Abstract
In this paper, a control scheme combining grid voltage sensorless control and natural frame control (NFC) has been proposed for single-phase cascaded H-bridge converter (CHB) under distorted grid conditions. Firstly, the virtual flux (VF) signal is estimated by a modified virtual flux estimator (VFE). Then the VF-based NFC is derived, using the estimated sinusoidal VF signal to generate the unit vectors for synchronization, which enables the omitting of the coordinate transformation, current quadrature signal generation, and phase-locked loop (PLL). Aiming at the problem that grid harmonic interference is not well considered in the conventional NFC and conventional voltage sensorless control, a current controller with enhanced harmonic-rejection ability is proposed in this paper. As a result, better steady-state performance and rapid transient response are achieved. The effectiveness of the proposed method has been verified on a prototype of the single-phase 3-cell CHB converter.
Highlights
To extract a more sinusoidal virtual flux (VF) signal used for generating unit vectors of natural frame control (NFC) under distorted grid conditions, a Cascaded delay signal cancellation (CDSC) proposed in [7] is used in this paper
In order to increase the harmonic impedance of current loop, the current controller combines PR and repetitive controller (RC) is proposed in this paper
When the voltage sensorless control method is implemented, compared with the traditional PR controller, the proposed method can significantly increase the harmonic impedance at integer frequencies ranging from 2nd- to 13th-order
Summary
With the development of renewable energy resources, large amounts of distributed generation (DG), distributed energy storage systems, and local loads are connected to the utility grid [1]. To improve the harmonic-rejection ability of the converter, the control strategy is required to eliminate the influence of grid voltage distortion on the output current. Regarding the problems mentioned above, in this paper, the grid voltage sensorless control for the single-phase grid-connected converter under distorted grid conditions has been studied. A novel control scheme that combines voltage sensorless control and NFC is proposed for a single-phase CHB converter. A controller has been proposed, which integrates the proportional-resonant (PR) controller and RC in natural frame to realize the tracking of fundamental current reference signal and rejection of grid harmonics interference.
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