Predictive Adaptive Filter for Reducing Total Harmonics Distortion in PV Systems

Liqaa Alhafadhi,Jiashen Teh,Ching-Ming Lai,Mohamed Salem

doi:10.3390/en13123286

Liqaa Alhafadhi, Jiashen Teh + Show 2 more

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https://doi.org/10.3390/en13123286

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Abstract

This paper presents a new method for reducing the total harmonic distortion (THD) of photovoltaic (PV) systems by using an adaptive filter based on a predictive model. Instead of reducing the produced THD at each stage of the PV system, a one-step process is implemented at the end stage. The connection topology of the adaptive filter is similar to normal active and passive filters. The main difference is its ability to adjust the filtering coefficients while others cannot. The proposed method is applied to a single-phase standalone PV system by adopting least mean square (LMS), normalized LMS (NLMS) and leaky LMS algorithms to verify the validity of the proposed method. Various values of filter length and step size are evaluated, and results indicate that the proposed method can reduce THD in the current signal of the PV system significantly by using all of the mentioned algorithms. Different step sizes and filter lengths directly influence the effectiveness of the THD reduction, with small step sizes and long filters being the most effective. Amongst the algorithms, NLMS reduces THD the most, and LMS reaches the peak current value the fastest.

Highlights

Photovoltaics (PV) is one of the most popular energy sources and has been used widely in the last decade due to the increasing demands on alternative clean energy sources
Unlike the fourth section of a PV system, which describes the manner through which the PV system delivers power to consumers, the first three sections (PV panels, DC–DC converters and DC–AC converters) are common to all types of PV systems
The total harmonic distortion (THD) of the current signal is 19.8% before filtering and successfully reduced to approximately 5.9%, 3.8% and 6.0% after filtering using least mean square (LMS), normalized LMS (NLMS) and leaky LMS (LLMS) algorithms, respectively, proving that the NLMS algorithm is superior to the others

Summary

Introduction

Photovoltaics (PV) is one of the most popular energy sources and has been used widely in the last decade due to the increasing demands on alternative clean energy sources. Standalone PV systems are further classified into those with and without a battery energy storage system to supply AC and DC power, respectively. Unlike the fourth section of a PV system, which describes the manner through which the PV system delivers power to consumers, the first three sections (PV panels, DC–DC converters and DC–AC converters) are common to all types of PV systems. The solar power delivered to customers is usually contaminated with high levels of distortion due to different factors, such as irradiance fluctuation, temperature uncertainty and frequent switching of converter and inverter parts. The total harmonic distortion (THD) index is the most common means to determine the amount of distortion in a signal. THD is defined as the ratio between the total power accounted for by harmonics and the main power of the signal.

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