Low EMI Voltage Modulation Technique for Three-level Inverter Using Random Numbers from the Samping Noises

In an electric drive with a high-power rating, the fast switching action of the involved inverter could lead to high dv/dt, which in turn generates high-frequency electromagnetic interference(EMI). These disturbances further affect the control unit via coupling paths such as radiation and the parasitic parameters of the power stage. Even though the multilevel inverter can mitigate dv/dt in some sense and improve the electromagnetic compatibility as a result, the harmonics concentrated around the carrier frequency are still considerable under the traditional space vector pulse width modulation(SVPWM). To address this issue, a novel dual-random SVPWM approach is proposed for a three-level inverter, and it utilizes a randomized carrier frequency as well as randomized small space voltage vectors. Uniquely, in this work, the randomness is enhanced by using true random numbers that are generated from the sampling noise. This method does not compromise the performance of the vector control, and it also effectively disperses the higher-order harmonics to the broader frequency spectrum, rather than around the carrier frequency and its nearby. As a result, the intensity of high-frequency harmonics can be significantly reduced, leading to a more evenly distributed voltage spectrum and consequently a decrease in EMI. The viability and effectiveness of this proposed method are supported through the experimental results.