Abstract
This paper presents an improved current control strategy for a three-phase grid-connected inverter under distorted grid conditions. The main challenge associated with the grid-connected inverter in distributed generation (DG) systems is to maintain the harmonic contents in output current below the specified values even when the grid is subject to uncertain disturbances such as harmonic distortion. To overcome such a challenge, an improved current control scheme is proposed for a grid-connected inverter, in which the fundamental and harmonic currents are independently controlled by a proportional-integral (PI) decoupling controller and a predictive basis controller, respectively. The controller design approach is based on the model decomposition method, where the measured inverter currents and grid voltages are divided into the fundamental and harmonic components by means of moving average filters (MAFs). Moreover, to detect the angular displacement and angular frequency with better accuracy, even in the presence of the grid disturbance, the MAF is also introduced to implement an enhanced phase-lock loop (PLL) structure. Theoretical analyses as well as comparative simulation results demonstrate that the proposed control scheme can effectively compensate the uncertainties caused by the grid voltages with fast transient response. To validate the feasibility of the proposed scheme, the whole control algorithms are implemented on 2 kVA three-phase grid-connected inverter system using 32-bit floating-point DSP TMS320F28335. As a result, the proposed scheme is an attractive way to control a grid-connected inverter under adverse grid conditions.
Highlights
Three-phase grid-connected inverters have been widely employed in various applications, including renewable power generation and regenerative energy systems
This is due to the recent development trend constructing the electrical grid in terms of distributed generation (DG) systems, in which grid-connected inverters are connected in parallel with each other to form a microgrid [1,2]
The main objective of this paper is to present a robust current control scheme for a three-phase grid-connected inverter under abnormal grid conditions like the distorted grid
Summary
Three-phase grid-connected inverters have been widely employed in various applications, including renewable power generation and regenerative energy systems. Other approaches to eliminate the harmonics from inverter current use nonlinear control techniques such as the sliding mode control (SMC) [12], predictive control [13], or repetitive control [14] These control strategies are often referred as non-selective method since the controllers work in wide range of frequency, in contrast to the selective method that only regulates the harmonics in some specified orders. Whereas the synchronous PI decoupling controller is employed to control the fundamental current component, a predictive basis compensator is introduced to suppress the harmonic components in inverter currents For this purpose, the harmonic contents are extracted by means of the MAFs. an MAF-PLL is employed to improve the detecting performance of the conventional SRF-PLL.
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