Constant Switching Frequency Based Predictive Delta Sigma Modulation of a Family of Z-source AC–AC Converters

AC–AC power converters can be categorized into direct and indirect AC–AC converters. Direct AC–AC converters enable power conversion in a single stage and have a smaller footprint, with common types including direct PWM AC–AC choppers (DPACs), matrix converters, and Z-source AC–AC converters (ZSACs). ZSACs have gained attention for their advantages such as high output-voltage range, phase angle control and reduced in-rush and harmonic current. In this paper, a novel modulation technique is proposed for ZSACs, which draws inspiration from delta sigma modulation (DSM) of voltage source inverters. The proposed modulation technique uses DSM for the control of multiple variables such as load voltage and source current with constant switching frequency (CSF). A predictive load model is employed to eliminate the requirement of current sensors at the output. The DSM controller makes switching decisions contrary to finite control set model predictive control (FCS-MPC), where prediction of load currents are carried out for finalized switching, enabling the elimination of load current sensors without the significant processor burden. The converter performance is evaluated through simulation studies in MAT-LAB/Simulink software, including steady-state response, dynamic response and total harmonic distortion (THD) of source current. The results indicate that all the ZSAC topologies modulated using the CSF-predictive DSM (PDSM) technique perform well.

I. Introduction

AC–AC power converters are classified as direct AC–AC converters and indirect AC–AC converters. Unlike indirect AC–AC converters, direct AC–AC converters enable power conversion in a single stage and have a smaller footprint owing to the absence of bulky DC link capacitors. The commonly used direct AC–AC converters are direct PWM AC–AC choppers (DPACs) [1], matrix converters [2], and Z-source AC–AC converters (ZSACs) [3]. [4]–[6] demonstrate a class of single-phase DPACs, which comprise buck, boost, buck-boost and ćuk converters and are best suited solely for voltage regulation applications. However, buck and boost converters are unable to simultaneously operate in buck-boost mode. Although the converters with buck-boost and ćuk topologies can exhibit step-down and step-up operation with reversible phase angle, they are subject to high switch voltage stresses. Matrix converters have a limited voltage gain and operate best in applications where voltage control at unlimited frequencies is required.