The fundamental phase shift compensation scheme in a digital-controlled VIENNA rectifier with variable carrier-fundamental frequency ratio under unbalanced grid conditions

Abstract

In the DC power distribution systems, One-cycle control (OCC) based three-phase VIENNA rectifiers achieves high power factor (PF) easily. However, under unbalanced grid conditions, the fundamental phase shift between the input current and corresponding phase voltage obviously deteriorates PF, especially when carrier-fundamental frequency ratio varies. In this paper, based on the mathematical model of the rectifier with OCC control under unbalanced grid conditions, the fundamental phase shift problem is analyzed in detail, including variable carrier-fundamental frequency ratio. Moreover, aiming at solving this problem, a fundamental phase shift compensation scheme is proposed. By introducing a second order generalized integrator (SOGI) to generate the complex vector grid currents feedback, which combines with unbalanced grid voltages, three-phase modulation signals are dynamically modified to eliminate the fundamental phase shift. To facilitate the digital control for the rectifier, the digital implementation of the proposed compensation scheme is described in this paper. At last, a digital-controlled VIENNA rectifier experimental test bench is built, and the effectiveness of the proposed scheme is verified by experimental results.

Keywords

• VIENNA rectifier
• One cycle control (OCC)
• Unbalanced grids
• Fundamental phase shift
• Variable switching frequency