Common mode voltage reduction of cascaded multilevel inverters using carrier frequency modulation

ABSTRACT

Cascaded multilevel inverters have been increasingly used in industrial applications. However, the quality of the output voltage of these inverters depends highly on the modulation techniques. One of the factors affecting the quality of the inverter output voltage is the existence of common mode voltage. This affects the life of three-phase electric motors connected to the inverter. This paper presents a method of modulating the carrier frequency for cascaded multilevel inverters to reduce common mode voltage and harmonics. In the proposed method, the carrier frequency modulator is considered an adaptive controller and the carriers are completely controlled by the control signal. Changes of control signals such as amplitude, frequency, and phase angle make the carrier frequency vary accordingly. In addition, the ability to reduce common mode voltage also helps increase the amplitude of the inverter output voltage. Moreover, an algorithm for reduction of switching commutations is also proposed to reduce the switching loss. The simulation and experiment results based on a cascaded 5-level three-phase inverter system with an induction motor load have confirmed the performance of the proposed method compared to that of the methods using unmodulated carriers through the comparison of output harmonics and number of switching commutations.

KEYWORDS:

• Carrier frequency modulation
• cascaded multilevel inverter
• common mode voltage
• number of switching commutations
• total harmonic distortion

Acknowledgments

This work belongs to the project in 2021 funded by Ho Chi Minh City University of Technology and Education, Vietnam.

Disclosure statement

No potential conflict of interest was reported by the author(s).