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Energies 2016, 9(6), 390; doi:10.3390/en9060390

A Wavelet-Based Unified Power Quality Conditioner to Eliminate Wind Turbine Non-Ideality Consequences on Grid-Connected Photovoltaic Systems

Department of Electrical Engineering, Harbin Institute of Technology, Harbin 150001, China
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Author to whom correspondence should be addressed.
Academic Editor: Neville R. Watson
Received: 16 March 2016 / Revised: 26 April 2016 / Accepted: 5 May 2016 / Published: 24 May 2016
(This article belongs to the Collection Smart Grid)
View Full-Text   |   Download PDF [6683 KB, uploaded 24 May 2016]   |  

Abstract

The integration of renewable power sources with power grids presents many challenges, such as synchronization with the grid, power quality problems and so on. The shunt active power filter (SAPF) can be a solution to address the issue while suppressing the grid-end current harmonics and distortions. Nonetheless, available SAPFs work somewhat unpredictably in practice. This is attributed to the dependency of the SAPF controller on nonlinear complicated equations and two distorted variables, such as load current and voltage, to produce the current reference. This condition will worsen when the plant includes wind turbines which inherently produce 3rd, 5th, 7th and 11th voltage harmonics. Moreover, the inability of the typical phase locked loop (PLL) used to synchronize the SAPF reference with the power grid also disrupts SAPF operation. This paper proposes an improved synchronous reference frame (SRF) which is equipped with a wavelet-based PLL to control the SAPF, using one variable such as load current. Firstly the fundamental positive sequence of the source voltage, obtained using a wavelet, is used as the input signal of the PLL through an orthogonal signal generator process. Then, the generated orthogonal signals are applied through the SRF-based compensation algorithm to synchronize the SAPF’s reference with power grid. To further force the remained uncompensated grid current harmonics to pass through the SAPF, an improved series filter (SF) equipped with a current harmonic suppression loop is proposed. Concurrent operation of the improved SAPF and SF is coordinated through a unified power quality conditioner (UPQC). The DC-link capacitor of the proposed UPQC, used to interconnect a photovoltaic (PV) system to the power grid, is regulated by an adaptive controller. Matlab/Simulink results confirm that the proposed wavelet-based UPQC results in purely sinusoidal grid-end currents with total harmonic distortion (THD) = 1.29%, which leads to high electrical efficiency of a grid-connected PV system. View Full-Text
Keywords: active series filter (SF); load-terminal voltage; synchronous reference frame (SRF) theory; phase locked loop (PLL); low–pass filter (LPF); wavelet; source current; advanced generalized theory of instantaneous power (A-GTIP) theory; unified power quality conditioner (UPQC); DC-link active series filter (SF); load-terminal voltage; synchronous reference frame (SRF) theory; phase locked loop (PLL); low–pass filter (LPF); wavelet; source current; advanced generalized theory of instantaneous power (A-GTIP) theory; unified power quality conditioner (UPQC); DC-link
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Rahmani, B.; Li, W.; Liu, G. A Wavelet-Based Unified Power Quality Conditioner to Eliminate Wind Turbine Non-Ideality Consequences on Grid-Connected Photovoltaic Systems. Energies 2016, 9, 390.

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