EMC Aspects of PMW Controlled Loads in Vehicles

Abstract

The number of electrically driven loads in a modern vehicle is constantly

increasing. Many loads that former were mechanically driven will in the future

be driven by electricity. This implies that a number of electronic systems have

to be packed together in the limited space in a vehicle. When different

electronic systems are placed close to each other, there is always a risk for

electromagnetic interference between the different systems causing

malfunction or even failure. It is important to ensure that this does not

happen, and this concept is called electromagnetic compatibility, EMC. EMC

implies that different electrical systems should be able to work in close

proximity without affecting each other. From the EMC point of view,

integration of electric traction drives in present vehicles represents a

considerable challenge.

In order to save energy, many electrical loads can be controlled on demand. A

common and energy efficient way to do this is to use a method called pulse

width modulation, PWM, where the load voltage is pulsed in order to create

the desired average output voltage. When this method is employed, the

voltage pulses are present on the conductors between the power electronic

converter and the load. Since the space in a vehicle is limited, it is often not

possible to place the power electronic converter close to the load.

Consequently, long conductors are often required between the power

electronic converter and the load. The steep edges of the voltage pulses and

the fundamental of the square wave, called the switching frequency, together

with the long conductors cause electromagnetic interference problems. These

disturbances could interfere with, for example, the radio in the vehicle. In this

thesis, different electromagnetic compatibility aspects of a pulse width

modulated system are investigated.

Some solutions are proposed in order to mitigate the disturbances. The

solutions involve increasing the rise and fall times of the voltage pulses and employing a randomly varying switching frequency. Also the effects from

different conductor layouts, such as using the vehicle body sheet metal as a

current return path or having the lead-in and return conductor close to each

other, are investigated. In order to evaluate the results from the different setups,

the voltage across the load and the radiated magnetic field are measured.

The experimental results in this thesis show that a conductor should be used

for current return and that this conductor should be placed as close to the

lead-in conductor as possible in order to suppress electromagnetic noise. It is

also shown that a randomly varying switching frequency will give a more

broadband noise in the switching frequency range. Increasing the resistance of

the gate resistor mitigates the disturbance in the higher frequency areas at the

expense of increased switching losses.

• author: Marksell, Sabine
• supervisor: Mats Alaküla; Gerhard Kristensson
• organization: Industrial Electrical Engineering and Automation
• publishing date: 2004
• type: Thesis
• publication status: published
• subject: Other Electrical Engineering, Electronic Engineering, Information Engineering
• pages: 143 pages
• ISBN: 91-88934-32-2
• language: English
• LU publication?: yes
• id: 91f21b8f-c65a-420f-af07-46f416790657 (old id 587921)
• alternative location: http://www.iea.lth.se/publications/Theses/LTH-IEA-1041.pdf
• date added to LUP: 2016-04-04 10:26:32
• date last changed: 2018-11-21 20:58:46