Voltage Balancing Control in Three Level Diode Clamped Inverter Using Carrier Based Offset Addition

Abstract: Three-level Neutral-Point Clamped (NPC) inverter has become established to be a preferred topology for medium-power motor drive applications operating at several kilovolts. Still several research continues to find solutions to the problem of maintaining a stable neutral-point voltage in the converter. This paper presents the analysis and simulation of a three-level diode-clamped multilevel inverter, employing a sine-triangle modulator with addition of continuous variable offset voltage which regulates the midpoint potential of the dc bus. By maintaining dc-bus voltage balance, a significant reduction in the voltage distortion at the neutral point and also allowing a definitive reduction in the required dc bus capacitance. The effectiveness of the Pulse Width Modulation (PWM) strategies developed with continuous offset addition is demonstrated by MATLAB/SIMULINK based simulation presented in this paper.

Keywords: NPC inverter; 3 phase induction motor; offset addition; carrier based PWM; dq theory; pi control