Random pulse-width modulation

However, when size is of great concern like in aircraft and automobile applications, one of the practical solutions to suppress conducted emissions is to use random pulse-width modulation (RPWM).

In conventional pulse-width modulation (PWM) schemes, the harmonics power is concentrated on the deterministic or known frequencies with a significant magnitude, which leads to mechanical vibration, noise, and EMI.

[4] Among the different RPWM techniques, RFM (random frequency modulation) is the most common method of the three major types, used in many power converter topologies to pass the electromagnetic compatibility (EMC) test.

In this type of modulation, the switching frequency of the PWM signal is varied randomly in order to spread the emitted noise of the power converters in which it is applied.

A greater degree of switching frequency variation can affect the proper functioning of the devices and components inside the power converter circuit.

However, in this modulation scheme, both the switching frequency and the pulse width are fixed so that the converter components like inductors and capacitors can function properly.

[1][3] In RDCM, the pulse width or the duty cycle of the PWM signal is varied randomly in order to spread the noise spectrum.

Since the power to the motor is already being "chopped" at a specific frequency to vary the voltage and current, introducing randomization into the process could cause detriments to the system's performance.

In addition, the word has a home in the telecommunications field, where a scrambler is any device (typically analog) that is used to encode a signal so that it will be unintelligible if intercepted before it can reach the intended recipient without an appropriately tuned de-scrambler.

As opposed to the normally steady, carrier-based whine of a classic SPWM convertor, the sound is more of a hiss, akin to white noise.

Indeed, recent studies have confirmed that RPWM applied to power converters to minimize conducted emissions can detrimentally interfere with the PLC system.