and manufacture optimized, energy-efficient, and high-speed electric motors requires knowledge on how to calculate magnetic losses, so as to understand how they are generated and how they could be reduced. This knowledge ranges from the accurate computation of the magnetic field in the machines considering the complex material properties to the computation methodology of the losses from the computed fields.

Although the problem of magnetic loss calculation has been studied for decades, and numerous magnetic loss models have been developed, there are still many unknown factors influencing the magnetic losses in electric machines.

Novel magnetic loss modeling frameworks

For his PhD research, Reza Zeinali looked at ways to improve the accuracy of calculating magnetic losses in electrical machines, with a specific emphasis on high-speed electric drives.

Zeinali addressed two interconnected areas in his study: the characterization of ferromagnetic materials and the numerical analysis of electromagnetic problems. In doing so, he developed phenomenological hysteresis models to describe the intrinsic magnetic properties of ferromagnetic materials.

These models were incorporated in 2D and 3D numerical electromagnetic solvers, which led to the development of three magnetic loss modeling frameworks. Two unique measurement setups were realized to experimentally validate the developed models in a wide frequency range varying from 50 to 1500 Hz.

Clear picture

In conclusion, Zeinali presented an all-inclusive and comparative study of different magnetic loss models that provides a clear picture for designers of electrical machines to choose a specific magnetic loss modeling technique based on the desired accuracy and computational efficiency.

Title of PhD thesis: Magnetodynamic Modeling Frameworks Applied to Hysteretic Ferromagnetic Devices. Supervisors: Elena Lomonova and Dave Krop.

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Barry Fitzgerald
(Science Information Officer)

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