Electromagnetic interference (EMI) is the radiation or induction of electromagnetic noise on a system. Like most electromagnetic circuit components, DC motors are a common source of EMI. They are potential sources of noise that can generate common mode currents. EMI can cause performance degradation, data corruption, or strong enough to cause the system to fail completely. EMI radiation or conduction comes from the magnetic source and the power source, respectively, and in the case of a direct current motor, there are radiated and conducted emissions.
Electromagnetic compatibility (EMC) is the practice of monitoring and reducing unwanted EMI. Depending on the purpose of the system and the country in which it is used or sold, there are usually different EMC regulations. EMC performance involves the entire system or the final product, so it is usually the responsibility of the OEM (original equipment manufacturer) rather than the person providing the component. The following are ways to reduce motor EMI to improve the EMC performance of the system.
Arc discharge (sometimes referred to as arcing or arcing) is a current characteristic in which current can flow through air or other materials that are generally not electrically conductive. You may have seen an arcing between the two wires or on the power rail of a train or tram. This is not the same as sparks because the arcs are continuous, although they look really similar.
Although arcs can be used for welding and lighting, in some cases it may be a source of EMI. In DC motors, arcing may be common due to periodic interruptions in current in the rotor windings. This very high frequency spectral content can be represented as broadband noise superimposed on other signals, while the structure of the DC motor provides a path for common mode current.
Another source of radiated and conducted emissions may come from the drive circuit. Ideally, a typical H-bridge circuit should provide a constant current to the motor, but this current has a fast rise time spike due to the fast and frequent switching of the current in the drive circuit. Another important issue is that the motor is usually far away from the drive, which creates a considerable loop area between the motor leads and the equipment frame. The radiation potential is a direct function of the loop area; the larger the loop, the greater the EMI noise.