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Single-phase dual-buck ac–ac (DBAC) converters are gaining attention due to their intrinsic protection from shoot-through and open-circuit problems of conventional ac–ac converters. However, research works on DBAC converters are mainly concentrated around unipolar topologies. In a few developed bipolar topologies to date, the inverting buck–boost operations (for series voltage injection and step-variable frequency outputs) are inefficient and burdened by large voltage and current stresses (${v}_{\text{in}} + {v}_o\ \text{and}\ {i}_{\text{in}} + {i}_o$) of switching devices and ripples of passive elements. In this article, an efficient dual-buck structured buck–boost ac–ac converter is proposed, with the following features: no voltage source shoot-through and inductor open-circuit problems, natural attainment of safe commutation without additional protection circuitry or complex control, no need for pulsewidth modulation dead times, and elimination of high-frequency conduction of mosfet’s body diodes and related slow reverse recovery issues. The proposed converter provides distinct types of efficient inverting and noninverting buck and boost operations, with smaller switch voltage/current stresses (${v}_{\text{in}}/{v}_o$ and $\ {i}_{\text{in}}/{i}_o$) and passive component ripples. Combined inverting and noninverting buck–boost operations are also proposed with separate tuning of buck and boost voltage transfer ratios. A simple adaptable switching strategy provides the switch control pulses for all circuit operations by modulating the buck and boost control reference signals. The proposed converter provides sustained input/output currents and performs well with nonresistive loads. Extensive theoretical analysis is presented followed by practical verifications on a 400-VA laboratory circuit.

Time-delay is an inevitable operator causing slow dynamic response of related systems employing harmonic sequence (HS) filters/extractors. This letter presents a new concept of flexible time-delay designs as a further generalization of two-sample methods (i.e., delayed signal cancellation) to improve the dynamic response and robustness of HS filters/extractors. The new concept offers flexible designs of filters/extractors to improve both the steady-state quality and dynamic response of filter/extraction stages. Comparative experimental results show significant improvements in filtering performance regarding fast dynamic response, small steady-state errors, improved robustness, and flexible designs to filter implicit harmonic sidebands. These feasibilities are especially beneficial for applications in power systems and power electronics with the available information on harmonic sidebands.

This article proposes a new multiobjective predictive control approach and an optimized switching scheme to precisely regulate the dc-voltages in bipolar dc-grid-based charging stations working under critical conditions. An angular region is preselected to reduce the size of control sets to seven candidates within minimized angle error of 30°. Then, two subregions are located to further simplify finite sets without losing options for multiobjective optimization. Lastly, a hybrid switching scheme is proposed to improve current regulation working under a reduced sampling frequency. Delayed-signal-cancellation technique and instantaneous power theory are also employed to ensure a resilient operation under grid-voltage distortions. Consequently, the proposed control strategy can precisely balance dc-voltages, track voltage references, and regulate grid-injected currents against unbalanced dc-loads and ac-grid distortions. MATLAB/Simulink and an experimental prototype are utilized to investigate the comparative performances between the proposed approach and the recent predictive control methods. The simulation and experiments show significant improvements in dc-link voltages including reference tracking, dc-voltage balance, fast dynamic response, and harmonic reduction of ac-currents under a reduced sampling frequency.