Page 6 - EE Times Europe September 2021

6 EE|Times EUROPE

COVER STORY

The Magnetics of Silence —

Advanced Materials

for New Challenges

BY JOSE ROCAMORA, Division Manager, and MARIELA FIERRO, Product Manager, Automotive
Standard Products, Würth Elektronik eiSos

NVH engineering in hybrid/electric vehicles must adapt to handle electrical challenges,
including conducted and radiated electromagnetic interference, a task that can be
addressed using high-performing magnetic materials.

oise vibration and harshness (NVH) engineering, a funda- Cable ferrites are typically applied to handle wide interference in
mental discipline for automotive designers, is encountering low- and middle-frequency ranges to ensure noise reduction at the
new challenges as hybrid electric vehicles (HEVs) and 100% inverter, DC/DC converter, and electric motor in the powertrain. The
Nelectric vehicles (EVs) become the most important models high-power inverters used to drive motors generate noise across a
in carmakers’ ranges. Minimizing NVH is essential to ensure both the broad spectrum starting at the switching frequency (<100 kHz), with
comfort of the passengers and the stability of the entire vehicle system. harmonics extending up to 30–50 MHz. Cable ferrites are also used
In HEVs and EVs, many NVH sources that were previously masked by for EMI suppression at the battery system, such as attenuating the
the noise of the combustion engine are now easily discernible. Root switching noise that occurs during cell balancing (Figure 1).
causes of NVH problems in electric motors can be divided into electro-
magnetic and mechanical noise, aerodynamic noise, and vibration. NEW MATERIAL TECHNOLOGY
Electromechanical noise includes that from auxiliary systems such as the To serve automotive applications, these cable ferrites and chokes must
air-conditioning compressor and power-steering motor. It adversely affects meet exacting criteria. Size and weight are major constraints: CMCs for
cabin comfort and can cause interference with other subsystems. common-mode noise suppression must provide excellent attenuation
Moreover, the high-power traction drive system causes electromagnetic properties within a small volume. Moreover, broadband noise sup-
interference (EMI) at the harmonics of the power supply and inverter pression must be maintained up to high operating temperatures. High
switching frequencies, as well as electromagnetically excited noise within mechanical and electrical stress resistance is also essential.
the motor itself. These detract from cabin comfort and can interfere with Requirements such as robustness and easy handling on the assem-
systems managing the combustion engine in an HEV. bly line must also be in place to help manufacturers maintain high
In addition, the battery is frequently charged and discharged during levels of productivity and ensure that each unit reaches the customer
operation, and various electromagnetic noise types, such as differen- in perfect condition. Meeting these requirements calls for new mate-
tial noise, common-mode noise, and radiated noise, are transmitted rials that can offer enhanced characteristics.
through power transmission lines.
Therefore, mitigating NVH is more difficult in HEVs and EVs
than in combustion-engine vehicles. The main problems stem from
the different NVH characteristics of the engine, powertrain, and Connection box
electric motor, as well as from the coupling contributions of the
different subsystems. Battery
Front ePT Ferrite HV Battery
heater
EMI MITIGATION
As with conventional NVH-engineering projects, many issues are Current
specific to a particular platform and relate to the design of various sensor
structural components, the location of subsystems relative to each
other, and the design of mountings and isolating bushes. On the other Main RLY
hand, NVH issues related to EMI need to be dealt with by applying
known electrical-engineering best practices to attenuate high-
frequency radiated and conducted EMI that can be coupled onto cables Internal electronic
as common-mode noise and transmitted into various subsystems.
These include the use of cable ferrites to prevent long wires acting as
radiating aerials or pickups and inline common-mode chokes (CMCs) Figure 1: EMI suppression at the battery system using cable
to attenuate EMI conducted onto power and signal lines. ferrites

SEPTEMBER 2021 | www.eetimes.eu