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The dc offset and scaling errors in the voltage and current measurements cause the injection of undesired dc and unbalanced currents into the three-phase input currents and subsequently lead to voltage ripple at the dc output voltage of the ac/dc converter. This paper proposes a compensation scheme for current measurement error where the dc offset and scaling errors in the current measurement are estimated from the voltage ripple characteristics of the dc output voltage ripple combining with simple band-pass and low-pass filters. Meanwhile, the dc offset and scaling errors in the voltage measurement can be rejected by using an advanced current controller developed with a proportional resonant plus a repetitive controller designed in the synchronous (d–q) reference frame. The proposed control algorithm is able to effectively reject the impact of both voltage and current measurement error so that the three-phase input currents are regulated to be balanced and sinusoidal with ultralow dc current component. Meanwhile, the dc output voltage is also well regulated to be pure dc with a negligibly small voltage ripple. The proposed compensation method is developed without the need of extra hardware circuit, sensor, or precise information of system parameters so that it can be considered as more cost effective and robust solution. The effectiveness of the proposed solution is verified by experimental results. [ABSTRACT FROM AUTHOR]

This article proposes a circulating current and second harmonic current (SHC) suppression method by introducing virtual impedance into the circulating current and output current feedback control loops of the dc solid-state transformer (DCSST). The virtual impedance is employed to adjust impedance in the circulating current feedback control loop to decrease the circulating current when the transmission efficiency of each dual active bridge is different. And a SHC suppression method, which introduces the virtual impedance containing a bandpass filter, is adopted to reduce the SHC and improve the dynamic performance of the DCSST. Moreover, a relatively independent modular control method, which is conducive to the modular expansion of the DCSST, is proposed. Compared with traditional DCSST control methods, the proposed method can simultaneously realize the output current sharing and effectively reduce the SHC with modular control. Finally, a DCSST prototype is built and the results of the experiment verify the validity and effectiveness of the proposed control strategy and solutions. [ABSTRACT FROM AUTHOR]