Acoustics of electrical drive systems: quieter is always better

Simulation: Holistic system analysis

We take a holistic approach to system analysis, focusing on control systems, inverters, electric motors, and transmissions. This applies to the automotive industry, but also to all other industries in which electric drives need to be calculated and tested. We also work with leading research institutions to develop future drive concepts. We create a physical understanding of the interaction of the components in terms of acoustic behavior. As our partner, you will receive a detailed excitation forecast with all effects from the control system as well as a wide range of validation options on specially developed test benches.

This is how we can contribute: 

• Coupled simulation across multiple physical domains (control/regulation, circuit simulation, electromagnetics, multibody simulation, structural dynamics, gear calculation)
• Development of control algorithms to influence acoustic system behavior
• Sensitivity analysis of manufacturing deviations and assembly influences
• Numerical magnetic field calculation with FEM
• Scalable electric machine models: fundamental wave model, position-dependent extended fundamental wave model, harmonic characteristics, skew influence, current harmonics due to pulsation (THD)
• Time step simulation for the design of controllers and filters for drive control and modulation methods

Control: We make your drive quiet and efficient.

You will be surprised at how much optimization potential software updates offer. We work with you to analyze the effects on the electric motor and gearbox excitation. Together, we calculate and measure the efficiency of the drive system. Together, we achieve reduced force excitation of your electric drive. As a result, we achieve a significantly lower noise level inside the vehicle.

Our particular strengths are: 

• Development of control algorithms to influence the acoustic behavior of the system
• Injection of current harmonics to reduce motor orders (“noise shaping”)
• Randomized pulse methods to avoid PWM fans
• Direct torque control, advanced control concepts
• Virtual torque sensor, observer design, sensorless methods
• Real-time implementation and rapid control prototyping of drive control

Services: We have the infrastructure to help you.

We have been working closely with our customers for many years and have a wide range of experience in the planning and design of test setups. NVH (Noise Vibration Harshness) investigations of drive systems are one of our core competencies, which we are continuously expanding. You can rely on the highly efficient working methods and expertise of our scientists.

How we can support you:

• NVH investigations of electric motors up to 200 kW in a Class 1 semi-anechoic chamber (DIN EN ISO 3745)
• Sound pressure measurements using the envelope method up to 10 kHz based on DIN EN ISO 3744/3745
• Direct and indirect (in-situ according to ISO 20270) determination of blocked forces at the bearing points
• Numerous analysis options for airborne and structure-borne noise (e.g., using an acoustic camera and 3D laser vibrometer)
• Arrangement of the test specimen back-to-back with a load machine or as a complete drive axle between two load machines possible
• Converter frequency of the load machines adjustable depending on power
• 200 kW source-sink system adjustable up to 800 VDC for HV test specimen supply
• Use of fast-switching SiC drive inverters (max. 30 kHz) for traction drives
• High-speed load machine (up to 18,000 rpm)
• CAN-FD rest bus simulation

Multidomain overall simulation and description of coupling points

The system components of an electric drive can be seprated in different physical domains like power electronics, magnetic circuit and mechanical structure. Additional systems can be coupled to the drive like transmission, fan wheel or linear guiding. All individual components of the mechatronic system influence its acoustical behavior and may interact with each other. In order to describe the overall system, it is necessary to identify and characterize the acoustically relevant effects of each physical domain. We seperate subsystems which are free of interactions to describe the relevant individual effects in an abstracted manner. Then the subsystems are coupled power-based using a flow- and a difference variable to describe the overall mechatronic system.

End-of-line testing for detection of production errors in electric vehicle drives

Selecting sensors, measuring positions and the actual testing program, and determining limit curves are major challenges in the automated end-of-line (EOL) testing of electric vehicle drives with integrated transmission and inverter. Preferably all errors which may occur are to be detected within a specific production cycle time. For this purpose, our employees catalog all potential errors at the manufacturer’s facilities, identify their characteristic error patterns by measurement and simulation, and ideally assign them to the matching cause in the production process. Subsequently, we support the manufacturer in developing a complete testing methodology and testing program. In order to evaluate the EOL measurement, strategies are examined that include dynamic limit curves, and reliably detect gradual exceedance of limit values.

Minimization of magnetic force harmonics in electric machines for vehicle drivetrains

The subjective noise perception of electric vehicles can be unfamiliar and uncomfortable because the combustion engine is no longer relevant as a noise source, and high frequency noise is increasing instead. The high frequency content is due to dynamic forces of the electric machine, which excite vibrations in the housing structures and the gear stage. Harmonic force orders result from the geometry of the magnetic circuit and have radial and tangential impact. They can be reduced by injection of vibration damping current harmonics, which results in reduced vibrations during vehicle operation. During a research project extending over several years, numerical calculations of the magnetic field are carried out to identify the amplitudes and phases of the current harmonics. Furthermore, the field-oriented control is extended to inject these vibration damping current harmonics into the drive. Moreover, we identify the influences of the active vibration control on relevant parameters such as efficiency and torque ripple. The algorithm is then experimentally validated on a drive test bench using acceleration sensors to measure structure-borne noise.