Understanding Magnetic Noise and Vibration in Electric Drives

Introduction

The automotive industry’s transition to electrification necessitates a comprehensive understanding of e-NVH (electric Noise, Vibration, and Harshness) to elevate vehicle performance. This blog covers the definitions and implications of e-NVH, examines magnetic noise and its sources, and presents analytical methods for evaluating these elements. Additionally, we will introduce Manatee, a practical tool for e-NVH analysis. This concise exploration will provide insights into the technical aspects of e-NVH and its significance in vehicle design and performance.

What is e-NVH?

When addressing noise and vibration in electric drives, it’s essential to recognize that these issues can originate from various exciting forces. These forces are generally categorized into mechanical, aerodynamic, and magnetic. It is necessary to account for all three mechanisms in the simulation to capture the total noise.

The SIMULIA portfolio offers specialized tools for each type of noise:

• Mechanical Noise: Simpack calculates gear force distribution and resulting vibrations (or acoustic noise when combined with Wave6), for instance, in a gearbox.
• Aerodynamic Noise: PowerFLOW calculates fluid flow and resulting airborne noise (or structure-borne noise when combined with Wave6), for instance, in a fan.
• Magnetic Noise: Manatee calculates magnetic force distribution and resulting vibrations and noise, for instance, in an electric motor.

It’s important to understand that there isn’t a universal solution. Electric drives involve all three types of forces. When noise and vibration are significant, assessing and managing each source individually is essential, as one noise source can mask another, complicating the overall assessment. For example, customers who focused on reducing fan noise have discovered unexpected magnetic noise issues that were being masked by the fan noise.

By employing the SIMULIA software portfolio, including Manatee, engineers can comprehensively address the e-NVH challenges in electric drives, ensuring optimal performance and minimizing noise-related issues.

What is Magnetic Noise?

Magnetic noise plays a crucial role in the noise and vibration of electric powertrains. Magnetic excitations come from variable electromagnetic fields, which can be produced by the electrical machine itself (for example, due to rotating permanent magnets) or by the interaction between the electrical machine and the inverter (for example, due to the Pulse Width Modulation strategy). It is paramount to manage magnetic noise to achieve optimal NVH performance effectively.

Magnetic noise in electrical machines can be categorized into two types: noise produced by the machine alone and noise induced by the inverter.

Pole/Slotting Noise

When it is supplied with sine current or operates in an open circuit, the electrical machine produces pole/slotting noise. This type of noise arises from fluctuations in the magnetic field within the air gap. These fluctuations are caused by space harmonics generated by the pole magnetomotive forces and slotting harmonics from the stator slots. In synchronous machines, pole/slotting noise occurs at multiples of twice the electrical frequency and is proportional to the drive’s speed.

Switching Noise

The inverter induces the second type of magnetic noise, switching noise. This occurs because the inverter adds time harmonics to the voltage waveforms, creating switching forces. Switching noise typically occurs at multiples of the switching frequency, resulting in a distinctive sound. For example, this noise is often quite noticeable in traction machines used for railway applications.

Resonance Phenomenon

Resonance plays a key role in understanding magnetic forces and structural dynamics. It can occur when the exciting forces interact with specific structural modes representing the mechanical behavior of the powertrain. It can be characterized by a series of structural modes obtained through linearization of the mechanical model.

Resonance happens when the frequency and shape of the exciting force match the frequency and shape of specific structural modes, leading to a high amplification of vibration and noise. These resonances can exceed NVH requirements and produce unpleasant sounds. Techniques such as spectrogram analysis and order tracking can help identify resonances in powertrain systems.

How to Analyze e-NVH?

e-NVH, or electromagnetic noise and vibration, is a complex multidisciplinary problem that requires a comprehensive understanding of various physical phenomena. To effectively address e-NVH, a multiphysics simulation approach is essential. This process begins with analyzing the inverter voltage to determine the resulting currents. These currents generate magnetic fields, which produce magnetic forces. These forces then excite the structural dynamic model, resulting in vibration and subsequent acoustic radiation.

Due to its multidisciplinary nature, analyzing and controlling e-NVH requires collaboration among different engineering disciplines. Control and electromagnetic engineers focus on managing the exciting forces generated by the inverter and electromagnetic fields. Meanwhile, mechanical and NVH engineers deal with understanding the noise and vibration transfer paths.

Identifying excitation sources and understanding noise transfer mechanisms are key to tackling e-NVH. Engineers must determine the physical origin of force harmonics (winding, slotting, pole shape, PWM…, etc.) and whether the noise is airborne or structural-borne. Then, they must explore solutions to modify the excitation sources and the transfer paths. Effective collaboration and communication between these disciplines leads to solutions that reduce e-NVH levels without compromising the electromagnetic design.

Specialized techniques have emerged in electromagnetic noise, vibration, and harshness to simulate and control e-NVH. These techniques enable engineers to modify excitations and dampen specific exciting forces while minimizing the impact on the electromagnetic design. Engineers can successfully reduce and control e-NVH levels by using these techniques, ensuring optimal performance and user experience.

What is Manatee?

Manatee, an acronym for Magnetic Acoustic Noise Analysis Tool for Every Engineer, is a specialized software dedicated to magnetic noise analysis. Developed by EOMYS over a decade ago, Manatee originated from the company’s service-oriented approach to troubleshooting and solving noise and vibration issues in electrical systems. Initially, EOMYS created scripts to address these problems, which gradually evolved into the comprehensive Manatee software.

A History of Manatee

Manatee’s development was driven by EOMYS’ extensive experience applying advanced e-NVH techniques to various industrial cases. Their hands-on expertise led to significant reductions in noise and vibration, with some projects achieving up to 40-decibel reductions in resonances. The software has been successfully employed across various sectors, including aerospace, automotive, industrial machinery (such as pumps and compressors), generators (like wind turbine generators), railway traction motors, naval propulsion, home appliances, and medical devices.

The use of electric motors in modern applications raises concerns about noise and vibration caused due to magnetic forces. While some industries have stringent noise level standards, like wind turbines, many customers are motivated to seek quieter designs to meet market demands and stay competitive.

Multiphysics Solvers in Manatee

Manatee software has a suite of weakly coupled multiphysics solvers to address the complex interplay of electrical, magnetic, structural, and acoustic phenomena in e-NVH analysis. These solvers include:

• Electrical Circuit Models: To determine currents from the applied voltage.
• Magnetic Models : Currently using Opera 2D for magnetic field calculations.
• Structural Dynamics Models: To analyze the mechanical response to magnetic forces.
• Acoustic Models: To simulate the resulting sound radiation.

Manatee can be used as a standalone executable for variable-speed e-NVH simulations without the need to access the 3DEXPERIENCE platform. This standalone capability allows engineers to perform design iterations directly within Manatee, facilitating collaboration between electromagnetic and mechanical teams. Electrical and control engineers can iterate on magnetic circuit dimensions and control strategies, while mechanical and NVH engineers can refine the mechanical integration to meet NVH targets.

Additionally, Manatee offers a range of import and export functions to streamline workflows:

• Current Import: Allows importing pre-calculated non-sinusoidal current distribution.
• Flux Import: Allows importing magnetic flux data from models created in Opera or CST.
• Structural Mechanics Import: Allows importing model bases from Abaqus for structural analysis.
• Acoustic Coupling: Allows exporting vibration data to refine acoustic calculation under Wave6 (under development).

Manatee recognizes that electric drive noise is not solely a matter of magnetic noise. The software provides the capability to import other noise sources, such as gear whine, allowing engineers to compare overall NVH levels against targets. This flexibility ensures a comprehensive analysis that accounts for multiple noise contributors.

What are Manatee’s Main Inputs and Outputs?

Manatee’s graphical user interface is designed to be a collaborative environment for engineers, supporting the prediction and control of magnetic noise and vibration levels at various design stages. Here are the main inputs and outputs of Manatee:

Inputs

Manatee links control & magnetic circuit geometry and system-level acoustic noise and vibration requirements within the same GUI. To use Manatee, you must start with an existing electrical machine design. The primary inputs include:

• Magnetic Circuit Geometry: The electrical machine’s magnetic circuit definition based on templated or CAD import (.DXF).
• Control Parameters: Current as a function of speed, typically represented by Id and Iq (direct and quadrature axis currents) for synchronous machines.
• Magnetic Material Properties: The characteristics of the magnetic materials used in the machine.

Outputs

Manatee provides a range of outputs to help engineers understand and optimize the NVH performance of their designs:

• Vibration Levels: Vibration data at specific nodes within the machine or average over specified surfaces.
• Sound Power Level: The overall sound power generated by the machine or by specified surfaces.
• Sound Pressure Levels: The sound pressure at a given distance from the electric drive.
• Sound Quality Metrics: When necessary, metrics that assess the quality of the sound produced.

These outputs can be generated at different levels:

• Single Operating Point: Spectrum analysis for a single speed.
• Variable Speed: Spectrograms that show the noise and vibration characteristics across a range of speeds.
• Torque/Speed Plane: NVH calculations can be run across the torque/speed plane to provide a comprehensive analysis.

Manatee provides access to all the intermediate physical quantities calculated during the analysis, offering a detailed insight into the underlying processes.

Conclusion

In conclusion, understanding e-NVH is crucial for advancing vehicles. By recognizing the various sources of noise and vibration—mechanical, aerodynamic, and magnetic—engineers can employ advanced tools like Manatee and the SIMULIA portfolio to analyze and mitigate these issues effectively. As we enter the age of quieter and more efficient electric powertrains, a comprehensive approach to e-NVH will ensure optimal vehicle design, enhance the driving experience, and meet growing consumer demands for performance excellence.

We appreciate your attention and invite you to explore the SIMULIA Community, where we have migrated a wealth of e-NVH learning materials. For more information, check out our detailed webinar.

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