The conventional control method for a single-phase cascaded H-bridge (CHB) multilevel converter is vector (dq) control; however, dq control requires complicated calculations and additional time delays. This paper presents a novel power control strategy for the CHB multilevel converter. A power-based dc-link voltage balance control is also proposed for unbalanced load conditions. The new control method is designed in a virtual αβ stationary reference frame without coordinate transformation or phase-locked loop (PLL) to avoid the potential issues related to computational complexity. Because only imaginary voltage construction is needed in the proposed control method, the time delay from conventional imaginary current construction can be eliminated. The proposed method can obtain a sinusoidal grid current waveform with unity power factor. Compared with the conventional dq control method, the power control strategy possesses the advantage of a fast dynamic response. The stability of the closed-loop system with the dc-link voltage balance controller is evaluated. Simulation and experimental results are presented to verify the accuracy of the proposed power and voltage control method.
For a single-phase distribution network static synchronous compensator (DSTATCOM) based on cascaded H-bridge (CHB) converter, the design of dq control-based system is difficult due to the coupling effect and current fiction. To address this issue, first, the mathematical model of dq control is derived, then the unit vector (UV) control based on αβ frame is proposed. In this paper, the compensation current reference is obtained through the instantaneous power theory and unit vector method. Proposed control structure eliminates the effects of the decoupling control and the complex current fiction. In addition, the DC-voltage balance is achieved. Finally, the effectiveness of the proposed control strategy is verified by the simulation and experiments.
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