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Instability problem is an important issue for dc/dc conversion cascaded systems (Cascaded system in short). Though most of the existing stabilization methods can stabilize the whole system very well, they may ignore their impacts on the dynamic performance of the original cascaded system. Unfortunately, these impacts are negative to some extent. Recently, an adaptive-series-virtual-impedance (ASVI) control strategy has been reported to address the above problem. It not only can stabilize the cascaded system via shaping the load input impedance, but also can reduce its impact on the original load converter. However, though the ASVI control strategy has already greatly reduced its impact on the load converter, its remaining impact is negative. To solve this problem, this paper moves the ASVI from the load side to the source side via a proposed source-side series-virtual-impedance (SSVI) control strategy for the source converter. This SSVI control strategy not only has the same stabilization function and adaptive characteristics as the ASVI control strategy, but also improves the performance of the source converter. In addition, since the SSVI control strategy is realized by changing the control block of the source converter, the performance of the load converter is not affected. Therefore, the SSVI control strategy can be treated as a supplement and expansion of the ASVI control strategy. Moreover, depending on the method of realization, the SSVI control strategy can be divided into the source stabilization methods of the cascaded system. Finally, a 100 W 48 V–32 V–24 V cascaded system has been fabricated to validate the proposed control strategy. [ABSTRACT FROM AUTHOR]

In this paper, a two-degrees-of-freedom control structure is proposed to minimize both total harmonic distortion and tracking error of inverter output voltage, adopting a resonant tracking controller and a modified uncertainty and disturbance estimator (UDE). Owing to the two-degrees-of-freedom feature of the proposed control strategy, tracking and disturbance rejection tasks are decoupled and treated almost independently. A time-delay action is introduced into a commonly adopted low-pass UDE filter to minimize the output impedance magnitude around the odd harmonics, which is typical to nonlinear loads. Once the disturbance is properly rejected, a tracking resonant controller is designed to force the output of the nominal system to follow a sinusoidal reference with near-zero amplitude and phase error. The performance of the proposed control structure is fully verified by the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a method to directly shape the output impedance of an inverter is proposed to reduce the total harmonic distortion of the output voltage, based on the uncertainty and disturbance estimator (UDE)-based robust control framework. It is shown that, because of the two-degree-of-freedom feature of the UDE-based control strategy, the UDE filter directly affects the inverter output impedance. A multi-band-stop filter instead of a commonly adopted low-pass filter is then proposed to directly minimize the output impedance around the harmonics to reduce the effect of nonlinear loads and assure robustness to frequency variations. Two tradeoffs are revealed: one between filter bandwidth and stability and the other between robustness and the number of harmonics suppressed. The effectiveness of the proposed control strategy is fully supported by experimental results. [ABSTRACT FROM PUBLISHER]