Constant switching frequency-based delta-sigma modulation of single-phase AC-AC zeta converter

Direct pulse width modulated (PWM) AC-AC converters, derived from their DC-DC counterparts, serve as promising media for AC-AC power conversion because they offer benefits, such as single-stage power conversion, absence of bulky DC links, and small footprint. In this study, a single-phase (1-phi$$ 1-\phi $$) AC-AC zeta converter was analyzed under buck, boost, and buck-boost operations. Delta-sigma modulation (DSM) technique, known for its simple logic implementation, excellent reference-tracking property, robust control, and fast transient response, was employed for the load voltage control of a 1-phi$$ 1-\phi $$ AC-AC zeta converter. However, the conventional DSM technique relies on a fixed hysteresis band (FHB) for restricting the integrated (sigma) error (delta) between the reference and estimated control voltages within a narrow band, which causes the converter to operate at a variable switching frequency (VSF). Although VSF enhances the converter performance with low total harmonic distortion (THD) and high degree of flexibility over waveform quality, it poses serious implications such as higher switching losses, putting more strain on thermal management of switches. This paper presents a constant switching frequency-based DSM technique based on an adaptive hysteresis band (AHB) for a 1-phi$$ 1-\phi $$ AC-AC zeta converter. The converter is controlled using FHB-DSM and AHB-DSM techniques, and a comparison is drawn between the two in terms of various performance indices. In this comparison, FHB-DSM serves as a benchmark and an optimum switching frequency based on AHB-DSM technique is determined, which exhibits low switching losses while maintaining the same THD limits, dynamic response, and waveform quality as that of FHB-DSM technique. The proposed strategy was validated by simulation studies in MATLAB/SIMULINK software. Furthermore, a real-time simulator, OPAL-RT (OP4510), was used to validate the study with real-time implementation.