Reducing Conducted Transients in Automotive Windshield Wiper Motors 2006-01-0297
When an electric motor is switched off, an amount of energy, dependent on the design of the motor, can be emitted to the power device. Some of this energy is stored in the capacitors and needs to be discharged when the circuit is shut off. Also, the current through the inductive components changes rapidly, causing a large voltage to be discharged from the circuit. This phenomenon poses potential problems in automotive applications since this energy surge, known generally as a conducted transient, could cause damage to other electrical devices that share the same power grid. Automotive motors generally also have radio frequency interference filtering devices, which are significant contributors to this conducted transient energy. This study attempts to analyze the various characteristics of the windshield wiper motor and relay system and assess what type of filtering devices or other designable components could be used to maintain the filtering capability while reducing the harmful transient emissions.
The first part of the approach includes creating a working circuit model. To accomplish this, several measurements are taken and several assumptions made about the components and their environment. Also, a known physical test result was used to aid in making the model representative. Once the model is complete, computer simulations of potential design solutions are executed and correlated to each other.
The second part of the approach involves performing hand calculations to confirm the magnitude of the voltage spike and better understand the influence of each of the factors on the end result. These equations are second-order differential equations based on the model contrived in the first part of the study.
Finally, the model is validated through the building and testing of physical samples. Experimental design and statistical analysis techniques are used to compare and optimize design options.
This approach results in a cost-effective solution that uses standard components and has minimal effects on motor performance and other electrical requirements.